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

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.

Thermal-induced Residual Stresses and Distortions in Friction Stir Welds - A Literature Review

“…Hence, a narrower NZ and tensile region are obtained. Recent studies [25][26][27] reported promising results regarding the capability of SSFSW as an in-situation mitigation technique. As compared to other techniques, SSFSW does not require expensive apparatus, making it practical for both research and industrial applications.…”

A detailed process design for conventional friction stir welding of aluminum alloys and an overview of related knowledge

“…The major limitation of the previous techniques is the added cost of special equipment. To avoid the additional expense, stationary shoulder friction stir welding is a promising distortion‐control technique, according to recent studies 60,61 …”

Effect of Welding Parameters on Mechanical Properties and Microstructure of Friction Stir Welded AA7075-T651 Aluminum Alloy Butt Joints

“…Generally, both increasing welding velocity and additional cooling give positive effects in terms of microstructure but, on the other hand, also increase residual stresses in welded elements [ 20 , 21 , 24 ]. Analyzing the used welding velocities, in many cases, the lowest value is 80 mm/min and the tool rotation speed exceeds 800 rpm [ 16 , 24 ].…”

“…Generally, both increasing welding velocity and additional cooling give positive effects in terms of microstructure but, on the other hand, also increase residual stresses in welded elements [ 20 , 21 , 24 ]. Analyzing the used welding velocities, in many cases, the lowest value is 80 mm/min and the tool rotation speed exceeds 800 rpm [ 16 , 24 ]. Moreover, many investigations focus mainly on microstructural aspects (the evolutions of the strengthening phase, participation of grain boundaries in each welded zone), simultaneously failing to provide the mechanical properties data in a broad range of welding parameters.…”

“…When it comes to investigations on 5-mm-thick AA7075-T651, a relatively low number of works are available. Data provided by Liu for 5-mm-thick AA7075-T651 cover the SSFSW technique, which is characterized by differences in heat distribution and plastic flow and cannot be directly extrapolated to the conventional FSW process [ 22 , 24 ]. In this field, Rajakumar et al contributed significantly, performing a study on the FSW of 5-mm-thick AA7075-T6 alloy in the following range of welding parameters: 900–1800 rpm tool rotation speed and 20–100 mm/min tool traverse speed [ 27 ].…”