Influence of Deep Rolling Process Parameters on Surface Residual Stress of AA7075-T651 Aluminum Alloy Friction Stir Welded Joint

Abstract

Friction stir welding is most commonly used for joining aluminum alloy parts. After welding, residual stresses occurred in the welded joint caused by non-uniform cooling rate. Friction stir welding usually generates tensile residual stress inside the workpiece which affects the strength in addition to the fatigue life of materials. Compressive residual stress usually is beneficial and it can be introduced by mechanical surface treatment methods such as deep rolling, shot peening, laser shock peening, etc. In this research, deep rolling was used for inducing compressive residual stress on surface of friction stir welded joint. The residual stresses values were obtained from X-ray diffraction machine. Influence of three deep rolling process parameters: rolling pressure, rolling speed and rolling offset on surface residual stresses at the welded joint were investigated. Each factor had 2 levels (23 full factorial design). The statistical analysis result showed that the rolling pressure, rolling speed, rolling offset, interaction between rolling pressure and rolling speed, interaction between rolling speed and rolling offset were statistically significant factors, with the most compressive residual stress value approximately -391.6 MPa. The appropriated deep rolling process parameters on surface residual stress of AA7075-T651 aluminum alloy friction stir welded joint were 1) rolling pressure about 150 bar 2) rolling speed about 1,400 mm/min 3) rolling offset about 0.1 mm.