2005 年 54 巻 12 号 p. 1255-1261
Degassed processing (DG) was used for decreasing cast defects such as porosities or micro shrinkage of casting aluminum alloy. So it was very excellent method for improvement of fatigue property on casting aluminum alloy. In this study, for the aim of more fatigue property improvement of the casting alumium alloy AC4CH, the shot peening treatment was applied to DG treated AC4CH alloy, and rotating bending fatigue tests were carried out. As the results of fatigue tests, the fatigue life property of the shot peened DG material is more improved. To investigate the cause of the fatigue life improvement, fracture surface of all specimens were observed with SEM. And surface cracks were observed using replication technique. Comparing the shot peened DG material with the DG material, the crack initiation life of shot peened DG material was shorter than that of non peened DG material, but in the other hand, the crack propagation rate da/dN of shot peened DG material was slower than that of non peened DG material.