Chapter one - Alloying Elements and Dopants: Phase Diagrams

Abstract

More than several dozen aluminum alloys are used in different areas of manufacturing and technology. Patents have been issued for thousands of alloy compositions. However, most of them contain a relatively limited number of alloying elements. All alloying elements that are used for aluminum (Al) alloy design can be classified into three principal groups: basic alloying elements, ancillary additions (or dopants), and impurities. Depending upon the nature of an alloy, the same elements could play different roles. In the overwhelming majority of all cases only four alloying elements are used: the metals magnesium, zinc, and copper; and the semiconductor silicon. These chemical elements are called “basic,” or “principal,” because they are introduced into aluminum alloys in large amounts and define their microstructure and properties. The introduction of relatively large amounts of principal alloying elements is possible because they are characterized by considerable solubility in Al. It is known that maximum solubility in Al exceeds 1% only for the following seven elements: magnesium, copper, silicon, lithium, manganese, germanium, and silver. However, not a single one of these chemical elements can form continuous solid solutions, that is, at some critical concentration none enters an intermediate compound or forms its own solid solution.