The electrochemical process that converts the surface of any metal into a thick, scratch-resistant, and corrosion-resistant substance is called anodization. It is a process in which you submerge the metal into an electrolyte liquid with a cathode. The cathode releases the hydrogen from the liquid, releasing oxygen from the metallic surface. This metal acts as an anode and hence the name anodized.
The surface of the metal, or in this case aluminum, becomes oxidized and gives a classic metallic look. It appears shiny and dull at the same time. Anodized aluminum becomes more durable because of anodizing.