Microstructure Evolution and Formation Mechanism of Interfaces in Parallel Gap Resistance Welding of Stranded Ag-Plated Cu Conductor to Ag Interconnector

Abstract

In flexible solar arrays, stranded hybrid-metal conductors and micro-foil interconnectors are preferred materials for energy transmission due to their high conductivity, flexibility and lightweight. However, achieving high-quality joints in parallel gap resistance welding (PGRW) between the stranded conductor and interconnector is challenging due to the complex microstructure formation at multiple interfaces. This study aims to clarify the correlation between interfacial microstructures and joint properties while elucidating the formation mechanisms of the interfacial microstructures. A shift in the bonding mechanism at interfaces from solid-state diffusion to brazing was found as the welding voltage reached a critical value of 1.5 V. The brazing-based bonding eliminated micro gaps while building nano-scale interlocking structures, resulting in substantial improvement in the mechanical properties of joints. Increasing the welding voltage from 1.2 V to 1.4 V was beneficial for the improvement in electrical conductivity due to the enlarged bonding area at interfaces. However, high welding voltage (1.6 V) led to degradation in the electrical conductivity of joints due to excessive Ag-Cu solid solution formed at interfaces. The key to fabricating high-strength and high-conductivity joints lies in achieving appropriate interfacial melting while reducing alloying by controlling peak temperature and shortening the duration above the Ag-Cu eutectic point.

Keywords: Parallel gap resistance welding, numerical simulation, Stranded hybrid-metal conductors, Interfacial microstructure, Mechanical and electrical properties