Grain Refinement and Fading Behavior of MgB2-Inoculated Magnesium

The light-weighting of automobiles is a prominent strategy toward increasing fuel efficiency, electric vehicle range and decreasing harmful emissions. As a light structural metal, magnesium has the potential to replace high density alloys such as steel. Based on lattice disregistry calculations, MgB2 was identified as a potent inoculant for magnesium. In this research, permanent mold castings of pure Mg refined with MgB2 were prepared and characterized using scanning electron and optical microscopy. Experimental results suggested that the primary Mg phase heterogeneously nucleated on the MgB2 particle surfaces, leading to a 36% reduction in grain size relative to the unrefined condition. The effect of MgB2 on grain refinement fading was also examined by preparing cast Mg samples refined with micro- and nano-particles of MgB2, with melt holding periods of 5, 10 and 20 min. The results indicated that the micro-particles were susceptible to fading and that the holding time should not exceed 5 min. It was also determined that the castings refined with nano-particles were more resistant to fading. The results from this study indicated that MgB2 displayed considerable potential as a grain refiner for Mg castings, with nano-particles especially suited to more complex commercial casting processes requiring longer melt holding times.