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Licensed Unlicensed Requires Authentication Published by De Gruyter May 12, 2021

STEM investigations of the influence of copper on alumina scale detachment during in-situ wetting experiments of Al-7Si-0.3Mg alloy with 95Sn-5Cu filler metal

Ashok Vayyala, Anke Aretz, Kirsten Bobzin, Wolfgang M. Wietheger, Julian Hebing, Riza Iskandar, Joachim Mayer and Alexander Schmidt

Abstract

Aluminum alloys have a strong tendency to form alumina layers on their surfaces when exposed to atmospheric air, even at room temperature. This is a severe challenge for brazing aluminum alloys as the alumina layer acts as a diffusion barrier and hinders the interactions between the filler metal and the base material. In order to achieve a good metallurgical bond between the filler metal and the aluminum alloy, it is of crucial importance to remove the alumina layer as well as to simultaneously prevent further oxidation of the aluminum alloy.

The current investigation focuses on the detailed micro-structural changes that occur during in-situ brazing of liquid filler metal, 95Sn-5Cu (wt.%) on an aluminum alloy, Al-7Si-0.3Mg. These in-situ studies were performed in a large chamber scanning electron microscope in order to monitor the interactions of the filler metal and the base material, particularly the role of Cu on alumina detachment. After the in-situ experiments, the local surface and cross-sectional regions were analyzed by scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy to understand the variation in chemistry across the wetted region, which includes the interfacial region between filler metal and the base material. As the alumina scale present on the aluminum alloy is very thin (<50 nm), nanoscale characterization techniques such as transmission electron microscopy in scanning mode, including selected area electron diffraction for crystal structure determination, were performed. From this investigation, it was found that the Cu in liquid filler metal diffuses into the base material via the oxide layer, resulting in the formation of Al2Cu intermetallic precipitates.


Julian Hebing M.Sc. Institut für Oberflächentechnik/Surface Engineering Institute RWTH Aachen University Kackertstraße 15 52072 Aachen

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Received: 2020-08-09
Accepted: 2021-02-02
Published Online: 2021-05-12
Published in Print: 2021-05-31

© 2021 Walter de Gruyter GmbH, Berlin/Boston, Germany

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