Journal article Open Access
Mangai, M. M.,; Johnson, Z.; Ihom, A. P.
Metal matrix composites have attracted considerable attention in engineering applications as a result of their relatively low cost and considerable isotropic properties. In an effort to achieve optimality in structure and properties, various fabrication and heat treatment techniques have been used. In this paper, aluminium metal matrix composites were fabricated through stir casting technique using 3.0wt% of SiO2 as reinforcement. The metal matrix composites were heat-treated by soaking at 450°C for 4 h in a muffle furnace so that the elements formed a solid solution. One set of the metal matrix composite was quenched in still air at room temperature, another set was quenched in water at room temperature (20°C – 35°C) while another set in boiling water. Samples of the metal matrix composites were further aged at 150°C for 4 h. The metal matrix composites were then subjected to hardness and tensile strength tests. Results of hardness and tensile strength tests showed that heat treatment had a significant effect on the hardness and tensile strength of the metal matrix composites compared to the as-cast sample. Samples quenched in water at room temperature had the highest improvement in hardness of 42.5HRB and ultimate tensile strength(UTS) of 120 N/mm2 at a peak load of 14724.7N showing an improvement of 10% in hardness and 7.5% in ultimate tensile strength over the as-cast samples. The improvements maybe attributed to the combined effects of bonding between the SiO2 particles and the aluminium matrix due to lower temperature and the formation and stabilization of Mg2Si intermetallic phase with the matrix. This shows that during solutionizing heat treatment, the cooling rate needs to be fast enough to prevent solid-state diffusion and precipitation of the phase. Rapid quenching creates a saturated solution and allows for increased mechanical properties of the metal matrix composite.