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High-temperature microscopy on laser-welded copper-aluminum mixed joints – a challenge for metallographic preparation

  • C. Obergfell

    Clemens Obergfell studied at the University of Stuttgart with a focus on composite materials and laser materials processing. He is pursuing a PhD at the TUM Chair of Materials Engineering in Additive Manufacturing on the topic of laser welding of dissimilar Al-Cu-joints while working as a production process development engineer for electric drivetrains at Mercedes-Benz AG.

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    , A. Lietz

    Annette Lietz graduated as technical assistant for metallography and physical materials analysis at Lette-Verein. After more than three decades in industry (medical, automotive, aerospace) with a focus on failure analysis, she is now supporting research and development with her knowledge and passion for metallography at the TUM Chair of Materials Engineering of Additive Manufacturing.

    , S. Rotzsche and P. Mayr
Published/Copyright: October 23, 2025
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Abstract

Traditional diffusion analysis involving aging and ex-situ analysis of various test specimens reaches its limits when applied to laser-welded copper-aluminum (Cu-Al) joints, which are commonly found in electric vehicle batteries. High-temperature confocal laser scanning microscopy (HT-CLSM) promises in situ observation of intermetallic phase growth (IMP). For this reason, a laser-welded sample with a characteristic mixed-phase structure and a rolled Cu-Al sample were observed at temperatures of 400–450 °C over a period of up to 24 hours. The video recordings show microstructural changes and IMP growth at the interfaces, but also the formation of a liquidus phase, which can only occur at temperatures of at least 548.2 °C. HT-CLSM has thus proven to be suitable for analyzing diffusion processes and IMP growth in complex microstructures. Challenges remain in precise temperature control and the complex metallographic preparation of the samples.

Kurzfassung

Die klassische Diffusionsanalyse mit Auslagerung und ex-situ Analyse verschiedener Probekörper stößt bei lasergeschweißten Kupfer-Aluminium-Verbindungen (Cu-Al), wie sie häufig in Elektrofahrzeugbatterien vorkommen, an ihre Grenzen. Die Hochtemperatur-Konfokallaserscanningmikroskopie (HT-kLSM) (eng.: high temperature confocal laser scanning microscopy HT-cLSM) verspricht eine in-situ Beobachtung des Wachstums intermetallischer Phasen (IMP), weshalb eine lasergeschweißte Probe mit charakteristischer Mischphasenstruktur und eine gewalzte Cu-Al-Probe bei Temperaturen von 400 – 450 °C und über einen Zeitraum von bis zu 24 Stunden beobachtet wurden. Die Videoaufzeichnungen zeigen Gefügeveränderungen und IMP-Wachstum an den Grenzflächen, aber auch die Bildung einer Liquidusphase, die erst bei mindestens 548,2 °C auftreten kann. Die HT-kLSM erwies sich als geeignet, um Diffusionsvorgänge und IMP-Wachstum in komplexen Mikrostrukturen zu analysieren. Herausforderungen bestehen in der präzisen Temperaturführung und der aufwändigen metallographischen Präparation der Proben.

About the authors

C. Obergfell

Clemens Obergfell studied at the University of Stuttgart with a focus on composite materials and laser materials processing. He is pursuing a PhD at the TUM Chair of Materials Engineering in Additive Manufacturing on the topic of laser welding of dissimilar Al-Cu-joints while working as a production process development engineer for electric drivetrains at Mercedes-Benz AG.

A. Lietz

Annette Lietz graduated as technical assistant for metallography and physical materials analysis at Lette-Verein. After more than three decades in industry (medical, automotive, aerospace) with a focus on failure analysis, she is now supporting research and development with her knowledge and passion for metallography at the TUM Chair of Materials Engineering of Additive Manufacturing.

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Supplementary Material / Begleitmaterial

The online version of this article offers videos as supplementary material./Die Onlineversion dieses Artikels bietet Videos als Begleitmaterial an (https://doi.org/10.1515/pm-2025-0072).

Received: 2025-08-19
Accepted: 2025-09-25
Published Online: 2025-10-23
Published in Print: 2025-10-27

© 2025 Walter de Gruyter GmbH, Berlin/Boston, Germany

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