| Raising the level of industrial technology depends on the development of new structural materials. As the lightest metal structural material, magnesium alloy has outstanding advantages in weight lighting and load bearing and other aspects. With the increasingly widespread application of magnesium alloy in all professions and trades, the connection problems of magnesium alloy become correspondingly more and more important. But the welding performance of magnesium alloy is very poor and it is very difficult to achieve reliable connection, and so the wide use of magnesium alloys is restricted. However, the vacuum diffusion bonding is a sophisticated connection method. The welding joint of diffusion bonding does not need the process of melting and solidification. Using diffusion bonding can reduce or avoid similar defects generated in fusion welding and it is also easier to achieve high-quality connection. The microstructure and properties of welding joint are more similar to those of base metal than other welding methods. And welding joint has high precision and small deformation. Using diffusion bonding can get precision welding structure, and the parts do not need further mechanical processing. Using diffusion bonding is also having remarkable economic benefit. Therefore, it is very important theoretical and practical significance to study the diffusion bonding of magnesium alloys.At present, AZ31B is not only the most widely used magnesium alloy but also a very important commercial magnesium alloy. Therefore, in the paper, the isothermal heat treatment and vacuum diffusion bonding of AZ31B are studied. The result of isothermal heat treatment experiment shows that grain size is 14.1μm which is the smallest grain size when the temperature is 300℃and the holding time is 30min. Then diffusion bonding experiment of magnesium alloy AZ31B at a reasonable temperature, holding time, pressure, and other parameters is studied. The results show that the microstructure of the diffusion bonding welding joint is the best when the temperature is 420℃, pressing 8MPa and holding for 90min. It is also can not be ignored that the influence of impurities on the welding joint. In order to improve the quality of welding joint, it is necessary to control temperature and time to avoid impurities gathering. Then, the microhardness of the welding joint is measured. Result shows that hardness at the fusion line is 81.8HV0.05, which is higher than other place. The farther from weld joint, the lower the microhardness value is. Finally, the shear strength of welding joint is measured by the use of universal testing machine. Result shows that the shear strength of the diffusion bonding welding joint is the highest when the temperature is 420℃, pressing 8MPa and holding for 90min. The highest shear strength is 49.9MPa. |
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