Comparison of Mixing Strategies and Hybrid Ratio Optimization for Mechanical Properties Enhancement of Al-CeO₂-GNP’s Metal Matrix Composite Fabricated by Friction Stir Processing

In this work, mechanical properties enhancement of AA6061 metal matrix composite (MMC) is carried out by synergizing nanoparticles mixing strategies and hybrid ratio. Dry mixing and solvent-based mixing of CeO₂ and graphene nanoplatelets (GNP) are compared separately as well as in volume percentages of 75/25, 50/50, and 25/75, respectively. Solvent-based mixing proved to be more effective in separating particles agglomerates and mixing them uniformly due to polar nature of solvent and agitation of sonicator. Nanoparticles of CeO₂ and graphene are embedded by friction stir processing (FSP) in metal matrix. Four numbers of passes are performed, and rotational and traverse speeds of 1000 rpm and 40 mm/min are kept for first three passes and 1000 rpm and 60 mm/min for fourth pass, respectively. Microstructure analysis of FSPed samples divulged the contribution of nanoparticles in refining grains due to their pinning effect in retarding grain growth. Because of grain refinements and obstacles posed by particles to dislocation movement, enhancements in hardness and tensile strength of MMC are observed. 50/50 volume percentage is recorded as optimum in improving tensile strength and microhardness. Fractography showed that fracture shifts from ductile to brittle with increasing content of graphene. It is suggested that formation of Al₄C₃ caused brittle failure. Highest improvement of 69.3% in microhardness and that of 12.9% in UTS are recorded as compared to base metal.