Friction stir spot fusion welding of low-carbon steel to aluminum alloy

Abstract

Dissimilar lap joints for a low carbon steel (SS400) sheet with thickness of 2mm on a 6061-T6 Al alloy sheet with thickness of 5mm or 10mm were created by a process called friction stir spot fusion welding (FSSFW) using an assembly-embedded rod (AER) tool under a downward force of 12kN and a rotational speed of 1200rpm at different dwell times. The Al alloy sheet was melted at the central area of the faying surface, so that two IMC layers were formed at this surface and identified as Fe2Al5 and Fe4Al13, as detected by XRD and SEM images. The IMC thickness increased along with dwell time, but its increment rate became slower for IMC thickness larger than 25μm. The failure load increased along with the IMC thickness, but the failure load decreased quickly for IMC thickness larger than 17μm. It was able to achieve 18–22kN for the thickness of the IMC layer in the range of 6–17μm for a dwell time from 35–55s. The larger the crack was, the smaller the failure load.