(1) very easy to oxidize. In the air, the aluminum is easy to oxidize and produce a dense three oxide two aluminum film (thickness of about 0.1-0.2 m), high melting point (about 2050 degrees Celsius), far beyond the melting point of aluminum and aluminum alloy (about 600 degrees Celsius). The density of 3.95-4.10g/cm3 is about 1.4 times that of aluminum, and the surface of alumina film is easy to absorb water. When welding, it hinders the fusion of basic metals, and it is easy to form pores, slag inclusions, incomplete fusion and so on.

(2) easy to produce porosity. Aluminum and aluminum alloy welding is the main reason for the formation of hydrogen, because liquid aluminum can dissolve a large amount of hydrogen, while the solid aluminum almost does not dissolve hydrogen, so when the molten pool temperature rapid cooling and solidification, hydrogen less than escape, easy to gather in the weld formation porosity. It is difficult to completely avoid hydrogen pores, a lot of sources of hydrogen, there is hydrogen in the atmosphere of arc welding, aluminum, wire surface adsorption of water in the air, etc.. Practice has proved that even if the argon according to GB/T4842 standards, the purity of more than 99.99%, but when the moisture content of 20ppm, there will be a large number of dense pores, when the air relative humidity of more than 80%, the weld will be significantly porosity.

(3) weld deformation and crack tendency. Aluminum wire expansion coefficient and crystal shrinkage rate steel is approximately twice as large, easy to produce large welding deformation of internal stress, the more rigid structure will lead to hot cracking.

(4) the coefficient of thermal conductivity of aluminum (pure aluminum 0.538 card /Cm.s. C). About 4 times of the steel, so the welding of aluminum and aluminum alloy, than the welding steel to consume more heat.

(5) the evaporation loss of alloy elements. Aluminum alloy containing elements such as magnesium, zinc, manganese and other low boiling point, in under the action of high temperature arc, extremely easy to evaporation loss, so as to change the chemical composition of the weld metal, lead to a decline in the performance of the weld.

(6) high temperature strength and low ductility. High temperature strength of aluminum and plastic is very low, destruction of the weld metal forming, sometimes easy to cause collapse of the weld metal and welding wear phenomenon.

(7) no color change. When the aluminum and the aluminum alloy transfer from the solid state to the liquid state, no obvious color change, make the operator is difficult to grasp the heating temperature.