What welding characteristics of aluminum and aluminum alloys is?
(2) the thermal conductivity of aluminum and aluminum alloys, and specific heat capacity was about twice as much carbon steel and low alloy steel. The thermal conductivity of aluminum is ten times of austenitic stainless steel. In the welding process, a lot of heat can be quickly transmitted to the base metals, the welding of aluminum and aluminum alloys and therefore, energy consumption in addition to the molten metal bath, but also have unnecessarily consume more calories of other metal parts, which kinds of useless energy consumption than steel welding is more significant, in order to obtain high-quality welded joints, should try to concentration of energy, power energy, and sometimes can also be used preheating process measures.
(1) and aluminum when welding easily oxidized in the air to produce alumina (Al2O3) high melting point, it is very stable and difficult to remove. Hindered base metal melting and fusing, the oxide film than a major, difficult to bubble to the surface, easy to generate slag, lack of fusion, incomplete penetration and other shortcomings. Surface oxide film and the lot of water absorption of aluminum, easy to weld porosity. Before welding should be used strictly chemical or mechanical surface cleaning, remove the surface oxide film. Strengthen the protection of the welding process, to prevent oxidation. When TIG welding, optional AC power supply, through the "cathode clean-up" effect, removing the oxide film. When welding, flux removal using the oxide film. When thick plate welding, welding heat can increase, for example, helium arc heat, the use of helium or argon-helium mixed gas, or MIG welding using a large specification, in the case of DC is connected, may not need to "cathode clean up. "
(5) aluminum and aluminum alloys can be dissolved in a large amount of liquid hydrogen, solid almost no dissolved hydrogen. In the weld pool solidification and rapid cooling process, hydrogen late overflow easily form hydrogen bore. Moisture in the atmosphere arc column, welding material and the base material surface oxide film adsorbed moisture, are an important source of hydrogen in the weld. Therefore, the source of hydrogen must be strictly controlled to prevent the formation of pores.
(4) aluminum light and heat reflective ability, solid, liquid or rotational time, no significant change in color, difficult to judge when the welding operation. High temperature strength aluminum is very low, difficult to support the pool, easy to wear welding.
(3) aluminum and aluminum alloy wire expansion coefficient is about twice the carbon steel and low alloy steel. Aluminum solidification volume shrinkage rate of large deformation and stress larger weldments, therefore, need to take measures to prevent welding deformation. Aluminum weld pool prone to solidification shrinkage, shrinkage, thermal cracks and high internal stress. Production can be used to adjust the composition of welding wire and welding of measures to prevent heat cracks. In the corrosion resistance permitting, it can be used in addition to aluminum-silicon alloy wire welding aluminum-magnesium alloy aluminum. Hot cracking tendency of 0.5% silicon in Al-Si alloy when larger with increasing silicon content, crystallization temperature range of smaller alloy, liquidity increased significantly, decreased shrinkage, hot tearing tendency is reduced accordingly. According to experience, when silicon 5% to 6% do not produce hot cracking, which uses SAlSi strip (silicon content of 4.5% to 6%) wire will have a better crack resistance.
