Effect of quench-controlled precipitation hardening on microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr alloys contain of Sc micro-alloying

•By performing QCM compared to CM, the hardness increased 30%.•Peak hardness for QCM was achieved at 120 °C for 12 h.•Tensile strength aged samples compared to the annealed samples increased by 185%.•Simultaneous increase in strength and elongation was due to the Al3(Sc,Zr) distribution.•In comparison with CM sample, the QCM sample had 17% increase in the QI index. The microstructural changes and mechanical properties of Al-Zn-Mg-Cu-Zr alloy samples with 0.05 and 0.1 wt% Sc were investigated after conventional and quench-controlled precipitation hardening treatments. The results showed that by the addition of Sc microcontent, grain-refined microstructures with smooth precipitates were obtained. It was also revealed that aging treatment after the hot rolling process reduced grain size to 20 µm and resulted in the formation of dual-morphology precipitates. Thus, the quench-controlled samples showed a higher precipitate content than the conventionally treated samples, which was related to the increase in the diffusion rate of the dissolved atoms. Furthermore, mechanical tests demonstrated that the quench-controlled samples had the highest yield strength (600 MPa) due to finer microstructure and higher precipitate content.