High-Strength AZ91 Alloy Fabricated by Rapidly Solidified Flaky Powder Metallurgy and Hot Extrusion

Abstract

A high-strength AZ91 alloy is produced via hot extrusion using flakes fabricated through the rapidly solidified flaky powder metallurgy. The AZ91 alloy flakes have an extremely fine dendritic structure without any second-phase particles owing to the fast cooling rate during solidification; these microstructural features considerably promote dynamic recrystallization and precipitation behaviors during extrusion process. As a result, the AZ91 alloy extruded using the flakes exhibits an almost fully recrystallized microstructure with a very small average grain size of 1.2 µm owing to an increase in the number of nucleation sites for recrystallization, and it shows a high microstructural homogeneity owing to the numerous Mg17Al12 precipitates uniformly distributed throughout the material. This extruded AZ91 alloy has a tensile yield strength of 345 MPa, ultimate tensile strength of 417 MPa, and total elongation of 5.6%. These superior tensile strengths are mainly attributed to the combined effects of precipitation hardening caused by abundant fine precipitates and grain boundary hardening caused by fine recrystallized grains.