NUCLEATION OF INTERMEDIATE PHASES IN ALUMINIUM-SILVER-COPPER ALLOYS

摘要

The nucleation of intermediate phases in aluminium alloys containing silver and copper has been examined. When aged isothermally these alloying elements precipitate as the metastable phases θ′(Al_2Cu) and γ′(Ag_2Al), forming on {100} and {111} habit planes respectively. This study focuses on determining the influence of the θ′ precipitate phase upon the nucleation of the γ′ phase. Alloys with equimolar amounts of copper and silver show a considerably more refined distribution of the γ′ phase than equivalent binary aluminium-silver alloys. In addition, the θ′ precipitate is seen in close association with one or more γ′ particles, with the silver-rich precipitate adjoining a growth ledge of the θ′ phase. This suggests that θ?, and in particular the growth ledges, play a role in the nucleation of γ′.