Aluminum and its alloys were introduced in your e-textbook. The history of the development and applications of aluminum and its alloys were covered in the video for this lesson. Now I am going to expand on this material and highlight the role of aluminum in airplane development.
Aluminum is the third most abundant element in the Earth's crust, after oxygen and silicon, and is the Earth's most abundant metal. It is about 8% of the crust by mass, but it is rarely found as a native metal as it is very chemically active. Its oxide forms more readily than the oxide of iron and, unlike the oxide of iron, once formed it blocks oxygen and water from penetrating the aluminum oxide. This results in aluminum being very corrosion-resistant. Iron, on the other hand, forms rust which does not block oxygen and water, so iron pieces will rust to completion if left long enough in a wet atmospheric environment. Aluminum has a low density, which makes it a candidate for lightweight applications.