Residual stress tests and predictive model of friction stir welded normal-strength aluminium alloy H-shaped sections

Abstract

To address the challenges of difficult extrusion for super-large cross-section aluminium alloy members, pairs of T-shaped sections were proposed to be longitudinally friction stir welded (FSW) to form the H-shaped sections widely used in structural engineering. It was significantly different from the previous member forming method that one web plate and two flange plates were welded at the flange-web junctions. To understand the novel FSW-induced residual stress distributions and magnitudes in the H-shaped sections, six specimens made of 6061-T6 and 6013-T6 normal-strength aluminium alloys, including various width-to-thickness ratio and plate thickness, were tested using the sectioning method, leading to over 4000 original readings of compressive and tensile residual stresses. The analysis results showed that great tensile residual stresses were clearly concentrated within the web weld, and then rapidly descended to lower compressive stresses near the weld region, followed by approximately linear regression to zero state from the weld edge to the flange-web junction, while the flange data points were relatively scattered. The compressive and tensile residual stresses in each flange and web plate were observed to be slightly associated with the width-to-thickness ratio and plate thickness. A simplified multi-linear residual stress distribution model, including the magnitudes and ranges of constant and linear variation curves, was proposed for the FSW aluminium alloy H-shaped sections, and good accuracy and consistency were observed between the test and predicted results.