The relation between mechanical properties and microstructural evolution induced by Sc microalloying in Al-20Zn-3Cu alloy

We demonstrate the effect of Sc microalloying on the mechanical properties of Al-20Zn-3Cu-xSc (x = 0, 0.1, 0.3, 0.5 wt%) alloys. Trace amounts of Sc addition (<0.5 wt%) simultaneously improve the mechanical strength and the ductility of the Al-20Zn-3Cu-xSc alloys. Among the developed alloys, the Al-20Zn-3Cu-0.3Sc alloy shows the highest tensile strength of 363 MPa with an elongation of 6.8%. Comprehensive microstructural investigation reveals that the Sc microalloying element induces macroscopic (~μm scale) and microscopic (~nm scale) structural changes. Macroscopically, the Al grain size and large particles typically formed in the grain boundaries are significantly reduced. Microscopically, the formation of nanoprecipitates is facilitated by the addition of trace amounts of Sc, resulted in generation of local strain field. Quantitative symmetry investigation then demonstrates that the formation of nanoprecipitates severely break the local symmetry of Al, which affects the mechanical properties of Al-20Zn-3Cu-xSc alloys.