Two-step ageing of 7xxx series alloys can reduce ageing time while obtaining similar mechanical properties as a longer isothermal heat treatment. In this paper, an intermediate deep-drawing step at 120–160 °C is introduced to produce elongated cup–shaped parts with near-T6 strength. A Cu-containing (Alclad 7075) and a non-standard low-Cu alloy (7021+) are used. Formability and the final mechanical properties after various second ageing steps are reported. Hardening precipitates are studied by means of transmission electron microscopy and differential scanning calorimetry. We found that the pre-aged 7021+ alloy can be deep-drawn at lower temperature (120 °C) than pre-aged Alclad 7075 (160 °C). Both alloys respond well to the two-step ageing regime with the parts achieving up to 99% and 98% of the T6 yield strength of Alclad 7075 and 7021+, respectively. Compared to T6, the distribution of hardening nanoscale Mg–Zn-precipitates is slightly coarser after two-step hardening regimes with intermediate warm-forming. Mechanical properties are closest to T6 for a final ageing step at 165 °C for 130 min and coarsening of hardening precipitates is less pronounced compared to a simulated paint-bake cycle (185 °C, 34 min).
|Seiten (von - bis)||1508-1515|
|Fachzeitschrift||Journal of Materials Research and Technology|
|Publikationsstatus||Elektronische Veröffentlichung vor Drucklegung. - 21 März 2021|
Bibliographische NotizFunding Information:
We thank AMAG rolling GmbH for providing 70721+ free of charge. We thank the technical staff at LKR and Montanuniversitaet Leoben for their assistance. We are grateful to the European Research Council (ERC) for funding this research through Horizon 2020 action via supporting the “TRANSDESIGN” project, number 757961, and to the Austrian Research Promotion Agency (FFG) for funding in the project AMALFI (FFG-No. 872641). The electron-microscopy facility was supported by the FFG in the project 3DnanoAnalytics (FFG-No. 858040 ). The funding sources had no involvement in study design nor in the collection, analysis and interpretation of data.
© 2021 The Author(s).