And strong oxidizing
Aluminum and oxygen affinity is so strong that in the air easily combines with oxygen to generate compact and sturdy AL2O3 films thickness of about 0.1 ¦ì m, melting point up to 2050, far exceeds the melting point of aluminum and aluminum alloys, and density is large, about 1.4 times the aluminum. During the welding process, alumina film would hamper the good combination between the metal and cause slag. Oxide adsorption of moisture, when welding to weld pores. These defects will decrease the performance of welded joints. In order to ensure the quality of welding before welding must be strict and clean weld surface oxides and to prevent re-oxidation in the welding process, the molten metal and the effective protection of metal at high temperature, which is an important feature of aluminum and aluminum alloy welding.
Specific protection measures:
1, by mechanical or chemical means to clear the workpiece before welding Groove and surrounding parts and wire surface oxide;
2, during the welding process to be carried out by qualified gas protection;
3, when gas welding, flux, welding wire for welding process of continuous prick oxide film on the surface of the melt pool.
II, aluminum's thermal conductivity and specific heat, thermal conductivity
Despite aluminum and the aluminum of melting point far than steel low, but aluminum and the aluminum of thermal conductivity coefficient, and specific heat are is big, than steel big 1 time times more, in welding process in the large of heat was quickly conduction to matrix metal internal, to get quality of welding joint, must used energy concentrated, and power big of heat, sometimes needed used Preheat, process measures, to achieved melt welding process.
Third, the coefficient of linear expansion
Linear expansion coefficient for aluminium and aluminium alloy is about twice times that of steel, solidification shrinkage rate of 6.5%-6.6%, so easy to produce distortion. Effective measures of preventing deformation in addition to selecting reasonable processing parameters and welding the order, the adoption of appropriate welding equipment is also very important, especially when welding sheet metal. In addition, some welding aluminium and its alloys, formation of solidification cracking in weld metal of tendentiousness and formed in the heat-affected zone cracking tendency of liquefaction were larger, often due to excessive stress and brittleness temperature range in thermal cracking. This is aluminum, especially one of most common serious defects in welding of high strength aluminum alloy. Practical measures to prevent such cracks in the welding field mainly improvement of joint design, reasonable selection of welding parameters and order, adapt to the characteristics of the base material welding filler material.