Design of high strength Al–Cu based alloy by minor addition of Hf and Zr

The present work explores the effect of minor additions of 0.1%Hf and 0.15%Zr in Al-2%Cu (all in at.%) processed through chill-casting followed by a three-stage heat treatment schedule towards designing a high strength, high-temperature Al–Cu-based alloy. The three-stage heat treatment involves direct aging at 400 °C, followed by solutionising at 530 °C and then aging at 190 °C. The heat-treated microstructure consists of a fine distribution of composite intermetallic precipitates coherently embedded in an fcc α-Al matrix. These intermetallics are Al₃(Hf,Zr) L1₂ spherical precipitates on which θ′′/ θ′ are heterogeneously nucleated. The former provides high-temperature strength and stability, while the latter strengthens the α-Al matrix at ambient temperatures. The heat-treated cast alloy shows a 0.2% proof stress of ~ 465 MPa at room temperature and ~ 270 MPa at 250 °C.