Characterization of S (Al2CuMg) phase particles present in as-cast and annealed Al–Cu–Mg(–Li)–Ag alloys

Scanning electron microscopy in combination with electron probe micro analysis have been used to evaluate the influence of small additions (i.e. 0.5 wt%) of Ag on the composition of S (Al2CuMg) phase particles present in as-cast and annealed Al–4wt%Cu–0.5wt%Mg and Al–5wt%Cu–1.2wt%Li–0.5wt%Mg alloys. It is shown that the S phase particles present in these alloys contain Ag, and that the Ag content varies from 1.6 to 5.3 wt%. Also, the Mg contents of the S phase particles present in as-cast Al–Cu–Mg alloys are increased by Ag additions, although such an effect appears to be counteracted by the presence of Li in the alloy. It is further revealed that the stability of the S phase particles during elevated temperature annealing is influenced by Li additions, as well as by relatively higher Mg contents of the alloy, and that these results have implications for the practical homogenizing annealing treatments.