Influence of tool thread on the mechanical properties of dissimilar Al-alloy friction stir spot welds

Abstract

The influence of threaded and wear simulated (half-thread) tools on the mechanical properties of dissimilar Al-alloy friction stir spot welds is investigated. The failure load properties of dissimilar A5754/A6111 lap joints produced using wear simulated (half-thread) tools were much poorer in joints made using tool rotational speeds of 1000 and 1500 rpm. Similar failure load properties were produced using these tools, when the tool rotational speed was increased to 2250 rpm. In joints made using a tool rotational speed of 3000 rpm, the failure load properties of joints made using the half-thread tool were higher than those of joints made using the threaded tool. Similar failure load properties were found in A5052/A6061 lap and butt joints made using threaded, half-threaded and no thread tools and a tool rotational speed of 1000 rpm. Also, the failure load properties of lap joints made using the different tools corresponded with their bonded widths and Y values. The area of the stir zone on the bonded cross section corresponded with the actual bonded region on the fracture surface of A5052/A6061 butt joints. However, the weld profiles were different from those in A5052/A6061 lap joints. It is, therefore, suggested that the failure load properties of lap joints are similar when the bonded widths and Y values are similar. In addition, the thread on the cylindrical probe has negligible influence on the mechanical properties of lap joints. The major role played by the thread involves stirring in the vertical direction. Stirring in the horizontal direction is unchanged in joints made using the different tools.