Characteristics and difficulties of aluminum welding wire

Aluminum and aluminum welding wire is widely used as filling material for aluminum alloy argon arc welding and oxygen-acetylene gas welding. The selection of welding wire is mainly based on the requirements of the type of base metal, the drop performance of the joint, the mechanical properties, the corrosion resistance and the color coordination of the weld base material after anodizing. Generally, welding aluminum and aluminum alloys are made of the same or similar grades as the base metal, so that good corrosion resistance can be obtained. However, when the heat-treated reinforced aluminum alloy has a large tendency to weld hot cracking, the selection of the welding wire is mainly to solve the resistance. Cracking starts, when the composition of the wire is very different from the base metal.

Aluminum is a silvery white light metal with outstanding plasticity, high electrical conductivity and thermal conductivity, 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.

Very simple oxidation. In 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, and it is very simple to form shortcomings such as pores, slag inclusion and unfusion. Causes the weld function to decrease.

It is prone to stomata. The primary cause of pores in the welding of aluminum and aluminum welding wire is hydrogen, because liquid aluminum can dissolve a lot of hydrogen, while solid aluminum hardly dissolves hydrogen, so 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 welding wire to absorb moisture in the air. Practice has proved that even if 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 air exceeds 80%, the weld will be significant. Presenting stomata.

Aluminum welding wire welds have a tendency to deform and form cracks. The coefficient of linear expansion and the rate of crystallization of aluminum are about twice as large as that of steel, and it is prone to large internal stresses of welding deformation. For structures with higher rigidity, the occurrence of thermal cracking will be promoted.