Die angle dependency of microstructural inhomogeneity in an indirect-extruded AZ31 magnesium alloy

The variation induced in the microstructural inhomogeneity of AZ31 alloy subjected to indirect extrusion was studied using tool steel dies with angles of 30°, 60° and 90°. Finite element modeling (FEM) of this extrusion process was also carried out to determine the metal flow, temperature evolution and effective strain distribution, which were then correlated with the observed microstructural changes. Although all extruded samples were found to have a bimodal microstructure consisting of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains, the inhomogeneity of their microstructural characteristics (i.e., DRX fraction and texture intensity) decreased in cross section with an increase in the die angle. The FEM analysis also demonstrated that a faster metal flow, higher temperature, and larger effective strain are generated in an alloy extruded with a 90° die angle, and that this enhances DRX behavior during extrusion and ultimately results in a homogeneously DRXed microstructure.