Effects of laser peening on plane bending fatigue properties of friction stir welded A6061-T6 alloy

Abstract

In recent years, friction stir welding (FSW) joints are used for structural components of cars, ships, aircrafts et al. It is important to investigate the fatigue properties of the FSW joints because the structural components are usually subjected to repeated stresses. In this study, laser peening without coating (LPwC) treatment was applied to improve the fatigue properties of the FSW joints of A6061-T6 aluminum alloy. After wire cutting out of specimens from an FSW joint plate, the specimen surface was finished by an end mill so as to remove surface notches due to traversing of a tool shoulder. Then, the LPwC treatment with an Nd:YAG laser was applied. High cycle plane bending fatigue tests were conducted at 1300cpm with a stress ratio of R=-1 in air at room temperature. High cycle fatigue strength of A6061-T6 material was improved by the LPwC treatment. On the other hand, although the fatigue strength at 107cycles of FSW specimens was improved by the treatments, the fatigue life of LPwC-treated FSW specimens was shorter than that of untreated specimens. In order to consider these fatigue test results, effects of the LPwC treatment on surface roughness, surface hardening and residual stresses on the specimens were investigated.