Understanding the role of welding parameters and tool profile on the morphology and properties of expelled flash of spot welds

Stir zone galling, excessive deformation and degraded weld strength are attributes of friction stir spot welds with excessive flash. In an attempt to determine the critical expelled flash required to maximize weld strength of joints, an experimental investigation of the role of welding parameters and tool profile on expelled flash properties of spot welds of 1.6 mm thick AA2219-0 alloy was carried out. The flash properties examined are pushed out length, thickness and resultant volume of expelled flash. The result shows that tool profile greatly influences the volume and morphology of expelled flash. Equally, the expelled flash properties were observed to be influenced by process parameters. However, the overall volume of expelled flash is affected by two process parameters which are tool rotational speed and plunge depth. The percentage contributions of plunge depth are 64.18% and 62.54%, and those of rotational speed are 20.25% and 32.83% in pinless and conical pin welds respectively. A nonlinear relationship exists between lap shear failure load of joints and ejected flash volume in all weld. A somewhat linear relationship is observed to exist between the expelled flash volume and the estimated stir zone energy at peak temperature in both pinless and conical pin welds. (C) 2016 Elsevier Ltd. All rights reserved.