Cleaning aluminum parts before welding is a two-step process. First, remove oils, grease, and other contaminants to prevent weld porosity. Second, eliminate oxide from the areas to be welded to prevent lack of fusion and other weld defects. Let’s address grease and other contaminants first. Oils, grease, lubricants, and other hydrocarbon contaminants usually are removed in one of two ways. For low and moderate volumes, you can use a degreasing solvent saturated into a clean, lint-free rag. Good degreasing solvents include acetone, toluene, methyl ethyl ketone, and most mineral spirits. Alcohols are not good degreasers. Let the degreasing solvent evaporate completely before fitting the parts together. Also, do not strike a welding arc until the solvent has evaporated completely. Striking an arc can cause a fire or release hazardous gases. Higher-volume industries typically use a mild alkaline cleaning solution at 140 to 160 degrees F to remove hydrocarbons. Parts can be dipped into or sprayed with this solution. After they’re cleaned, parts should be rinsed in clean hot water and dried. Hand or power wire brushing with a clean stainless steel wire brush usually removes oxides. Use this brush only on aluminum, and degrease parts before wire-brushing. Wire-brushing before degreasing makes it significantly more difficult to remove hydrocarbons from the surface. The wire brush you use should be relatively flexible. Also, avoid brushes with stiff or knotted bristles. Use only light pressure when wire-brushing. Strong alkaline or acid solutions also can be used to remove oxides. However, these chemicals require several cautions during use; this will be addressed in a future column.