Mechanical Properties and Fatigue Crack Propagation Behavior of Hybrid Metal Matrix Composites

The objective of this study is to investigate mechanical properties and fatigue crack propagation behavior in hybrid metal matrix composites by squeeze infiltration method (15% Al₂O₃ + SiC_w/6061Al). The mechanical properties of Al₂O₃+SiC_w/Al composites including tensile strength, yield strength, Young's modulus, were improved compared with those of unreinforced alloy and Al₂0₃/Al composites. The hybrid composites were more ductile than Al₂O₃/Al composites. Fatigue crack propagation rates of both Al₂O₃/Al and Al₂O₃+SiC_w/Al composites showed a similar behavior in region II. Their propagation rates were higher in entire ▵K region compared with that of 6061 Al alloy. From the crack path morphology, fatigue cracks propagated linearly and smoothly in 6061 Al alloy. However, in the metal matrix composites cracks tend to avoid the reinforcements promoting crack deflection. It was observed that crack deflection enhanced crack closure due to wedging phenomenon. The effects of crack closure level, K_cl/K_max were indicated by the relations with ▵K. Differences in crack propagation mechanism between 6061 Al alloy and metal matrix composites were discussed through the fractographic study.