EFFECT OF A NOVEL Al-SiC GRAIN REFINER ON THE MICROSTRUCTURE AND PROPERTIES OF AZ91E MAGNESIUM ALLOY

摘要

Spark Plasma Sintering (SPS) process was used to fabricate a novel Al-SiC master alloy for AZ91E magnesium alloys. The master alloy enabled homogeneous distribution of SiC particles in the alloy matrix. With an addition of 0.1 wt.% Al-SiC master alloy, the mean grain size decreased by 15%. It is proposed that binary Mg-C carbides possibly provided heterogeneous nucleation sites for grain refinement. However, further additions of Al-SiC caused grain coarsening, where formation of the MgC carbides was inhibited by precipitation of undesirable AlCMn_3 intermetallic particles. The grain refining and coarsening mechanisms were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (XEDS) and differential scanning calorimetry (DSC). Concurrent with finer grain size and relatively homogeneous interdendritic network at the 0.1 wt.% Al-SiC addition level, the interdendritic porosity remained at a low value of 1.9%. The β-Mg_(17)Al_(12) phase precipitation monotonically increased with addition of Al-SiC master alloy, while the alloy hardness remained unaffected for all Al-SiC addition levels investigated.