Alcad is a metal consisting of

• A. Pure aluminum surface layers on an aluminum alloy core
• B. Aluminum alloy surface layers on pure aluminum core
• C. Pure titanium surface layers on aluminum core
• D. Copper surface layers on aluminum core

Answer: (A)

Alclad is aluminum-clad material: thin layers of pure aluminum on the outside bonded to a core of aluminum alloy. The pure outer layers resist corrosion very well because pure aluminum forms a stable oxide film, while the aluminum alloy core provides the strength needed for structural use. This combination gives high strength with excellent corrosion resistance, which is why Alclad is used for aircraft skins. The other configurations would not deliver the same corrosion protection and mechanical balance—pure aluminum outer layers on an alloy core are essential, rather than alloy outer layers, or layers of titanium or copper on an aluminum core.