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.