Effect of Thermal Deformation Treatment Regimes on Al–4.5Zn–4.5Mg–1Cu–0.12Zr–0.1Sc Alloy Structure and Properties

The microstructure and change in strength of Al–4.5%Zn–4.5%Mg–1%Cu–0,12%Zr–0,1%Sc alloy during annealing after hot deformation in the temperature range 300–450°C are studied. It is established that recrystallization hardly occurs during annealing: at temperatures of 350°C and 400°C softening does not occur, which microstructural studies confirm. During annealing at 450°C yield strength is reduced by increasing the proportion of recrystallized volume to 15%. The structure formed after hot and cold rolling and subsequent annealing has a significant effect on sheet ageing kinetics compared with an ingot. The maximum effect of ageing in the sheet is observed after treatment at 125°C, whereas similar strengthening is achieved in an ingot at 150°C. Test alloy after hot and cold rolling, quenching and ageing at 125°C for 28 hours exhibits a high level of mechanical properties: yield strength 480 ± 5 MPa; ultimate strength 545 ± 7 MPa; relative elongation 6.3 ± 0.4%.