Aluminum and aluminum alloys have the advantages of low density, high strength, high thermal conductivity, strong corrosion resistance, excellent physical properties and mechanical functions, so they are widely used in the welding structure of industrial commodities.For a long time, because of the improper selection of welding methods and welding technical parameters, forming aluminum alloy parts after welding due to excessive stress convergence occurred severe deformation, or because of weld porosity, slag inclusion, not weld penetration and other shortcomings, resulting in weld metal crack or raw material loose, seriously affected the quality and function of goods.

1. Aluminum alloy data characteristics

Aluminum is a silver white light metal with excellent plasticity, high electrical and thermal conductivity, together with the ability to resist oxidation and corrosion.Aluminum is very simple oxidation to produce aluminum oxide film, in the weld simple inclusion, and then damage the continuity and uniformity of the metal, reduce its mechanical function and corrosion resistance.Chemical composition and mechanical function of common aluminum alloy base metal and welding wire.

2. Welding difficulties of aluminum alloy materials

(1) Very simple oxidation.In the air, aluminum with simple oxidation, the formation of fine oxide 2 aluminum film (thickness of about 0.1-0.2μm), high melting point (about 2050℃), far beyond the melting point of aluminum and aluminum alloy (about 600℃).The density of alumina is 3.95-4.10g/cm3, about 1.4 times that of aluminum. The appearance of alumina film is easy to absorb moisture. When welding, it prevents the fusion of the fundamental metal.

(2) easy to occur stomata.Hydrogen is the primary cause of pores in aluminum and aluminum alloy welding, because liquid aluminum can dissolve a lot of hydrogen, while solid aluminum almost does not dissolve hydrogen, so when the molten pool temperature rapidly cooling and condensation, hydrogen has no time to escape, simply assemble in the weld to form pores.Hydrogen pores are difficult to avoid completely at present. There are many sources of hydrogen, such as hydrogen in arc welding atmosphere, moisture in the air absorbed by the surface of aluminum plate and welding wire.Practice has proved that even if the purity of argon reaches 99.99% or more according to GB/T4842 standard, when the moisture content reaches 20ppm, there will be a lot of fine pores, and when the relative humidity of air exceeds 80%, the weld will show significant pores.

(3) Large weld deformation and forming crack tendency.The linear expansion coefficient and crystallization shortening rate of aluminum are about two times larger than that of steel, and the internal stress of welding deformation is easy to occur, which will promote the occurrence of hot crack for the structure with greater rigidity.

(4) The thermal conductivity of aluminum is large (pure aluminum 0.538 CAL/cm. s.℃).About four times as much as steel, so it takes more heat to weld aluminum and aluminum alloys than to weld steel.

(5) the transpiration of alloying elements burning loss.Aluminum alloy contains low boiling point elements (such as magnesium, zinc, manganese, etc.), under the effect of high temperature arc, very simple transpiration burn loss, and then change the chemical composition of the weld metal, so that the function of the weld is reduced.

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