Development of metal matrix nanocomposite based on AZ91 magnesium alloy using conventional stir casting assisted ultrasonic treatment processing

Magnesium metal matrix nanocomposites (Mg-MMNCs) have recently gained attention in the aerospace and automotive sectors due to their superior strength, ductility, and creep resistance compared to conventional alloys. Nevertheless, for the manufacturing of Mg-MMNCs, it is significantly challenging to distribute ceramic nanoparticles homogeneously in the molten magnesium using liquid metallurgy owing to their poor wettability and high surface-to-volume ratio. In this study, the AZ91D magnesium nanocomposite reinforced by SiC nanoparticles (1.0 wt.%) was fabricated using stir casting assisted by ultrasonic treatment. Several particle feeding techniques were developed to incorporate SiC nanoparticles into the AZ91D melt. The majority of them have been unsuccessful due to the formation of oxide layers on the melt surface and increased melt viscosity. However, a master pellet feeding technique has shown substantial potential for enhancing particle engulfment into the melt. The microstructural analysis revealed a relatively uniform distribution of the SiC nanoparticles within the AZ91D matrix. As compared to the unreinforced AZ91D alloy, the microhardness improved by 28%. Also, the yield strength, ultimate tensile strength, and elongation to fracture were simultaneously increased by 63%, 34%, and 88%, respectively. Additionally, the master pellet feeding technique was employed to produce AZ91D nanocomposites with varying SiC contents (1, 1.5, and 2 wt.%). It was found that increasing SiC concentration improved the grain refinement, particle distribution, and tensile properties of the composites. However, when the SiC content was increased to 2.0 wt.%, the tensile properties considerably decreased because of the higher porosity content and particle clusters in the microstructure. Moreover, the as-cast AZ91D/1.0 wt.% SiC nanocomposite was heat-treated to improve its quality and properties. The findings indicated that T6 heat treatment considerably affected the microstructure of the composite, leading to an increase in hardness and tensile properties compared to the composite without heat treatment.