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Overview Light MetalsThe very low density and excellent castability of magnesium is leading to increased use in various applications, especially in automobiles, despite poor galvanic corrosion resistance and a higher cost than aluminum. Further expansion of the magnesium market should come from reduced cost, an increased design base, a better understanding of the scientific underpinning of magnesium alloys, improved protection systems, and the development of cost-affordable cast and wrought products.

Attractive elevated-temperature properties and low density make the titanium aluminides very interesting for both engine and airframe applications, particularly in the aerospace industry. The challenge to the materials scientist is to maintain these characteristics while building-in "forgiveness". The basic phase diagram and crystal structure of both the Ti3AI and TiAI phases are reviewed, followed by a consideration of chemistry-processing-microstructuredeformation/fracture-mechanical property relationships in monolithic material. Conventional and innovative synthesis methods are presented, including use of hydrogen as a temporary alloying element. Composite concepts as a method to enhance not only "forgiveness" but also elevated-temperature behaviour are discussed. Environmental effects are evaluated prior to consideration of present and projected applications of both monolithic and composite material. It is concluded that while the titanium aluminides in monolithic form can be used now in non-demanding applications, much further research and development is required before this material class can be used in critical applications, especially in composite concepts.

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