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Metals 2019, 9(3), 305; https://doi.org/10.3390/met9030305

Characterisation and Comparison of Process Chains for Producing Automotive Structural Parts from 7xxx Aluminium Sheets

1
LKR Light Metals Technologies, Austrian Institute of Technology, Lamprechtshausener Strasse 61, 5282 Ranshofen, Austria
2
Institute of Materials Science, Joining and Forming, Graz University of Technology, Kopernikusgasse 24, 8010 Graz, Austria
3
Chair of Materials Science, University of Rostock, Albert-Einstein-Strasse 2, 18051 Rostock, Germany
4
Magna Steyr Fahrzeugtechnik AG & Co KG, CoC Material & Process Engineering, Liebenauer Hauptstrasse 317, 8041 Graz, Austria
*
Author to whom correspondence should be addressed.
Received: 11 February 2019 / Revised: 26 February 2019 / Accepted: 28 February 2019 / Published: 7 March 2019
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Abstract

Due to their high specific strength, EN AW-7xxx aluminium alloys are promising materials for reducing the weight of automotive structural parts. However, their formability at room temperature is poor due to pronounced natural ageing. Therefore, we investigated hot stamping and W-temper forming for EN AW-7075 and a modified variant of EN AW-7021. For hot stamping of the modified EN AW-7021, a low-temperature stabilisation heat treatment (pre-aging at 80 °C for 1 h) was incorporated into the process chain design to inhibit natural ageing after forming. The process chains were compared with respect to dimensional accuracy, mechanical properties, microstructure, precipitation status (assessed by differential scanning calorimetry) and crashworthiness. It was found that hot stamping is suitable to form failure-free parts with good dimensional accuracy for both alloys while W-temper forming suffers from springback. Within a time-span of 21 days after forming, hardness values of hot stamped and stabilised parts did not increase significantly. Compared to non-stabilised parts, stabilised parts also showed significantly improved folding behaviour in quasi-static compression testing and absorbed approximately 15% more energy. View Full-Text
Keywords: aluminium; 7021; 7075; hot stamping; W-temper forming; stabilisation heat treatment; crashworthiness aluminium; 7021; 7075; hot stamping; W-temper forming; stabilisation heat treatment; crashworthiness
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Schuster, P.A.; Österreicher, J.A.; Kirov, G.; Sommitsch, C.; Kessler, O.; Mukeli, E. Characterisation and Comparison of Process Chains for Producing Automotive Structural Parts from 7xxx Aluminium Sheets. Metals 2019, 9, 305.

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