Table of Contents Author Guidelines Submit a Manuscript
Advances in Materials Science and Engineering
Volume 2017, Article ID 7679219, 10 pages
https://doi.org/10.1155/2017/7679219
Research Article

Investigations on the Hot Stamping of AW-7921-T4 Alloy Sheet

1LKR Leichtmetallkompetenzzentrum Ranshofen GmbH, Austrian Institute of Technology, Lamprechtshausnerstrasse 61, Postfach 26, 5282 Ranshofen, Austria
2Robinson Research Institute, Victoria University of Wellington, 69 Gracefield Road, P.O. Box 33-436, Petone, Lower Hutt 5046, New Zealand

Correspondence should be addressed to M. Kumar; moc.liamg@rtii.mkm

Received 23 August 2016; Revised 24 November 2016; Accepted 26 January 2017; Published 26 February 2017

Academic Editor: Gianfranco Palumbo

Copyright © 2017 M. Kumar and N. G. Ross. 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.

Abstract

AW-7xxx alloys have been nowadays considered for greater light weighting potential in automotive industry due to its higher strength compared to AW-5xxx and AW-6xxx alloys. However, due to their lower formability the forming processes are still in development. This paper investigates one such forming process called hot stamping. The investigation started by carrying out hot tensile testing of an AW-7xxx alloy, that is, AW-7921 at temperatures between 350°C and 475°C, to measure the strength and formability. Formability was found to improve with increasing temperature and was sensitive to the strain rate. Dynamic recovery is considered as usual reason for the formability improvement. However, examining the precipitation states of the as-received condition and after hot stamping using differential scanning calorimetry (DSC), the dissolution of precipitates was also believed to contribute to this increase in formability. Following solution heat treatment there was no precipitation during cooling across the cooling rates investigated (5–10°C/s). Samples taken from parts hot stamped at 10 and 20 mm s−1 had similar yield strengths. A 3-step paint baking heat treatment yielded a higher postpaint baking strength than a single step treatment.