Precipitation processes in an Al-2.5Cu-1.5Mg (wt. %) alloy microalloyed with Ag and Si

Abstract We have produced precipitation on and along both the α and the {111}α crystal systems by microalloying an Al-2.5Cu-1.5Mg (wt. %) base alloy with Ag and Si. Using electron microscopy and atom probe field ion microscopy, we have demonstrated that Ag+Si additions produce multi-component clustering reactions. When compared to comparable quaternary compositions, the quinary alloy exhibits a higher hardness. The first precipitates observed were GPB zones, rich in Cu and Mg and containing traces of both Si and Ag. Following ageing at 200 °C, the peak hardness microstructure consisted of rod-shaped GPB zones along α together with X′ and Ω precipitation, both as plates on the {111}α planes. The Ω phase was less stable than the X′ phase and dissolved soon after ageing to peak hardness. This was associated with a rapid drop in hardness. The overaged microstructure was dominated by S phase.