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

Highlights: • Joints brazed at 800 °C exhibited multiple single-phase layers. • Brazing at higher temperatures gave rise to multiphase layers within diffusion zone. • Copper and zinc diffused away from the BFM towards the base materials. • Nickel coating on base material helped in minimizing loss of aluminum by diffusion. • The joint brazed at 820 °C was found to have the highest lap shear strength. 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 °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 °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 °C brazing temperature. Detailed mechanism behind the formation of different phases across the brazed joint and its correlation with joint strength are also presented.