ã€China Aluminum Industry Network】The following seven points should be noted during the welding process of aluminum profiles:
(1) Easily oxidized. In the air, aluminum is easily oxidized to produce a dense Al2O3 thin film (thickness of about 0.1-0.2μm) and a high melting point (about 2050°C) far beyond the melting point of aluminum and aluminum alloys (about 600 °C or so). The density of alumina is 3.95-4.10g/cm3, which is about 1.4 times that of aluminum. The surface of alumina film is easily adsorbed with water. When welding, it impedes the fusion of basic metals and easily forms pores, slag, Defects such as non-fusion, causing weld performance degradation.
(2) easy to produce pores. The main reason for the generation of pores during the welding of aluminum and aluminum alloys is hydrogen. Since liquid aluminum can dissolve a large amount of hydrogen, while solid aluminum hardly dissolves hydrogen, when the bath temperature rapidly cools and solidifies, hydrogen is too late to escape, making it easy to weld. Slots form in the seams. Hydrogen pores are difficult to completely avoid at present, and there are many sources of hydrogen, such as hydrogen in the arc welding atmosphere, moisture adsorbed on the surface of the aluminum plate and the welding wire, and the like. Practice has proved that even if the argon gas meets the requirements of GB/T4842, the purity reaches more than 99.99%, but when the moisture content reaches 20ppm, a large number of dense pores will also appear. When the relative air humidity exceeds 80%, the weld will be Obvious appearance of air holes.
(3) The weld deformation and crack formation tend to be large. The coefficient of linear expansion and crystal shrinkage of aluminum are approximately twice as large as those of steel, and the internal stress of the larger welding deformation is easily generated, and the structure with greater rigidity will promote the generation of hot cracks.
(4) The thermal conductivity of aluminum is large (pure aluminum 0.538 card/Cm.s. °C). About four times that of steel, welding aluminum and aluminum alloys consumes more heat than welding steel.
(5) Evaporation loss of alloying elements. Aluminum alloys contain low-boiling elements (such as magnesium, zinc, manganese, etc.), which can easily evaporate and burn under high-temperature arcs, thereby changing the chemical composition of the weld metal and deteriorating the weld performance.
(6) High temperature strength and low plasticity. Aluminum has low strength and plasticity at high temperatures, which destroys the formation of the weld metal, and sometimes causes the weld metal to fall down and wear through.
(7) No color change. When aluminum and aluminum alloys change from a solid state to a liquid state, there is no noticeable color change, making it difficult for operators to grasp the heating temperature.
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