Physical Properties and Welding Characteristics of Aluminum and Aluminum Alloys
Release time:
2022-10-30
【Summary Description】 2.1 easily oxidized Aluminum has a strong affinity with oxygen. At room temperature, the aluminum surface can be oxidized into a dense AL2O3 film with a thickness of about 0.1~0.2 m. Although this aluminum oxide film is dense, it can prevent the continued oxidation of the metal, which is conducive to natural corrosion protection, but it brings difficulties to welding. This is because the melting point of aluminum oxide (2050 ° C.) is much higher than the melting point of aluminum (about 600 ° C.), and its specific gravity is about 1.4 times that of aluminum. In the welding process, it will hinder the fusion between metals, and it is easy to form slag. Moreover, the aluminum oxide film also absorbs more water, which will promote the formation of pores in the weld. 2.2 thermal conductivity and specific heat capacity The thermal conductivity of aluminum is about four times that of steel. Therefore, when welding aluminum pipes, more heat is consumed than steel pipes. In order to obtain high-quality welded joints, it is necessary to use energy-concentrated and powerful heat sources. 2.3 easy to form hydrogen holes As well as aluminum and aluminum alloy welding pores, mainly hydrogen holes. Aluminum can absorb and dissolve a large amount of hydrogen in the liquid state, and its solubility in the molten state is 0.0069 ml/g, while in the high-temperature solidified state it is 0.00036 ml/g, a difference of nearly 20 times. Aluminum has a high thermal conductivity. Under the same welding process conditions, the cooling rate is 4 to 7 times that of steel, which accelerates the crystallization of the metal. In the process of rapid cooling of the weld pool, the solubility of hydrogen decreases sharply, and a large amount of supersaturated gas is precipitated at this time, so that hydrogen is too late to precipitate in the weld metal to form pores. Therefore, when aluminum is welded, the weld is prone to porosity. 2.4 easy to form hot cracks The linear expansion coefficient and crystallization shrinkage of aluminum are about twice that of steel, which is prone to large welding deformation and stress. In addition, the adverse effects of some impurities or alloying elements can cause cracks in joints with higher stiffness. 2.5 burn through and collapse When aluminum and aluminum alloys change from solid to liquid, it is difficult to judge the temperature of the molten pool because there is no obvious color change. The temperature during welding is too high to be detected, which often leads to burn-through or severe collapse.
2.1 easily oxidized
Aluminum has a strong affinity with oxygen. At room temperature, the aluminum surface can be oxidized into a dense AL2O3 film with a thickness of about 0.1~0.2 m. Although this aluminum oxide film is dense, it can prevent the continued oxidation of the metal, which is conducive to natural corrosion protection, but it brings difficulties to welding. This is because the melting point of aluminum oxide (2050 ° C.) is much higher than the melting point of aluminum (about 600 ° C.), and its specific gravity is about 1.4 times that of aluminum. In the welding process, it will hinder the fusion between metals, and it is easy to form slag. Moreover, the aluminum oxide film also absorbs more water, which will promote the formation of pores in the weld.
2.2 thermal conductivity and specific heat capacity
The thermal conductivity of aluminum is about four times that of steel. Therefore, when welding aluminum pipes, more heat is consumed than steel pipes. In order to obtain high-quality welded joints, it is necessary to use energy-concentrated and powerful heat sources.
2.3 easy to form hydrogen holes
As well as aluminum and aluminum alloy welding pores, mainly hydrogen holes. Aluminum can absorb and dissolve a large amount of hydrogen in the liquid state, and its solubility in the molten state is 0.0069 ml/g, while in the high-temperature solidified state it is 0.00036 ml/g, a difference of nearly 20 times. Aluminum has a high thermal conductivity. Under the same welding process conditions, the cooling rate is 4 to 7 times that of steel, which accelerates the crystallization of the metal. In the process of rapid cooling of the weld pool, the solubility of hydrogen decreases sharply, and a large amount of supersaturated gas is precipitated at this time, so that hydrogen is too late to precipitate in the weld metal to form pores. Therefore, when aluminum is welded, the weld is prone to porosity.
2.4 easy to form hot cracks
The linear expansion coefficient and crystallization shrinkage of aluminum are about twice that of steel, which is prone to large welding deformation and stress. In addition, the adverse effects of some impurities or alloying elements can cause cracks in joints with higher stiffness.
2.5 burn through and collapse
When aluminum and aluminum alloys change from solid to liquid, it is difficult to judge the temperature of the molten pool because there is no obvious color change. The temperature during welding is too high to be detected, which often leads to burn-through or severe collapse.
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