Interdiffusion and microstructure evolution during brazing of austenitic martensitic stainless steel and aluminum-bronze with Ag-Cu-Zn based brazing filler material

Brazing of austenitic martensitic stainless steel (AMSS) with Al-bronze was carried out using Ag-26Cu-3.64Zn (wt%) as brazing filler material (BFM) and the interdiffusion behavior of various elements and microstructure evolution were investigated. Brazing was carried out at four different brazing temperatures (800, 820, 840, and 860 degrees C) for 15 min. It was found that in addition to increasing wettability of BFM, Ni-coating also plays a significant role in minimizing the loss of aluminum by diffusion from bronze side as well as in enhancing the joint strength. It caused partitioning of Cu and Zn from liquid BFM towards the base materials and formed (Cu, Ni) based solid solutions at the two interfaces. In addition, it reacts with aluminum from aluminum bronze to form intermetallic based on nickel and aluminum. In the joints brazed at 800 degrees C, continuous single phase layers were formed in the diffusion zone. However, at higher brazing temperatures, formation of multiphase zone was observed across the joints. Lap shear strength was found to be maximum in the joints prepared at 820 degrees C brazing temperature. Detailed mechanism behind the formation of different phases across the brazed joint and its correlation with joint strength are also presented. (C) 2018 Elsevier B.V. All rights reserved.