Influence Of Electric Field On The Interfacial Diffusion Reaction And Microstructure Of Diffusion Dissolution Layer Of AZ31B/Cu Joint

Magnesium alloy is the lightest metallic structural material widely used at present and has some advantages such as high specific strength, specific modulus, excellent performance of damping and processing. Copper and copper alloy have excellent electrical conductivity, thermal conductivity, corrosion resistance, good ductility and good cold or hot processing properties. Now, the research of diffusion bonding of magnesium alloy and copper alloy has become a hotspot and rub. In recent years, the study about activation of the applied electric field in the solid phase diffusion process provides a new approach to magnesium-copper diffusion bonding mechanism.In this paper, Mg-Cu diffusion dissolution layer was formed at the interface between magnesium alloy and copper in short time by applying the electric field. The experiment, the optical microscope(OM), SEM and XRD were applied to observe the microstructure and determine the phase of the diffusion dissolution layer and elements profile across interface. And the microhardness of the diffusion dissolution layers and Shear resistance of the diffusion couple were evaluated too.The bonding of magnesium alloy (AZ31B) and copper is carried out using field-activated diffusion bonding technology at the temperature of450℃,475℃and500℃and holding for5to60minutes under the pressure of30MPa. The results show that the interface of diffusion is smooth at the temperature of450℃, which proves solid diffusion. And the width of diffusion layer increases gradually as holding time increase. The interface of diffusion presents curve shape at the temperature of475℃, which indicates the presence of liquid phase. Eutectic structure appears next to Mg2Cu which is close to the side of magnesium alloy and finally merges itself along the whole interface with the increase of time at500℃. Compared with thermal diffusion, electric field reduces the diffusion activation energy of the metallic element and increases the diffusion coefficient at the same temperature. The diffusion coefficient of Mg and Al increases while the diffusion activation energy decreases with the increase of electric intensity. The decrease of diffusion activation energy prompts the nucleation rate of the new phase. But electric field cannot change the formation mechanism of the new phase. When the current density is35Acm-2the thickness of the diffusion dissolution layer is10μm which is5 times wider than that of current-free condition at450℃for30min. The enhanced growth of diffusion dissolution layers was contributed to increment of the concentration and mobility of point defect.