Extruded Mg-Zn-Ca-Mn alloys with low yield anisotropy

Rare-earth-free Mg-5.99Zn-1.76Ca-0.35Mn (wt%) magnesium (Mg) alloys with low yield anisotropy and moderate performances were developed by utilizing hot extrusion. The sample extruded at 350 degrees C exhibited a high compression/tension yield ratio close to 1 along the extrusion direction due to its high volume fraction of the dynamically recrystallized (DRXed) grains (approximately 98%), its fine DRXed grains (average of 2.7 mu m) and its extremely weak basal texture (nearly the same as that of the as-homogenized sample). The sample extruded at 300 degrees C also exhibited a compression/tension yield ratio of 0.89 with a tensile elongation to failure of 16% and a tensile 0.2% proof stress of 289 MPa. The high compression/tension yield ratio and the medium performances of the sample extruded at 300 degrees C are attributable to its refined microstructure consisting of the fine DRXed grains (average of 1.4 mu m) and the elongated unrecrystallized regions of approximately 12 mu m in width with high number density of fine Mg6Zn3Ca2 and a-Mn precipitates. During compression test, nearly no {10-12} extension twinning was observed in the fine DRXed grains region and the formation of {10-12} extension twinning was also effectively restrained in the unrecrystallized regions due to their refined size in width, their high density of precipitates and their relatively weaker basal texture than other basal-textured Mg alloys. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.