Relieving residual stress and enhanced mechanical properties by novel sandwich composites filler metal

Abstract

Sandwich composite filler metal is a crucial approach to relieve the residual stress and obtain a reliable joint between non-metallic and metals. A novel sandwich composite filler metal, BAg40CuZnNi/CuMn2/BAg40CuZnNiMnCo, was originally prepared by roll bonding and annealing. The microstructure, mechanical properties and residual stress of the YG15/42CrMo joints brazed were characterized by scanning electron microscope, universal testing machine, and X-ray residual stress diffractometer. During annealing, diffusion layers were formed at the BAg40CuZnNi/CuMn2/BAg40CuZnNiMnCo interfaces, the growth of the diffusion layer conformed to the parabolic relationship and was dominated by the diffusion mechanism. During the early stage of brazing, the brazing seam was divided into seven different regions, accompanied by the formation of an interfacial diffusion layer. With brazing time increased, the width of the CuMn2 interlayer in the brazing seam and the amounts of Cu-rich phase gradually decreased, while enriched the Ag-Cu eutectic structure. The increased brazing time and reduced thickness of the CuMn2 interlayer decreased the shear strength of the brazed joint. An appropriate thickness of the CuMn2 interlayer changed the microstructure in the brazing seam, reduced the residual stress on the YG15 surface, further effectively improving the shear strength of the brazed joint with dimple fracture. The results provide a reference for the brazing of nonmetals and metals.