Influence of Softening Mechanisms on Base Materials Plastic Behaviour and Defects Formation in Friction Stir Lap Welding

Abstract

The AA6082-T6 and AA5754-H22 aluminium alloys were selected as the base materials to fabricate similar and dissimilar friction stir lap welds. Three lap configurations, AA6082/AA5754, AA5754/AA6082 and AA6082/AA6082, were produced using three pin profiles and tested to analyse the role of the plastic behaviours of the base materials on the welding conditions. The macrostructural characterisation was carried out to understand the material flow response and hook defect formation. The mechanical characterisation of the joints was done by microhardness and lap tensile shear testing. The finite element analysis and phase simulation were conducted to predict the phase dissolution temperatures and the softening kinetics. The welding torque and axial forces registered were analysed to quantify differences in the alloy’s flowability during welding. The analysis of the welding machine outputs enabled to conclude that higher axial forces were registered when the AA5754 alloy was placed at the top of the dissimilar lap joint, showing that the non-heat-treatable alloy has lower flowability than the heat-treatable alloy. These results were associated with the flow-softening of the AA6082 alloy in plastic deformation at high temperatures. The coupled experimental and numerical analysis revealed that the plastic behaviour of the base materials strongly influenced the material flow and, in this way, the hook defect formation and the shear tensile properties of the welds.

Shoulder Related Temperature Thresholds in FSSW of Aluminium Alloys

“…The coatings were produced in 12 mm diameter tools which were tested in the welding of the AA6082 aluminium alloy at 660 rpm. The selection of the base material for testing the coated tools was based on previous works from the authors Leitão et al 2012 [39] and Sabari et al 2020 [40], which showed that this alloy experience intense flow softening during welding, a characteristic favourable for ensuring that the coating The welds were produced in a MTS I-STIR PDS [38] machine, in position control, using pinless tools with flat shoulders, in a three-stage welding operation. First, the plunging phase, in which the tool was moved vertically with a plunging speed of 0.125 mm/s, until a 0.5 mm depth was reached.…”

“…The coatings were produced in 12 mm diameter tools which were tested in the welding of the AA6082 aluminium alloy at 660 rpm. The selection of the base material for testing the coated tools was based on previous works from the authors Leitão et al 2012 [39] and Sabari et al 2020 [40], which showed that this alloy experience intense flow softening during welding, a characteristic favourable for ensuring that the coating The influence of the tool material on the heat generation was also analysed by testing uncoated and coated WC tools. Monolithic CrAlN and CrAlAgN coatings and a multilayered CrAlN/TiAlN film were tested for the coated tools.…”

“…The coatings were produced in 12 mm diameter tools which were tested in the welding of the AA6082 aluminium alloy at 660 rpm. The selection of the base material for testing the coated tools was based on previous works from the authors Leitão et al, 2012 [ 39 ] and Sabari et al, 2020 [ 40 ], which showed that this alloy experience intense flow softening during welding, a characteristic favourable for ensuring that the coating was not destroyed/removed during welding. The tool diameter was also selected based on previous studies on the heat generation in FSSW of steels, performed by Andrade et al [ 37 , 41 ], which indicated that no saturation in heat generation would occur when welding with this tool diameter.…”

Thermo-mechanical modelling of the Friction Stir Spot Welding process: Effect of the friction models on the heat generation mechanisms

“…Typically, the mechanical properties of the AA6082-T6 aluminium alloy exhibit a significant decrease during welding, due to the dissolution of the strengthening precipitates ( β family). 28 In fact, starting at temperature 100 °C, the precipitates exhibit further growth (overaging) that weakens the precipitate-dislocation interaction, which induces the decrease of the yield strength. This material behaviour should be considered in the FSSW process simulation.…”

Experimental and numerical analysis of intermetallics in Al–Mg friction stir welds

“…Friction stir welding (FSW) does not exhibit the melting and solidification phase of joining the materials and so the problems encountered during the fusion welding process will be overcome [9][10][11]. Demonstrations of the joining of dissimilar combinations like Al-Fe [12], Al-Cu [13], Al-Brass [14], and dissimilar Al-Al [15] joints were attempted by various researchers.…”