Influence of Silicon Carbide and Graphite Reinforcements and T6 Aging Heat Treatment on the Fatigue Characteristics of AZ91D Magnesium Alloy

This study evaluated the high-cycle fatigue strength of AZ91D alloy and AZ91D-5SiC-1Gr (wt.%) hybrid magnesium composite. The samples were produced through the stir casting process, and properties were studied in as-cast and T6 aging heat-treated conditions. Microstructural characterizations, density, porosity, tensile properties, and high-cycle fatigue strength of produced alloy and hybrid composite were evaluated. The maximum obtained ultimate tensile strength, yield strength (0.2%), and ductility for T6-heat-treated hybrid composite were 176, 56.5 MPa, and 8.1%, respectively, and density of 1.855 g/cc. Stress-controlled, fully reversed high-cycle fatigue test was performed on the samples subjected to axial load and rotary bending load fatigue test. Fatigue results indicated that produced hybrid composite possessed higher cycle fatigue strength than the parent AZ91D alloy. AZ91D-5SiC-1Gr (wt.%) (T6) sample reported 55,434 cycles to failure at 28.25 MPa stress amplitude which is 4.33 times higher than as-cast AZ91D alloy. Maximum rotary bending load fatigue life of 101,916 cycles was obtained for T6-hybrid composite samples at 18.2 MPa stress amplitude. The reliability of fatigue strength has been studied through the R–S–N method, and results indicate that the fatigue life of the T6-hybrid composite possesses 81,377 cycles at 99% reliability and 98,627 cycles at 50% reliability. Hence, the addition of SiC and graphite and aging heat treatment at 100 °C enhances the tensile and fatigue strength of the parent AZ91D alloy.