UBC Theses and Dissertations

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UBC Theses and Dissertations

Grain refinement of magnesium alloy AZ91E Azad, Amit


Spark Plasma Sintering (SPS) process has been used to develop a novel grain refiner Al-SiC master alloy for AZ91E Mg alloys. When the Al-SiC master alloy was added to molten AZ91E alloy, the Al matrix melted and allowed the SiC particles to distribute homogeneously throughout the molten AZ91E alloy. After addition of 0.1 wt.% Al-SiC master alloy to AZ91E alloy, the mean grain size decreased from 227.5 ± 5.0 µm to 197.5 ± 5.0 µm; however, the mean grain size increased when the amount of added Al-SiC exceeded 0.1 wt.%. The grain refining and coarsening mechanisms were investigated using scanning electron microscope (SEM), energy dispersive spectroscopy (XEDS) and differential scanning calorimetry (DSC). It is proposed that the binary carbides (e.g., MgC), possibly acted as heterogeneous nucleation sites for grain refinement. The formation of ineffective nuclei AlCMn₃ with the increased amount of grain refiner exceeding 0.1 wt.% Al-SiC has inhibited formation of MgC, resulting in grain coarsening. The effect of Al-SiC on the mean area percentage of β-Mg₁₇Al₁₂ phase and porosity were investigated using optical microscopy, while hardness was measured using a Rockwell hardness tester. It was found that increasing the addition of Al-SiC had an effect on β-phase and porosity. The highest mean area percentage of β-phase was found 6.6 ± 1.3 % with the addition of 1 wt.% Al-SiC, while the lowest mean area percentage of porosity was 1.9 ± 0.5 % with the addition of 0.1wt.% Al-SiC. It was found that adding the Al-SiC master alloy to AZ91E alloy had no influence on hardness.

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