It is important that the surfaces to be joined are cleaned before welding. Oils, paint, grease, moisture and the thick oxide layer should be removed. Hydrogen released by contaminents can cause porosity.
The surface oxides are best removed either by mechanical or chemical means. A wire brush with stainless steel bristles approx. 0.010 - 0.015 in. in diameter is a recommended mechanical tool. The brush must be kept free from contaminents.
Table 1 lists some common chemical treatments that are used to remove oxides. The cleaning should take place before fitup or fixturing since the joint may be difficult to access for cleaning afterward.
Typically, the geometries for aluminum joints are equivalent to geometries for steel, but since the aluminum weld pool is more fluid and the welding gun nozzle a little larger, the geometry generally has smaller root openings and greater groove angles than designs for steel.
A groove angle of 60º is a minimum for a thickness of 0.12 in. Greater thicknesses may require angles of 75º to 90º.
