Experimental investigation of laser peening effects on tensile properties of AA2195-T6 friction stir welded joints

Abstract

The considerable local dissolution of strengthening phases under gradient thermo-mechanical effects of friction stir welding leads to a noticeable decrease in material local hardness and tensile properties in friction stir welded Al-Li joints at the joint central area, known as the thermo-mechanical coupling zone, compared to its surrounding regions. Consequently, the resulting high gradient in joint local properties at borders of the joint center leads to high local stress concentration and tensile failure under relatively low loading values at this region. In this study, firstly, effects of joint center laser-peening-induced local compressive residual stresses evolution and work hardening are investigated on the enhancement in local hardness and tensile properties of AA2195-T6 friction stir welded joints. Then overall induced joint mechanical property homogeneity effects from these effects are evaluated on the improvement in joint global tensile properties. LP-induced local residual stresses are measured through the depth using the X-ray diffraction method. X-ray diffraction pattern peak broadening analysis is utilized to measure dislocation density local variations after LP which represent plastic work hardening effects. Local tensile properties are characterized by the digital image correlation technique with the corporation of the monotonic tensile test approach. Considerable increments in local material properties lead to the enhancement of overall joint tensile yield strength up to about 31% and ultimate tensile strength to 11% as a result of LP-induced compressive residual stresses, surface work hardening and joint tensile homogenization effects.