Microstructural Control of the Interface Layer for Strength Enhancement of Dissimilar Al/Cu Joints via Ni Addition during TIG Arc Brazing

Abstract

Dissimilar metal joining between Al and Cu is effective for reducing the weight and cost of electrical components. In this study, dissimilar lap joining of pure Al to pure Cu with an Al-Ni filler material was conducted using tungsten inert gas (TIG) arc brazing, and the effect of Ni on the joint strength associated with the microstructure of the intermetallic compound (IMC) layer at the dissimilar interface was examined. The addition of Ni effectively increased the interfacial strength of the joints. Regardless of the addition of Ni, the joints fractured in the thick Al2Cu layer formed at the Al/Cu interface. However, the Ni addition reduced the thickness of the IMC layer and led to the formation of Al7Cu4Ni particles in the weakest Al2Cu layer. Both the thickness reduction and reinforcing Al7Cu4Ni particle formation are thought to contribute to the increase in joint strength of the Al/Cu dissimilar interface.

Effect of Ni Addition on the Interfacial Strength of Al/Cu Dissimilar Welds Produced by Friction Stir Lap Welding

“…The thickness of the IMC layer with 3 at.% Ni was 2.4 µm, while without Ni, it was 1.4 µm, indicating that the addition of 3 at.% Ni increased the thickness of the IMC layer. In contrast, it was reported that an IMC layer thicker than 30 µm formed at the interface of an Al/Cu weld produced via GTAW with 2.3 at.% Ni [28]. Because FSW is a low-heat-input joining process, it effectively reduces the thickness of the IMC layer.…”

“…The phases on the fracture surfaces were examined using X-ray diffraction (XRD) to identify the fracture location of the weld. [28] reported that the addition of 2.3 at.% Ni to the Al/Cu weld produced by GTAW exhibited the most effective improvement in the weld strength, reaching 50 MPa. Therefore, the strength of the Al/Cu weld produced by FSLW was higher than that of the weld produced by GTAW.…”

“…This implies that the Al/Cu weld without Ni failed at the CuAl 2 /Cu 9 Al 4 interface. Figure 12 shows the effect of Ni addition on the tensile shear strength of Al/Cu dissimilar welds produced by GTAW [28], laser brazing [27], and FSW. Unfortunately, the Al/Cu weld produced by FSLW exhibited a lower strength than that of the welds obtained by GTAW and laser brazing, although it had the thinnest IMC layer.…”

“…Furuya et al [27] examined the effect of alloying elements on the weld strength and interfacial microstructure of Al/Cu dissimilar joints produced by laser lap brazing and reported that the addition of Ni to the Al alloy distinctly improved the weld strength through the formation of a (Ni,Cu)Al layer at the weak CuAl 2 /Cu 9 Al 4 interface. Furuya et al [28] also examined the effect of alloying elements on the strength of welds produced by gas tungsten arc welding (GTAW) with Al-X filler materials (X = Mn, Si, Cr, Zn, Ni, or Sn), showing that the addition of Ni effectively improved the Al/Cu weld strength. These results show that Ni is an effective alloying element for improving the strength of Al/Cu dissimilar fusion welds.…”

“…The tensile shear strength of the joint produced without Ni was approximately 30 MPa, and the addition of Ni effectively improved the Al/Cu weld strength, reaching approximately 60 MPa at 3 at.% Ni. Furuya et al[28] reported that the addition of 2.3 at.% Ni to the Al/Cu weld produced by GTAW exhibited the most effective improvement in the weld strength, reaching 50 MPa. Therefore, the strength of the Al/Cu weld produced by FSLW was higher than that of the weld produced by GTAW.…”