Problems and treatment methods in the welding process of aluminum and aluminum alloy

Aluminum and aluminum alloys have a series of problems in the welding process due to their unique physical and chemical properties. Specifically, the following are the main points:

First, strong oxidation

Aluminum has a strong affinity with oxygen. It is easily combined with oxygen in the air to form a dense and strong AL2O3 aluminum oxide film on the surface of the metal. The thickness is about 0.1μm and the melting point is as high as 2050°C. The aluminum oxide film hinders the good bonding of the metal during the soldering process to form a slag inclusion. The oxide film also adsorbs moisture, causing the weld to form pores during welding. These defects will reduce the performance of the welded joint. In order to ensure the quality of welding, it is necessary to strictly clean the oxide on the surface of the weldment before welding and prevent re-oxidation during the welding process. It effectively protects the molten metal and the metal at high temperature, which is an important part of the welding of aluminum and aluminum alloy. Measures. The specific protection measures are:

1. Before welding, mechanically or chemically remove the oxides on the groove and surrounding parts of the workpiece and the surface of the wire; 2. Use a qualified protective gas for protection during the welding process; 3. In the case of gas welding, use flux in the welding process. Constantly use the wire to break the oxide film on the surface of the bath.

Second, the thermal conductivity and specific heat of aluminum are fast, and the heat conduction is fast.

Although the melting points of aluminum and aluminum alloys are low, the thermal conductivity and specific heat capacity are large. During the welding process, a large amount of heat energy is quickly transferred to the interior of the base metal. In order to obtain high-quality welded joints, energy concentration and power must be used. The heat source sometimes needs to adopt preheating and other technological measures to achieve the welding process.

Third, the coefficient of linear expansion is large

The linear expansion coefficient of aluminum and aluminum alloy is about twice that of steel, and the volume shrinkage during solidification is 6.5%-6.6%, so welding distortion is easy to occur. An effective measure to prevent deformation is that in addition to selecting reasonable process parameters and welding sequences, it is also important to use suitable welding fixtures, especially when welding thin sheets. In addition, when some aluminum and aluminum alloys are welded, the tendency to form crystal cracks in the weld metal and the tendency to form liquefaction cracks in the heat affected zone are large, often in the brittle temperature range due to excessive internal stress. Hot cracks are generated. This is one of the most common serious defects in the welding of aluminum alloys, especially high-strength aluminum alloys. The measures to prevent such cracks in the actual welding site are mainly to improve the joint design, select reasonable welding process parameters and welding sequence, and adopt welding filler materials that are suitable for the characteristics of the base metal.

Fourth, easy to form stomata

The air holes in the welded joint are the defects that are easily generated when welding aluminum and aluminum alloys, especially the welding of pure aluminum and rust-proof aluminum. Hydrogen is the main cause of pores in the welding of aluminum and aluminum alloys, which has been proven by practice. The source of hydrogen is mainly the moisture in the arc column atmosphere, the welding material and the moisture adsorbed by the base material, and the surface oxide film of the welding wire and the base material.