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Influence of pin imperfections on the tensile and fatigue behaviour of AA 7075-T6 friction stir lap welds

Abstract

Friction stir lap welds in AA 7075-T6 aluminium alloy were produced using tools with and without geometrical imperfections and varying welding pitch. Geometrical imperfections, resulting from the damage of the tool during the welding of the hard aluminium alloy, were simulated by machining small flats in the pin threads. Material adhesion to the worn tool was simulated by increasing the welding pitch. The welds produced were characterised, in the as-welded and heat-treated conditions, by performing monotonic and cyclic tensile-shear tests, micro-hardness measurements and metallography. The peak temperatures reached during welding were calculated using the spindle torque. No important differences in heat generation were registered when varying the welding conditions. The morphology and size of the lap weld defects were analysed in order to assess the influence of tool damage on welds properties. Material adhesion to the tool, simulated by increasing the welding pitch, showed to have a stronger influence on defect size than the thread imperfections. The small changes in welds defect size had no important effect on the monotonic strength of the welds, but had important influence on the fatigue behaviour. An increase of around 10% in the effective sheet thickness of the CL joints resulted in an increase of 500% in the fatigue life. Improved fatigue performance was also registered for the welds performed with the tool with pin imperfections indicating that sensitive tool damage will have no negative influence on the performance of the lap welds.

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Acknowledgements

This research was co-financed through Fundação para a Ciência e a Tecnologia (UID/EMS/00285/2013), COMPETE 2020 (POCI-01-0145-FEDER-007633) and FEDER (CENTRO-01-0145-FEDER-000006). The author, C. Leitão is supported by the Portuguese Foundation for Science and Technology through SFRH/BPD/93685/2013 fellowship. All supports are gratefully acknowledged.

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Correspondence to D. M. Rodrigues.

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Balakrishnan, M., Leitão, C., Arruti, E. et al. Influence of pin imperfections on the tensile and fatigue behaviour of AA 7075-T6 friction stir lap welds. Int J Adv Manuf Technol 97, 3129–3139 (2018). https://doi.org/10.1007/s00170-018-2172-x

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Keywords

  • FSW
  • Lap welding
  • Tool
  • Wear
  • Fatigue