Effects of Different Types of Interlayers on the Interfacial Reaction Mechanism at the Cu Side of Al/Cu Lap Joints Obtained by Laser Welding/Brazing.

Ruican Zhu,Chao Huang,Xinrui Zhang,Shixiong Guo,Zhenglong Lei,Jinge Liu

doi:10.3390/ma14247797

Abstract

The influence of tin foil and Ni coatings on microstructures, mechanical properties, and the interfacial reaction mechanism was investigated during laser welding/brazing of Al/Cu lap joints. In the presence of a Zn-based filler, tin foil as well as Ni coating strengthened the Al/Cu joints. The tin foil only slightly influenced the joint strength. It considerably improved the spreading/wetting ability of the weld filler; however, it weakened the bonding between the seam and the Al base metal. The Ni coating considerably strengthened the Al/Cu lap joints; the highest tensile strength was 171 MPa, which was higher by 15.5% than that of a joint without any interlayer. Microstructure analysis revealed that composite layers of Ni3Zn14–(τ2 Zn–Ni–Al ternary phase)–(α-Zn solid solution)–Al3Ni formed at the fusion zone (FZ)/Cu interface. Based on the inferences about the microstructures at the interfaces, thermodynamic results were calculated to analyze the interfacial reaction mechanism. The diffusion of Cu was limited by the Ni coating and the mutual attraction between the Al and Ni atoms. The microstructure comprised Zn, Ni, and Al, and they replaced the brittle Cu–Zn intermetallic compounds, successfully strengthening the bonding of the FZ/Cu interface.

Highlights

Copper is widely used in various industries such as refrigeration, electrical, building, coinage, and transport owing to its excellent thermal and electrical conductivities [1]
The findings of this study show that, compared with the joint with only a Zn-based filler, tin foil significantly enhanced the wetting ability of the filler, while the Ni coating had only a slight effect on it
With the 0.3 mm tin foil, the spreading width of the Zn–2Al filler increased to 8.54 mm and the contact angle was 46.74◦, and the filler showed high wetting/spreading ability

Summary

Introduction

Copper is widely used in various industries such as refrigeration, electrical, building, coinage, and transport owing to its excellent thermal and electrical conductivities [1]. Aluminum and copper have similar thermal and electrical conductivities, machinability, and corrosion resistance; in addition, the density of aluminum is lower and its reserves are more abundant compared with those of copper [3,4]. Al/Cu dissimilar joints have future-orientated applications in various fields such as refrigeration, transportation, high-capacity batteries, and aerospace [5]. Studies have focused on developing Al/Cu dissimilar joints for such applications. The differences in the thermal expansivities of Al and Cu and the formation of brittle metallic compounds at the joints cause huge residual stresses and cracks [7,8,9,10]

Methods

Findings

Discussion

Conclusion