Why does cylinder head made of alluminium?

Answer 1

Aluminum is used for cylinder heads and engine blocks to make the entire engine lighter. A lighter engine is desired for a number of reasons, including better gas mileage, better handling, better braking response and better chassis balance.

Since the aluminum used in standard engines and cylinder heads does not provide a good surface for high-friction areas, such as valve guides and piston cylinders, where aluminum-to-aluminum surfaces would wear out too quickly, other metals such as steel is used for the aluminum component to slide on. For example, an aluminum piston rides inside a steel liner which is inserted into the aluminum engine block.

Since aluminum and steel respond very differently to the heat and cold in an engine, very careful design engineering is required when using these two metals together.