|dc.description.abstract||Given their low density and high specific strength, magnesium alloys show excellent potential for use in lightweight structural applications. Current challenges facing these materials are poor strength levels and limited low temperature formability in comparison to the conventionally used steel and aluminum alloys. As such, the focus of this thesis is twofold. First, the effects of different deformation mechanisms on the ductility of a magnesium alloy are systematically investigated, in order to ultimately shed light on potential strategies for enhancing low temperature formability. Second, the need for higher strength magnesium alloys is addressed.
With this in mind, this thesis first investigates deformation and failure mechanisms at low and elevated temperatures, from 25°C to 200°C, under different favored deformation modes (basal slip, prismatic slip, and tension twinning) on the most commonly wrought magnesium alloy, Mg-AZ31. Here, a main finding was that ductility and strength levels can be simultaneously optimized when prismatic slip is the most active deformation mechanism. In addition, dynamic recrystallization (DRX) was found to be most active under basal and prismatic slip at elevated temperatures and positively enhanced ductility. In contrast, tension twinning suppressed DRX and was correlated with comparatively poor ductility.
In the second part of this thesis, a precipitation hardenable alloy, Mg-ZKQX6000, was processed via Equal Channel Angular Processing (ECAP) in the attempt to obtain ultra-high strength levels via grain refinement. Here, ECAP produced ultra-fine grain sizes with ultra-high strength levels approaching ~400 MPa along several orientations. The roles of precipitation, grain size, and texture were investigated, where it was determined that ductility for ECAP processed samples was limited due to a high volume fraction of precipitates after ECAP. In addition, prismatic slip could be correlated with optimal strength and ductility, confirming findings from the first part of this thesis.||en