How does the addition of zinc affect the corrosion resistance of aluminum alloys?

The addition of zinc to aluminum alloys significantly enhances their corrosion resistance. Zinc forms a protective layer on the surface of aluminum, which prevents the metal from reacting with corrosive elements such as oxygen and moisture. This protective layer, known as a passive layer, is self-healing and can regenerate if damaged, maintaining its effectiveness over time. Additionally, zinc's presence in aluminum alloys can improve the alloy's overall mechanical properties, making it more resistant to stress corrosion cracking. This is particularly useful in marine environments or other corrosive conditions where aluminum alloys are commonly used.