Welding of Titanium Articles

Several articles on the welding of titanium

Heat Treatment of Welded Joints of Titanium Alloys
In short, the heat treatment.

Annealing of Titanium Welded Joints
on weld annealing

Hardening Heat Treatment of Titanium Welded Joints
hardening heat treatment of welded joints of titanium and alloys.

Special Modes of Hardening Heat Treatment of Welded Structures
welded structures made ​​of thermally hardened titanium alloys presents numerous technical difficulties.

Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
introductory article on the subject of welding

Structure and Properties of Heat Affected Zone
how to change the structure heat affected zone (HAZ)

Structure and Properties of Welded Joints
weld structure when welding titanium

Properties and Structure of Welded Joints of Industrial Titanium Alloys
presented data on the effect of heat treatment and prolonged heating of the operational structure and properties of welded joints.

Welding of Titanium

Properties and Structure of Welded Joints of Industrial Titanium Alloys

presented data on the effect of heat treatment and prolonged heating of the operational structure and properties of welded joints.

Alpha-alpha-and pseudo alloys
alloys belonging to the first group: alpha-alloys (BT1-00 VT1-0, VT5; BT5-1, 4200) and the pseudo-alpha-alloys (OT4-0, OT4-1, OT4, VT4, OT4-2, AT2, ATZ, AT4, VT20, TC5) are low-alloy (J-stabilizing-forming alloys with elements of $ K <= 0.25. These alloys are well welded by all types of welding and weld strength and Plasticity is approaching the base metal. alloys do not require stabilizing annealing after welding. Since the weld may be present then, the strength of the welded joint is taken into account by a factor of welding weakening equal to 0.9-0.95 of the strength of the base material. With the increase strength of welded joints of these alloys are more susceptible to weld defects (pores, stress concentrators, etc.) and a slight increase in the difference between strength and ductility of the weld and base metal. Technical titanium VT1-00 is made of the purest grades of titanium sponge. It contains fewer impurities such as carbon, iron, silicon, oxygen, than allowed for other titanium alloys. Titanium VT1-00 has low strength characteristics and high plasticity. Well deformed in the hot and cold conditions. Of titanium VT1-00 made ​​virtually all types of semi-finished: aluminum foil, tape, sheet, plate, forgings, stampings, profiles, tubes, wire, etc. Typical mechanical properties of titanium VT1-G0 at room and elevated temperatures are given in Technical Titanium grades 1-00 Tues due to its low strength as a structural material used is limited. When welding with an addition of a filler material used welding wire in titanium VT1-00 and VT1-0. The welded joints of titanium VT1-00, received Td H doped with VT1-00, after partial annealing have the following mechanical properties at room temperature: a * = 0.9, aB base metal; en> = 9.0 kgf * m/sm2 and = 180 ° to the sheet thickness of 1.5 mm and a = 140 ° for a sheet thickness of 3.0 mm.

Technical titanium VT1-0 prepared from unalloyed sponge, somewhat inferior in purity titanium sponge, used for the manufacture of titanium VT1-00. Nevertheless, the content of impurities in titanium VT1-0 is less than in the doped titanium alloys.

The alloy VT1-0 with a smaller ductility compared to the technical titanium VT1-00 has a higher strength and under-wide changes as a structural material. Typical mechanical properties at room and elevated temperatures of titanium VT1-0 are shown in Table. 28. Titan brand BT1-0 is well welded by all types of welding. From Tues 1-0 produce sheets, strips, foils, rods, profiles, tubes, wire, etc. The alloy VT1-0 used in the construction of continuously operating at temperatures ranging from -253 to +150 ° C. The welds are plastic and allow considerable cold deformation [52]. The ductility of the welded joint (bending angle a) is practically not affected by cold work up to 20% (Fig. 64). Heat treatment after welding is not required. Mechanical properties of welded joints of titanium VT1-0, obtained with an addition of H DT, after partial annealing have the following mechanical properties at room temperature: GMT = 0.9, aB base metal; en> = 7 kgf m/sm2, and = 135 ° C for sheet thickness of 1.5 mm and a = 110 ° to the sheet thickness of 3.0 mm. When welding with an addition of a filler material is used for welding wire of VT1-00 and VT1-0. Alloy VT5 is a typical single-phase a-titanium alloy system T1-Al. VT5 alloy forgings are manufactured, stamping, forged and rolled bars and rods, welded rings. The alloy VT5 has moderate strength low ductility. These explained that this alloy does not produce leafy semis. alloy VT5 are well welded by all types of welding applied to titanium. Tensile strength at short-term and long-term tensile strength of the welded joint are equal to 0.9 and 0.9 and aB ^ base material, respectively, at all operating temperatures. As the filler wire is used in titanium VT1-00 alloy, or BT2.

Alloys with alpha + β-structure of the martensitic type This group includes srednelegirovannye p-stabilizing elements yuschimi alloys with Ka = 0.3-0.9, thermally hardened by quenching and aging. The alloys of this group immediately after the welding has reduced weld ductility due to the formation of the joint structure is quite strong martensitic a'-phase. To restore the ductility of welded joints in alloys of this type use a stabilizing heat treatment, which resulted in a 'phase becomes stable in a + p-components. Most welded structures of a + b-martensitic alloys are made ​​with the strength of welded joints of 85-100 kg / mm2. Less commonly, welded construction is subjected to hardening heat treatment on the strength of 105-130 kgf/mm2, and then the joints thicken, and annealed, and the strength balance achieved by the design and provide sufficient the reliability of the welded joint. alloy VT6 - analogue of the widely used overseas alloy Ti-6Al- 4V [2, 121], as well as domestic VT6S alloy. Made in the form of a sheet of alloy plates, bars, forgings, stampings, welded rings. The alloy can be used both in the annealed and thermally hardened in the I (quenching + aging) conditions. Hardening heat treatment the strength of the alloy can be increased by 15-20%. Alloy satisfactorily welded by all kinds of welding used for titanium. Welded joints of VT6 alloy immediately after welding has a number of reduced ductility. To restore the ductility of welded joints requires a stabilizing heat treatment. The strength of welded joints of alloy VT6 made ​​AArDES non-consumable electrode without the additive is, after annealing at 760 - 800 ° C and after quenching from 900 ° C and aging at 500 ° C for 2 h and 105 kgf/mm2 95-100, respectively. Alloy I welded sheet with all titanium alloys. As the filler wire is used in alloys VT1-00, BT1-0, BT2, SPT2, VT6S. VT6 alloy is used for welded parts, for a long time working in the Institute was annealed at temperatures up to 450 ° C, and in the thermally hardened state - with temperatures up to 400 ° C. Alloy VT6S recommended for the manufacture of stamped and welded structures; working for a long time at temperatures up to 400-450 ° C and briefly at temperatures up to 700-750 ° C. The tensile strength of welded joint, fusion welding is not less than 90% of the tensile strength of the base metal. When welding heavy sections of metal use progressive methods of welding, submerged arc welding for example, joints VT6S alloy obtained in this way, of equal strength annealed base metal, and their toughness higher by 1,2-4,0 kgf m/sm2.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Structure and Properties of Welded Joints

weld structure when welding titanium

Consider the effect of different types of welding on the chemical composition, properties and structure of welded joints of different types of titanium alloys. Each specific type of welding alters the structure and the degree of alloying of the weld metal due to different base metal dilution of weld and the additional introduction of the metal electrode, whose composition may differ from that of base metal, as well as due to changes in gas content of the weld metal. Thus, the impact of type of welding on the properties of the weld metal of titanium alloys is determined by several factors: the chemical composition of the metal electrode, which provides the optimum combination of strength and ductility, the ratio percentage of the ground and the electrode metal in various forms of cutting edges, typical for this type of welding structure and phase composition, depending on the thermal cycle of welding and subsequent heat treatment, the possibility of formation of various defects inherent in this type of welding, and influence them (especially the poor penetration and porosity) on the physico-mechanical and operational characteristics, the additional gas saturation of the molten metal gas (nitrogen, oxygen and hydrogen) and the influence of these gases on the various properties and especially the tendency to brittle fracture and the detainee. The influence of these factors increases with increasing strength of the alloys. The choice of a particular type of welding is mainly dependent on the chemical composition of the alloy and the weld thickness.

Welds of a-and pseudo-alloys. In the single-phase and pseudo-alloys, and alloys, for almost the entire range of thicknesses can be welded using different methods of welding in which the formation of the molten weld metal occurs as a direct penetration of the base metal, as well as an additional input electrode filler metal. At the same basic meaning as in welding and pseudo-alloys are the interaction of the molten weld metal with protective environments and the ability to provide the minimum gas saturation of the weld metal. Mechanical properties of cast metal, regardless of thickness similar to those of base metal, and reduction of ductility due to the peculiarities of formation of the cast structure. For these alloys is characterized by a significant amount of die-cast grain, which depends on the value of this type of heat input welding. For all the a-and pseudo-alloys can be used electrode metal of technical titanium VT1-00, BT2 alloy (Ti-ZA1) or an alloy of similar composition to the base metal. In all cases, regardless of changes in the weld cooling rate and fixed-or a'-phase. The nature of the formation of a-or a'-phase in the joints mainly depends on the cooling rate in the range of p wo-MH or a pre-rotation.

At low cooling rates produced a wide and long plate, high cooling rates, and formed melkoigolchataya or a 'phase. By varying the cooling rate can be controlled within certain limits, structural transformations in the weld metal. Thus, the characteristic of the electroslag welding heat input increases, slowing the rate of cooling in the martensite range, leads to the transformation of thin needles of a-phase alloy VT1-0 in the large grains with serrated boundaries. Dispersity of the structural components significantly affect the plastic properties of the weld metal. For these alloys, the change of plasticity, depending on the cooling rate is on a curve with a peak and is associated with a grain size of cast structure and dispersion of a-or a'-phase. Slow cooling of a decrease in ductility of cast metal as a result of increasing the size of the grains. The high cooling rate leads to a decrease in ductility due to the formation or a 'phase.

For the alloys of this group is characterized by the fact that the mechanical properties and structure of the weld metal during welding is only marginally affected the entire range of thicknesses and different methods of welding. Annealing after welding stabilizes the structure but does not affect the mechanical properties of the weld, and therefore the heat treatment of welded joints of these types of alloys, including titanium and maintenance is carried out only to reduce the magnitude of internal stresses from the welding process, as well as to reduce the peak concentration of hydrogen in different zones of the welded joint. This is confirmed by the structures of welds that are shown in Fig. 46. Influence of different technological factors on the mechanical properties of weld metal, excluding the effect of alloying elements is convenient to consider the example of alloy BT1-0.

For all types of welding alloy BT1-0 strength of the weld metal is determined by the initial strength of the base-metal and filler wire. If welding is a significant increase in the grain, as well as additional gas saturation of the weld metal, its strength may exceed the original while reducing ductility. The research results presented in this study showed that the welding of alloy VT1-0 non-consumable electrode without the additive increase in the hydrogen content in the main influence on the toughness and the bending angle of the weld metal without altering its hardness. The increase in oxygen and nitrogen strongly influences the strength and ductility when tested in the bending angle. Especially dangerous gas saturation of the surface layers of the seam. Increasing the oxygen content from 0.15 to 0.38% (while 0,02% N) reduces the bending angle of the weld metal in the alloy VT1-0 1.5 mm from 180 to 100 ° C. With increasing thickness of the weld metal and the increase heat input welding depth of the layer with high hardness (contaminated with oxygen and nitrogen) increases, while the hydrogen content in weld metal during welding without the introduction of the filler wire is lower than the base metal due to its desorption and diffusion from the melt in the weld zone . Reduced ductility of the weld metal, associated with oxygen and nitrogen, increases its sensitivity to the influence of the level of hydrogen and a tendency to brittle fracture and the detainee. The data confirm the influence of oxygen and nitrogen on the tendency of the weld metal of alloy VT1-1 to the formation of cracks with increasing hydrogen content.

Thus, the type and technology of welding depends directly on the gas content in the weld metal and, consequently, its mechanical and performance properties. Research has shown that the condition of the protective gas atmosphere in a strong influence on the intensity of the absorption and gas content in the weld metal, depending on the type and mode of welding is the change in the effective thermal capacity of the arc, which leads to a change in the amount of hydrogen supplied to the gas phase, the protective atmosphere.

the source of the saturation of the weld metal hydrogen may be adsorbed, and the moisture, which is at the electrode edges and welded wire. The solubility of hydrogen in the weld pool depends largely on the content of alloying elements in the weld metal. Experimental data on the magnitude of the hydrogen content in weld metal obtained in the studies show that when all the major types of fusion welding in shielding gases argon, the use of the first composition and the electrode wire, held vacuum annealing isoderzhaschey up to 0.0006% N, allows to obtain the weld metal with a lower hydrogen content than the base metal due to its obezvodorazhivaniya and transition of hydrogen in the gas phase. When the automatic submerged arc welding (without additional protection with argon), as well as for ESW, there is additional gas saturation of the weld metal oxygen and hydrogen.

At the same time the implementation of automatic welding in vacuum drastically reduces the gas saturation of the weld metal due to its additional degassing, thus there is decrease in strength and increase ductility weld. Similar processes occur during the degassing electron-beam welding, and the value of reducing the concentration of gases in the weld metal depends primarily on the depth of depression, as well as the heat input welding process and the cooling rate of weld metal. Increasing the concentration of oxygen or nitrogen in the weld metal depends on the amount and the age of the weld pool, which depends on the type and welding conditions and the partial pressures of these gases in a protective atmosphere.

Regardless of the type of alloys for welding of structures is recommended to conduct the process in the cells with a protective atmosphere or to provide a thorough , steady defense throughout the weld zone. For example, in electroslag welding of thick metal of titanium alloys is impossible to completely prevent the molten metal from the effects of atmospheric gases using slag alone, so the additional gas is created by filing a protective atmosphere of argon above the slag bath [ON]. Violation of these conditions leads to significant gas saturation of the weld metal, particularly its surface layers. When welding in a controlled atmosphere, increasing the total gas content in the weld metal slightly, and the hydrogen content in weld metal due to its desorption and diffusion of heat-affected zone, even in decline. Results of the study of the microhardness and gas saturation of welds show that only electron-beam welding in vacuum does not increase the hardness of the seam. All other welding methods lead to an increase in hardness by increasing the amount of gas in the surface layers of the seam.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint

introductory article on the subject of welding

A characteristic feature is the presence of titanium polymorphic transformation. This leads to significant changes in the structure and mechanical properties of titanium alloys for welding and structural features of the zone of thermal influence of welding process.

welded joint is determined by the presence of two fundamentally different to each other zones - the weld and heat affected. In the area of weld metal is heated to the melting point and some time in the liquid state. At the same time actively develop the processes of saturation of the metal fumes, grain growth, different types of physical, chemical and structural heterogeneity of Education metastable phases, which significantly alters the properties in comparison with the metal to the welding. After crystallization of the metal in the weld zone acquires a characteristic cast structure.

Most of the famous wrought titanium alloys in the cast state has a lower ductility indices. In such cases, to improve the properties of the metal in the weld zone filler materials are used to manage the chemical composition of the weld.

Zone, which determines the weldability of titanium alloys, is a zone of thermal influence. The most dramatic changes in the structure and properties occur in the area directly adjacent to the weld, where there is a fusion of several grains. The metal in this area is heated to a temperature of TPl (the temperature of melting) to ~ 0.9 TPl. This zone is called the weld. Next is the area where the metal undergoes phase recrystallization. When cooling is metastable phases are fixed. The final structure depends on the temperature and cooling conditions. At the boundary of heat affected zone and base metal is part of recrystallization - the site of the gradual transition to the base metal.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Special Modes of Hardening Heat Treatment of Welded Structures

welded structures made ​​of thermally hardened titanium alloys presents numerous technical difficulties.

Production of welded structures of heat-hardenable titanium alloys presents numerous technical difficulties. When hardening of large parts or non-rigid structures are considerable leashes, which are very difficult and in some cases can not be eliminated; lengthy welded structures is generally difficult to transfer to the quenching medium, in the process of heating for quenching and transfer to a quenching medium thin sheet structure is oxidized, Even if it be carried out in the heating furnace with protective atmosphere, formed by heating the dross must be removed, which presents some difficulties, and sometimes impossible (eg, etching of structures with lap joints in spot or seam welding), descaling chemical method accompanied by the hydrogenation of thermally hardened alloys, which contain a glycol * ^-tional to the stabilizing elements, the assembly structure by welding of hardened elements, followed by the aging of the whole structure, as a rule, does not provide optimal mechanical and service properties of welded joints because the thermal cycle of welding creates a rather vague state of the seam and the transition zone, which depends on a number of difficult factors considered.

Circumstances above are the main factors hindering the development of thermally hardened alloy sheet in welded structures.

In connection with the above, we were sought special treatment hardening heat treatment of titanium alloys,
allowing to process large welded design in a protective atmosphere. For this purpose are the most promising high-alloy R-stabilizing elements of titanium alloys with a p-phase with increased stability.

Thus, the alloy VT16 with a Ka = 0.8 was found as a hardening effect of the base metal and weld at a certain rate of cooling from the annealing temperature.

With increasing cooling rate up to 4 - 8o C / min and above is observed a continuous increase in tensile strength and lower ductility characteristics of the alloy VT16. When the cooling rates within the 12-17O C / min can increase the strength of alloy VT16 with 85 kgf/mm2 annealed to 105 and above kgf/mm2 after hardening heat treatment of this type. The proposed method of hardening heat treatment was effective in the manufacture of honeycomb structures by welding, brazing and diffusion joining. It was enough to perform the operation of soldering or diffusion annealing, carried out usually at temperatures around 900 ° C and cooled honeycomb in an oven or container at a rate of ~ 15 ° C / min, as its strength (as the base metal and weld) increased to 105 kgf/mm2 and above. With this technological process is easy to protect from oxidation ponds with inert gases or vacuum.

Ratio of strength and ductility in this type of hardening heat treatment is about the same as during quenching and aging.

Hardening mechanism for this kind of heat treatment consists in the fact that in titanium alloys with a + p-structure is determined lennogo composition (with a certain amount of p-phase) at some cooling rates of decay occurs metastabnlnyh phases with the formation of dispersed particles of a-and p-sostavlyayushey, which leads to hardening of the alloy. In this case, the cooling rate of the alloy is such that there is no fixed metastabnlnyh phases, and at the same time is so small that it does not allow to pass to the equilibrium conversion of a + p-states.

Even more interesting way of hardening heat treatment can be applied for processing of alloys supercritical composition. It was found that titanium alloys of supercritical with further increase in the content of p-stabilized-reducing elements of the metastable P-phase can be fixed at very low cooling rates commensurate with the rate of cooling of large industrial furnaces, together with the SADC (4 - 10 ° C / min .) Further isothermal heating of a "hardened" alloy at temperatures of aging leads to the decay of the metastable P-phase and the formation of a dispersed-and P-components, ie, leads to a significant hardening. Obviously, the maximum capacity for hardening heat treatment of this type have titanium alloys with K = 1.6-2.2. At the least, and other titanium alloys can be heat-hardened to perceive this type. Na.etoy basis have developed a way of hardening heat treatment of large welded structures from titanium alloys of supercritical free transfer in the quenching medium. The proposed method is deprived of all the shortcomings of the hardening heat treatment associated with the transfer of cages in a quenching medium. It allows the hardening heat treatment in vacuum furnaces and industrial furnaces with protective atmosphere. So, for example, welded parts or structures of titanium alloy VT32 (Ti-2, 5% Al-8, 5% Mo-8, 5% V-1, 2% Fe-1,2% Cr), treated in a vacuum furnace under the regime: heating at 750 ° C for 1 h, cooling in the furnace at a rate of> = 4 ° C / min to 500 ° C, holding at 500 ° C for 4 h, provided for in the *> = 120 kgf / mm2, bb> = 7%, while in the annealed condition the alloy has s = 82 kgf/mm2 and 65 = 16%. Widespread use of the above-described method of heat treatment found in the manufacture of welded components and structures made ​​of alloy VT22. welded construction of this alloy require stabilizing annealing at 850 ° C, ie, at temperatures limits a + p = p-transformation. After annealing, the alloy has a tensile strength of about 100 kgf/mm2. Hardening heat treatment of the regime: heating at 850 ° C for 1 h, cooling in the oven to 750 ° C, holding 2 h, cooling with furnace to 500 ° C, exposure at 600 ° C for 4 h yields on welded constructions from alloy VT22 = 110 kgf/mm2. For such a heat treatment used vacuum furnaces and furnaces with protective atmosphere to allow thermal processing of finished parts or structures.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Hardening Heat Treatment of Titanium Welded Joints

hardening heat treatment of welded joints of titanium and alloys.

Hardening heat treatment of welded joints of titanium alloys, consisting of quenching and aging (vacation), serves as an additional reserve for increasing the strength of welded structures. However, it should be noted that the use of hardening heat treatment on the welded joint is more limited compared with the base metal. This is due to the fact that coarse acicular structure is poorly perceived hardening heat treatment, ie does not provide sufficiently good combination of strength and ductility after quenching and aging. Therefore, for the use of welded joints "soft" hardening heat treatment, which increases the strength by 10-20% compared with the strength of the annealed condition. In this case, moderate strength is possible to obtain satisfactory characteristics of plasticity of the welded joint. In recent years several new methods of hardening heat treatment of welded joints of titanium alloys, which allow multiple applications to empower the hardening heat treatment of welded structures, which we will also be considered in this section. All the more widespread hardening heat treatment of welded structures, when the base metal hardened by quenching and aging to the required level and weld is thickened and contained in the annealed condition by the local heat treatment. This method allows to obtain equal strength as the design of the base metal and weld on a high capacity for work.

Here are some questions hardening heat treatment of welded joints of titanium alloys.
Hardening heat treatment consisting of quenching and aging, is applicable to welded joints with the two-phase + p titanium alloys, since the martensitic alloys and ending with the pseudo-Riemannian alloys.

The principle of hardening heat treatment of welded joints, as well as the base metal is the fact that the accelerated cooling of metastable retained Me-p, a '(' L-phase and the subsequent artificial aging is an allocation of dispersed particles of a-and p- phases. The effect of the hardening heat treatment depends on the type, quantity and composition of the metastable phases, as well as the dispersion of the particles formed after the aging of a-and p-phases.

The peculiarity of hardening heat treatment of welded joints of titanium alloy is used in some cases, the thermal cycle of welding as a hardening heat treatment for hardening. Welded joints with single-pass weld metal of small thickness can be regarded as a tempered temperature p-type region.

Metastable components of p-and a'-phase in titanium alloys are prone to degradation during isothermal heating at low temperatures with the formation of equilibrium a + p-structure. On initial stage of aging and the formation of dispersed allocation-and p-phase is accompanied by a significant hardening of the alloys.

decay of a metastable g-phase is on the way:
rnestab Trieste-a-b + k + p.
For isothermal heating, a '(a') phase falls under the scheme a '(a') - + a '(a') {0botgtts-a-+ a-{'Rnestab * a + p.
collapse a '(a') phase is accompanied by the first stage of the formation of ct phase and a '(a')-enriched phase of p-stabilizing elements.

These schemes transformation of metastable phases during isothermal heating are valid for the processes taking place at temperatures above 450-500 ° C. At lower temperatures, the isothermal heated wa decay processes can be take place with the formation of an intermediate phase. In practice, the hardening heat treatment of welded joints as well as the base metal heat treatment regimes preclude the formation of ©-phase.

Depending on the mode of hardening heat treatment - quenching temperature, aging temperature and time (vacation) - Mechanical properties of welded joints will vary widely. With the increase of quenching temperature in the welded joint is preserved more and more (by volume) of the metastable phases. In alloys of subcritical composition is first raised the number of metastable g-phase, and then a '(a') phase. In alloys of supercritical composition is a continuous increase in the number of metastable g-phase with increasing quenching temperature to the point of complete polymorphic transformation in the alloy. The volume of metastable phases in the alloy determines the effect of hardening, which can be obtained during the subsequent aging of the quenched alloy. As a rule, with increasing temperature quenching of thermally hardened alloy with a + p-structure increases its strength and reduced ductility. With continued aging time with increasing aging temperature increases the volume and rate of decay of metastable phases and highlights the dispersed particles. This is accompanied by an increase of strength and, as a rule, reduction in ductility. At a certain temperature aging resistance reaches a maximum at higher temperatures the strength is gradually reduced to the level of the strength of the annealed metal. This portion of the curve is characterized by a coagulation of dispersed-and p-particles to an equilibrium state with increasing aging temperature. duration of aging factor expressed in the fact that the maximum strength on the curve is shifted to higher temperatures, and the maximum value decreases as the duration of aging. Such a character of strength change depending on the mode of aging due to the fact that with increasing duration of aging can provide more complete decomposition of metastable phases, while maintaining a high dispersion of the reinforcing particles. Practical use of modes of aging, as a rule, the strength of the downward branch of the curve, i.e, the modes. This allows us to provide the best combination of strength and ductility in thermally hardened metal at a satisfactory stability of mechanical properties. This is even more true of the welded joints of titanium alloys with a + p-structure, which is used for hardening plan with even more profound structures. In these modes, the hardening heat treatment at a loss of strength can get some gain in ductility, which is very necessary for welded joints with a cast structure, which is worse than the structure of deformed metal.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Annealing of Titanium Welded Joints

on weld annealing

Annealing of welded joints of titanium alloys consists of heating to the recrystallization temperature or until the phase-transition temperature, holding at a given temperature and subsequent cooling (honey lennogo the furnace, in air or step). Annealing of a-titanium alloys, as a rule, the first joke like that) because it is not associated with phase transformations. On annealing, a + p-titanium alloys in all cases accompanied by a change in the ratio of the content of a-and | 3-phase and should be attributed to the annealing of the second kind. Annealing of the full phase recrystallization for both base metal and weld a titanium-, pseudo-a and a + p-martensitic alloys has not yet found industrial applications as it prevents further improve the physical and mechanical properties. However, currently publishing a series of papers on the application of annealing in p-type region in order to increase the fracture toughness (K1c) semi-finished titanium alloys. For titanium alloys with a + I transition structure and pseudo-Riemannian alloys with phase recrystallization annealing finds industrial application. For welded joints of titanium alloys used full-and part joke. The difference between the partial annealing of the total lies in the fact that the first derivative, is found at lower temperatures and is intended primarily for the partial removal of internal stresses in welded structures, as well as for partial-term stabilization of the structure. Part-time annealing can be used as an intermediate operation in the process of welding of complex design or as the final annealing. The advantage of partial annealing is that it can be done in a furnace with air atmosphere without the need for subsequent removal of slag and contaminated gases, the surface layer of the Me-Full annealing of welded joints would greatly stabilize the structure of the weld and completely remove the residual stresses. Because it is carried out usually at temperatures above 700 ° C, it should be carried out in furnaces with protective atmosphere (argon, helium) or in vacuum furnaces. Titanium alloys with a-structure and pseudo-alloys is almost insensitive to the cooling rate after annealing. Two-phase a + p-type alloys, martensitic (VT16, VTZ-1, VT23, and others) and especially in transition alloys (VT22, VT30, and others), by contrast, are highly sensitive to cooling rate and, therefore, their rate of cooling from the annealing temperature regulated. To do this, apply a joke and then cooled in the furnace at speeds regulated to a certain temperature, and then in air or annealing step, which can be double or isothermal. Double annealing consists of heating to a temperature above the recrystallization temperature and the transformation of metastable phases formed as a result of the thermal cycle of welding, exposure, air cooling and subsequent heating at bo-Lee a low temperature, but sufficient to stabilize the structure formed after the first stage of heat treatment, exposure at this temperature and cooling in air. Isothermal annealing comprises heating to a temperature above the recrystallization temperature and the transformation of metastable phases formed during isothermal cycle of welding, self-control, transfer of alloys in the furnace at a temperature sufficient for transformation of metastable phases in the stable a + p-structure, endurance and cooling in air. When used with subsequent annealing of the alloy in the furnace-cooled (double or isothermal), the temperature at which the cooling air must be so low as to ensure sufficient stability of the a-and p-components in the welded joint is not only to the use of alloy at normal temperatures, but also for its operation at elevated temperatures. Therefore, the annealing regimes for the welded joints of titanium alloys is selected, as a rule, not only to obtain an optimal balance of strength and plasticity characteristics, but also for their thermal stability. Therefore, for titanium alloys depending on their composition, and sometimes on the conditions of welded choose one or another type of annealing. For example, to obtain the specified physical and mechanical properties after welding and annealing of the pseudo-p-alloys (VT15, VT32, and others,) the rate of cooling from the annealing temperature plays no role. However, the stability of the welded joint during the operation at elevated temperatures, it should be a joke, followed by slow cooling at a rate of no more than 2-4 ° C / min.

Although some features of the weld, in all cases to apply the general principles of a heat treatment that and the base metal. Dwell time during annealing starts from the moment the heating cages. Obviously, the a-alloys and pseudo-alloys annealed in all cases, followed by cooling in air. These regimes of thermal-mechanical treatment provide welded joints the floor-ing the removal of internal stresses and the optimum the relation of strength and ductility. Weld compounds of this group of alloys, heat-stable, ie can be used at temperatupax working for a long time without significant changes in physical and mechanical properties. The welded joints of titanium alloys with a + p-structure of the martensitic type can in some cases, annealed and then cooled in air, which often provides the optimal values ​​of strength and ductility, since the majority of the annealing temperature of martensitic alloys are below! the critical temperature for this alloy. In this case, the subsequent cooling in air is not accompanied by, the formation of martensite or at least large amounts of it, which provides a welded-| th compound rather good ductility compared to the ductility of the base metal. At the same time, the welded joints of titanium alloys of the martensitic type, operating continuously at temperatures increase the service should be annealed by mode, which provides a sufficiently high stability of the structure, or in the process of welded joints lose their plasticity. Stabilizing annealing regimes weld alloys such as martensitic-tion are given in Table. 7. It should also be noted that compounds of welded titanium alloys VT6 VT6S and adjacent to the p-stabilyziruyuschih content elements to the pseudo-a-alloys do not require stabilizing annealing, since the decay of metastable phases during prolonged heating is not accompanied by significant dispersion hardening of the weld . As for the VT16 alloy, the stabilizing annealing of welded joints of this alloy is needed to maintain the thermal stability of the welded joint during the operation at elevated temperatures and to obtain the optimal relation of strength and ductility of the welded joint in a state after welding and annealing. Titanium alloys with ct + p-structure transition, which is representative of the VT22 alloy are welded joints that require stabilizing schego annealing for optimum mechanical properties, and to improve the thermal stability during long-term operation at elevated temperatures. Stepwise annealing of VT22 alloy can greatly stabilize the structure and properties of its welded joint. Welds pseudorational alloys VT15 and TC6 directly after the weld has a good combination of strength and ductility. Subsequent annealing in air cooling makes it possible to somewhat stabilize the structure of the welds in these alloys, but does not allow for their thermal stability at elevated temperatures during continuous operation. In principle, titanium alloys, pseudo-Riemannian space by a special annealing could stabilize the structure of the weld, but the alloys VT15 and TC6 contain large amounts of evtektoidoobrazuyu schego-element (chromium), and therefore the stabilizing annealing occurs eutectoid metal embrittlement. For example, an experienced titanium alloy having a brand BT32 (Ti-8, 5% Mo-8,5% V-1% Cr - 2.5% A1-1% Fe) and is also a pseudo-Riemannian space-tion alloys, weld can be stabilized by annealing in the regime: heating to 780o C, exposure 1 h, cooling in the furnace at a rate of 2-4 ° C / min to 300 ° C, then in the air. This alloy welded joint after welding has good ductility, which persists even after annealing at the specified mode. However, if this alloy weld immediately after welding tends to prolonged heating to embrittlement, after welding and annealing, it is thermally stable and does not change its properties after prolonged heating. To illustrate the behavior of welded joints of titanium alloys of various types of thermal treatment present some evidence. Mechanical properties of welded joints of alloy OT4 little change as a function of heat treatment. This is explained by the fact "that the a'-phase alloys of this type in their mechanical properties is not very different from the a-phase dispersion hardening of the decay of a 'phase in these alloys is insignificant, and the amount of p-phase is so small that no significant impact the mechanical properties of welded joints. eutectoid transforma-tion of alloys of this type can not be detected under certain lenii-mechanical properties, or when Mr. rentgenostruktur or metallographic analysis. Similarly, for once behave welded joints and other pseudo-a-titanium ... ssh1avol.lri such heat treatment processing. We now consider changes in the structure and properties of welded joints representative a + p-titanium alloys of the martensitic type - VT14 alloy. In titanium alloy VT14 martensitic grades with Kp = 0.35 is already a trend towards a significant influence on the heat treatment, mechanical properties of the weld. In more heavily doped p-stabilizing elements martensitic titanium alloys with K $ = 0.6-0.8 there is a bo-Lee has a significant change in mechanical properties depending on the heat treatment.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Heat Treatment of Welded Joints of Titanium Alloys

In short, the heat treatment.

Heat treatment of welded joints of titanium alloys is carried out in order to relieve internal stresses, optimum physical and mechanical properties and structure of stable (not prone to changes in phase composition and properties during prolonged heating of the Ori operating temperatures). Welded joints, as well as the base metal is subjected to annealing, tempering, quenching and aging (tempering). In this chapter we consider the modes and features of heat treatment of welded joints of titanium alloys of various types. Annealing of welded joints is used for all types of titanium alloys and is the only type of heat treatment for a-, pseudo-a-and p-alloys. This type of heat treatment is performed to relieve internal stresses generated during thermal cycle of welding, as well as to stabilize the structure of the weld in order to obtain optimal properties in the annealed condition and retain their unchanged after prolonged heating at temperatures. Annealing, conducted in a vacuum, along with the decision of the above tasks are used for decontamination of the welded joint of hydrogen. Quenching and tempering, with aging (tempering) is used for alloys with a + p-structure. A hardening of welded joints for practical use does not yet have. Quenching and aging (vacation) is used to increase the strength of the welded joint. In some cases, to increase the strength of using a single aging, because the welds immediately after welding are essentially in the hardened state. When heat-treated titanium, as with other technological operations associated with heating, it is necessary to consider an active interaction with the atmosphere. Oxygen atmosphere not only forms a scale, but also diffuses into the crystal lattice of titanium, dramatically increasing the hardness of the surface layers of metal. This fully applies to the base metal and to weld. At the same time it is considered that heat treatment in furnaces with an air atmosphere at temperatures above 600-650 ° C is admissible and lead to a marked deterioration in the mechanical properties of welded joints and base metal. Heat treatment of welded joints at higher temperatures should generally be carried out in furnaces to protections's atmosphere or in vacuum furnaces. Otherwise, the oxidized layer and polluted gases must be removed by chemical etching or mechanical] way.

See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium

Dissimilar Metals, Nonferrous

welding together aluminum, copper, titanium, tantalum, etc.

Welding of aluminum and its alloys with copper.

Also significant differences in physical and chemical properties of aluminum and copper welding of metals, the formation of brittle intermetallic difficult phase.

Usually perform TIG welding in argon and the layer of flux. To improve the process of welding on copper after cleaning is necessary to apply the coating, which activates the surface of a refractory metal, improves wetting the surface of copper with aluminum. The best is the zinc coating thickness of 50-60 microns, applied by electroplating. Welding technology of aluminum and copper, such as aluminum and steel, ie, the shift in the arc of a heat-conducting metal, in the case of copper, the thickness of 0.5-0.6 base metal.

Bond strength is the strength of commercial aluminum ( kgf/mm2 8.10), the resistivity is slightly higher weld (0.037 Ohm-mm2 / m) than aluminum (0.0313 ohms-mm2 / m). Welds do not change their strength during prolonged heating to a temperature of 150 deg. C. At higher heating bond strength decreases due to the sharp increase in the brittle intermetallic layer. On the border of the connection of the copper intermetallic layer is formed (GuAl2) thickness of 10.3 microns, by a strip of aluminum solid solution of copper in aluminum of the same size. Microhardness of intermetallic layer adjacent to the copper reaches 450-550 kgf/mm2. The presence of this zone causes a relatively low bond strength. If the thickness of the intermetallic layer is less than 1 micron, it does not affect the bond strength. strength of the connection, as well as in steel-aluminum compounds, increases with the doping of the weld metal silicon (4-5%) and zinc (6-8%), as these elements inhibit the growth of intermetallic layer. To ensure the stable strength of welded joints on weld bevel edge of the copper is needed at an angle of 45-60 degrees. When welding aluminum with copper Ml grade A5 layer on a standard flux used for welding aluminum (AN-A1) with metal thickness up to 20 mm, use the wire mark AD1 2.5 mm in diameter. When welding electrode is necessary to shift from the bevel to 5-7 mm in the direction of copper. When welding on a layer of flux strength of welded joints is 7-8 kgf/mm2, the electrical conductivity remains at the level of electrical conductivity of aluminum.

Welding of aluminum alloy with titanium OT4. usually used argon-arc welding with tungsten, titanium front edge which is purified from a layer and pollution and alitiruyut in pure aluminum at a temperature of aluminum, 800 - 830 deg. C for 1-3 min. In this case, during the formation of a connection between aluminum and titanium is less than the period of retardation and brittle intermetallic compounds along the line did not have time to form. edges are pre-cut up (V - shaped cutting) Before welding on the edge of the overlay layer is aluminized pure aluminum (5-8 mm) using a wire mark AB00 5-8 mm. The connection is welded by the usual method, as an aluminum alloy. Tensile strength of welded joints of alloys OT4 + AMg6 depends on the layer of aluminum and is 11-27 kgf/mm2, bending angle 17-30 degrees.

Welding of titanium and copper and its alloys. Welding difficult properties and a large difference in the formation of brittle intermetallic compounds. The most successful fusion welding using intermediate insertion of a specially melted alloys of titanium alloyed with molybdenum, niobium or titanium, which lower the temperature of the transformation of al; P and provide the uniform titanium alloy with a stable structure that is not very different from the structure of the copper. You can use the combination of paste alloy Ti + 30% Nb alloy, and VT15. These alloys for welding copper to provide a tensile strength of MH connection 22-22,5 kgf/mm2 and bending angle of 140-180 degrees., and welding with bronze 26 - 28 kgf/mm2 and the bending angle 100-160Q. In the interlayer of the line connecting the hardness reaches 470 - 480 kgf/mm2 at a hardness of bronze BrH 0.8 120 kgf/mm2. Welding of niobium, tantalum and molybdenum alloy steel and nonferrous metals. The theoretical possibility of welding of niobium, tantalum and molybdenum from the steel and nonferrous alloys, partly shown above, since these metals are used as intermediates in welding titanium inserts with steel, aluminum and copper.

Tantalum and niobium on the characteristics are close to titanium welding and with it form a solid solutions without the fragile connections. Niobium is also satisfactorily welded with copper and copper alloys, which forms a limited solutions. Tantalum and copper solutions and does not form compounds. Typically used beryllium bronze BrB2. Performed TIG welding in inert gas-shielded, often in chambers with controlled atmosphere and the electron beam.

Welding bimetals. now known application of bimetallic billets of carbon and corrosion-resistant steel, aluminum alloys, steel and copper-nickel alloy MNZH 5 -1 12X18H9T steel and titanium alloy OT4, OT4-1 for welding dissimilar metals. In bimetallic rolled carbon and low alloy steels and aluminum alloys AMg3 and AMg6 thickness ratio in the package 1: 1 and 1.5: 1. Aluminum alloy is connected with the steel at the box office on the sublayer of pure aluminum. Tensile strength of bimetal by the slice, and 9.7 kgf/mm2 Peel 10-15 kgf/mm2. strength of welded joints is highly dependent on the strength of adhesion layers of bimetal and, consequently, on the area of bi-metallic insert. However, non-constructive node connectivity and the lack of quality control of adhesion layers of bimetal often lead to the fact that the compounds of this type do not have the vacuum density. To prevent the occurrence of brittle intermetallic compounds within the bimetal in heating during the welding process must be strictly withstand welding mode. For the bi-metal thickness of 10 - 12 mm we recommend the following regime: by argon-arc welding of aluminum alloy tungsten electrode on the mode I = 140 -160 A, Ud = 14 - 18; v St = 6-7m / h from steel welding in CO2 on the mode I = 100 - 130 A, Ud = 18 - 20 V, v = St. 17 - 20 m / h is most likely the formation of brittle intermetallic compounds in the bimetal StZsp, 12X18H9T AMg6 and alloy when heated above the line of junction temperature of 450 deg. C. When heated to a temperature of 550 deg. C and above bimetal fibers. It is recommended to start from the welding of aluminum, and after cooling the entire site - from the steel.

See also:
Welding of Aluminum
Welding of Titanium
Welding of Copper
Welding of Steel and Aluminum
Welding Steel with Copper
Dissimilar Metals, Nonferrous

Welding Non-ferrous Metals

Welding technology of non-ferrous metals and their alloys

Welding of Aluminum
Aluminum - fusible material, but the welder knows, form oxides during welding, melting at 2050 C (evaporation temperature of aluminum). On the welding of aluminum.

Titanium
titanium welding ability, "behavior" of titanium welding, weldability of titanium and its alloys.

Welding Magnesium
Welding of magnesium is usually performed in a tungsten inert gas-shielded. Details in this article.

Welding of Titanium
welding titanium methods - gas shielded, submerged arc welding, electroslag welding.

Copper
welding copper and copper alloys

Welding of Copper
technology and welding technique of copper in the protective gas is considered

Refractory Metals
The technology of welding metals like zirconium, hafnium, niobium, tantalum, molybdenum.

Refractory Metals

The technology of welding metals like zirconium, hafnium, niobium, tantalum, molybdenum.

Refractory and chemically active metals,

consider only the refractory and reactive metals, which can be used as structural materials such as zirconium, hafnium, niobium, tantalum, molybdenum. Materials such as vanadium, tungsten, chromium, used as construction is much less and only in the combined welded joints.

Welding materials considered difficult heat of fusion, high affinities for gases: oxygen, nitrogen and hydrogen, which leads to the formation of pores in the weld and reduce its plastic properties, susceptibility to grain growth during heating. In terms of the behavior of individual metals in welding should be noted.

Zirconium has two allotropic modifications: alfa-phase with the hexagonal close-packed lattice, existing prior to the transformation temperature 865 degrees. C, and beta-phase with a cubic, body-centered lattice, the existing above 865 deg. C. Due to the fact that the metal has a polymorphism in the heat affected zone and weld hardening occurs with the formation of beta-phase. The formation of mixed-phase structure can lead to the formation of makrogalvanopar and cause localized corrosion of the alloy. To eliminate this danger weldment is subjected to vacuum annealing at a temperature of 575 deg. to align the structure. When the temperature rises above 800 degrees. With zirconium reacts vigorously with nitrogen to form nitrides (ZrN), and at temperatures of 300-1000 degrees. Since it absorbs hydrogen to form hydrides (ZrH2). are used zirconium alloys with tin, iron, nickel and chromium have strength of 44-54 kgf/mm2 and high corrosion resistance.

Hafnium - polymorphic transformation temperature of the metal to 1760 degrees. C. Before this temperature is hexagonal close-packed hafnium lattice alfa-phase at higher temperatures - a body-centered lattice of beta-phase. When heated, hafnium reacts with the atmosphere of air, forming NfO2 dioxide, nitrides.

Niobium and tantalum - metals that are close in their physical properties, polymorphic transformations do not have. They have a very high resistance under the action of the most corrosive substances (liquid metal coolants,) and are used in some reactor designs. Tantalum is also used in medicine, surgery, made ​​from a rod, brackets and similar items may be in for a long time in the tissues of the human body without causing it significant inflammation. The technique also used in alloys of niobium with a small amount of alloying elements (molybdenum, tungsten, zirconium, vanadium, titanium) and alloys, tantalum, tungsten, with the addition of vanadium, niobium (up to 10%). When heated, these metals are strongly absorbing gases of the atmosphere: at temperatures above 300 degrees. C - oxygen, above 350 degrees. C - hydrogen, more than 400 degrees. N - nitrogen. As a result, the metal oxides are formed, nitrides, hydrides, the metal is strengthened, while the ductility decreases sharply. When welding these metals in the weld metal and heat affected zone are also possible grain growth and embrittlement of the metal, which can be enhanced by the formation of grain boundary carbides (Nb2C, Ta2S) if there are impurities in the metal carbon.

Molybdenum, which has a high melting point, high values mechanical properties and modulus of elasticity, is used as a sheet of small thickness for the individual elements of the combustion chambers, turbochargers, etc. In some environments, it has a high corrosion resistance. Metal has no polymorphic transformations. welding difficulties associated with its increased tendency to the formation of crystallization cracks due to the formation of various low-melting eutectics (MoO3 + M0O2 - Mo; mp = 780 deg. C), as well as ohrupchpvaniem weld metal and heat affected zone due to the possible ingress of atmospheric gases or other pollutants.

Molybdenum is sensitive to pollution of various kinds, depending on the content of oxygen, nitrogen and carbon changes the critical temperature of the transition metal in a fragile state. The most dramatically affected by oxygen, 0.0002% of O 2 Ta increases up to 200 degrees. C. Effects of thermal cycle of welding leads to grain growth in the weld zone, with a thickening of intergranular layers, the enrichment of impurities and a sharp embrittlement of the base metal in the area. In the presence of carbon in the metal, the formation of pores (due to the reaction of MoO3 + Mo + ES = SBV), which are located along the axis of the weld and fusion line. Therefore, along with a thorough cleaning of the base metal and welding materials are presented particularly stringent requirements for cleanliness of the base metal ( oxygen <0.0002%, N <0.0001%, carbon <0.003%) in the weld pool is administered active deoxidizers 0 5-1% Ti; to 0.1% Ce, up to 0,25% Zr, welding is carried out at the minimum heat input . on weldability of the materials in question can be divided into two groups. The first group metals (zirconium, hafnium, and tantalum dioby), with the welding process conditions have good weldability. Welding Group II metals (molybdenum, tungsten) is in serious difficulties because of their high sensitivity to impurities, embrittle the metal. Heated to a temperature of 200-315 molybdenum deg. C and removal of residual stresses after welding (when heated to 980 deg. C) reduces the probability of formation of cold cracks. main ways of obtaining welds with satisfactory properties: reduction of harmful contaminants in the ground and filler metal, reducing the time (temperature) and the residual stresses in welded joints, preventing contamination of the weld metal and heat affected zone during welding, especially gases of the atmosphere. Therefore, the metals welding is performed mainly by the electron beam in vacuum or in chambers with controlled atmosphere. In the latter case, the use of argon and helium are high frequency, which further drained from the gas by passing it through silica gel, alumina gels, and heated to 900 - 1000 deg. With titanium shavings. Performed TIG welding with direct current straight polarity. To reduce contamination of the weld metal welding is usually performed without filler metal. In some cases, the welding performed on the air, but use the burner with extra nozzles for supplying a protective gas, and blowing on the back side. Strength and ductility of welded compounds are at 80-95% of the base metal properties. When the electron beam welding in vacuum chambers with a 10 ~ 4 pm. of Art. contains hundreds of times less impurities than in the most pure argon premium. In this method of welding it is possible to clean the base metal from the edges of the gases heated defocused electron beam. In the most successful degassing of hydrogen is removed, to a lesser extent oxygen and nitrogen, and only the surface layers. most common method is to weld the materials in question arc and gas shielded electron beam. Arc welding of zirconium alloys most successfully sealed in chambers with a controlled environment, filled with helium, after preliminary evacuation of air to 0.03 mm Hg. of Art. Material of filler wire corresponds to the composition of the alloy: Zircaloy-2 and Zircaloy-3 (Table 109). There is information about the modes of welding of niobium and tantalum thickness of small tungsten electrode direct current straight polarity with the use of blast protection with an additional supply of gas through the nozzle and the back side seam. Welding molybdenum using ink-jet protection can successfully run using helium of high purity tungsten and consumable electrode. Molybdenum thickness of 3 mm welded tungsten electrode diameter of 3 mm at a constant current of direct polarity mode: I = 425 A; U = 18 V ; v = 18 m / h The diameter of the burner nozzle 15 mm helium flow through the burner, and a prefix of 20 l / min, with the back of the 5 l / min. Welding of molybdenum greater thickness can be carried out consumable electrode diameter of 1-1.2 mm dostoyannom current of reversed polarity on the mode: I = 400 - 500 A; U = 32 V; v St = 30 - 40 m / h; v = pp 600 - 900 m / h, the flow of helium through the burner and the prefix 140 l / min, with the back of 20 l / min. The electrode wire is pre-activated cesium chloride-coated it. known welding technique hafnium in a chamber filled with helium or argon, tungsten electrode diameter of 3.2 mm on the regime: I = 125-135 A; U = 14-18 B; v = 10 m / h, a constant current, the polarity of the line. When the electron-beam welding connection is made ​​by remelting the base metal. Along with welding butt welding is possible with overlapping seams and slash type of cork. For refractory and reactive metals is of great importance to the possibility of pre-treatment in vacuum degassing. In principle, electron beam welding in two passes allows the weld metal thickness up to 100 mm.

See also:
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals

Welding of Copper

technology and welding technique of copper in the protective gas is considered

Welding of copper.

Consider welding in protective gases. This method allows to obtain welds with the highest properties (mechanical, corrosion, etc.) as well as the weld metal contains a minimal amount of impurities.

Perform Welding TIG (tungsten) and consumable electrodes. Use inert with respect to the copper gases: argon, all in accordance with GOST 10157-73 varieties, helium (99.9%), nitrogen (with an additional drainage and cleaning of its sat-Kagel). These gases do not dissolve in the copper and with it, do not interact. It is advisable to use gas mixtures such as 70-5 - t-80% Ar + 20 g-30% N2, and argon for the economy to increase productivity (increased depth of penetration).

Use a tungsten or lantanirovannye ittrirovan nye-electrodes with a diameter of 6 mm. As filler metal for welding consumable and non-consumable electrode wire of suitable copper and its alloys, which are identical to the composition of the base metal, but contain deoxidizing agents (copper grades MO, Ml, M2; copper-silicon bronze BrKMts 1.3, chrome bronze BrH 0 and 7).

Welded edges and the welding wire is carefully cleaned of oxides and contaminants: the edge - by mechanical means (sandpaper, wire brush, etc.), wire - etching in a solution consisting of nitric, sulfuric and hydrochloric acids, followed by washing in water, alkali, water and dried with hot air. In some cases (welding in nitrogen) is used to improve the quality of the flux on the basis of boron, which is applied to the filler metal, or lay in the ditch lining. Preparation of edges depends on the thickness of the metal. When the thickness of the metal d <5 mm - without bevel edges, at h = 6 - 12 mm - V-shaped and with a greater thickness - X-shaped cutting with an opening angle of 70-90 degrees. for non-consumable electrode and 60 - 70 deg. for melting without blunting. Details of welding are collected at the tack (increment up to 400 mm) or in a special rigid devices, less strain. To form the root of the weld using backing from the pre-pro-tempered graphite or copper (in this case with water cooling it.) Metal thickness of 5 mm welded heated to a temperature of 350 deg. C. With increasing thickness of the metal heater increases up to temperatures of 600-800 degrees. C. For non-consumable electrode welding performed on an alternating current or direct current, straight polarity. When welding with consumable electrode using DC reverse polarity. The choice of the diameter of the tungsten electrode and additives depends on the thickness of the base metal. welding current during welding tungsten electrode is selected depending on the diameter of the electrode current and the type of shielding gas. When welding in nitrogen or a mixture of nitrogen and helium, the current strength is reduced by 10-15%, and the voltage increases by 15-20%. When welding consumable electrode in inert gases are used for conventional semi-automatic gas-shielded welding, and welding wire with a diameter of 1-2 mm , welding current 150 - 200 A for wire 1 mm in diameter and 300-450 A for wire 2 mm in diameter, arc voltage 22-26 V, welding speed depends on the section of the seam. When welding brass, bronze and copper-nickel alloys most commonly used tungsten electrode,% as welding consumable electrode is more intense evaporation of zinc, tin, etc. If you are using consumable electrode of small diameter (0.8-1.4 mm) it is sufficient for well-welded brass and copper alloys. Due to the lower thermal conductivity of these alloys preheating (100-150 deg. C) is required when the metal thickness over 12 mm. Other methods of welding. Among other methods of welding copper and its alloys are the most important manual arc welding with consumable electrode and  mechanized submerged arc welding.

Mechanized submerged arc welding can be non-consumable carbon or graphite electrode in the usual way, and consumable electrode. When welding carbon electrode edges are collected on a graphite lining, top brass strip joint is applied, which serves as a filler metal. Arc between a carbon electrode, in the form of a flat edged spatula, and the product under a layer of flux. Typically used the flux grade OSC-45 is deoxidizers zinc contained in the filler metal. method is suitable for welding of metal up to 10 mm. Electrode diameter to 18 mm, current up to 1000 A, arc voltage 18-21 V, welding speed 6-25 m / h Welding is performed at a constant current of reverse polarity. Preliminary heating of the electrode short-circuiting the product prior to welding. For mechanized welding consumable electrode submerged arc welding machines use a standard type DT-1000, and fluxes such as OSC-45, AN-348A and AN-20. Welding wire with a diameter of 3-5 mm of copper grades Ml, M2 or bronze CMC 3-1, 4-3 and others Brotze containing deoxidizing agents. single pass welding, the first layers in the multi-pass welding is carried out on the graphite lining and cushioned flux. In the absence of preheating the beginning suture is placed on pin bar. When the thickness of sheets up to 15 mm connection without bevel edge, with a greater thickness - V-shaped cutting with an opening angle of 90 deg., Blunting of 2-5 mm, no gap. With Dual (split) of the electrode metal thickness up to 30 mm can be welded without cutting edge with the location of the electrodes across the joint. Welding lead to a direct current of reverse polarity welding wire with a diameter of 5 mm without preheating edges. flux used for welding and lining prior to welding, must be calcined at a temperature of 300-400 degrees. C. When used for welding filler wire of copper weld metal and its properties are slightly different from those of the parent metal. Alloying of the weld metal during welding deoxidizers using filler metal of bronze greatly reduces its thermal and electrical conductivity. used for welding brasses fluxes grades ANF-5 or CPE-5 and the electrodes of copper wire, which reduces the waste of zinc positive results when welding copper and copper alloys are attained when using ceramic flux of K-13 School) and the IMS-1.

For manual metal arc welding electrodes use electrodes brands "Komsomolets 100", ST, and ABI-1. To mark the electrode rods "Komsomolets" used copper grade Ml and M2, has a thick coating composition: 15% fluorspar, feldspar 12.5%, 25% of the siliceous copper, ferro-manganese 47.5% (sodium silicate 20% by weight of dry ingredients .) The coating thickness of 0.4 mm, it is applied by dipping, followed by drying and calcination at 300 deg. C for 2 h in the ST electrodes are used a rod of bronze BrKMts 3-1. Welding electrodes are 4-6 mm in diameter, short arc without transverse vibrations of a direct current of reverse polarity. Welding current I = (50 - 60) de. Welding with coated electrodes can obtain joints with good strength properties, but because of what is happening deoxidizers weld metal doping affects its thermal and electrical properties (electrical conductivity of the seam is 20-25% of the electrical conductivity of the base metal). Carbon electrodes used is limited, graphite or carbon rods have diameters of 4 20 mm, as the filler metal wire rods are used with a diameter of 3-5 mm of copper grades M0 or Ml, or bronze Br.KMts 3-1. Welding can be performed without special protection or use of flux in the form of borax or boric slag. Flux can be applied to the pre-filler rods by dipping it into a solution of sodium silicate or on edge in the form of powder. sheets up to 4 mm thick welded with no cutting edges, with a greater thickness is required cutting with an opening angle of 70 - 90 deg. Welding lead to a direct current straight polarity long-arc (Ud> 40), it is necessary to prevent carburization of the metal during the formation of CO and porosity. Before you start welding requires heating to a temperature of initial sites of 250 deg. C. Welding current I = (45 - 55) / de, the arc voltage U = 40 - 50 V. The welding is feasible only in the down position after welding is recommended to weld forging at a temperature of 550-800 degrees. C and subsequent cooling in water, as the rapid cooling of the prevention-ical Su2O segregation at grain boundaries and embrittlement of the metal. Among other methods for welding copper, sometimes used are arc plasma (metal thickness up to 50 mm) and an electron beam.

See also:
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals

Copper

welding copper and copper alloys

Copper and its alloys

In the beginning, we note the following technical characteristics of copper and its alloys, such as high resistance to the effects of various chemicals, maintenance of high mechanical properties in the deep cold, high thermal conductivity and electrical conductivity. Technical copper depending on the brand may have different amounts of impurities: Bi, Sb, As, Fe, Ni, Pb, Sn, S, Zn, P, O. In the most pure copper grade M00 impurities can be up to 0.01%, grade M4 - 1%. Alloys of copper-based, depending on the composition of the alloying elements are brass, bronze, copper-nickel alloys.

Brass. Brass called copper-zinc alloys (brass for short) zinc content can reach 42%. If, in addition to zinc, the alloy contains other alloying elements (Al, Fe, Ni, Si), referred to as a complex fusion of brass. Brass has higher strength than pure copper (up to 50 sigmav kgf/mm2) (or the endurance limit of up to 470 MPa). However, if they contain more than 20% Zn alloy are prone to stress-corrosion cracking and the formation of cracks at the local heating. Brass is widely used as a structural material with high corrosion stand-bone and more durable than copper. copper-based alloys in which zinc is not a major alloying element, called bronzes. The name specified for the bronze main alloying element, by which bronze acquires certain properties. Are widely used tin bronze (2-10% Sn), aluminum (A1 4-11,5%), siliceous (0,5-3,5% Si), manganese (4.5 - 5.5% Mn) Beryllium (1,9-2,2% Be), chromium (0.4-1% Cr). tin bronze has good corrosion resistance and antifriction properties. Therefore, they are widely used in the manufacture of corrosion-resistant fittings for different pipes, bearings, etc. Bronze aluminum and silica have high mechanical properties and good corrosion resistance. They are cheaper. If the permit conditions, they are widely used instead of tin. Manganese bronze, in addition to good corrosion resistance, have high heat resistance. Beryllium bronze has high corrosion resistance and after heat treatment are nonmagnetic with very high strength, corresponding to the strength of steel. Of these bronzes are produced a range of flexible, durable items in the various instruments and devices, Copper-nickel alloys may contain up to 30% Ni, as well as iron and manganese. Alloy MNZH 5-1, durable and corrosion-resistant, widely used as a construction for the manufacture of pipes and vessels operating in hostile environments (sea water, salt solutions, organic acids). The complex composition of copper-based alloys, the presence of various components in the form of copper impurities in the technical difficulties are responsible for the welding of these metals. should consider the following features of copper and its alloys, affecting the welding technology.

Features of copper

1. Due to the high temperature and thermal conductivity, hindering local heating requires more concentrated sources of heat and increased welding modes. However, due to the tendency of copper to grain growth during welding of multilayer metal joints of each passage for grain prokovyvayut at temperatures 550-800 deg. C.

2. Ease of oxidation of copper at high temperatures leads to clogging of the weld metal refractory oxides. Cuprous oxide is soluble in the liquid metal and limited - in the solid. With copper oxide forms a fusible eutectic Cu-Cu2O (melting point of 1064 deg. C), which is concentrated along the grain boundaries and reduces the ductility of copper, which can lead to hot cracking. As follows from the phase diagram of the copper - oxygen, a small concentration of oxygen decreases the temperature melting point of copper, with an oxygen content of 0.38% (which corresponds to 3.4% Su2O) forms a eutectic with a melting point of 1064 degrees. C. In connection with this, and because of the limited time the possibility of steel metal weld pool (short lifetime due to the high thermal conductivity of copper) to the introduction of energetic deoxidizers - phosphorus, manganese, silicon, and others with limited oxygen content up to 0.03% and in critical constructions (eg, marine pipelines, vessels, etc.), the oxygen content of no more than 0.01%. For the destruction of refractory oxides, which form a film on the surface of the weld pool, use of borax-based fluxes (95% Na2B4O7 and 5% Mg), which contribute to chemical cleaning, translating the refractory oxides in the low-melting complexes. However, the use of phosphorus for the purpose of deoxidation should be limited, since it also gives a low-melting eutectic. Reducing agent, participating in the steel during the welding process, not only deoxidized metal, but at the same time and alloying it, which could reduce its corrosion resistance and electrical conductivity.

3.Some impurities may contribute to addiction weld cracking. For example, bismuth, forming a series of oxides of BiO, Bi2O3, Bi2O4, Bi2O5, gives low-melting eutectics with a melting point 270 deg. C, and the lead, forming oxides of PbO, RO2, R2O3 gives a fusible eutectic with a melting point of 326 deg. C. For this reason, should be sharply limited by the content of these impurities (Bi <0,002%; Pb <0,005%), or they must be related to the introduction of refractory compounds in the molten pool of elements such as cerium, zirconium, while playing the role of modifiers. In welding of aluminum bronzes is readily formed a refractory oxide Al2O3, littering the weld pool, worsening the fusion of metal and welded joint properties. For its destruction fluxes used, consisting of fluorides and chlorides, alkali and other metals.

4. When welding brass zinc vaporization (boiling point 907 deg. C, ie below the melting point of copper) can occur. The resulting zinc oxide is toxic, so welding is needed ventilation. Evaporation of zinc can cause weld metal porosity. This complication can be overcome pre-heated metal to a temperature of 200 -300 degrees. C and higher welding speed, which reduces the spreading of liquid metal and the evaporation of zinc. high coefficient of linear expansion (1.5 times greater than that of steel) can cause elevated temperatures during welding and the welding residual stresses and strains. The combination of high thermal stresses with a decrease in mechanical properties may contribute to the formation of cracks. To reduce the welding deformation of the structure are hard to consolidate, to tack. With increased thickness of the metal regulate the magnitude of the gap.

5. Copper in the molten state absorbs significant amounts of hydrogen. During the crystallization of the metal weld pool at high speed due to the high thermal conductivity of copper and a sharp decrease in solubility of hydrogen in the metal atomic hydrogen does not have time to leave the metal due to desorption. Cuprous oxide reduced by hydrogen to form water vapor, which leads to the formation of pores and cracks the seam. in the weld zone of diffusion-mobile hydrogen interacts with Su2O, located along the grain boundaries, forming water vapor, which are not soluble in copper, and can not get out of it create significant stress in the metal, leading to the formation of a large number of microcracks. This phenomenon is called hydrogen illness copper. To prevent disease of the hydrogen copper should reduce the amount of hydrogen in the weld zone (calcination of electrodes and fluxes, the use of dried-GOVERNMENTAL shielding gas). Carbon monoxide can also participate in the deoxidation of copper, which also contributes to the formation of pores. The affinity of copper to nitrogen is very small, so the nitrogen can be used for welding copper as shielding gas.

6. The increased fluidity of the molten copper and its alloys (especially brass) makes it difficult to weld in vertical and overhead positions, so most are welded to the lower position. To form the root of the weld defect-free pads are needed. For copper and alloys based on it can be used by all major methods of fusion welding.

See also:
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals

Welding of Titanium

welding titanium methods - gas shielded, submerged arc welding, electroslag welding.

Welding of Titanium.

Main methods of welding titanium - arc welding in inert gas, submerged, electroslag and electron beam.

Arc welding in inert gases, titanium and its alloys can be carried out or ittrirovannym lantanirovannym nonconsumable tungsten electrode and consumable electrode argon is applied only to the premium GOST 10157-73 or helium of high purity. Welding is performed with the use of elongated nozzles at nozzle (up to 500 mm) with gas from the back side through a special lining, as well as in chambers with controlled atmosphere. Titan small thickness (up to 4 mm) tungsten arc welded to the conventional apparatus for automatic argon- non-consumable electrode arc welding. Filler rod is fed only with metal thickness of 1.5 mm. It is also possible manual welding with direct current straight polarity. No feed filler rod bond strength is the strength of the base metal. When submitting his rod heated surface adsorbs a certain amount of atmospheric gases, which leads to a decrease in ductility of the weld metal by 40-50%. When the thickness of the metal used more than 4 mm groove V, and X-shaped ryumkoobraznuyu. To increase the depth of penetration during welding tungsten electrode is used, the paste flux AN-TA, which is applied a thin layer on the surface of the edges. They allow no cutting edges sva-regarded metal thickness up to 12 mm smaller than the conventional methods, welding currents. This technology reduces the deformation of welded structures and reduces the porosity of the joints, and promotes a partial refinement of the weld metal. When welding, submerged arc, with no cutting edge, you can also connect the metals increased thickness. When welding consumable electrode for the two runs (both sides) can be welded without the metal bevel edge thickness of 36 mm. As the inert gas argon and helium are used (Table 106). When welding in two passes in the joints obtained by argon relatively narrow (Fig. 164, a), and helium - a wide-Kimi (Fig. 164, c), which is associated with the physical properties of protective gases for welding in helium requires a a high voltage arc. Welding lead to a direct current of reverse polarity. Mechanical properties of weld metal and the strength of the connection in general depend on the type of titanium grade filler wire and can be communicated to the relevant parameters of the base metal. For automatic welding under this scheme uses the modernized machine DT-500 M, DT-1000-24, for welding fillet welds - Automatic ACS-MI and semi-urban village type 2. When upgrading standard equipment (for welding steels) focuses on increasing the feed rate wire (instead of the usual 50-600 m / h it was adjusted to 2500-3000 m / h) and create the conditions for full protection of the metal during welding. Power Supply - with a rigid characteristic. From the standpoint of reducing the consumption of scarce and expensive materials and welding performance is important to the welding of titanium to narrow the gap - cutting a slit that runs non-consumable tungsten or consumable electrode. In the first case, collect the sheets with a gap of a - 6 h, 12 mm diameter tungsten electrode, d = 3-4 mm diameter filler wire 1.5-2 mm, the welding current 200-300 A, argon flow rate 12.9 l / minutes after the burner and 2-3 l / min from the reverse side. If you are using MIG wire diameter of 1.6-2 mm at the same argon flow rate, strength of the welding current 360-420 A and voltage of 32-36 V. In submerged arc welding and electroslag welding using oxygen-free fluxes (AN-AN-T1 and T2 ), the main components of which - fluoride (GaF2, Na2F) and chloride (KC1, NaCl). To reduce the risk of getting the hydrogen in the weld metal is required that the moisture content in the flux did not exceed 0.05%. Titanium welded under flux in the standard equipment on the DC reverse polarity. This method is economically efficient in combined metal thickness greater than 6-8 mm, although the weld metal and thinner. Strength and ductility of welded joints are not lower than the base metal. In electroslag welding to protect the slag bath and the cooling of the metal is carried out blowing argon through special channels in the sliders at the rate of 5.12 l / min for the metal thickness 30-120 mm.

See also:
Welding of Titanium Metal
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals

Welding Magnesium

Welding of magnesium is usually performed in a tungsten inert gas-shielded. Details in this article.

Welding of magnesium and its alloys.

Magnesium in its pure form due to the low corrosion resistance and durability for the manufacture of structures unsuitable. The technique used for this purpose magnesium alloys, because of its doping with some elements greatly improves its mechanical properties without increasing weight.

Main alloying elements: manganese, aluminum, zinc, and supplements - zirconium and cerium. Tensile strength alloy grades MAI, MA8, mostly manganese-doped (1,3-f-2,5%), reaching 21-23 kgf/mm2 at 10% elongation, and the conditional yield point 11.9 kgf/mm2. Tensile strength alloy grades MA2, MA21, MH, M5, more complexly (up to 7-9% A1 to 1,5% Zn, 0.8% Mn), up to 26-30 kgf/mm2, yield 14-15 kgf/mm2, elongation 5-8%. Rolled Alloys of this type are used in the annealed condition.

Magnesium alloys ML4, ML5, and others (the letter A indicates that the alloy casting) is used to produce castings. Eliminate welding defects in casting. These alloys have a higher tendency to form hot cracks in the seams, pores and shrinkage porosity. Alloys based on magnesium is actively oxidized in air. Magnesium oxide film of their own on the metal surface is loose and unstable. Therefore, the surface of magnesium alloys artificially protect the film from the salts of chromic acid. By UCA-zannoy reason prior to welding the edges and adjacent to the surface of the base metal (the width to 30 mm) by etching or by mechanical means carefully remove the protective film, oxides and other contaminants. After welding, the surface of the weld re-applied protective film.

Magnesium alloys are used in aircraft, rocket, ship, for the manufacture of various capacities for kerosene, mineral oil, for the manufacture of various magazines, etc.


Features of magnesium

1. The resulting welding refractory oxide film of magnesium MgO (mp = 2500 deg. C) makes it difficult to weld. For its failure to apply the flux, or use the effect of cathode sputtering during welding Tungsten inert gas-shielded (alternating current).

2. Tendency to crack the appearance of crystallization associated with the possibility of the formation of fusible eutectics: MgCu (Tm = 485 deg. C); MgAl (Tm = 436 deg. C); MgNi (Tm = 508Q degrees. C). Therefore, the beginning and end of the welds must be placed on pin bars. The sequence of fusion: long-welded joints and seams with a large cross-section should be shorter weld seams and joints with a smaller cross section.

3. The tendency of alloys, particularly those containing manganese, a metal grain growth in heat-affected zone does not allow for significant overheating of the metal (eg, cluster in one spot welds in multilayer welding without a break to cool the metal, etc.).

4. The increased absorption of the active gas liquid metal generates a tendency to the formation of pores, which also requires a reliable weld zone from the surrounding air.

5. The high coefficient of linear expansion of magnesium alloys leads to a significant warping of welded structures.

Main method of welding of magnesium alloys - tungsten arc welding in a protective atmosphere of inert gases. Such methods of welding, as gas, coal and metal electrode coated with the use of which necessarily fluoride-chloride fluxes of different compositions (eg, flux composition of 34% KF and 66% LiCl or composition of 40% LiCl, 20% CaF2 and 40% NaCl) , is now rarely used in industry. Flux residues and slag on the surface of the joints causing corrosion of magnesium alloys, so that after welding their remains should be washed off with hot water. welding in inert gas (argon high and first grades of high purity helium) tungsten electrode ittrirovannym lantanirovannym or perform on alternating current. Filler wire composition is close to the base metal or has impurities (eg, cerium), providing a more ductile weld metal. Welding is feasible for all types of connections. When assembling the necessary close fit edges. Metal thickness of 3 mm with no weld bevel edges of sheets with a thickness of 3-6 mm is required V-shaped cutting and a thickness exceeding 6 mm - X-shaped with blunt 1.5-2 mm. to prevent contact with the metal oxide film on the back side edges of the weld should be conducted with full penetration of edges on the pads of the metals with low thermal conductivity (usually from high-alloy steel). They also serve to protect the back of the seam. From this perspective, lap, corner and T-joints less technical. For manual welding metal thickness of 3 mm diameter tungsten electrode is used 2-3 mm, the current Isv = (30 - 40) / dw in the argon flow rate 9.7 l / min. Automatic welding is possible for a metal thickness of 1 mm or more tungsten electrode diameter of 2-6 mm on the welding current Isv = (40 ​​- 75) / dw in the distribution of argon during 6-10 l / min. The diameter of filler rods 1.5 - 3 mm. To reduce the heat to be welded at high speed. length of the arc support the minimum (1.0-1.5 mm), as in this case, a vigorous destruction of the oxide film by cathode sputtering, and improved protection of weld zone by inert gas. The main and filler metals before welding must be thoroughly cleaned of the oxide film and contamination by mechanical or chemical means. When TIG welding, weld strength as compared with the base metal up to 85-90% in arc welding carbon and a metal electrode of 70-80% and 60-75% of the gas only.

See also:
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals