Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy |
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Authors: | Adrian Gerlich Peter Su Motomichi Yamamoto Tom H North |
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Affiliation: | (1) Department of Materials Science & Engineering, University of Toronto, 184 College St., Rm. 140, Toronto, ON, Canada, M5S 3E4 |
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Abstract: | The stir zone microstructure, crystallographic texture, temperature and strain rate in the stir zones produced during Al 2024
spot welding using different tool rotational speed settings are investigated. The calculated strain rate during spot welding
decreases from 1600 to 0.6 s−1 when the tool rotational speed increases from 750 to 3000 rpm. The low strain rate values are associated with tool slippage
resulting from spontaneous melting of S phase particles at temperatures ≥490 °C. However, the calculated strain rate is 1600 s−1 in Al 2024 spot welds made using tool rotational speed of 750 rpm since the temperature never reaches 490 °C. Material transfers
downwards via that pin thread during the dwell period in Al 2024 spot welding. It is proposed that this downward transfer
of material provides a continuous supply of undissolved S phase particles, which melt spontaneously when the welding parameter
settings produce stir zone temperatures ≥490 °C. A weak crystallographic texture where the {100} planes are oriented at about
45° to the θ-direction exists in the stir zones of spot welds made using different tool rotational speeds (from 750 to 3000
rpm). Another crystallographic texture where the {100} planes are parallel to the Z-direction (to the tool axis) is stronger
in spot welds made using higher tool rotational speed settings. Also, material located at the root of the pin thread has a
quite different crystallographic texture from that in the bulk of the stir zone. |
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