The effect of ternary trace additions on the nucleation and growth of γ′ precipitates in an Al-4.2 At. Pct Ag alloy

Abstract

The role of trace elements on the nucleation and growth kinetics of γ′ precipitates in an aged Al-4.2 at. pct Ag alloy was determined. Comparing the characteristic properties of different trace elements on the precipitate dimensions and density after aging showed that a combination of high solute/vacancy binding energy and diffusivity was required to significantly affect the length, thickness, and density of γ′ precipitates. The elements which had the most pronounced effect were In and Sn, and the high solute/vacancy binding energy of In and Sn appears to be largely electronic in origin. The mechanism by which these trace elements affect the micro-structure is to reduce the number of quenched-in dislocation loops for heterogeneous nucleation of γ′ precipitates. The decreased number of nucleation sites leads to a prolonged matrix super-saturation, which causes an increase in the length, thickness, and ledge density of γ′ precipitates.