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Mechanical properties of Al–Si–SiC composites

This paper dealt with cyclic stress properties of Al-Si (LM13) alloy and 10 wt% SiC particle reinforced composite in the cast and T6 temper conditions at ambient temperature. Fully inverse loading was applied to the materials with stress amplitude maximum up to 50 000 cycles. Stress versus No of cycle curve was generated. Fatigue strength of artificially aged LM13 alloy was found more than the cast alloy; however, dispersion of SiC particles deteriorated the fatigue life under the present domain of experiments. The mechanical properties such as ultimate tensile strength, offset yield strength and % elongation were found inferior for composites compared to the base alloy. Remarkable improvement in mechanical properties was observed in heat-treated alloy and composites. Scanning Electron Microscopic examinations of fatigue fractured surfaces of LM13 alloy depicted interface decohesion, was the predominant mechanism for failure in T6 tempered alloy, whereas fracturing of eutectic silicon was predominant in cast alloy. In (Al–Si)–SiC composites, cracks were initiated due to decohesion of the particle-matrix interface and in some instances breaking of the SiC particles. It was observed that heat treated eutectic silicon, which was near-spherical in shape, resisted fatigue crack growth because of better cohesive force with the Aluminium matrix as compared to SiC particle and fewer sites for stress riser. Better bonding between eutectic silicon and Aluminium matrix caused the crack to pass through the interface whereas Si particle endures fatigue load and ultimately, crack surpassed particle by fracturing it.