Brushes are used for pre-welding cleaning of aluminum materials_FAQ

When welding aluminum and aluminum alloys, there is an important step before welding: that is, the oxide film and oil stains on the weld joint of the workpiece and the surface of the welding wire should be strictly removed. It is an indispensable tool in the cleaning process. 1. Chemical cleaning The chemical cleaning efficiency is high and the quality is stable. 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 running 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 dry at low temperature.　　 2. Mechanical cleaning: mechanical cleaning is often used when the workpiece is large in size, longer in the production cycle, multi-layer welding or chemical cleaning. First wipe the surface with acetone, gasoline and other organic solvents 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 24 hours), it should be processed again.　　3, 　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, etc. 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 skilled welding operation or strict automatic feedback control of arc welding energy and other advanced technological measures. 4. 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 blowtorch, etc. are heated. Preheating can reduce the deformation of the weldment and reduce the defects such as pores. 5. Post-weld treatment 　　 (1) Clean up after welding. 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 they 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 brush in hot water, they are then immersed in a chromic anhydride aqueous solution or potassium dichromate solution at a concentration of 2% to 3% at a concentration of about 60℃～80℃5 Min to 10 minutes, 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.