There are some difficulties in the welding process of aluminum alloy products, mainly including the following aspects:
1. Oxide film problem
There is a dense oxide film on the surface of aluminum alloy, the main component of which is aluminum oxide. The melting point of this oxide film is as high as 2050℃, while the melting point of aluminum alloy is generally around 600℃. During the welding process, the oxide film will hinder the fusion of metals and reduce the welding quality. Therefore, effective measures must be taken to remove the oxide film before welding, such as mechanical cleaning, chemical cleaning or using special welding processes, such as high-frequency arc ignition or "cathode atomization" during argon arc welding to break the oxide film.
2. Thermal crack tendency
The linear expansion coefficient of aluminum alloy is large, about twice that of steel. During the welding process, due to local heating and cooling, large welding stress will be generated. At the same time, during the solidification process of aluminum alloy, low-melting-point eutectic will be formed. These factors increase the tendency of aluminum alloy to produce thermal cracks. In order to prevent the occurrence of thermal cracks, it is necessary to select appropriate welding materials and welding process parameters, such as controlling welding current, welding speed and preheating temperature.
3. Porosity problem
Aluminum alloys are prone to pores during welding. The main reason is that the solubility of hydrogen in liquid aluminum alloys is high, while the solubility in solid aluminum alloys is very low. When the liquid aluminum alloy solidifies, hydrogen will escape from the molten pool to form pores. In addition, oxide film, oil stains, moisture, etc. during welding can also cause pores. In order to reduce the generation of pores, strict welding process measures need to be taken, such as drying welding materials and parent materials, using inert gas shielded welding, controlling welding current and welding speed, etc.
4. Welding deformation
Due to the high thermal conductivity and large linear expansion coefficient of aluminum alloys, large welding deformation is easy to occur during welding. Welding deformation will not only affect the appearance quality of the product, but also affect the dimensional accuracy and performance of the product. In order to control welding deformation, reasonable welding sequence, fixture fixation, preheating and post-weld heat treatment can be adopted.
5. Welding joint strength problem
The strength of aluminum alloy welding joints is generally lower than that of the parent material. This is because some defects such as pores, cracks, and lack of fusion will occur during the welding process, and the structure and properties of the welding heat-affected zone will change. In order to improve the strength of the welding joint, measures such as optimizing welding process parameters, selecting appropriate welding materials and welding methods can be adopted.
