Bi-directional dynamic recrystallization behavior of AZ31 alloy by Al-RE precipitation control

Abstract

Texture weakening by dynamic recrystallization (DRX) control has been a challenging issue on improving the mechanical performance of wrought Mg alloys. Here we report the attainment of bi-directional DRX in an AZ31-0.9Nd-0.3Y alloy, which accelerated DRX and weakened the basal texture. The nature and content of secondary phase particles in the solidification microstructures were modified by the mixed-addition of rare-earth elements, and a dispersive distribution of Al₁₁RE₃ particles located at grain boundaries (GBs) and grain-interior Al₂RE particles was achieved in the AZ31-0.9Nd-0.3Y alloy. Compared with the AZ31 and the alloys with sole-element addition, DRX in AZ31-0.9Nd-0.3Y occurred at a smaller critical strain at the same strain rate and extrusion temperature. Upon extrusion, GB bulging, continuous DRX, twin-induced nucleation and particle-stimulated nucleation (PSN) were operative but play a different part in the different stages of deformation. The Al₁₁RE₃ and Al₂RE particles induced respectively inward and outward growth of DRXed grains at large strains, representing a bi-directional DRX behavior. The twin-induced DRX ceased to occur while the PSN carried by grain-interior particles caused substantial orientation randomness of the DRXed grains. Multiple dislocation slip systems were activated in the particle deformation zones to form dislocation cells, nucleating DRXed grains with a rich variety of orientations in the neighborhood of the particles. The extruded AZ31-0.9Nd-0.3Y alloy exhibited simultaneous improvement of strength and ductility performance.