Microstructure and phase constitution at the interface of double-sided electron beam welded Cu/Al clad metal sheet

Abstract

The microstructure of the interfa ce zone is the most important factor to determine the properties of the Cu/Al clad metal sheet joint. The composition distribution and phase constitution at the interface of the double-sided electron beam welding (DSEBW) joint of 6.5 mm thick Cu (1.5 mm)/Al (5 mm) clad metal sheet were revealed by means of technologies of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was confirmed that there formed a distinct transition zone with a length of about 5.8 mm at the interface, and it consisted of a thin layer of IMC and a large area eutectic structures. Moreover, the thickness distribution of IMC layer in the center and edges of the interface zone was nonuniform, and gradually decreased from the center (7.5 μm) to the edges (1.5 μm and 2.6 μm) by means of SEM and EBSD. Furthermore, the eutectic structure performed the superior laminar, and the grey IMC dispersed in Al-rich dendrites inside the eutectic structure. In addition, the interface zone mainly consisted of two slices, including Cu/IMC interface (Interfaces I and III) and IMC/eutectic structure interface (Interfaces II and IV). For interfaces I and III, this IMC was Al2Cu, and there was no other IMCs between Cu and Al2Cu IMC by means of TEM; For interfaces II and IV, the eutectic structure was composed of Al2Cu and α-Al, while there was also no other IMCs between Al2Cu IMC and (Al2Cu + α-Al) eutectic structure. In short, the microstructure characterizations at the whole interface of the DSEBW joint were Al2Cu IMC and (Al2Cu + α-Al) eutectic structure.