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Difficulties of aluminum welding

Addtime:2014��10��24��  Times:
     1, before welding + mechanical methods using chemical oxide removal groove and the surrounding parts of the workpiece and the wire surface, the order is the first chemical cleaning, mechanical polishing; 
     2, the welding process to be used to protect a qualified protective gas; 
     3, when gas welding using flux, constantly use during welding wire prick pool surface oxide film. 
Welding difficulty 
    (1) easily oxidized. In the air, aluminum oxide combined with easy to generate a dense aluminum oxide film (thickness of about 0.1-0.2μm), high melting point (about 2050 ℃), far more than the melting point of aluminum and aluminum alloys (about 600 ℃ or so). Alumina density 3.95-4.10g / cm3, is about 1.4 times of aluminum, aluminum oxide surface film easily adsorbed moisture, welding, it prevents the fusion of basic metals, easy to form pores, slag, lack of fusion defects, causing the weld performance. 
    (2) easy to produce pores. The main reason of pores generated during welding of aluminum and aluminum alloys is hydrogen, since a large amount of molten aluminum is soluble hydrogen and hardly soluble solid aluminum hydroxide, so that when the temperature of rapid cooling and solidification bath, hydrogen too late to escape easily in the weld cracks aggregate to form pores. Hydrogen is difficult to completely avoid the holes, many of the hydrogen source, an electric arc in the atmosphere of hydrogen, aluminum, an oxide film on the wire surface adsorption of moisture in the air. Practice has proved that even argon by GB / T4842 standards, purity of 99.99%, but when the moisture content of 20ppm, there will be a lot of dense pores, when the relative humidity over 80%, if not take heat and other measures, there will obviously weld porosity. Meanwhile, using a small welding current slow, increase the weld cooling time, and use the pool stir welding arcs can better help the gas discharge bath. 
    (3) Weld tendency of large deformation and crack formation. Linear expansion coefficient and crystallization shrinkage than steel, aluminum is about twice as large, easy to produce large welding stress deformation of the rigid structure will lead to thermal cracking. 
    Thermal conductivity (4) Large aluminum (aluminum 0.538 card /Cm.s.℃). About four times that of steel, therefore, when welding aluminum and aluminum alloys, welding steel than to consume more calories. 
    Loss by evaporation (5) of alloying elements. Aluminum alloy containing low boiling point elements (such as magnesium, zinc, manganese, etc.), the role of the arc at high temperatures, burning easily evaporate, thereby changing the chemical composition of the weld metal, weld performance. 
    (6) high-temperature strength and ductility is low. High temperature strength and ductility of aluminum is low, undermining the weld metal forming, sometimes also likely to cause collapse of weld metal and weld wear phenomenon. 
    (7) no color change. Aluminum and aluminum alloy from the solid state into liquid, no obvious color change, so that the operator is difficult to grasp the heating temperature.