Microstructure evolution and mechanical properties of copper/304 stainless-steel joints by low-temperature soldering

Abstract

Pure copper (Cu) soldering joints with 304 stainless steel (SS) at different soldering temperatures (240–[Formula: see text]C) were prepared by using Sn–3.5 Ag (wt.%) as a soldering filler-metal material. The mechanical properties and microstructure evolution were investigated. Sound Cu/304 SS joints were obtained by soldering at 240–[Formula: see text]C for 90 s and the highest average joint shear strength was [Formula: see text] MPa when brazed at [Formula: see text]C. The Cu6Sn5 and Ag3Sn phases were typical intermetallic compounds (IMCs) in the joints at a soldering temperature of [Formula: see text]C. Cu3Sn IMCs were formed at the Cu/Cu6Sn5 interface as the soldering temperature increased to [Formula: see text]C and above. Shear fracture analysis by scanning electron microscopy (SEM) with energy dispersive spectroscopy showed that the joints fractured mostly inside the Cu6Sn5 layers.