First, strong oxidation capacity

Aluminum and oxygen affinity is very strong in the air easily combined with oxygen to produce dense and strong AL2O3 film, the thickness of about 0.1μm, the melting point of up to 2050 ℃, far more than the melting point of aluminum and aluminum, and the density is large, About 1.4 times the aluminum. In the welding process, the alumina film will hinder the good combination between the metal, and easily lead to slag. The oxide film will absorb moisture, welding will cause the weld to generate pores. These defects, will reduce the performance of welded joints. In order to ensure the quality of welding, welding must be strictly cleaned before the surface of the weld oxide, and to prevent re-oxidation in the welding process, the molten metal and metal at high temperatures for effective protection, which is aluminum and aluminum alloy welding an important Features.

The specific protection measures are:

1, before welding with mechanical or chemical method to remove the workpiece groove and the surrounding parts and wire surface oxide;

2, the welding process to use qualified protective gas for protection;

3, in the gas welding, the use of flux, in the welding process continue to use the wire to break the surface of the molten film pool.

Second, the thermal conductivity of aluminum and specific heat, thermal fast

Although the melting point of aluminum and aluminum alloy is much lower than that of steel, but the thermal conductivity of aluminum and aluminum alloy, the specific heat capacity is much larger than steel more than doubled in the welding process a lot of heat is quickly transmitted to the base metal inside, in order to obtain High-quality welded joints, must use energy concentration, power of the heat source, and sometimes need to use preheating and other technical measures to achieve the welding process.

Third, the linear expansion coefficient

Aluminum and aluminum alloy linear expansion coefficient of about 2 times the steel, solidification when the volume shrinkage of 6.5% -6.6%, so easy to produce welding deformation. Effective measures to prevent deformation are in addition to the selection of reasonable process parameters and welding sequence, the use of suitable welding tooling is also very important, especially when welding thin sheet. In addition, some aluminum and aluminum alloy welding, the weld metal in the formation of the tendency of crystal cracks and the formation of liquefied cracking in the heat-prone areas are relatively large tendencies, often due to excessive internal stress in the brittle temperature range Produce hot cracks. This is one of the most common serious defects in aluminum alloys, especially high strength aluminum alloys. In the actual welding site to prevent such cracks in the main measures to improve the joint design, select a reasonable welding process parameters and welding sequence, using the characteristics of the base metal to adapt to the welding filler.