Precipitation in melt-spun AI-based binary alloys with transition metals

Abstract

Supersaturated binary solid solutions of various transition metals in A1 have been prepared by melt spinning and the thermal stability of these alloys determined using analytical transmission electron microscopy. It has been found that there are two very different mechanisms whereby these alloys return to equilibrium. The first of these, exhibited by AI-Mo and AI-V, involves the generation of dislocations during annealing which allow pipe diffusion to the grain boundaries where precipitates of the equilibrium phase are formed. In the second, observed in AI-Fe and AI-Cr alloys, equilibrium precipitates are observed in the grain centres and in the grain boundaries but it has been shown that this precipitation is preceded by the formation of quasicrystals. The significance of these observations on the stability of high-temperature Al alloys is discussed together with the implications for the development of alloys with improved high-temperature properties.