Transient Local Melting in Al 7075-T6 Friction Stir Spot Welds


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Transient local melting can account for the remarkable decrease in the strain rate when the tool rotational speed, heating rate and cycle time produce temperatures exceeding the 475 °C in Al 7075-T6 spot welds. The calculated strain rate is about 20 s-1 in Al 7075-T6 spot welds produced using tool rotational speeds from 1500 RPM to 3000 RPM and dwell time of 4 s. However, the peak temperature is less than less than 475 °C when a low tool rotational speed setting (1000 RPM) is used; transient local melting and tool slippage are precluded and the calculated strain rate is high (about 650 s-1). It is proposed that transient local melted films directly influence formation of the stir zone microstructure in Al 7075- T6 spot welds. It is suggested that the stir zone microstructure in spot welds made using high tool rotational speed settings are determined by a combination of grain boundary sliding and the limitation of cavity interlinkages when transient local melted films form.



Materials Science Forum (Volumes 539-543)

Main Theme:

Edited by:

T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran




T.H. North et al., "Transient Local Melting in Al 7075-T6 Friction Stir Spot Welds", Materials Science Forum, Vols. 539-543, pp. 3826-3831, 2007

Online since:

March 2007




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