Aluminium and oxygen have a high affinity and can be oxidized in the atmosphere to produce a dense and insoluble oxide film of aluminum oxide, which has a melting point of up to 2050 degrees Celsius, and the second phase increases with time and temperature. The thickness of the oxide film is also increasing. When soldering, the word oxide film is covered on the liquid aluminum, which hinders the bonding between the filler metal and the base metal, and hinders the wetting of the molten metal; in addition, the density of the oxide film (3.95~) 4.18 grams per cubic centimeter) is also large, about 1.3 times that of aluminum, and it is easy to form slag. Therefore, when welding aluminum and aluminum alloy is =, in order to ensure the welding quality, the oxide film on the welding surface must be clearly known before welding, and The molten metal and the metal at high temperatures are effectively protected against reoxidation during the soldering process.
Second, it is easy to produce pores. Since aluminum and aluminum alloys do not contain carbon, there is no condition for generating CO. The gas produced during welding is mainly hydrogen. The solubility of hydrogen in the molten metal is the largest in aluminum. Therefore, aluminum can dissolve a large amount of hydrogen at high temperature; while the solubility of hydrogen in the valley is reduced from 0.69 to 0.036 by about 20 times, so when welding aluminum, Henan There is a great tendency for the street to produce stomata.
Third, the welding deformation and the formation of cracks tend to be large, the linear expansion coefficient of aluminum is twice as large as that of steel, and the shrinkage rate during two solidification is twice as large as that of steel, and therefore the stress and welding deformation caused by welding. Secondly, the high temperature and high temperature plasticity of the aluminum alloy is low, and hot cracks are easily generated under a large internal stress.
At four high temperatures, the strength is low, the alloying elements are easy to evaporate and burn, and the strength of aluminum at 370 degrees Celsius is about 0.1 MPA. Often, because the support main body also loves the weight of the molten pool, the formation of weld metal is sometimes caused by breakage. Weld metal is slumped and burnt through, so it is generally welded by the reverse scale method.
5. There is no color change. When the temperature of the same and the temperature is close to the melting point, color change will occur, indicating that it melts quickly, but the temperature of aluminum and aluminum alloy is lower, and the solid state liquid has no obvious color change, so it must be carefully operated during welding;
Article source: www.bombgroup17.com Aluminum alloy processing Aluminum welding process