Influence of porosity on fatigue resistance of cast SiC particulate-reinforced Al–Si alloy composite

The effect of cast pores on cyclic deformation and fatigue behavior of cast aluminum 9% silicon alloy (Al–Si) reinforced with 20% SiC particles was investigated experimentally by comparing with its extruded counterpart. The cast composite experiences cyclic strain softening under low applied cyclic strain at which level there is no macroscopic plastic strain. It is found that the elastic modulus and yield stress of the cast composite are fairly close to that of the extruded composite; however, the extrusion process considerably enhances the ductility, fracture strength and fatigue life of the composite. The cyclic strain softening and poor low cycle fatigue resistance of cast composites are mainly attributed to the existence of porosity in the cast composites. A fatigue life prediction, based on modeling large size pores in cast composites as pre-existing cracks, agrees well with the experimental results of the cast composite.