1, chemical cleaning
Chemical cleaning is high efficiency and stable, suitable for cleaning welding wire and small size, batch production of the workpiece. There two ways, immersion cleaning and scrubbing. Acetone, gasoline, kerosene and other organic solvents can be used to remove surface grease, cleaning 3 min ~ 7 min (pure aluminium time slightly longer, but not more than 20 min) with 40 ℃ ~ 70 ℃ 5% ~ 10% NaOH solution alkaline. Water rinse. then pickling 1 min ~ 3 min with the 30% HNO3 solution at room temperature 60 ℃, water rinse. Finally, make it dry.
2. Mechanical cleaning
In the large size, long production cycle, multi - layer welding products or contaminated after chemical cleaning, often use mechanical cleaning. First, use acetone, gasoline and other organic solvents to wipe the surface to remove oil, then brush directly until the metallic luster with a diameter of 0.15mm ~ 0.2mm copper wire brush or stainless steel wire brush brush. Generally, it is not advisable to use grinding wheel or common sandpaper to polish, so as to avoid the sand particles remaining on the metal surface. In addition, scraper and file are available to clean up the surface to be welded.
After cleaning, if the storage time is too long (more than 24h), it should be reprocessed.
3. Backing plate
Aluminum alloy strength at high temperature is very low, liquid aluminum flow performance is good, when welding the weld metal prone to collapse phenomenon. In order to ensure the penetration of welding and not collapse, often use pad to support the pool and nearby metal. The backing plate can be graphite plate, stainless steel plate, carbon steel plate, copper plate or copper bar. Make a circular arc groove on the surface of the backing plate to ensure that the weld side is formed. It can also be formed without backing plate, but it requires skilled welding operation or strict automatic feedback control of arc welding energy and other advanced technological measures.
Preheating before welding. Generally, thin, small aluminum pieces needn’t preheat. Aluminum parts with a thickness of 10mm ~ 15mm can be preheated before welding. According to the different types of aluminum alloy preheating temperature is 100 ℃ ~ 200 ℃. It can be heated by oxyacetylene flame, electric furnace or torch. Preheating can make the welding parts reduce deformation and defects such as porosity.
4. Post-welding treatment
1. After welding, residual flux and slag left in the vicinity of the weld can damage the passivation film on the aluminum surface and sometimes corrode the aluminum parts, so must clean the surface after welding. Workpieces with simple shapes and general requirements can be cleaned by simple methods such as hot water scrubbing or steam brushing.High requirement and complex shape aluminum, after scrubbing with a bristle brush in hot water, Then immersion clean at the concentration of 2% ~ 3% of chromic anhydride or potassium dichromate solution immersion 5 min ~ 10 min at 60-80℃. Brush with a stiff bristle brush, then rinse in hot water. Finally, make it dry.
2, Generally, Aluminum pieces do not require heat treatment after welding.