Heterogeneous nucleation-driven precipitation of densely distributed nanoscale phases in a low-alloyed magnesium alloy

Abstract

In this work, we report a heterogeneous nucleation-driven precipitation in a low-alloyed magnesium (Mg) alloy, in which tri-atomic-layer η' phases serve as nucleation sites for Al-Mn-(Ca) precipitates. After peak aging, the alloy exhibits a high density of nanoscale Al-Mn-Ca phases (∼2.5 × 10²³ m⁻³), resulting in a substantial age-hardening response of ∼61 MPa, with no decline observed even after prolonged over-aging for up to 300 h. Atomic-resolution HAADF-STEM and APT analyses reveal a three-stage phase evolution: (I) initial η' phase formation, (II) heterogeneous nucleation of Al-Mn clusters on η' phases, and (III) transformation of Al-Mn clusters into Al-Mn-Ca phases, accompanied by partial η' phase dissolution. Molecular dynamics simulations further identify non-equilibrium stress sites around the tri-atomic-layer Al-Ca η' phases, driving the preferential aggregation of Al-Mn clusters. This work presents a new strategy for precipitate inoculation in solid-state precipitation, offering pathways to enhance precipitate density in Mg alloys.