Material preparation: during welding aluminium, the welder must be careful to clean the material and remove any oxide and hydrocarbon from the surface of the aluminium by oil or solvent. The melting temperature of oxide on the surface of aluminium is 3700 degrees Fahrenheit, and the base aluminium material below melts at 1200 degrees Fahrenheit. Therefore, any residual oxide on the surface of the base material will restrict the penetration of the filler material to the welding aluminium parts.
To remove oxides on the surface of aluminium, stainless steel wire brush or solvent corrosion can be used. When you use stainless steel brush, you can only brush it in a fixed direction. Be careful not to be too hard and careless: rough motion will cause oxide to be embedded in aluminium base material. At the same time, only use stainless steel brush on the surface of aluminium, do not use the brush used on stainless steel or carbon steel.
1) Chemical Cleaning
The efficiency of chemical cleaning is high and the quality is stable. It is suitable for cleaning of the welding wire, the small-sized workpiece and batch production. Two kinds of immersion cleaning and washing method can be used. Deoiled by using the organic solvents such as acetone, gasoline, kerosene and other organic solvents, and washed 3 min ~ 7 min (3 min to 7 min) by using 5% ~ 10%NaOH solution at 40℃～70℃. (pure aluminium was slightly longer but not more than 20 min), and rinsed with clean water and then washed with 1 min to 3 min in 30%HNO3 solution at room temperature to 60℃, and rinsed with clean water, dry by wind or dry at low temperature.
2) Mechanical Cleaning
Mechanical cleaning is often used when the work piece size is large, the production period is long, and the contamination occurs after multi-layer welding or chemical cleaning. First use acetone, gasoline and other organic solvents to wipe the surface to remove the oil, then directly use a copper wire brush with a diameter of 0.15mm to 0.2mm or a stainless steel brush to brush for revealing the metallic luster. Generally, it is not suitable for grinding with grinding wheel or ordinary sandpaper to prevent sand from remaining on the surface of the material and entering the weld pool when welding aluminium. In addition, scrapers and files can be used to clean up the surface to be welded.
After the cleaning and washing of the workpiece and welding wire, the oxide film will be reproduced during the storage process, especially in the wet environment. In the environment of steam pollution such as acid and alkali, the oxide film grows faster. Therefore, the storage time between the workpiece and welding wire after cleaning and the welding process should be as short as possible. In the case of humid climate, it should be welded in 4 h after cleaning. After cleaning, if the storage time is too long (if more than 24 h), it should be reprocessed.
Preheating: preheated welding aluminium parts can help to avoid welding cracks. The preheating temperature should not exceed 230 degrees Fahrenheit. Use a thermometer to monitor the temperature to prevent overheating. In addition, the intermittent welding can be used to enhance the preheating effect at the beginning and end of the welding area. Welders should also preheat a thick aluminium sheet when welding aluminium of thin sheets.
Processing speed: the process of welding aluminium needs high temperature and high speed treatment. Unlike steel, the higher thermal conductivity of aluminium requires higher temperature and higher current setting and higher welding speed. If the welding speed is too slow, there will be too much welding penetration, especially when welding aluminium of thin sheets.
Protective gas: argon is used as the most commonly used welding gas for welding aluminium because of its excellent cleaning performance. When welding 5XXX- series aluminium alloy, the protective gas used is argon and helium mixture gas. Up to 75% of the helium ratio can achieve the best effect of reducing the influence of magnesium oxide.
Gas metal arc welding and pulsed gas metal arc welding are used more and more widely (argon or argon / helium mixture).