1. Aluminum has a strong affinity with oxygen, and it is easy to combine with oxygen in the air to form a refractory and dense Al2O3 oxide film; The oxide film hinders the fusion and formation of the weld, and easily causes defects such as slag inclusion and porosity in the deposited metal. Therefore, before welding aluminum and aluminum alloy profiles, it is necessary to strictly clean the oxide film on the surface of welding parts, and adopt inert gas protection in the welding process to prevent the molten pool from being oxidized.
2. Aluminum thermal conductivity is high, so that a lot of heat in the welding process is rapidly into the interior of the aluminum profile; Large specific heat capacity makes welding aluminum and aluminum alloy profiles of the same thickness consume more heat than steel. Therefore, when welding, energy concentration and high power heat source must be used, and sometimes with preheating and other technological measures;
3. It is easy to form a hot crack at the weld; The linear expansion coefficient of aluminum is large, and the volume shrinkage rate reaches about 6.6% during solidification, resulting in greater internal stress, deformation and crack tendency in the welded joints. Often by adjusting the composition of wire, liquid metal fluidity to slow down the generation of cracks;
4. Porosity is easy to occur in the weld seam; The performance of aluminum and aluminum alloy profiles and the surface of welding wire often adsorbed water, water in the arc high temperature decomposition [H] dissolved into the liquid metal; In the welding process, the dissolution pool is cooled and solidified rapidly, and [H] has no time to escape and remains in the weld to form pores.
5. At high temperature, the strength and plasticity of the aluminum profile are very low, so that it can not support the liquid metal in the molten pool, resulting in poor weld forming, and even collapse and burn through defects; Therefore, in general, fixtures and pads are required;
6. Aluminum alloy profiles containing low boiling point elements (such as magnesium, zinc, etc.) in the welding process, these elements are easy to evaporate and burn, so as to change the chemical composition of the weld metal, reduce the performance of the welding joint;
7. Due to the strong reflection ability of aluminum profile to radiation energy, aluminum profile has no obvious color change from low temperature to high temperature and from solid state to liquid state. It is not easy to judge the heating condition of welding from color change, which brings difficulties to welding operation.
