Precipitate assemblies formed on dislocation loops in aluminium-silver-copper alloys

TL;DR

This study investigates the unique precipitate assembly microstructure of the b3' phase in aluminium-silver-copper alloys, revealing novel faceted elliptical formations influenced by copper, which impact alloy properties.

Contribution

It reports a new faceted elliptical assembly morphology of b3' precipitates in aluminium-silver-copper alloys, differing from binary alloys, due to copper's effect on defect structures.

Findings

b3' precipitates form as two-variant assemblies with elliptical faceted morphology

Copper modifies the defect structure, altering precipitation behavior

The morphology influences precipitate density and mechanical properties

Abstract

The precipitation microstructure of the \gamma' (AlAg2) intermetallic phase has been examined in aluminium-silver-copper alloys. The microstructure developed in an Al-0.90at.%Ag-0.90at.%Cu alloy was significantly different from that reported for binary Al-Ag alloys. The orientation relationship between the matrix and precipitate was unchanged; however, the \gamma' phase formed as aggregates with a two-dimensional open assemblies. Each such assembly contained two variants of the \gamma' phase alternately arranged to form a faceted elliptical unit. The \theta' (Al2Cu) phase formed on these assemblies after further ageing. The faceted elliptical assembly morphology has not been previously reported for the \gamma' precipitate. The change in precipitation behaviour was attributed to copper modifying the as-quenched defect structure of the matrix. This precipitation morphology clarifies earlier observations on the precipitate number density and mechanical properties of aluminium-silver-copper alloys.