The influence of 0.5 wt % Ag on defect structures in an Al/3.2 wt % Cu/1.5 wt % Mg alloy

A quantitative study has been made by electron microscopy of the defect structures in an Al/3.3 wt % Cu/1.6 wt % Mg alloy. The main defects observed in the quenched and lightly aged alloy were prismatic dislocation loops, while in an alloy of similar copper and magnesium contents, but containing also 0.5 wt % Ag, fewer defects were observed, these being mainly dislocation helices. In the quenched condition the average loop and helix diameters increased with increase in quenching bath temperature, and on ageing the loop and helix size increased with ageing time. These observations have been interpreted on the basis of silver increasing the solute/vacancy interaction, possibly with the formation of complex clusters of Cu, Mg and Ag atoms with vacancies.