Research On Diffusion Bonding Of Extruded AZ61Magnesium Alloy

As a kind of metal structure materials, magnesium alloy has some good features such as low density, good damping, vibration resistance, high thermal conductivity, anti-electromagnetic interference, high electronegativity, recyclable and hence recently attracted extensive researches. With magnesium alloy being extensively applied to design in different trade, the welding of magnesium alloy has become a hotspot. Due to the physical property of magnesium alloy, the weldability is poor and it is difficult to gain reliable welding joint. After using normal welding method, magnesium alloy often appears various welding defects. It greatly limits the application of magnesium alloy.Vacuum diffusion welding is a solid phase linking method and because of welding joint being no melting, there is no fusion welding defect and heat affected zone. After diffusion bonding, the deformity of weldment is small and out of machining. The vacuum diffusion bonding could be a kind of welding method for precision parts connection. Vacuum diffusion welding could also be used for the connection of dissimilar materials that has extreme physical feature variations. Consequently, Vacuum diffusion welding has special advantages for the property of magnesium alloy.At present, AZ61is a kind of magnesium alloy which is widely used. In this report, by recrystallization anneal the grain of as-extruded AZ61magnesium alloys had been refined. With the refined AZ61magnesium alloys, the vacuum diffusion bonding was studied. The suitable craft parameters of recrystallization anneal:Annealing Temperature is300℃and annealing time is30min.The grain size was refined to14.29μm. Comparing with the primary crystalline size, the percentage of refined grain size is up to30.22%and the shapes of recrystallized grain boundaries were fine equiaxed crystal grains. The experimental results demonstrate that, in a particular situation that bonding pressure and vacuum degree were fixed as lOMPa and18Pa respectively, diffusion temperature and holding time were the main influence factors for diffusion bonding joint, meanwhile the cleanliness of diffusion surface could not be neglected to the quality of bonding joint. In this experiment, the optimum craft parameters of AZ61magnesium alloys vacuum diffusion welding: Diffusion temperature was470℃and holding time was90min. The maximum shear strength that was about46.78%of the base metal was up to51.95MPa and the shear strength of base metal was111.05MPa. The quality of bonding joint could meet the demand of the practical application. The microhardness measurement data of diffusion welding joint and base metal showed that the maximum microhardness was82.48HV at the welding joint and the farther from weld joint, the lower the microhardness value was. This was because micro-plastic deformation occurred at the welding joint.