Microstructural Evolution of the Magnesium Alloy AZ31 with and without SiC Particles during Ultrasonic Melt Treatment

The aim of this study is to reveal the influence of ultrasonic treatment in the molten state on microstructural evolution of the magnesium alloy AZ31 with and without the addition of SiC particles. Therefore, a heatable wedge-shaped mold for holding the magnesium melt on the required temperature was constructed with the possibility to insert an ultrasonic horn into the melt. Previously ingots of AZ31 were molten in an electrical furnace under a protective gas atmosphere. SiC particles with an average diameter of 2 μm were added to the melt. Mechanical stirring was conducted to ensure homogeneous distribution of the particles. The molten Mg was subjected to ultrasonic sound with constant frequency of 20,000 Hz and amplitude of 12.4 μm. The time of ultrasonic treatment was defined on 60 seconds. The material solidified quickly due to the cooling with water nozzles after withdrawing of the ultrasonic horn. AZ31 without SiC particles was treated under the same conditions. The resulting microstructure was observed by optical and scanning electron microscopy. Depending on resulting intensity and the effective area a refinement in grain size and also more homogeneous distribution of precipitations in the material is achieved. The resulting microstructures of AZ31 with and without SiC addition were compared and discussed.