Welding characteristics of aluminum and aluminum alloys

1. Oxide film: Aluminum in the air and welding is easy to oxidize, the alumina (Al2O3) high melting point, very stable, not easy to remove. Hinder the melting and fusion of the base metal, the ratio of the oxide film is significant, it is not easy to surface, easy to produce slag inclusion, not fusion, not penetration and other defects. The surface of aluminum oxide film and adsorption of a large amount of water, easy to make the weld porosity. Before welding, the surface shall be strictly cleaned by chemical or mechanical methods to remove the oxide film on the surface. Strengthen protection during welding to prevent oxidation. In GTAW, ac power supply is used to remove the oxide film through “cathode cleaning”. In gas welding, flux to remove oxide film is used. In thick plate welding, welding heat can be increased, for example, helium arc heat, using helium or argon-helium mixture protection, or the use of large specification of fusion gas welding, in the case of direct DC connection, “cathode cleaning” is not required. 2. High thermal conductivity The thermal conductivity and specific heat capacity of aluminum and its alloys are about twice that of carbon steel and low alloy steel. The thermal conductivity of aluminum is more than ten times that of austenitic stainless steel. In the welding process, a large amount of heat can be rapidly transmitted to the interior of the base metal, so when welding aluminum and aluminum alloy, in addition to the energy consumed in the melting metal pool, there is also more heat wasted in other parts of the metal, this useless energy consumption is more significant than steel welding. In order to obtain high quality welding joints, energy concentration and high power should be used as far as possible, and sometimes preheating and other technological measures can also be used. 3. Large linear expansion coefficient, easy deformation and thermal crack The linear expansion coefficient of aluminum and its alloys is about twice that of carbon steel and low alloy steel. The volume shrinkage rate of aluminum during solidification is large, and the deformation and stress of welding parts are large. Therefore, measures should be taken to prevent welding deformation. It is easy to produce shrinkage cavity, shrinkage porosity, thermal crack and high internal stress during solidification of aluminum welding pool. In production, measures can be adopted to adjust the composition of welding wire and welding process to prevent the occurrence of hot cracks. Aluminum alloys other than al-mg alloys can be welded with al-si alloy wires if corrosion resistance is allowed. With the increase of silicon content, the crystallization temperature range of the alloy decreases, the fluidity increases significantly, the shrinkage rate decreases, and the hot cracking tendency decreases correspondingly. According to the production experience, when the silicon content is 5%~6%, there is no hot cracking, so the use of SAlSi strip (silicon content is 4.5%~6%) wire will have better cracking resistance. 4. Highly soluble hydrogen Aluminum and its alloys dissolve large amounts of hydrogen in liquid form, but hardly in solid form. In the process of solidification and rapid cooling of welding pool, hydrogen has no time to overflow and hydrogen pores are easily formed. The moisture in the arc column atmosphere, the moisture absorbed by the oxide film on the surface of welding material and base metal are the important sources of hydrogen in the weld. Therefore, the source of hydrogen should be strictly controlled to prevent the formation of pores. 5. The joints and heat-affected areas are easily softened Alloying elements are easy to evaporate and burn, so that the performance of weld decreases. When the base metal is strengthened by deformation or solution aging, the welding heat will decrease the strength of the heat affected zone. Aluminum is a face-centered cubic lattice with no isomers and no phase transformation during heating and cooling. The weld grain is easy to coarse and cannot be refined by phase transformation. Welding method: Almost all welding methods can be used to weld aluminum and aluminum alloys, but the adaptability of aluminum and aluminum alloys to various welding methods is different, and each welding method has its own application. Gas welding and electrode arc welding method, simple equipment, easy to operate. Gas welding can be used for repair welding of aluminum sheet and casting with low welding quality requirements. Electrode arc welding can be used for repair welding of aluminum alloy castings. Inert gas welding (TIG or MIG) is the most widely used welding method for aluminum and aluminum alloys. Aluminum and aluminum alloy sheet can be tungsten ac argon arc welding or tungsten pulse argon arc welding. The thick aluminum and aluminum alloy plate can be used in the tungsten he arc welding, argon-he mixed tungsten gas welding, fusion gas welding, pulse fusion gas welding. Gmaw and PULSE GMAW are more and more widely used.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods