Rapid solidification processing with specific application to aluminium alloys

The critical need for high strength, high performance, and cost effective materials has resulted in the use of novel processing techniques for the development of new aluminium alloys for structural applications. The highly attractive combinations of microstructure and mechanical properties achievable through rapid solidification technology (RST) have prompted the study and application of rapid solidification as a means of improving the behaviour of existing alloy systems and also developing novel alloying compositions. The rapid extraction of thermal energy associated with RST permits large deviations from equilibrium, as evidenced by the extension in solid solubility limits, sharp reductions in grain size, and a reduction in the size and number of segregated phases with concomitant development of non-equilibrium phases. In the present paper, the fundamental scientific principles underlying RST are discussed and particular emphasis is given to published studies of composition-processing-microstructure relationships in rapidly solidified aluminium alloys. The scope of the present work encompasses the development of consolidated RST aluminium alloys, including both dispersion and precipitation strengthened materials. The various processing techniques used to achieve rapid quenching are reviewed, with specific application to aluminium alloys. Microstructure-property relationships in powder processed, precipitation hardened, and dispersion strengthened aluminium alloys are critically examined with specific reference to matrix microstructural features, dislocation-microstructure interactions, and matrix slip characteristics. The deleterious effects of surface oxides on mechanical behaviour is also highlighted.