Characterization of High-Cycle Bending Fatigue Behaviors for Piston Aluminum Matrix SiO2 Nano-composites in Comparison with Aluminum-Silicon Alloys

In automotive industries, one failure mechanism in engine pistons is due to the fatigue phenomenon. Therefore, to enhance fatigue properties of piston aluminum alloys is a major concern for designers. One reinforcement method could be the addition of nano-particles in the aluminum matrix. In this article, high-cycle fatigue properties of the aluminum matrix nano-composite were characterized under bending loadings and then compared to those of the aluminum-silicon alloy. For this objective, fully reversed bending fatigue tests were performed on standard specimens, based on the ISO-1143:2010 standard. Before testing, nano-composite samples were stir-casted by the addition of 1 wt% SiO2 nano-particles, and aluminum specimens were gravity-casted in a cast-iron mold. The microstructure of materials and the distribution of nano-particles in the aluminum matrix were evaluated by the optical microscopy and the field emission scanning electron microscopy. Experimental data indicated that nano-particles had a significant effect on the high-cycle fatigue lifetime. The reason for this improvement in high-cycle fatigue properties could be finer grains, higher hardness, the proper distribution of nano-particles in the aluminum matrix and stronger bonding strength at the Al/Si interface. However, based on fracture surfaces, all samples had the brittle behavior due to cleavage and quasi-cleavage marks.