Mechanical properties of Al(Sc,Zr) alloys at ambient and elevated temperatures

This study investigates the mechanical properties of ternary Al(Sc,Zr) alloys containing 0.27-0.77 vol.% of Al₃(Sc,Zr) precipitates with an average radius 〈r〉=2-24 nm. Microhardness values at ambient temperature follow predictions of the Orowan dislocation bypass mechanism, with a transition to the precipitate shearing mechanism predicted for 〈r〉 larger than 2 nm. Addition of Zr to binary Al(Sc) alloys delays the onset and kinetics of over-aging at 350 and 375 °C, but has little influence on the magnitude of the peak microhardness. Creep deformation at 300 °C is characterized by a threshold stress, which increases with 〈r〉 in the range 2-9 nm, in agreement with prior results for binary Al(Sc) alloys and a recently developed general climb model considering elastic interactions between dislocations and coherent, misfitting precipitates. At constant 〈r〉 and precipitate volume fraction, Zr additions do not significantly improve the creep resistance of Al(Sc) alloys.