Particle pinning effect on grain boundary and double peak-aging characteristic in a hot-extruded Mg-Zn-based alloy

Abstract

To overcome bottleneck of strength-ductility trade-off is a challenge in Mg-Zn-based alloys. In this work, we develop an age-hardening Mg-1.0Zn-0.1Ca-0.1Al-0.1Mn (wt.%) hot-extruded alloy with better strength-ductility synergy by synergistic heterostructure and nanoprecipitate, exhibiting a tensile yield strength of 352 MPa, an ultimate tensile strength of 413 MPa and an elongation of 15.2 %, respectively. Besides, dynamic recrystallization and dynamic precipitation at different die angles (30° and 90°) and extrusion temperatures (220°C, 235°C and 250°C), and aging precipitation are systematically investigated. Particle pinning effect on grain boundary (GB) considering particle radius and strengthening effects are further clarified. Firstly, under large die angle (90°) and low extrusion temperature (220°C), typical heterostructure containing recrystallized regions and non-recrystallized regions is achieved due to significant particle pinning effect of nanoscale Ca₂Mg₆Zn₃ and Al₈Mn₅ particles, and solute dragging effect of Zn and Ca elements on GB. Phase-field simulation and experimental validation showing the evolution of bow-shape GB under significant particle pinning force during the particle-GB interaction. Meanwhile, the phase-field simulations show that the maximum particle pinning force is enhanced as increasing of the particle radius. Secondly, upon ageing at 180°C, a distinct double peak-aging characteristic emerges in the hetero-structured Mg-1.0Zn-0.1Ca-0.1Al-0.1Mn hot-extruded alloy. The first ageing peak mainly arises from the precipitation of GP zones, while the second ageing peak primarily originates from the co-precipitation of β₁´ and β₂´ phases. Finally, hetero-deformation induced strengthening, nanoprecipitate-reinforced Orowan strengthening and deformation coordination by twins and non-basal slips contribute to the strength-ductility synergy. These results provide valuable insights for developing high-performance Mg-Zn-based alloys.