Abstract
Recently, we have found that fully recrystallized ultrafine-grained (UFG) microstructures could be realized in a commercial precipitation-hardened Magnesium (Mg) alloy. The UFG specimens exhibited high strength and large ductility under tensile test, but underlying mechanisms for good mechanical properties remained unclear. In this study, we have carried out systematic observations of deformation microstructures for revealing the influence of grain size on the change of dominant deformation modes. We found that plastic deformation of conventionally coarse-grained specimen was predominated by {0001} <11–20> slip and {10–12} <10–11> twinning, and the quick decrease of work-hardening rate was mainly due to the early saturation of deformation twins. For the UFG specimens, {10–12} <10–11> twinning was dramatically suppressed, while non-basal slip systems containing <c> component of Burgers vector were activated, which contributed significantly to the enhanced work-hardening rate leading to high strength and large ductility. It was clarified by this study that limited ductility of hexagonal Mg alloys could be overcome by activating unusual slip systems (<c + a> dislocations) in fully recrystallized UFG microstructures.
Highlights
We have found that fully recrystallized ultrafine-grained (UFG) microstructures could be realized in a commercial precipitation-hardened Magnesium (Mg) alloy
We found that plastic deformation of conventionally coarse-grained specimen was predominated by {0001} slip and {10–12} twinning, and the quick decrease of work-hardening rate was mainly due to the early saturation of deformation twins
The change of nano-precipitates during the present processing was investigated by transmission electron microscopy (TEM)
Summary
We have found that fully recrystallized ultrafine-grained (UFG) microstructures could be realized in a commercial precipitation-hardened Magnesium (Mg) alloy. Basal slip can realize only 2-dimentional deformation in each grain, which is far less than the 5 independent slip systems required for free deformation in polycrystalline materials in von Mises criterion, resulting in limited cold-forming capability as well as pronounced mechanical anisotropy in Mg alloys[6,7,8]. Deformation twinning is another important deformation mechanism in addition to basal slip, which can accommodate strains along the c-axis during plastic deformation[9,10]. Fully recrystallized ultrafine grained (UFG) structures which have not been achieved by other researchers were obtained in the HPT processed material after subsequent rapid annealing[17]
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