Abstract:The Zn, Cu, and Sc contents of 7xxx Al alloys were adjusted according to the chemical composition of a 7085 Al alloy, and the effects of Zn and Cu contents and Sc addition on the microstructures, hardness, and quench sensitivity of the 7xxx Al alloys were studied. The alloys with high Zn content and Sc addition exhibited higher hardness than the 7085 alloy at the position 3 mm away from the quenching end. The density of η and T phases increased with the increase in Zn and Cu contents, and the Sc addition led to the formation of the Y phase and more η phases at the position 120 mm away from the quenching end. Compared with the 7085 alloy, the high Zn-high Cu and Sc-added alloys exhibited higher quench sensitivity, while the simultaneous increase in Zn content and decrease in Cu content could enhance the hardness and reduce the quench sensitivity of the 7085 alloy.

Key words: Al-Zn-Mg-Cu alloy; quench sensitivity; Al₃(Sc,Zr); Y phase; grain boundary