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. 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 tungsten alternating current argon arc welding or tungsten pulse argon 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, pulse MIG welding have more and more applications (argon or argon/helium mixture)

　　Pre-welding preparation

　　1. Cleaning before welding: When welding aluminum and aluminum alloys, the oxide film and oil stains on the welding joints of the workpiece and the surface of the welding wire should be strictly removed before welding;

　　1) Chemical cleaning Chemical cleaning has high efficiency and stable quality. It is suitable for cleaning welding wire and small-size, batch-produced workpieces. Two kinds of dipping method and scrubbing method are available. Use acetone, gasoline, kerosene and other organic solvents to degrease the surface, use 5%～10% NaOH solution at 40℃～70℃ for alkaline washing for 3 min～7 min (the pure aluminum time is slightly longer but not more than 20 min), and rinse with flowing water , Then pickling with 30% HNO3 solution at room temperature to 60℃ for 1 min to 3 min, rinse with running water, air-dry or low-temperature drying.

　　 2) Mechanical cleaning: When the workpiece size is large, the production cycle is longer, and the contamination is contaminated after multi-layer welding or chemical cleaning, mechanical cleaning is often used. First wipe the surface with organic solvents such as acetone and gasoline to remove oil, and then directly use a copper wire brush or stainless steel wire brush with a diameter of 0.15 mm to 0.2 mm until the metallic luster is exposed. Generally, it is not advisable to use a grinding wheel or ordinary sandpaper for sanding, so as to prevent the sand particles from staying on the metal surface and entering the molten pool during welding to cause defects such as slag inclusion. In addition, scrapers, files, etc. can also be used to clean the surface to be welded.

　　 After cleaning, if the storage time is too long (such as more than 24h), it should be processed again.

　　2. Backing plate: Aluminum alloy has very low strength at high temperature, and liquid aluminum has good flow properties, and the weld metal is prone to collapse during welding. In order to ensure the penetration of the weld without collapsing, a backing plate is often used to support the molten pool and nearby metal during welding. The backing plate can be graphite plate, stainless steel plate, carbon steel plate, copper plate or copper rod. An arc-shaped groove is opened on the surface of the backing plate to ensure the formation of the reverse side of the weld. It is also possible to weld on both sides without backing plate, but it requires skillful welding operation or adopts advanced technological measures such as strict automatic feedback control of arc welding energy.

3. Pre-heating before welding: Thin and small aluminum parts generally do not need to be pre-heated. When the thickness is 10 mm to 15 mm, pre-welding can be performed. According to different types of aluminum alloys, the pre-heating temperature can be 100 ℃ to 200 ℃, and oxygen can be used. An acetylene flame, electric furnace or torch heating. Preheating can reduce the deformation of the weldment and reduce the defects such as pores.

　　 post-welding treatment

　　 (1) Clean up after welding The residual flux and welding slag left on the weld and nearby after welding will destroy the passivation film on the aluminum surface and sometimes corrode the aluminum parts, so it should be cleaned up. Workpieces with simple shapes and general requirements can be cleaned by simple methods such as hot water washing or steam blowing. Aluminum parts with high requirements and complex shapes, after scrubbing with a hard-bristled brush in hot water, they are then immersed in chromic anhydride aqueous solution or potassium dichromate solution at a concentration of 2% to 3% at 60℃～80℃5 Min to 10min, and scrub with a hard brush, then rinse in hot water, dry in an oven, or blow dry with hot air, or dry naturally.

　　 (2) Post-weld heat treatment aluminum containers generally do not require heat treatment after welding.