The synergetic effect of in-situ TiB2 and ex-situ Al2O3 in Al-Si binary alloys for the enhancement of wear properties

In metal matrix composites (MMCs), non-metallic or inter-metallic phases are commonly introduced into a metal or an alloy in a required proportion with an aim to develop a new material that possesses attractive engineering properties. Aluminium matrix composites (AMCs) have been known for their high strength-to-weight ratio, and these are utilized to meet specific requirements in the field of various automotive and aerospace applications. In this study, the hypoeutectic and hypereutectic Al-Si composites have been fabricated through two step stir casting process. TiB₂ incorporation has been facilitated by an exothermic reaction between the molten metal and halide salts (K₂TiF₆ and KBF₄), leading to the in-situ formation of the reinforcement. To develop hybrid composites, Al₂O₃ particles were further added to the melt. The resulting microstructures were analysed using scanning electron microscopy. The presence of Al₂O₃ and TiB₂ phases was confirmed by X-ray Diffraction (XRD). The composites were also evaluated for hardness, density, and dry sliding wear behaviour. The results indicate that the wear rate decreases with increasing TiB₂ content, whereas this improvement is restricted to the addition of 1 wt. % Al₂O₃. Higher applied loads resulted in increased wear rates. Density values of the composites have been found to increase marginally with higher reinforcement content. Hardness improves with Al₂O₃ addition up to 1 wt. %; and a further addition of 2 wt. % causes a decrease in hardness due to particle agglomeration.