Microstructure and mechanical properties of as-cast and heat treated Mg-Ca-Y-Zr AlloysFriday (10.11.2017) 09:15 - 09:35 Part of:
The microstructure and mechanical properties of as-cast and heat treated Mg-Ca-Y-Zr alloys with different Ca and Y contents were investigated. It was observed that the as-cast alloy containing 0.6 wt.% Ca exhibited finer grains compared with the alloy containing 0.3 wt.% Ca. In contrast, no significant change in grain size was found with the increase of Y content. Scanning electron microscope observations showed that the microstructure of as-cast alloys consist of α-Mg dendrites and Mg2Ca phases distributed at dendrites and grain boundaries. The solute Y segregated at dendrites and grain boundaries. No Mg-Y binary or Mg-Ca-Y ternary phase was detected. The content of Y had no obvious effect on the morphology and distribution of Mg2Ca phases, but the amount of Y contained in Mg2Ca phase remarkably increased with the increasing Y content according to EDS analysis. This can be explained by the formation of Mg2(Ca,Y) compounds in which Ca was partly substituted by Y atoms. In addition, the formation of Mg2(Ca,Y) was identified by XRD and EDS analysis in Mg-Ca-Y alloys with high content of alloying elements. The two-phase Mg-Ca-Y-Zr alloys with α-Mg+Mg2Ca exhibited a weak age-hardening response, which contributed to the sluggish precipitation of coarse equilibrium Mg2Ca phase. Both the room temperature tensile and compressive strength were largely improved with Y content increasing from 0.5 wt.% to 5 wt.%, but only slightly improved with the increase of Ca content.
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