Atomic simulation of bimodal microstructure in wrought Mg-Al-Zn-Ca-Mn alloy

Multiscale characterization and molecular dynamics (MD) simulations were combined to reveal a dynamically enhanced inhibition mechanism of static recrystallization (SRX) in Mg-Al-Zn-Ca alloys. Compared with the rapid and full SRX of Mg-3Al-1Zn-0.3Mn alloy, the recrystallized fraction increases rapidly at the early stage of SRX but then slows and stabilizes at ∼46% after annealing up to 30 min in a Mg-3Al-1Zn-1Ca-0.3Mn alloy. It is shown that Al₂Ca precipitates thicken from 1 to 4.3 nm during annealing, increasing their pinning stress on low-angle grain boundaries (LAGBs) by up to threefold and reducing LAGB energy by ∼45%. Increasing precipitate length from 3.9 to 17.6 nm further doubles the dragging effect. Even without precipitate growth, increasing the LAGB misorientation from 4° to 14° also triples the pinning stress. This study demonstrates that the dynamically enhanced retardation of SRX originates from precipitate growth and increasing LAGB misorientation during annealing.