Welding of steel and aluminum.
Difficult process of physical and chemical properties of aluminum. Performed mainly argon-arc welding with tungsten electrode. Preparation of steel parts for welding butt joint provides for double-sided bevel the edges with an angle of 70 degrees, because at this angle of the bevel joint strength reaches a maximum value. Welded edge carefully cleaned mechanically or sandblasting process, or chemical etching, and then they applied an activating surface. Impermissible use of blasting as well as on the surface of the metal oxide are included. The cheapest cover - zinc, applied after machining.
The process of electroplating and hot dip galvanizing shall be preceded by degreasing components, washing and drying, pickling in sulfuric acid solution followed by rinsing and drying. When galvanizing before dropping items in the zinc bath having a temperature of 470-520 degrees. Since it is necessary fluxing components in a saturated solution of flux. The simplest flux consists of two components: 50% KF +50% KCl. It is totally unacceptable application of zinc or aluminum coatings by the method of shoopirovaniya, since the particles have time to cover oxidised and satisfactory weld aluminum to steel is not possible. When galvanic zinc coating layer should reach 30-40 m, with galvanizing 60-90 microns. In the latter case is considerably facilitated the process of applying layers of aluminum, especially on small details. For austenitic steels (12X18H9T etc.) calorizing possible after mechanical cleaning without the use of flux. Optimal (on the strength of the connection) mode aluminizing - the temperature of the aluminum bath 750-800 deg. C. Holding time for aluminizing - up to 5 minutes depending on the size of parts. It is also possible calorizing steel parts with the use of high frequency currents.
Welding technology involves the use of standard welding systems such as UDG-300 with lantanirovannyh tungsten electrodes with a diameter of 2-5 mm and argon, the 1st and 2nd grades according to GOST 10157-73. feature of welding aluminum and steel as compared to the usual process of TIG welding of aluminum alloys is the location of arc welding at the beginning of the first joint - in the filler rod, and during the welding process - on the filler rod, and a forming roll, as prolonged exposure to the heat of the arc on the surface of the steel is premature burn-out cover, which prevents the further process of welding. After the initial appearance of the arc of the roller should be lit again (after the break) on an aluminum shaft. When welding arc butt are on the edge of the aluminum parts, as an additive - on the edge of the steel parts so that the molten aluminum accumulates on the surface of steel coated with zinc or aluminized. When the thickness of metal to be welded to 3 mm welding current 110-130 A, with a thickness were 6-8 mm 130-160 A, at a thickness of 9-10 mm 180-200 A, but in this case provided sufficient details of the heating and the formation of the necessary connective layer. As a filler wire is used brand AD1 (pure aluminum-doped silicon with a small , a positive effect on the formation of stable quality of the diffusion layer). Additive alloy AMg6 should not be used, as in this case, the formation of intermetallic layer takes part magnesium, which reduces the strength of the connection. Apparently, the presence of magnesium atoms instead of the aluminum atoms in the crystal lattice of one phase determines the presence of weak links - magnesium is practically insoluble in iron. Magnesium dramatically accelerates the growth of the brittle intermetallic layer, intensifies the development process of reactive diffusion. Depending on the type of connection must be observed during welding sequence of weld overlay rolls, providing the necessary overlap. The alternation of ridges on the front and back of the steel components prevents overheating and premature burnout of zinc from its surface. The importance of a correct choice of welding speed, as it determines the interaction between liquid aluminum and steel, ie, determines the thickness and stability of the intermetallic layer. For the first layers of the welding speed is prescribed in the range of 7-10 m / h, for later (when the steel is sufficiently warmed up) in the range 12-15 m / h When examined under static weld joint strength at break corresponds to the technical strength of aluminum (10 kgf/mm2). increase the bond strength can increase the working section of the joint or combined application of coatings. The resulting welds are suitable for the perception of static load and have a high fatigue strength under the action of the alternating bending loads. The endurance limit of specimens at the basis of 10 ^ 7 cycles is 5 - 6 kgf/mm2, ie, at a level normal for the alloy AMg6. The destruction of the samples, usually occurs on the alloy AMg6 the outer hub. Only at high voltages, the individual samples are destroyed along the seam. Welded joints are also at a high density of hydraulic, pneumatic and vacuum tests, as well as high corrosion properties in seawater in the presence on their surface coatings. Combination coating steel - copper-zinc and nickel-zinc improves mechanical properties of welded joints. In this case, put a layer of copper or nickel thickness of 4-5 microns and the second zinc layer thickness of 30-40 microns. Layer of connective iitermetallidov complex composition is somewhat less than the thickness and hardness. Static strength of welded joints (in the presence of the weld reinforcement) 14-22,3 kgf/mm2. When welding high-alloy steel 18-8 with aluminum, if there were only a zinc coating thickness of 50 microns, the bond strength is reached 21,3-28, 7 kgf/mm2. If the zinc sublayer of thickness 25-30 microns to produce calorizing previously mentioned technologies, achieved strength of the connection 29,5-32,8 kgf/mm2. process of TIG welding of aluminum and its alloys and steel can be easily mechanized.
See also:
Welding of Aluminum
Welding of Steel and Aluminum
Welding Steel with Copper
Dissimilar Metals, Nonferrous
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