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

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.