Effects of loading methods on microstructure of diffusion welded joint of AZ31B/Cu with Ni interlayer

摘要

Diffusion brazing was carried out to weld AZ3 IB magnesium alloy and copper with Ni foil interlayer under different loading methods that are divided into intermittent gradient pressure, gradient pressure and constant pressure. The microstructure and element diffusion of welded joint were analyzed by SEM and EDS. The results show that the AZ31B/Cu can achieve good bonded joint composed of brazing seam zone and magnesium substrate grain boundary penetration zone at 500 'C for 20 min. The loading methods have great influence on the thickness of brazing seam zone, microstructure and a-Mg grain size of the welded joint. At intermittent gradient pressure, the brazing seam zone reaches the biggest width of 0.18 mm, and the microstructure of brazing seam zone is composed of Cu_(11)Mg_(10)Ni9, (a-Mg+Mg2Cu+Mg2Ni)eutectic structure and a-Mg. Under gradient pressure, the width of brazing seam zone reduces, and the microstructure of brazing seam zone is mainly dominated by (a-Mg+Mg2Cu+Mg2Ni)eutectic structure and Cu_(11)Mg_(10)Ni9 compounds closed magnesium matrix. When using constant pressure, the microstructure of joint is similar to that under intermittent gradient pressure, the brazing seam zone reaches the smallest width of 0.11 mm, and the size of a-Mg grains reduces.