Chances are if you’ve bought a nice aftermarket part for your car that was made from aluminum, it was anodized. Anodizing is used to create a tough finish that doesn’t add a layer of thickness to an otherwise precision machined aluminum pieces like paint or powder coat. This is accomplished by purposely oxidizing, aka rusting, the aluminum. Unlike steel, when the surface of aluminum oxidizes it becomes very hard and it seals the rest of the aluminum from oxygen. Anodizing runs electricity through the aluminum to grow an extra thick layer of aluminum oxide while sealing in dyes to give your aluminum parts a good lucking durable finish. Check out this video by The Engineer Guy explaining the titanium and aluminum anodizing process.