Effect of SIMA-imitated Brazing on the Microstructure and Shear Strength of Mn-Cu/430 Stainless Steel Joints

In this paper, Cu-Mn-Ni-Sn brazing filler metal was used to braze Mn-Cu alloy and 430 stainless steel (SS) by ordinary brazing (as-cast brazing filler metal, 850℃) and SIMA-imitated brazing process (rolled brazing filler metal, semi-solid temperature 790℃), respectively. The effects of brazing temperature on the microstructures, the formation of compounds and the mechanical properties of the joints were studied. In ordinary brazed joint, (Mn, Fe, Cr) solid solution diffusion layer was formed at the interface between stainless steel and brazing seam, however, cracks were formed at the interface between the diffusion layer and the brazing seam. The penetration of Sn-rich phase at grain boundaries of Mn-Cu alloy promoted the melting of alloy. The excessive dissolution of SS and partial melting of Mn-Cu alloy resulted in the formation of a large number of needle-like Mn-Cr-Cu-Fe compounds in the brazing seam. In SIMA-imitated brazed joint, the interface between stainless steel and brazing seam was well bonded. At the semi-solid temperature, the diffusion of filler metal to SS was decreased, and the dissolution of SS to filler metal was decreased as well. At the Mn-Cu alloy side, the penetration of Sn-rich phase along the grain boundaries was also effectively suppressed. Since the interaction between the substrates and filler metal was weaker, the amount of needle-like compounds decreased obviously in the brazing seam. In shear test, both brazed joints were broken in the distribution area of needle-like compounds in the brazing seam. The shear strength of ordinary brazed joint was 173 MPa, and that of SIMA-imitated brazed joint was 230 MPa. © 2020, Materials Review Magazine. All right reserved.