Introduction

The use of aluminum as a structural material is a fairly recent development. Originally, aluminum was considered to be a precious metal. In fact, when the Washington Monument was completed in December, 1884, it was capped with a 100-ounce pyramid of pure aluminum. The problem that initially impeded the use of aluminum as a structural material was the fact that aluminum is a reactive metal. It is never found in its elemental state in nature, but is always tightly bound with oxygen as aluminum oxide, Al₂O₃.

Aluminum oxide, found as bauxite ore, was always plentiful; however, no direct reduction method, such as that used to make steel, was found to produce aluminum from bauxite until 1886, when the American, Charles M. Hall, and the Frenchman, Paul Heroult, almost simultaneously, yet independently, discovered electrolytic processes for obtaining pure aluminum from aluminum oxide. As a result, aluminum became available in commercial quantities. These processes, with some modifications, are still used today.

Since that time, aluminum has found wide use in numerous applications:

 • It conducts electricity and heat almost as well as copper.

 • It is widely used in electrical bus bars and other conductors, heat exchangers, and cookware.

 • It does not become brittle with decreasing temperature, but instead becomes stronger, so it has found wide application in cryogenic equipment at temperatures as low as –452°F.

 • It is very corrosion resistant in most environments, so it has found wide applications in marine and chemical environments.

The characteristics of aluminum alloys, which make them attractive as structural materials for many applications, are their light weight (one third the weight of steel for equal volumes) and their relatively high strength (equal in many cases to that of construction steel grades). This combination has resulted in increased use of aluminum alloys in applications such as automobiles, trucks, over-the-road trailers, and railroad cars. Additionally, the structure of most aircraft is fabricated mainly from aluminum alloys, although in this application, pieces are most often joined by riveting.