Characterisation of Precipitation Hardening Response and As-Quenched Microstructures in Al-Mg(-Ag) Alloys

Abstract

The age-hardening response in Al-Mg alloys, with and without trace additions of Ag, aged isothermally at 160°C, 200°C and 240°C was investigated. Additionally, the effects on ageing response of cold work introduced after solution treatment, water quenching and prior to the ageing treatments were clarified for the Al-Mg-(Ag) alloy. The dislocation populations in the as-quenched microstructures of Al-10 mass% Mg alloys with and without trace additions of Ag were characterised. Trace additions (0.5 mass%) of Ag to Al-Mg alloys with low solute Mg contents (<5 mass%) promote an age-hardening response, while similar additions to Al-Mg alloys with higher solute Mg contents (e.g. 10 mass%) enhance significantly the age-hardening response. The age-hardening response in an Al-10Mg-0.5Ag (mass%) alloy is significantly enhanced by the introduction of 7% cold work, post solution treatment and prior to ageing at 160°C and 200°C. The identity of the dislocations in as-quenched Ag-free and Ag-modified Al-10 mass% Mg alloys has been confirmed as unit perfect a/2‹110› type. The addition of Ag does not appear to modify the form of the dislocations and no dissociation of these dislocations was observed. The density of dislocations in the solution treated and quenched condition in the Al-10 mass% Mg alloy was higher by a factor of ∼2 compared to that in the Al-10Mg-0.5Ag (mass%) alloy subjected to similar treatment.