Characteristics and difficulties of welding aluminum alloy materials
2021-04-04 20:10:50

Aluminum and aluminum alloy materials are widely used in the welding structure of industrial products because of their low density, high strength, high thermal conductivity, strong corrosion resistance, outstanding physical and mechanical properties. For a long time, due to improper selection of welding methods and welding technical parameters, the aluminum alloy parts are severely deformed due to excessive stress accumulation after welding, or due to defects such as weld porosity, slag inclusion, and incomplete penetration, resulting in weld metal cracks or The loose raw materials have severely affected the quality and function of the products.

1. Characteristics of aluminum alloy materials

Aluminum is a silvery white light metal with outstanding plasticity, high electrical conductivity and thermal conductivity, and together with resistance to oxidation and corrosion. Aluminum is very simple to oxidize to form a film of Al2O3, which simply causes inclusions in the weld and then damages the continuity and uniformity of the metal, reducing its mechanical function and corrosion resistance. The chemical composition and mechanical function of common aluminum alloy base materials and welding wire.

2. Welding difficulties of aluminum alloy materials

(1) Very simple oxidation. In the air, aluminum is simply oxidized to form a fine aluminum oxide film (thickness of about 0.1-0.2 μm) with a high melting point (about 2050 ° C), far exceeding the melting point of aluminum and aluminum alloy (about 600 ° C) . The density of alumina is 3.95-4.10g/cm3, which is about 1.4 times that of aluminum. The appearance of alumina film is easy to adsorb moisture. When welding, it prevents the fusion of essential metals, which is very simple to form pores, slag inclusions, unfused, etc. Causes the weld function to decrease.

(2) It is prone to stomata. The primary cause of pores in the welding of aluminum and aluminum alloys is hydrogen, because liquid aluminum can dissolve a lot of hydrogen, and solid aluminum hardly dissolves hydrogen. Therefore, when the temperature of the molten pool is rapidly cooled and condensed, hydrogen does not come out, simply The collection in the weld constitutes a pore. Hydrogen holes are currently difficult to avoid completely, and hydrogen has a lot of origins, such as hydrogen in an arc welding atmosphere, aluminum plates, and the appearance of the wire adsorbing moisture in the air. Practice has proved that even if the argon gas meets the requirements of GB/T4842, the purity reaches 99.99% or more, but when the moisture content reaches 20ppm, it will also show many fine pores. When the relative humidity of the air exceeds 80%, the weld will be significant. Presenting stomata.

(3) The deformation of the weld and the tendency to form cracks are large. The linear expansion coefficient and the crystallization shortening ratio of aluminum are about twice as large as that of steel, and the internal stress of large welding deformation is likely to occur, and the occurrence of thermal cracking is promoted for the structure having a large rigidity.

(4) The thermal conductivity of aluminum is large (pure aluminum 0.538 cal/cm.s. °C). It is about 4 times that of steel. Therefore, when welding aluminum and aluminum alloy, it takes more heat than welding steel.

(5) Burning loss of transpiration of alloying elements. The aluminum alloy contains low-boiling elements (such as magnesium, zinc, manganese, etc.). Under the high-temperature arc effect, it is very simple to transpire and burn, and then the chemical composition of the weld metal is changed to reduce the weld function.

(6) Low temperature strength and low plasticity. At high temperatures, the strength and ductility of aluminum is low, damaging the formation of weld metal, and sometimes simply forming the appearance of weld metal collapse and weld penetration.

(7) No color change. When aluminum and aluminum alloys are changed from solid to liquid, there is no significant color change, making it difficult for the operator to grasp the heating temperature.