Corrosion Resistance

What are some common methods for increasing corrosion resistance for both bare Aluminum and Steel?

Hint
Apple typically advertises a certain method in their keynotes for the aluminum iPhone chassis. Sometimes these processes act as a sacrificial layer to improve corrosion resistance.
Hint 2
To prevent dissimilar metal corrosion and thread galling, you would coat the threaded hardware in _____.
Anodizing or Chemical Filming Aluminum are common methods to increase corrosion resistance. Passivation is a common chemical process for enhancing corrosion resistance on Steel. You can also post process plate (silver, nickel, zinc etc) hardware to prevent dissimilar metal corrosion and thread galling.
Anodizing or Chemical Filming for Aluminum. Passivation for Steel. You can also post process plate (silver, nickel, zinc etc) the hardware.