Although the GMAW provides some cleaning action this should not be relied on for all the cleaning.aluminum must also be precleaned mechanically or chemically to remove the oxide film and other residue or contaminants.
aluminum oxidizes so rapidly the interval between welding and cleaning should be as short as possible.
you can select one of many ways to clean the metal wiping with a clean rag or emery cloth will remove any oil dirt or oxide film.for more stubborn residue use sandpaper,stainles steel wire brush or stainless steel wool.if this doen't work you may have to use a acetone.caustic soda solutions or a sulfuric acid bath. after precleaning rinse with a distilled water.
Remember when working with any of these solutions safety comes first gloves glasses and sheild is best.