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Welding methods: Almost all welding methods can be used for welding aluminum and aluminum alloys, but aluminum and aluminum alloys have different adaptability to various welding methods, and various welding methods have their own application occasions. Gas welding and electrode arc welding methods are simple and easy to operate. Gas welding can be used to repair welding thin aluminum plates and castings that do not require high welding quality. Welding electrode arc welding can be used for welding aluminum alloy castings. The inert gas shielded welding (TIG or MIG) method is a widely used aluminum and aluminum alloy welding method. Aluminium and aluminum alloy sheets can be tungsten arc argon arc welding or tungsten electrode argon arc welding. Aluminium and aluminum alloy thick plates can be tungsten arc xenon arc welding, argon xenon hybrid tungsten gas shielded arc welding, gas metal arc welding, pulsed gas metal arc welding. MIG welding and pulsed gas metal arc welding are more and more widely used (argon or argon/helium mixture)
1. Pre-weld cleaning: When welding aluminum and aluminum alloys, the oxide film and oil stains on the workpiece weld and the surface of the wire should be strictly removed before welding.
1) chemical cleaning chemical cleaning, high efficiency, stable quality, suitable for clean welding wire and small size, batch production of the workpiece. Available dip method and scrub method two. Can be used acetone, gasoline, kerosene and other organic solvents to surface oil, with 40 °C ~ 70 °C 5% ~ 10% NaOH solution alkaline wash 3 min ~ 7 min (a little longer but not more than 20 min pure aluminum), flow water rinse Then, it is pickled with 30% HNO3 solution at room temperature to 60°C for 1 min to 3 min, rinsed with flowing water, air-dried or dried at low temperature.
2) Mechanical cleaning: Mechanical cleaning is often used when the workpiece has a large size, a long production cycle, multi-layer welding or chemical cleaning. First use acetone, gasoline and other organic solvents to wipe the surface to remove oil, then directly use a copper wire brush with a diameter of 0.15 mm to 0.2 mm or a stainless steel wire brush to brush until the metal luster is exposed. Generally, it is not suitable to grind with grinding wheel or ordinary sandpaper, so as to avoid the sand particles remaining on the metal surface, and the defects such as slag inclusion will be generated when welding. In addition, the surface to be welded can be cleaned with a spatula, a trowel, or the like.
After cleaning, if the storage time is too long (eg more than 24 h), it should be reprocessed.
2. Backing plate: The strength of aluminum alloy is very low at high temperature, and the flow properties of liquid aluminum are good. The weld metal will easily fall down during welding. In order to ensure penetration without collapse, welding pads are often used to support the weld pool and nearby metal. Pads can use graphite plates, stainless steel plates, carbon steel plates, copper plates or copper bars. An arc-shaped groove is formed on the surface of the pad to ensure that the weld seam is formed on the reverse side. It is also possible to weld double-sided molding without single-sided welding of the backing plate, but it is required that the welding operation be skilled or adopt advanced technological measures such as strict automatic feedback control of arc welding energy.
3, preheating before welding: thin, small aluminum generally do not have to preheat, the thickness of 10 mm ~ 15 mm can be preheated before welding, according to different types of aluminum preheat temperature can be 100 °C ~ 200 °C, available oxygen An acetylene flame, electric furnace or torch heating. Preheating can reduce the deformation of the weldment, reduce the porosity and other defects. Post-weld treatment
(1) After welding, the residual flux and welding slag that remain in the weld and its vicinity after welding will destroy the passivation film on the aluminum surface, and sometimes it will corrode aluminum parts and should be cleaned. Simple shapes and common parts can be cleaned by simple methods such as hot water flushing or steam blowing. High-demanding and complex-shaped aluminum parts are brushed with a bristle brush in hot water, and then immersed in an aqueous solution of chromium anhydride or potassium dichromate at a concentration of about 20% to 3% at about 60°C to 80°C. Min ~ 10 min, and scrubbing with a bristle brush, then washing in hot water, drying with an oven, or drying with hot air, can also be naturally dry.
(2) Post-weld heat treatment Aluminum containers generally do not require heat treatment after welding.