Welding of aluminum and light alloys of aluminum has a relatively low melting point (657 ° C) with relatively high thermal conductivity, which is about three times the thermal conductivity of carbon steel, it is also characterized by a significant coefficient of thermal expansion (22 ∙ 10 ^ -6). Aluminum is very fragile when heated, but the main difficulty in welding of aluminum is its light oxidation with the formation of highly refractory and mechanical strength of the oxide Al2O3, which melts at 2050 ° C, which exceeds the boiling point of aluminum (1800 ° C). Aluminum oxide is an extremely strong chemical compound that responds poorly to the action of reactive flux materials due to neutral. The formation of aluminum oxide is the main difficulty in welding this metal.
Aluminium can be welded by melting, gas flame and arc. Before welding, the metal edges shall be thoroughly cleaned by mechanical means - sandblasted, steel brushes, scouring or chemical means - by washing in an aqueous solution of caustic soda or gasoline. After washing soda solution required a long and thorough rinsing with running water to prevent corrosion. When repairing aluminum castings are often used to preheat the product to a temperature of 300 ° C. For the repair of thick-walled aluminum castings can sometimes do without the special flux. In this case aluminum oxide at all times to clean off the surface of the bath with a scraper made of steel wire, and the end of the filler rod to reduce the oxidation dipped into the molten bath. In normal cases, is absolutely necessary to use special fluxes for welding aluminum, aluminum oxide strongly solvent at low temperatures. Especially strong are the solvents for aluminum oxide halides of alkali metal lithium. In fluxes for aluminum chloride is administered often, or lithium fluoride (LiCd or LiF). Good aluminum fluxes contain 15-30% of lithium salts, which are expensive. So were and are working to create a cheaper substitute fluxes that do not contain lithium. It has also the meaning and filler material. If you do not want the identity of the chemical composition of the ground and weld metals, as the filler material is recommended to use an alloy of aluminum and silicon content of about 5% Si. This alloy provides minimal shrinkage during solidification, forms a dense and durable seams, with a good smooth surface. The size of the burner for welding aluminum to a number less than for welding mild steel the same thickness. Excellent results are obtained by argon-arc welding with a nonconsumable and consumable tungsten electrode, which does not require the use of flux, which is a great technical advantage. Despite the fusible aluminum, it can be welded to a metal electrode. Can automatic arc welding of aluminum submerged special composition. Fluxes and coating for aluminum should produce from chemically pure components. Satisfactory results are obtained and the welding of aluminum. Butt welding of aluminum is usually done on a continuous fusion machines with electric drive. Is widely used spot welding of aluminum, but the essential difficulty in this case are the high electrical conductivity and the rapid melting of aluminum metal in the welding process, which requires high-speed movement of the electrode to maintain the machine and the pressure contact with the base metal. It is also possible and seam welding of aluminum for this purpose need powerful machines with ion breakers. Quite an exceptional ability to cold welding of aluminum, in this respect it surpasses all metals used in engineering. It is widely used in engineering the various aluminum alloys with higher mechanical strength compared with the strength of pure aluminum and retain its low density (2.7 - 2.8). Very many aluminum alloys can be divided into two groups: alloys are not heat-hardened and heat-hardened alloys. An example of heat-hardenable alloys can not be AMg alloys with magnesium and manganese AMts with a tensile strength of 13-35 kg/mm2, depending on the composition and processing. Because these alloys are insensitive to heat treatment of welded joints for strength close to the base metal in the annealed condition. from alloys, heat-hardened, anodized aluminum is the most important, widely used in aircraft and has a number of varieties, with a tensile strength of 50 kg/mm2. The problem of fusion welding of this important alloy is still not completely solved. During the welding process is a local overheating of the metal, causing a sharp decrease in the mechanical properties of the metal. Reduced strength can not be eliminated followed by heat treatment. More satisfactory results gives the resistance spot welding aluminum. addition of aluminum alloys in engineering are increasingly used magnesium alloys characterized by sufficient strength especial ease. The density of these alloys, the average is 1.7, ie, they are much lighter than aluminum alloys, the density is not lower than 2.7. The disadvantage of magnesium alloys is their ability to remain on the air under certain conditions, which limits the application of these alloys in some cases. The most common magnesium alloy is an alloy of AI-1, also known as "electron", which contains about 2% Mn, with a tensile strength of 20-25 kg/mm2. Magnesium is easily oxidized, forming on the surface of highly refractory oxide MgO. To improve the corrosion resistance of magnesium alloy sheets treated with different reagents, chromic acid is usually formed on the surface of the alloy solid protective film, diminishing the impact on the fusion of air, moisture, etc. Before welding protective film must be removed first by mechanical or chemical means. refractoriness of magnesium oxide makes use of flux, dissolving this oxide, as well as for welding aluminum and magnesium alloys. The basis of magnesium flux, as well as aluminum, are generally alkali metal halide layers, including lithium. Magnesium alloys will respond well to fusion welding. Of particular note is the argon-arc welding, which gives quite good results and does not require the use of fluxes. for cold welding of magnesium alloys are not suitable.
See also:
Welding of Aluminum Metal
Welding of Aluminum
Titanium
Welding Magnesium
Welding of Titanium
Copper
Welding of Copper
Refractory Metals
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