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Can Aluminum Sheet Be Soldered
May 30, 2018

It can be welded completely. This is the choice of welding process.

Aluminum and aluminum alloy welding characteristics

(1) Aluminum is easily oxidized in air and during welding. The resulting alumina (Al2O3) has a high melting point and is very stable and difficult to remove. Obstructs the melting and fusion of the base metal, the oxide film has a large specific gravity, and does not easily float to the surface. It is easy to produce defects such as slag inclusions, incomplete fusion, and incomplete penetration. Aluminum surface oxide film and adsorption of a large amount of water, easy to make pores in the weld. Prior to welding, chemical or mechanical methods should be used to conduct a rigorous surface cleaning and remove the surface oxide film. In the welding process to enhance protection against oxidation. 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."

(2) The thermal conductivity and specific heat capacity of aluminum and its alloys are more than 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 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 welded joints, energy-intensive, high-power energy sources should be used as much as possible, and preheating and other technical measures may be used.

(3) The coefficient of linear expansion of aluminum and aluminum alloy is approximately twice that of carbon steel and low alloy steel. The bulk shrinkage of aluminum during solidification is large, and the deformation and stress of the weldment are large. Therefore, measures to prevent welding deformation must be taken. The aluminum welding pool is prone to shrinkage, shrinkage, hot cracking and high internal stress during solidification. In the production, the measures of adjusting the wire composition and welding process can be adopted to prevent the generation of hot cracks. In the case of corrosion resistance, aluminum-silicon alloy welding wire can be used to weld aluminum alloys other than aluminum-magnesium alloys. When the Al-Si alloy contains 0.5% silicon, the hot cracking tendency tends to be larger. With the increase of silicon 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 content of silicon is 5% to 6%, no thermal cracking occurs. Therefore, the use of SAlSi (4.5% to 6% silicon content) wire will provide better crack resistance.

(4) Aluminum has a strong ability to reflect light and heat. When solids and liquids change state, there is no obvious change in color. It is hard to judge when welding. High temperature aluminum is very low strength, supporting the bath is difficult, easy to wear.

(5) 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.

(6) The alloying elements are easy to evaporate, burn, and deteriorate the weld performance.

(7) If the matrix metal of the base metal is strengthened by deformation or strengthened by solid solution aging, the heat of welding will reduce the strength of the heat-affected zone.

(8) Aluminum is a face-centered cubic lattice with no allotropes. There is no phase transition during heating and cooling, and the grains of the weld are easily coarse. Grain cannot be refined by phase transformation.