[China Aluminum Network] 7075 Frequently Asked Questions about Aluminum Strip and Aluminum Alloy Welding Process Along with the continuous development of aluminum profiles, aluminum processing technology has also developed rapidly. However, due to the fact that aluminum has many physical and chemical properties such as strong oxidation, low melting point, high thermal conductivity, large coefficient of linear expansion, and large latent heat of fusion, when selecting a welding method, the following common problems tend to occur:
1. Aluminum and aluminum alloys can dissolve a large amount of hydrogen in the liquid state and hardly dissolve hydrogen in the solid state.
In the process of solidification and rapid cooling of the weld pool, hydrogen is too late to overflow and hydrogen holes are easily formed. The moisture in the arc column atmosphere, the welding material, and the moisture absorbed by the oxide film on the base metal surface are all important sources of hydrogen in the weld. Therefore, the source of hydrogen must be strictly controlled to prevent the formation of pores. Aluminum wire 2,7075 aluminum strips are easily oxidized in air and during welding. The resulting alumina (Al2O3) has a high melting point and is very stable and difficult to remove.
Prior to welding, chemical or mechanical methods should be used to conduct a rigorous surface cleaning and remove the surface oxide film. In tungsten argon-arc welding, AC power is used to remove the oxide film by "cathode cleaning". During gas welding, the flux removing oxide film is used. In the thick plate welding, the welding heat can be increased, for example, the heat of the Xenon arc is large, the use of helium or argon-helium mixed gas protection, or the use of large-scale gas metal arc welding, in the case of DC connection, do not need the "cathode Clean up."
3, aluminum and aluminum alloy thermal conductivity and specific heat capacity are about twice as much as carbon steel and low alloy steel.
In the welding process, a large amount of heat can be quickly transferred to the inside of the base metal. Therefore, when welding aluminum and aluminum alloys, the energy is consumed in the molten metal bath, and more heat is consumed in other parts of the metal. The useless energy consumption is more significant than that of steel welding. In order to obtain high-quality welding joints, energy sources with concentrated energy and high power should be used as much as possible, and preheating and other technical measures may be used.
4,7075 aluminum belt and aluminum alloy linear expansion coefficient is about two times that of carbon steel and low alloy steel.
7075 aluminum alloy welding pool is easy to produce shrinkage porosity, shrinkage, thermal cracking and high internal stress during solidification. Measures of adjusting the wire composition and welding process can be used to prevent the occurrence of hot cracks. In the case of corrosion resistance, aluminum-silicon alloy wires can be used to weld aluminum alloys other than aluminum-magnesium alloys. When the Al-Si alloy contains 0.5% Si, the hot cracking tendency is large. With the increase of Si content, the crystallization temperature range of the alloy becomes smaller, the fluidity is significantly increased, the shrinkage rate is decreased, and the hot cracking tendency is also reduced accordingly. According to the production experience, when the silicon containing 5% to 6% does not generate thermal cracks, the use of SAlSi?l (silicon content of 4.5% to 6%) has better crack resistance.
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