There are several welding methods for aluminum; how to weld it?

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Welding methods for aluminum: Almost all welding methods can be used to weld aluminum and aluminum alloys, but these materials respond differently to various welding methods, and each method has its own appropriate applications. Oxyacetylene welding and shielded metal arc welding are methods that feature simple equipment and easy operation. Oxyacetylene welding can be used for patch welding thin aluminum sheets and castings where high welding quality is not required. Shielded metal arc welding can be used for patch welding aluminum alloy castings. Gas shielded welding (TIG or MIG) is the most widely used welding method for aluminum and aluminum alloys. Aluminum and aluminum alloy thin sheets can be welded using AC TIG welding or pulsed TIG welding. Thick plates of aluminum and aluminum alloys can be welded using tungsten inert gas welding, argon-helium mixed tungsten inert gas welding, metal inert gas welding, and pulsed metal inert gas welding. Gas metal arc welding and pulsed gas metal arc welding using argon or an argon/helium mixture are being used more and more frequently. Pre-welding preparations: 1. Pre-welding cleaning: When welding aluminum and aluminum alloys, it is essential to thoroughly remove the oxide films and oil residues from the surfaces of the workpiece joints and the welding wire before welding; 2. Chemical cleaning: This method offers high efficiency and consistent quality, and it is suitable for cleaning welding wires as well as workpieces that are not very large and are produced in batches. Two methods can be used: immersion and scrubbing. The surface oil can be removed using organic solvents such as acetone, gasoline, or kerosene. Follow this by treating it with a 5%–10% NaOH solution at 40°C–70°C for 3 minutes to 7 minutes (slightly longer time for pure aluminum, but not more than 20 minutes). Rinse with running water, then acid-wash it with a 30% HNO3 solution at room temperature to 60°C for 1 minute to 3 minutes. Rinse again with running water and dry it by air or at low temperature. 3. Mechanical cleaning: It is commonly used when the workpiece is large in size, the production cycle is long, multi-layer welding is employed, or the surface becomes contaminated again after chemical cleaning. First, wipe the surface with organic solvents such as acetone and gasoline to remove oil, then brush it directly with a copper wire brush or stainless steel wire brush having a diameter of 0.15 mm to 0.2 mm until a metallic luster appears. It is generally not advisable to use grinding wheels or ordinary sandpaper for polishing, as this can leave sand particles on the metal surface, which may enter the molten pool during welding and cause defects such as inclusions. Additionally, a scraper, file, or similar tool can be used to clean the surface to be welded. If it is stored for an extended period after cleaning (e.g., more than 24 hours), it should be processed again. 　 4. Shims: Aluminum alloy has very low strength at high temperatures, and liquid aluminum has good flow properties; as a result, the weld metal is prone to sagging during welding. To ensure full penetration without collapse, backing plates are often used during welding to support the molten pool and the surrounding metal. The backing plate can be made of graphite plate, stainless steel plate, carbon steel plate, copper plate, or copper rod, etc. An arc-shaped groove is made on the surface of the backing plate to ensure proper formation on the reverse side of the weld. It is also possible to perform single-sided welding for double-sided formation without using shims, but this requires skilled welding techniques or the use of advanced process measures such as strict automatic feedback control of the arc welding energy. 　　 5. Preheating before welding: Thin and small aluminum parts generally do not require preheating. For parts with a thickness of 10 mm to 15 mm, preheating can be carried out. Depending on the type of aluminum alloy, the preheating temperature can range from 100°C to 200°C. Heating can be done using an oxy-acetylene flame, an electric furnace, or a torch. Preheating can reduce deformation in the welded parts and minimize defects such as pores. Post-weld treatment: After welding, the residual flux and slag remaining on and around the weld can damage the passivation layer on the aluminum surface; in some cases, they may even corrode the aluminum parts. Therefore, these residues must be removed thoroughly. Workpieces with simple shapes and moderate requirements can be cleaned using simple methods such as flushing with hot water or cleaning with steam. For aluminum parts with high requirements and complex shapes, after brushing them with a hard-bristled brush in hot water, they are immersed in an aqueous solution of chromic anhydride or potassium dichromate at a concentration of 2%–3% at a temperature of around 60°C–80°C for 5 minutes to 10 minutes, followed by brushing again with a hard-bristled brush. After that, they are rinsed in hot water, dried in an oven or with hot air, or allowed to dry naturally. 　　 Post-weld heat treatment: Aluminum containers generally do not require heat treatment after welding.