Aluminum Melt Flux Refining

When welding aluminum, cleanliness is key. You must thoroughly remove the oxide layer and impurities from the material before welding, otherwise you'll get porosity and a weak weld. For that, use a stainless steel brush that you only use for aluminum, and wipe the weld areas again with a clean cloth and acetone just before welding. If you're TIG welding, AC helps break up the oxide layer. Also make sure your shielding gas (argon) is really clean and the nozzle is not contaminated; that's usually enough for a good result.