Study On Interfacial Reaction Of Mg/Cu Diffusion Couple And AZ31B/Cu Diffusion Brazing

Magnesium alloys are known to be the most potential materials for the development in twenty-first Century because of many advantages. Copper alloys have been widely used in the fields of electronic and electrical engineering. In order to give full play of their advantages, it is necessary to carry out welding. In this paper, do experiment of Mg/Cu diffusion couple at 430?-485? for thermal diffusion firstly, study the evolution of microstructure by means of SEM, EDS. Secondly, using aluminum foil, nickel foil as intermediate layer, analyze the influence of loading methods on microstructure and properties of AZ31B/Cu diffusion brazing joints. Finally, the effect of heating temperature and holding time on microstructure and properties of AZ31B/Cu with ZnAl15 interlayer was studied.The results show that: when Mg/Cu thermal diffusion experiment carried out below 485?,the microstructure of interfacial reaction layer mainly composed large Mg matrix diffusion zone,Cu2Mg zone and narrow Cu based solid solution region, while the large Mg matrix diffusion zone consisted of ?-Mg solid solution and granular Mg2Cu phase which distributed along the grain boundaries. Diffusion of Cu atoms in the Mg matrix is dominated by grain boundary diffusion. Relationship between the thickness of the Cu2Mg layer and temperature is exponential increasing. The microstructure of interface reaction is mainly composed of Mg matrix diffusion region,(?-Mg+Mg2Cu)eutectic structure and Cu(Mg) solid solution at 485?for 4h.Micro-hardness of the diffusion zone was significantly higher than both sides of the base metal, the maximum value appeared near the copper substrate when the temperature below 485?,while the maximum appeared in the eutectic zone at 485?.AZ31B/Cu diffusion brazing joint with aluminum, nickel foil as interlayer can be achieved metallurgical combination under constant pressure, gradient pressure, intermittent gradient pressure at 500? for 20 min.Loading methods have more influence on AZ31B/Cu joint with aluminum foil as interlayer. The microstructure of the joint was mainly dominated by coarse intermetallic compound at constant pressure; while the joint formed discontinuous chrysanthemum eutectic structure at gradient pressure. Uniform and continuous eutectic structure produced at intermittent gradient pressure. The microstructure of interface zone are ?-Cu?AlCu4?(Mg2Cu+?-Mg) eutectic structure?Al2CuMg?(Al12Mg17+?-Mg) eutectic structure and ?-Mg. For the joint of AZ31B/Cu with aluminum as interlayer, the maximum hardness appeared when the pressure is constant, the minimum emerged at gradient pressure. The maximum shear strength appeared at intermittent gradient pressure, while the minimum appeared at constant pressure.On the condition of 480?-500?,10min-30 min,the joint of AZ31B/Cu with ZnAl15 as interlayer can be achieved metallurgical combination. Interfacial diffusion zone are mainly composed of magnesium based permeable layer, the mixed layer of eutectic and the compound structure and copper based solid solution. The microstructure from the copper matrix are ?-Cu?AlCu4?Al6CuMg4?(Al12Mg17+?-Mg) eutectic structure?(Mg2Cu+?-Mg) eutectic structure?(MgZn+?-Mg) eutectic structure and ?-Mg. At 480?-500? for 20 min, the micro-hardness of AZ31B/Cu with ZnAl15 as interlayer shows the distribution of middle high and both sides low. With the increase of temperature, the micro-hardness of the joint increased, while the shear strength increased first and then decreased. The shear strength of the joint reached the maximum at 490?, which is about 64 MPa.