Q: What’s the best way to clean aluminum before welding?
A: Cleaning aluminum parts before welding requires two operations.
1. Remove Oil and Grease
First, remove oils, grease, lubricants, and other hydrocarbon contaminants from the surface to prevent weld porosity. Some people try to do this with a wire brush, but a brush won’t remove these materials—it only spreads them around and creates small scratches and other nooks and crannies on the surface that hold oil and grease, making them impossible to remove later.
Don’t use alcohol as a degreaser on aluminum either, as it does a poor job. And vapor degreases emit volatile compounds into the air, so most of them have been prohibited over the years for environmental reasons. For the same reason, many shops have stopped using organic solvents as well.
So what can you use to degrease aluminum?
For low and moderate volumes, effective solvents include acetone, toluene, methyl ethyl ketone, and most mineral spirits. Apply them by saturating them into a clean, lint-free rag. 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.
For higher volumes, a mild alkaline cleaning solution (such as strong soap) at 140 to 160 degrees F will typically remove hydrocarbons. You can dip parts into this solution or spray it on. After parts are clean, rinse them in hot water and dry them.
2. Remove Oxide
Second, eliminate oxide from the areas to be welded to prevent lack of fusion and other weld defects.
For this task, a wire brush is a good choice. Light-pressure manual or powered wire brushing with a clean stainless steel wire brush usually removes oxides. The brush should have relatively flexible bristles that are not knotted. Be sure to use this brush only on aluminum and only after removing oil and grease from the aluminum surface.
