Preface
Almost all kinds of 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 application occasions.
Aluminum welding methods
Gas welding and arc welding methods have simple equipment and convenient operation. Gas welding can be used for the repair welding of aluminum thin plates and castings with low welding quality requirements. Arc welding can be used for the 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 tungsten inert gas AC argon arc welding or tungsten inert gas pulse argon arc welding. Aluminum and aluminum alloy thick plates can be welded by tungsten inert gas helium arc welding, argon-helium mixed tungsten inert gas shielded welding, metal inert gas shielded welding, and pulse metal inert gas shielded welding.
Metal inert gas shielded welding and pulse metal inert gas shielded welding are becoming more and more widely used (argon or argon/helium mixture).
Preparation before welding
1. Cleaning before welding
When welding aluminum and aluminum alloys, the oxide film and oil stains on the weld joint and the surface of the welding wire should be strictly removed before welding;
2. Chemical cleaning
Chemical cleaning has high efficiency and stable quality, and is suitable for cleaning welding wires and small-sized, batch-produced workpieces. There are two methods: immersion and scrubbing. The surface can be degreased with organic solvents such as acetone, gasoline, and kerosene, and alkaline washed with 5% to 10% NaOH solution at 40℃ to 70℃ for 3 min to 7 min (pure aluminum takes a little longer but not more than 20 min), rinsed with running water, and then pickled with 30% HNO3 solution at room temperature to 60℃ for 1 min to 3 min, rinsed with running water, and air-dried or low-temperature dried.
3. Mechanical cleaning
Mechanical cleaning is often used when the workpiece is large in size, the production cycle is long, and it is contaminated after multi-layer welding or chemical cleaning.
First, wipe the surface with acetone, gasoline and other organic solvents to remove oil, and then directly brush it with 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 suitable to use a grinding wheel or ordinary sandpaper to polish, so as to avoid sand particles remaining on the metal surface and entering the molten pool during welding to produce defects such as slag inclusions.
In addition, scrapers, files, etc. can also be used to clean the surface to be welded. If the storage time after cleaning is too long (such as more than 24 hours), it should be reprocessed.
4. Pad
The strength of aluminum alloy is very low at high temperature, and the flowability of liquid aluminum is good. The weld metal is prone to collapse during welding. In order to ensure full penetration without collapse, pads are often used to support the molten pool and nearby metals during welding.
The pad can be made of graphite plate, stainless steel plate, carbon steel plate, copper plate or copper rod. A circular arc groove is opened on the surface of the pad to ensure the reverse side of the weld is formed. It is also possible to weld on one side and form on both sides without adding a backing plate, but it requires skilled welding operation or the adoption of advanced process measures such as strict automatic feedback control of arc welding energy.
5. Preheating before welding
Thin and small aluminum parts generally do not need to be preheated. Preheating before welding can be performed when the thickness is 10 mm to 15 mm. The preheating temperature can be 100℃ to 200℃ according to different types of aluminum alloys. It can be heated by oxyacetylene flame, electric furnace or blowtorch. Preheating can reduce deformation of welded parts and reduce defects such as pores.
Post-weld treatment
Post-weld cleaning The residual flux and welding slag left in 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. Workpieces with simple shapes and general requirements can be cleaned by simple methods such as hot water flushing or steam blowing.
Aluminum parts with high requirements and complex shapes should be brushed in hot water with a hard brush, then immersed in a chromic anhydride aqueous solution or potassium dichromate solution at a concentration of 2% to 3% at about 60℃ to 80℃ for 5 min to 10 min, and brushed with a hard brush, then rinsed in hot water, dried in an oven, or blown dry with hot air, or dried naturally.
Post-weld heat treatment Aluminum containers generally do not require heat treatment after welding.