Precipitation in an A1-0.212 wt.% Au alloy

Abstract

Electron microscope observations show that aging a supersaturated solid solution of Al-0.212 wt.% Au alloy produces a distribution of plate precipitates of the equilibrium phase η (AuAl2) on the matrix cube planes without the formation of any metastable phases (contrary to previous report). Dislocations in the matrix act as heterogeneous sites for the nucleation of these precipitates. The large coherency strain field due to a mismatch of 4.8% parallel to their broad faces gives rise to a large age-hardening effect. Misfit dislocations nucleated at longer ageing times to accommodate the mismatch reduce this effect.