Effect of Rolling on Strength of Friction Stir Welded Joint of Aluminium Alloys

Abstract

Friction stir welding (FSW) technique is one of the best options especially for joining dissimilar aluminium alloys. However, there is a limitation to weld thin plate using this method since it produces due to less amount of materials mixing in the stir zone hence result in bad aesthetics of the welding surface. In this study, two different types of aluminium alloys, namely AA6061 and AA1100, were butt-joined by using FSW method. The rotational and transverse speeds of the tool were 1,000 rpm and 100 mm/min, respectively. The friction stir welded samples were subsequently cold rolled to a different thickness reduction percentages of 10, 20, and 40%. From the microscopic observation of the sample’s cross-section, no internal defect was detected at the welding area for both the as-welded joints and the rolled specimens. The tensile strength of FSWed sample was 93 MPa. This was only 80% of welding efficiency as compared to the tensile strength of AA6061 at 116 MPa. The results showed that the tensile strength of the dissimilar joint increased with the increase of the rolling percentage. The welding efficiency of samples after 10, 20, and 40% rolling were 86, 94 and 110%, respectively. However, the total elongation of the sample decreased from 29 to 56% with an increase in the rolling percentage. It is worth to acknowledge that there was no crack or defect observed at the FSW joint after the rolling of 40 % thickness reduction. Furthermore, the fracture location of the rolled FSW joints was near the thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) and indicated ductile fracture behaviour with evidence of dimples on the fracture surface. In conclusion, reducing the thickness of dissimilar FSW joint aluminium alloys plate by the rolling process is possible without any defect nucleation.