Effects of solution treatment on microstructure and mechanical properties of Al-9.0Zn-2.8Mg-2.5Cu-0.12Zr-0.03Sc alloy

Effects of additions minor contents of 0.03% Sc and 0.12% Zr and solution treatment on microstructure and mechanical properties of Al-9.0Zn-2.8Mg-2.5Cu alloy were studied by metallographic microscopy, differential thermal analysis (DSC) and transmission electron microscopy (TEM), in order to obtain high-performance Al alloys. The minor additions of Sc (less than 0.1%) were carried out. The results show that with the additions of 0.03% Sc and 0.12% Zr, the petaloid Al3(Sc,Zr) precipitated phases occur in Al-9.0Zn-2.8Mg-2.5Cu alloy, and Al3(Sc,Zr) particles obviously hinder the recrystallization of Al-9.0Zn-2.8Mg-2.5Cu alloy during homogenizing and extruding processes due to their strong pinning effect on dislocation. Multi-stage solution is better than single solution, for it can avoid recrystallization of Al-9.0Zn-2.8Mg-2.5Cu alloy with the minor contents of Sc (less than 0.1%). The proper solution treatment is (420 °C, 3 h)+(465 °C, 2 h) under which Al-9.0Zn-2.8Mg-2.5Cu-0.12Zr-0.03Sc alloy obtains a tensile strength of 777.29 MPa and a elongation of 11.84%.