Effect of the Sc addition and pre-recovery multi-stage solution heat treatment on recrystallization and mechanical properties in spray-formed Al–Zn–Mg–Cu–Zr alloys

The influence of the Sc addition and pre-recovery multi-stage solution heat treatment on the recrystallization and mechanical properties in spray-formed Al–Zn–Mg–Cu–Zr alloys has been compared by hot extrusion, following single-stage, two-stage, and pre-recovery two-stage solution heat treatments. The Sc addition and pre-recovery multi-stage solution heat treatment have a significant impact on the recrystallization behaviors. The Sc addition alters the dynamic recrystallization (DRX) mechanisms, which change from the dynamic recovery and continuous dynamic recrystallization (CDRX) of the Al–Zn–Mg–Cu–Zr alloy to the CDRX and geometric dynamic recrystallization (GDRX) of the Al–Zn–Mg–Cu–Zr-Sc alloy during the hot extrusion process. During the subsequent solution heat treatment, the Sc addition and the pre-recovery multi-stage solution heat treatment modify static recrystallization (SRX) mechanisms, which change strain-induced boundary migration (SIBM) of the Al–Zn–Mg–Cu–Zr alloy to particle-stimulated nucleation (PSN) effect of the Al–Zn–Mg–Cu–Zr-Sc alloy. Although the Sc addition refines the grain size, the redissolution of primary phases with the Sc and Zr elements is suppressed during the single-stage and two-stage solution heat treatments. The pre-recovery multi-stage solution heat treatment can promote the redissolution of primary phases with the Sc and Zr elements, thereby promoting the precipitation of the η′ phases. The enhancement of the yield strength mainly originates from the grain refinement and precipitation of the precipitates. The yield strength, tensile strength, and elongation of the Al–Zn–Mg–Cu–Zr-Sc alloy subjected to the pre-recovery multi-stage solution heat treatment are 793.2 ± 4.0 MPa, 813.5 ± 3.6 MPa, and 8.1 ± 0.5%, respectively. This study provides a new approach for the preparation of the ultra-high-strength Al–Zn–Mg–Cu alloys.