Controlling residual stress and distortion of friction stir welding joint by external stationary shoulder

Weiliang He,Gongdong Wang,Wenjing Chen,Wei Hu,Jinglin Liu

doi:10.1515/htmp-2019-0005

Abstract

Abstract Friction stir welding (FSW) can achieve a sound welding joint, but its residual stress and distortion cannot be avoided due to the non-uniformity of temperature distribution during welding. Stationary shoulder friction stir welding (SSFSW) was employed to butt weld 6005A-T6 aluminum alloy plates. The effects of welding speeds ranging from 200 mm/min to 600 mm/min on residual stress and distortion were investigated in detail. A thermo-mechanical model was utilized to compare the residual stress distribution between conventional FSW and SSFSW. SSFSW was beneficial to decreasing the peak temperature of stir zone (SZ) and then obtaining a narrower SZ. The peak residual stress produced by SSFSW was 50% lower than that by conventional FSW and a narrower tensile stress region was attained by SSFSW. Moreover, the stationary shoulder applied a function of synchronous rolling during the welding, which controlled the distortion effectively.

Highlights

Friction stir welding (FSW) technology was invented by Wayne Thomas at TWI in 1991 [1]
The peak residual stress produced by Stationary shoulder friction stir welding (SSFSW) was 50% lower than that by conventional FSW and a narrower tensile stress region was attained by SSFSW
Li et al [24] found that the ratio of rotating speed to welding speed (n/v) greatly influenced the quality of FSW joint, and the distortion of the joint becomes more obvious with increasing the n/v

Summary

Introduction

Friction stir welding (FSW) technology was invented by Wayne Thomas at TWI in 1991 [1]. The SSFSW is a latecomer in the welding techniques and was initially invented to weld titanium alloy to overcome uneven temperature distribution along the joint thickness [16]. Avettand et al [17] demonstrated that the external stationary shoulder absorbed a large quantity of frictional heat, thereby resulting in a relatively narrow and uniform through-thickness temperature field. Li et al [18] indicated that SSFSW was developed to improve the asymmetry and inhomogeneity of microstructure in aluminum alloy joint. A major thrust of current research focused on employing the ABAQUS software to analyze the temperature and stress field during SSFSW. The controlling effect of residual stress produced by the external stationary shoulder has been discussed

Experimental procedures

Finite element modelling

Results and discussion

Temperature and stress fields during welding

Welding residual stress and distortion

Conclusions