Synergy of strength-plasticity via dynamic heating process: A non-isothermal annealing strategy to regulate recrystallization of 7B50 aluminum alloy

Abstract

Traditional isothermal annealing processes often face the strength-plasticity trade-off dilemma due to recrystallization softening effects. In this study, a novel non-isothermal annealing method named dynamic heating process was proposed to achieve simultaneous improvement of strength and plasticity by regulating the recrystallization process. Microstructural investigations revealed that the percentage of low-angle grain boundaries (LAGBs) decreased with increasing solid-state temperature. Multi-scale second-phase particles (predominantly η phases) pinned LAGBs, promoting the formation of dislocation walls and ultimately leading to refined subgrains. Particle-stimulated nucleation and strain-induced boundary migration dominated the recrystallization behavior at a semi-solid temperature range. The solidified liquid phases interacted synergistically with both elongated and equiaxed grains, significantly improving the elongation (El) along the rolling direction (RD) at 535°C. With further dynamic heating to 595°C, equiaxed recrystallized grains became dominant. Simultaneously, Cu-rich liquid phase generation at grain boundaries caused material weakening. The optimized non-isothermal annealing process was dynamic heating to 485°C at a rate of 10°C/min. Under these conditions, the alloy demonstrated superior mechanical performance: in RD, the ultimate tensile strength (UTS) reached 556 MPa with yield strength (YS) of 365 MPa and El of 14%. The transverse direction (TD) specimens achieved UTS of 529 MPa, YS of 335 MPa, and El of 17.5%. Compared to the initial samples, these specimens showed 19.0% El, 114.6% YS, and 78.9% UTS enhancement in the RD, and 41.4% El, 104.8% YS, and 71.6% UTS elevation in the TD. This work provided an efficient heat treatment strategy for the synergistic regulation of strength and plasticity in high-strength aluminum alloys.