Technology Research On Diffusion Bonding Of Extruded AZ91Magnesium Alloy

Due to their light weight, high specific stiffness and specific strength, magnesium alloys have been widely used for3C (Computer, Communication and Consumer Electronics) industries and vehicles recently. However, it is easy to form welding defects because of the low melting point、higher linear expansion coefficient and large thermal conductivity, it is limited in practical use. Compare with normal welding methods, Vacuum diffusion welding is an advanced solid phase connection method. Diffusion welding has t melting welding defects such as heat-affected zone, and would not appear microscopic plastic deformation after welding, it could be applied to precision parts connection. So, Vacuum diffusion welding is a relatively effective method to solve the magnesium alloy welding difficulty. The research of magnesium alloy diffusion welding is of important theoretical significance and practical application value.This paper mainly discussed the vacuum diffusion welding experiments of AZ91magnesium alloy. Before and after the welding experiment, samples were made recrystallization annealing treatment. the transformation law of structure, shear strength, hardness, etc were analyzed in the heat treatment process. Also the influence factors which exist in the whole process are illustrated.The results of recrystallization anneal show that, the best technological parameter is300℃×30min,then the grain size was refined to12.31μm. Compared with the original grain size21.41μm, the percentage of refined grain size is up to42.5%. Effect of diffusion temperature and holding time is the most important for diffusion bonding, when bonding pressure is lOMPa and vacuum degree is18Pa respectively. The better experiment process parameters of vacuum diffusion bonding as follows:temperature470℃, diffusion time90min. average shear strength of diffusion welded joints is64.70MPa, about46.2%of the shear strength of AZ91base. The diffusion welded joint was annealed in the condition of reasonable temperature and holding time, shear strength of some welded joints got from diffusion bonding experiment had been further improved. Such welded joint as under the condition of470℃and90min process, its shear strength rose from64.70MPa to76.93MPa after postweld heat treatment, increased by about18.9%.Within a certain range, the lower the welding temperature, and the shorter the holding time, the higher shear strength of the diffusion bonding joint; but welding joint in higher temperature and longer time, through the same postweld heat treatment, had not received a significant boost in performance.