Improvement of microstructure and mechanical properties for Al7075 aluminium reinforced with hybrid graphite and SiC particles via a combination of mechanical alloying and stir casting

Abstract This research focuses on the fabrication of Al7075 composites reinforced with varying amounts of nano-sized SiC particles (1.0, 1.5, and 2.0 wt%) combined with 0.5 wt% graphite (Gr), employing a hybrid process of mechanical alloying and semi-solid stir casting. The study investigates the influence of SiC content, nanoparticle feeding method, and the role of Gr on the microstructures, mechanical characteristics, and machinability of the composites. Microstructural analysis revealed that integrating milled powders into the molten Al7075 alloy produced a uniform dispersion of nanoscale SiC particles within the α-Al matrix, avoiding the particle agglomeration observed with the conventional method. Higher SiC content resulted in finer grains and improved mechanical performance. The Al7075-0.5Gr-2.0SiC composite exhibited a 16% increase in hardness relative to the unreinforced Al7075 alloy. The inclusion of nanoscale SiC particles notably enhanced tensile strength, while the presence of Gr acted as a lubricant, improving surface roughness.