At present, the processing technology of aluminum has been greatly improved with the development of aluminum profiles. However, since aluminum has many physical and chemical properties such as high oxidizability, low melting point, fast heat conduction, large coefficient of linear expansion, and large latent heat of fusion, the following problems are often encountered during welding.
1. Aluminum alloys such as aluminum and 7075 aluminum can dissolve a large amount of hydrogen in a liquid state, but they hardly dissolve at all in a solid state. Therefore, if hydrogen does not come out during the welding process, it is easy to form hydrogen holes. The main source of hydrogen in the weld is moisture. Therefore, it is necessary to pay attention to controlling the source of water during welding.
2, 7075 aluminum material is very easy to oxidize during the formation of aluminum oxide, because of the high melting point of alumina and high stability, it is not easy to remove. For this, a strict surface cleaning can be performed by chemical or mechanical means to remove the oxide film before soldering. In the case of tungsten argon arc welding, the oxide film can be removed by the action of cathode cleaning. When welding gas, a flux removing oxide film is used. When welding thick plates, the heat of welding can be increased. For example, the heat of the arc is large, and it can be protected by helium or argon-helium mixed gas, or by a large-scale gas-shielded welding, and in DC. In the case of a positive connection, cathode cleaning may not be required.
3. In the linear expansion coefficient, 7075 aluminum and aluminum alloy are twice as high as carbon steel and low alloy steel. When the weld pool is solidified, the 7075 aluminum material is prone to shrinkage, shrinkage, hot cracking and high internal stress. During the production process, adjustment of the wire composition and welding process can be used to prevent the occurrence of hot cracks.