Study on process, microstructure and mechanical properties of 6061/AZ31 dissimilar metal joining with direct contact reaction brazing

Abstract

In this study, 6061-Al and AZ31-Mg were successfully joined using the contact reaction brazing process without an interlayer under a pressure of 2 MPa and a vacuum of 1 Pa. The study examined the microstructure and mechanical properties of 6061/AZ31 joints, as well as the impact of process parameters including heating mode, cooling rate, heating temperature, and holding time on the joints. The results show that the 6061/AZ31 brazing seam can be divided into two zones: the liquid-phase solidification zone and the diffusion reaction zone. The liquid-phase solidification zone consists of the (α-Mg + Al12Mg17) eutectic organization and precipitation phases distributed therein. The diffusion reaction zone mainly consists of the Al3Mg2 layer in the brazing seam close to the 6061. Fractures in joints mainly occur in the diffusion reaction zone, where the hard and brittle Al3Mg2 layer is located and extends into the liquid-phase solidification zone. Brazing joint quality was better with a cooling rate of 5 °C/s and heating without pre-weld and post-weld holding processes. The highest joint shear strength of 37 MPa was achieved at 445 °C with a holding time of 5 s. The joint exhibited no obvious defects, and the axial shrinkage of the specimen was 0.414 mm, with minimal deformation.