EFFECT OF HEAT TREATMENT ON MECHANICAL, THERMAL AND ELECTRICAL PROPERTIES OF AL-ZN-MG-CU(-SC-ZR) ALLOYS

1 LEIBNER Michal
Co-authors:
1 VLACH Martin 1 KODETOVÁ Veronika 1 CIESLAR Miroslav 1 KUDRNOVÁ Hana 2 OČENÁŠEK Vladivoj 3 VOLKMAR Neubert 3 VOLKMAR-DIRK Neubert
Institutions:
1 Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, CZ-121 16, Prague, Czech Republic, EU, mleibner@seznam.cz
2 SVÚM a.s., Tovární 2053, CZ-250 88, Čelákovice, Czech Republic, EU
3 Institut für Materialprüfung und Werkstofftechnik Dr. Neubert GmbH, Freiberger Strasse 1, D-38678, Clausthal-Zellerfeld, Germany, EU
Conference:
28th International Conference on Metallurgy and Materials, Hotel Voronez I, Brno, Czech Republic, EU, May 22nd - 24th 2019
Proceedings:
Proceedings 28th International Conference on Metallurgy and Materials
Pages:
1589-1594
ISBN:
978-80-87294-92-5
ISSN:
2694-9296
Published:
4th November 2019
Proceedings of the conference were published in Web of Science and Scopus.
Metrics:
35 views / 14 downloads
Abstract

The as-cast commercial Al-6 wt% Zn-2.5 wt% Mg-1.3 wt% Cu-0.8 wt% Fe, Si, Cr (AA7075) and AA7075-ScZr (0.19 wt% Sc-0.06 wt% Zr) alloys were investigated during isochronal annealing from room temperature up to 450 °C. Precipitation reactions were studied by microhardness, conductivity measurements and differential scanning calorimetry. Microstructure observation by scanning electron microscopy and transmission electron microscopy proved the Zn, Mg, Cu-containing eutectic phase at grain boundaries in the as-cast state of both alloys. The melting of this eutectic phase was observed for both alloys at ~ 480 °C in the DSC curves at heating rate of 20 K/min. The distinct changes in microhardness and conductivity curves as well as in heat flow of the alloys studied are mainly caused by dissolution of GP zones and by formation of the metastable phase particles of the Al–Zn–Mg–Cu system. The hardening effect after isochronal annealing at temperatures above ~ 270 °C reflects the Sc, Zr-addition in the AA7075-ScZr alloy – the secondary Al3(Sc,Zr) particles precipitation causes a pronounced hardening in the temperature range of 270–450 °C. The eutectic Zn,Mg,Cu-containing phase partly disappeared after the isochronal annealing at 450 °C as it was observed by scanning electron microscopy.

Keywords: AA7xxx series, DSC, SEM, phase transformation, Al3(Sc,Zr) phase
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