2.1. Sample preparations
Structural AA5754 aluminium alloy in 2.0 mm gauge was used to form a (2.0 mm+2.0 mm) stack for the fundamental trials in laboratory condition. Spot welded samples were produced on a strip containing 11 welds with the 1st weld un-shunted. The geometry of the strip is shown in Fig. 1. The welds were made using Medium Frequency Direct Current (MFDC) welding equipment, which is specified to meet the high current and force requirements for RSW aluminium [10]. The electrodes used for this study were made of copper–zirconium (0.2%) and supplied by Luvata with the manufacturer's code of MN 16Z64. A spherical geometry (50 mm radius) electrode was chosen as this acts to increase the weld current density at the start of the weld cycle. Weld parameters were set to achieve a range of spot weld sizes and qualities to evaluate the NDT capability.