Abstract
Degassed processing (DG) is used for decreasing cast defects such as porosities or micro shrinkage. So it is 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 aluminum alloy AC4CH, the laser peening treatment was applied to DG treated cast aluminum alloy, and rotating bending fatigue tests were carried out. As the results of fatigue tests, the fatigue life property of the laser peened DG material was 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. As a results, although the ratio of fatigue crack initiation life to total fatigue life was decreased by laser peening treatment, the fatigue crack growth rate was decelerated by compressive residual stress caused by laser peening treatment. In addition, residual stress at the surface of laser peened specimen was estimated from the result of fatigue crack propagation behavior. And then the estimated residual stress value corresponded with the value of X-ray diffraction method.
