Self-optimization in tool wear for friction-stir welding of Al 6061+20% Al2O3 MMC

A numerical comparison of the flow behaviour in Friction Stir Welding (FSW) using unworn and worn tool geometries

“…Experimental investigations into the mechanisms of tool wear have concluded that the main mechanisms causing of loss of pin material during the welding process are sliding wear and removal of material through excessive shear deformation [14,15].…”

“…Both of these effects can lead to self-optimization of the pin geometry during the process for some material combinations [15]. Self-optimization can be defined as a phenomenon that occurs after a preliminary wear period, when the wear becomes low, resulting in the development of specific tool shapes.…”

“…The work of Prado et al [15], Shindo et al [17] and Contorno et al [18] measured the wear of FSW tools by assessing the change in tool shape using this technique when welding an aluminium-matrix composite. They showed that tool rotational speed and weld traverse speed are the most important factors that contribute to wear and self-optimization of the tool shape [15]. These studies also compared the microstructure and hardness of welds created with the worn and unworn tools and revealed a homogenous metal flow and uniform grain size in the stirring zone for the self-optimized pin.…”

“…The authors demonstrated that the presence of this homogenous microstructure and the low wear rate of a self-optimized pin could be related to the reduction of turbulent flow around the pin during the process after self-optimization; moreover, it was shown that a self-optimized tool generated thinner flow layers, compared to the unworn tool, leading to a more uniform flow. While the work of Prado et al [15], Shindo et al [17] and Contorno et al [18] considered the wear of the tool during the FSW process, their main focus was on the wear phenomena rather than the resulting effect on the material flow and the shape and size of the weld zone. While they did investigate the hardness profile from the weld carried out with the worn tool, it was limited to measurements taken from the mid thickness of the welded plate and little detail was provided on the effects on the weld root area.…”

Microstructure and texture evolution during accumulative roll bonding of aluminium alloy AA5086

“…Different variations of SPD processes, e.g. equal channel angular pressing (ECAP), high pressure torsion (HPT), multi-axial forging (MAF), etc., have been successfully applied to fabricate UFG materials [4][5][6][7][8][9][10][11][12][13][14][15]. Accumulative roll-bonding (ARB) is one such SPD process which has great potential for industrial scaling up since it does not need forming facilities with large load capacity [16].…”