Effect of Er additions on the precipitation strengthening of Al–Hf alloys

Precipitation strengthening was investigated in dilute Al–Er, Al–Hf and Al–Er–Hf alloys. Combined addition of 0.045 at.% Er and 0.18 at.% Hf in Al gives a maximum hardness of 640 MPa, which is significantly higher than that of the Al–0.18Hf and Al–0.045Er alloys. The remarkable strengthening can be attributed to the addition of Er, which accelerates the precipitation kinetics and stimulates the decomposition of Al–Hf. The effect of Er and Hf on precipitation strengthening in Al–Er–Hf alloys is discussed.