Microstructures and properties of Al–Zn–Mg–Mn alloy with trace amounts of Sc and Zr

Microstructures and properties of Al–Zn–Mg–Mn alloy with trace amounts of Sc and Zr have been investigated. The results show that the addition of minor Sc and Zr to Al–Zn–Mg–Mn alloy can effectively refine grain size caused by the formation of Al3(Sc, Zr) particles with cubic L12 structure, which is coherent with α(Al) matrix. After solution treatment at 470 °C for 1 h, more homogenous recrystallization grains are observed in Al–Zn–Mg–Mn alloy; partial recrystallization occurs in Al–Zn–Mg–Mn–0.12Sc–0.12Zr alloy. However, Al–Zn–Mg–Mn–0.24Sc–0.12Zr alloy still remains an unrecrystallized fiber-like structure, which reveals that minor Sc and Zr can remarkably inhibit the occurrence of recrystallization. After aging treatment at 24 h for 120 °C, the tensile strength of Al–Zn–Mg–Mn–0.12Sc–0.12Zr alloy increased by 40 MPa as compared to Al–Zn–Mg–Mn alloy. When the Sc content increased to 0.24 wt%, the tensile strength of Al–Zn–Mg–Mn–0.24Sc–0.12Zr alloy reached a maximum. The main strength mechanisms are grain refinement strengthening with combined Sc and Zr additions and precipitation strengthening of Al3(Sc, Zr) particles. Compared with Al–Zn–Mg–Mn alloy, Al–Zn–Mg–Mn alloy with trace amounts of Sc and Zr exhibits higher corrosion resistance due to the discontinuity distribution of η precipitates along the grain boundary and the resistance effect on recrystallization behavior by Al3(Sc,Zr) particles.