The improvement of high cycle fatigue properties of AC4CH alloy with shot peening treatment

Rotating bending fatigue tests on shot-peening treatment (SP-treated) AC4CH aluminum alloy were carried out in order to investigate the effect of SP treatment on the high cycle fatigue properties. As the comparing fatigue property of the SP-treated material with fatigue properties of non-peened material, HIP-treated material and semi-liquid die casting (SL) material, the following conclusions were obtained. (1) Although the fatigue property of SP-treated material is most excellent in all materials, they are a few differences as compared with HIP-treated material and SL material. (2) The fatigue strength at 107 cycles of AC4CH alloy is governed by the existence of cast defects near the surface. If the cast defects do not exist there, the fatigue strength at 107 cycles of AC4CH alloy is as practically equal as HIP-treated materials and SL materials. (3) The fatigue life property of AC4CH alloys is significantly affected by fatigue crack initiation behavior. The reason why the SP-treated material has longer fatigue life than other material ones is that it has no cast defects near the surface by the effect of SP treatment. Moreover, the miniaturization of microstructure near the surface by SP treatment affect on fatigue life since generation of the slip in crystal grain, which cause the surface fatigue crack initiation, is prevented.