Fatigue Crack Propagation Behavior and Fatigue Strength of Al2O3/A6061 MMCs at Room and Elevated Temperatures

In order to investigate the effects of alumina short fiber volume fraction on the fatigue property at room and elevated temperature, the rotating bending fatigue tests were carried out on alumina short fiber reinforced aluminum alloy composites (MMCs). A6061 aluminum alloy and the three kinds of MMCs with 10%, 18% and 25% volume fraction were prepared and the five temperature conditions with room temperature, 200, 350, 400 and 450°C were performed. Fracture surface observation by FE-SEM of all specimens and surface crack observation using replication technique at room temperature and 200°C were performed. As results, the followings were found: The fatigue strength at 107 cycles increased with increase in alumina short fiber volume fraction at all test temperature conditions. Fatigue crack origins of all MMCs were large size alumina short fibers, some kinds of cluster of short fibers and large size alumina particles independently of the alumina short fiber volume fraction. The short fatigue crack of all MMCs propagated with avoiding the short fiber. But the da/dN-ΔK relation of all MMCs agreed with the A6061 one's. The effect on fatigue strength of short fiber compounding was more remarkable in the higher test temperature region.