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Effects of high shear deformation from equal channel angular pressing-conform on the microstructural and mechanical properties of magnesium alloys
Davis, Casey F.
Davis, Casey F.
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2019
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Magnesium (Mg) and magnesium alloys are of great interest in the medical industry due to their high specific strength and biocompatibility. Mg is a hexagonal close-packed (hcp) metal that inherently has limited ductility. Previous work has shown the potential to alter the mechanical properties of Mg with severe plastic deformation (SPD) via equal channel angular pressing (ECAP). This research develops the processing parameters for a continuous method of ECAP, equal channel angular pressing – conform (ECAP-C), to develop an industrially relevant method to produce Mg with enhanced strength and ductility. In this dissertation, the effects of the processing parameters (temperature, feed rate, number of passes, and route) on microstructural and mechanical properties of AZ31 are studied. The microstructural changes in the alloy are primarily measured by electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) with x-ray line profile analysis (XLPA); the mechanical properties are measured by tensile tests with 2D digital image correlation (DIC). Processing temperature has the largest impact on the grain size and dislocation density of ECAP-C processed Mg where higher temperature produces larger grains and smaller dislocation densities. The number of passes directly impacts the grain size distribution. The processing route affects the crystallographic texture and the arrangement of dislocations. The processing feed rate has very little effect on the microstructure or mechanical properties. The measured mechanical properties show that grain refinement causes an increase in strength of up to 30% while crystallographic texture from different processing routes can increase strength of AZ31 by 60%. The dislocation density has little apparent effect on the mechanical properties, though the arrangement of dislocations can affect the strength. Ultimately, ECAP-C was found to have the ability to tailor Mg (specifically, AZ31) to have enhanced strength and ductility by carefully controlling the processing parameters.
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