Strengthening in Thermomechanically Processed Magnesium Alloys

Commercial Mg alloys, compared to other engineering materials such as steels or aluminum materials have inferior strengths (Y.S. = ~120 MPa), limited ductility and poor formability. Furthermore, due to high costs their use in structural applications for transportation industry is still rather limited. Therefore, there is significant interest in developing microstructure modification routes to produce novel Mg base alloys with an attractive combination of strength and ductility at room temperature as-well as warm temperature formability. In order to promote use of such microstructurally engineered Mg materials, better understanding of the relationship between microstructure, texture etc. with mechanical properties must be developed for a range of different alloys. In this work, microstructure evolution and mechanical response of two thermomechanically processed Mg alloys AZ61L and AZ70-TH were investigated. Initial findings of this work are presented here. The processed materials exhibited a good combination of strength and tensile ductility at room temperature that was further enhanced (Y.S. > 250 MPa, El. % > 10%) by low temperature (180°C) annealing treatment for 1 hr. The ductility and in-plane anisotropy in mechanical property was found to be related to basal texture formation in the sheet plane. In addition to the Hall-Petch strengthening due to near ultrafine grain size, β-particles from as-molded microstructure, complement strengthening by sub-dividing and possibly solutionizing/re-precipitating into nano-sized, well-dispersed, obstacles to dislocation motion and grain growth.