Structure-mechanical property relationship for Al(Sc,Zr) alloys

A study of the relationship between the microstructural and mechanical properties of Al(Sc,Zr) alloys containing less than 1 vol.% of coherent Al₃Sc_1-xZr_x precipitates, with an average radius <r>=2-24 nm, is presented. Classical precipitation-strengthening deformation mechanisms are observed at 24°C, where a transition from precipitate shearing to Orowan dislocation looping is calculated to occur for <r> = 2.0 nm. For alloys aged above 300°C, Zr additions delay the onset and kinetics of over-aging, but have no effect on the magnitude of the peak hardness. Creep experiments of Al(Sc,Zr) alloys at 300°C yield high stress exponents (27-50), and threshold stress values between 0.06 and 0.33 of the Orowan stress. The dislocation climb controlled threshold stress is dependent on the average precipitate radius, which is in agreement with Al(Sc) alloys and a model describing the elastic interactions between dislocations and coherent precipitates.