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Journal of Materials Science

, Volume 42, Issue 24, pp 9954–9965 | Cite as

Formation and retention of local melted films in AZ91 friction stir spot welds

  • Peter Su
  • Adrian GerlichEmail author
  • Motomichi Yamamoto
  • Thomas H. North
Article

Abstract

The formation of local melted films during friction stir spot welding of as-cast AZ91D and thixomolded AZ91 material is investigated. The average temperatures close to the tip of the rotating pin vary from 438 to 454 °C during the dwell period in friction stir spot welding. These measured temperature values are higher than the melting temperature of α-Mg + Mg17Al12 eutectic (437 °C). It is suggested that the temperature in the stir zone during the dwell period is determined by the relative proportions of α-Mg and (α-Mg + Mg17Al12) eutectic material, which are incorporated during friction stir spot welding. Based on the stir zone temperature measurements and a detailed examination of material located at the root of the pin thread it is suggested that material is moved downwards via the pin thread and into the stir zone during the dwell period in friction stir spot welding. Evidence of local melted film formation is observed in the stir zone of AZ91 spot welds. It is suggested that melted films are retained since their dissolution rate is much slower in the high temperature stir zone than it is when melted films is formed in the stir zone during Al 7075-T6 friction stir spot welding. The spontaneous melting temperature, solute diffusion rate and the thermodynamic driving force for droplet dissolution are much higher during Al 7075-T6 friction stir spot welding.

Keywords

Spot Welding Spot Weld Tool Rotational Speed Friction Stir Spot Welding Friction Stir Spot Weld 

Notes

Acknowledgements

The authors wish to acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada during this project.

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Peter Su
    • 1
  • Adrian Gerlich
    • 1
    Email author
  • Motomichi Yamamoto
    • 1
  • Thomas H. North
    • 1
  1. 1.Department of Materials Science & EngineeringUniversity of TorontoTorontoCanada

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