Aluminum welding method, aluminum alloy welding method

Aluminum welding method, aluminum alloy welding method

Aluminum welding method

1. Welding characteristics of aluminum and aluminum alloys

(1) Aluminum is very easy to oxidize in the air and during welding. The resulting aluminum oxide (Al2O3) has a high melting point, is very stable, and is not easy to remove. It hinders the melting and fusion of the base material. The oxide film has a high specificity and is not easy to float on the surface. It is easy to generate defects such as slag inclusion, lack of fusion, and incomplete penetration. The oxide film on the surface of aluminum and the absorption of a large amount of moisture can easily cause pores in the weld. Before welding, chemical or mechanical methods should be used for strict surface cleaning to remove the surface oxide film. Strengthen the protection during the welding process to prevent its oxidation. In tungsten argon arc welding, an AC power source is used to remove the oxide film through the "cathodic cleaning" function. For gas welding, use flux that removes the oxide film. When welding thick plates, the welding heat can be increased. For example, the helium arc has a large heat, using helium or argon-helium mixed gas protection, or adopting large-scale molten electrode gas shielded welding. In the case of direct current connection, there is no need for "cathode Clean up".

(2) The thermal conductivity and specific heat capacity of aluminum and aluminum alloys are about twice that of carbon steel and low-alloy steel. The thermal conductivity of aluminum is ten times that of austenitic stainless steel. During 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, in addition to the energy consumed in the molten metal pool, more heat is needlessly consumed in other parts of the metal. This kind of useless energy consumption is more significant than steel welding. In order to obtain high-quality welded joints, energy concentrated and high-power energy should be used as much as possible, and sometimes preheating and other technological measures can be used.

(3) The coefficient of linear expansion of aluminum and aluminum alloys is about twice that of carbon steel and low-alloy steel. The volumetric shrinkage rate 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. When the aluminum welding molten pool is solidified, shrinkage cavities, shrinkage porosity, thermal cracks and high internal stress are prone to occur. In production, measures to adjust the composition of the welding wire and the welding process can be used to prevent the occurrence of hot cracks. Where the corrosion resistance permits, aluminum-silicon alloy welding wire can be used to weld aluminum alloys other than aluminum-magnesium alloys. When the aluminum-silicon alloy contains 0.5% silicon, the hot cracking tendency is greater. As the silicon content increases, the alloy crystallization temperature range becomes smaller, the fluidity is significantly improved, the shrinkage rate decreases, and the hot cracking tendency decreases accordingly. According to production experience, when the silicon content is 5% to 6%, thermal cracking does not occur, so the use of SAlSi (silicon content 4.5% to 6%) welding wire will have better crack resistance.

(4) Aluminum has a strong ability to reflect light and heat. There is no obvious color change when the solid and liquid transition states, and it is difficult to judge during welding operations. High-temperature aluminum has very low strength, it is difficult to support the molten pool, and it is easy to weld through.

(5) Aluminum and aluminum alloys can dissolve a large amount of hydrogen in the liquid state, but hardly dissolve hydrogen in the solid state. During the process of solidification and rapid cooling of the weld pool, hydrogen is too late to overflow, and hydrogen pores are easily formed. The moisture in the arc column atmosphere, the moisture absorbed by the welding material and the oxide film on the surface of the base metal 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) Alloy elements are easy to evaporate and burn, which reduces the weld performance.

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

(8) Aluminum is a face-centered cubic lattice, without allotropes, and there is no phase change during heating and cooling. The welded seam grain is easy to be coarse and cannot be refined through phase change.

2. Welding method

Almost various welding methods can be used to weld aluminum and aluminum alloys, but aluminum and aluminum alloys have different adaptability to various welding methods, and various welding methods have their own applications. The gas welding and electrode arc welding methods have simple equipment and convenient operation. Gas welding can be used for repair welding of aluminum sheets and castings that do not require high welding quality. Electrode arc welding can be used for repair welding of aluminum alloy castings. Inert gas shielded welding (TIG or MIG) method is the most widely used aluminum and aluminum alloy welding method. Aluminum and aluminum alloy thin plates can be welded by AC argon tungsten arc welding or pulsed argon tungsten arc welding. Aluminum and aluminum alloy thick plates can use tungsten helium arc welding, argon-helium mixed tungsten gas shielded welding, MIG welding, pulse MIG welding. MIG welding and pulse MIG welding have become more and more widely used.

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