The effect of a paint bake treatment on joint performance in friction stir spot welding AA6111-T4 sheet using a pinless tool

Abstract

It has been previously shown that it is possible to produce friction stir spot welds (FSSW) in thin (1 mm thick) aluminium sheet, when using a tool without a probe, which has the significant advantage of not leaving a keyhole in the weld. The aim of this paper was to investigate the effect of a post-weld paint bake cycle on the performance and precipitation behaviour of FSSW joints produced using a pinless tool, in the heat-treatable Al automotive alloy AA6111-T4, with rapid, industrially relevant, weld cycle times. It has been demonstrated that strong joints could be obtained within < 1 second, that exhibited a nugget pull-out failure mode, and the weld strength increased further after the paint bake treatment. After the paint bake cycle the weld zone was found to be considerably harder than the parent material and this behaviour has been attributed to 2 the shorter delay time between welding and artificial ageing, relative to the longer pre-natural ageing time experienced by the parent sheet. With a rapid (< 1 sec) weld cycle, no hardness minima were observed in the heat affected zone (HAZ) after the paint-bake treatment.

Process optimisation and microstructural evolution of friction stir spot-welded Al6061 joints

“…This can be explained by the influence of severe plastic deformation and frictional heating. 28,38 Figure 15a and b shows the micrographs observed at the BM and HAZ, respectively, by means of scanning transmission electron microscopy (STEM). A large number of round precipitates, which were identified as Feand Si-bearing β ′′ dispersoids, were seen within a single grain matrix.…”

Process parameter optimisation in pinless friction stir spot welding of dissimilar aluminium alloys using Multi-start algorithm

“…This method was initially employed by Mazda in the year 2003 to join the hood structures in cars. 3–5 Although this technique provides unique advantages over RSW and SPR, the keyhole left behind by the tool is a matter of concern because it acts as a stress concentration factor and reduces corrosion resistance. The keyhole formation in FSSW of thin sheets is avoided by using pinless or probe-less tools.…”

Microstructure, mechanical properties and failure behaviour of protrusion friction stir spot welded 2024 aluminium alloy sheets

“…Its main disadvantage is a keyhole [10] while it remains on the surface of the joint. The keyhole remained in the FSSW joints, as shown in Figure 1, seriously reduces the joint properties such as tensile shear strength and fatigue strength, and the corrosion can take place preferentially at the keyhole [11]. Some techniques have been developed to prevent the formation of the keyhole.…”