Effects of laser peening treatment without protective coating on axial fatigue property of aluminum alloy

Axial fatigue tests with stress ratio of −1 and 0.1 were conducted in order to investigate effects of laser peening treatment without protective coating (LPwC) on fatigue property such as the fatigue strength and the surface crack behaviors of rolled aluminum alloy A7050-T7451 for aircraft structures. As results, The LPwC treatment was effective for the fatigue strength improvement in fatigue lives regime before 2∼3×106 cycles, but the treatment reduced the strength after the cycles at the both stress ratios conditions. Fatigue cracks initiated at the surface on the higher stress amplitude levels, but the cracks initiated in the internal positions on the lower stress levels. From these results, it is clear that the LPwC treatment could control the crack initiation and propagation behaviors. The fatigue crack propagation property from the pre-crack by the LPwC treatment was evaluated by the stress intensity factor range including the residual stress induced by the LPwC treatment.