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Difficulties In Welding Aluminum Alloy Materials
- Difficulties In Welding Aluminum Alloy Materials
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Difficulties In Welding Aluminum Alloy Materials
Keganhirl > 07-25-2019, 09:21 AM
(1) Extremely easy to oxidize. In the air, aluminum is easily oxidized to form a dense film of Al2O3 (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 or so). The density of alumina is 3.95-4.10g/cm3, which is about 1.4 times that of aluminum. The surface of the alumina film is easy to absorb moisture. When welding, it hinders the fusion of the basic metal, and it is easy to form pores and slag. Defects such as infusion cause a drop in weld performance.
![[Image: 5d16de377c201.png]](https://www.xindongrui-aluminum.com/data/upload/ueditor/20190629/5d16de377c201.png)
(2) It is easy to produce pores. The main cause of pores in the welding of aluminum and aluminum alloys is hydrogen. Since liquid aluminum can dissolve a large amount of hydrogen, solid aluminum hardly dissolves hydrogen. Therefore, when the temperature of the molten pool is rapidly cooled and solidified, hydrogen does not come out easily, and it is easy to weld. The slits gather to form pores. Hydrogen holes are currently difficult to avoid completely, and there are many sources of hydrogen, such as hydrogen in an arc welding atmosphere, aluminum plates, and the surface of the wire adsorbing moisture in the air. The practice has proved that even if argon gas meets the requirements of GB/T4842, the purity is above 99.99%, but when the moisture content reaches 20ppm, a large number of tight pores will also appear. When the relative humidity of air exceeds 80%, the weld will be There are obvious stomata.
(3) The deformation of the weld and the tendency to form cracks are large. The coefficient of linear expansion and the rate of crystal shrinkage of aluminum are about twice as large as that of steel, which tends to cause large internal stresses of welding deformation, and the structure with higher rigidity will promote the generation of hot cracks.
(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 alloys, it consumes more heat than welded steel.
(5) Evaporation of alloying elements. Aluminum alloys contain low-boiling elements (such as magnesium, zinc, manganese, etc.), which are easily evaporated and burned under the action of high-temperature arc, thus changing the chemical composition of the weld metal and degrading the weld performance.
(6) Low-temperature strength and low plasticity. The strength and plasticity of aluminum at low temperatures are low, which destroys the formation of weld metal, and sometimes causes the weld metal to collapse and weld.
(7) No color change. When aluminum and aluminum alloys is changed from solid to liquid, there is no obvious color change, which makes it difficult for the operator to grasp the heating temperature.