【作者】 李会；

【导师】 林飞；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 工业技术水平的提高依赖于新结构材料的研发,而作为最轻的金属结构材料的镁合金,在结构减重与承载等方面均具有突出的优点。随着镁合金在各行各业中日益广泛的应用,镁合金的连接问题也相应地成为人们关注的焦点,但是镁合金的焊接性能差,很难实现可靠连接,制约了镁合金的广泛应用。真空扩散焊接是一种精密连接方法,接头区不需要经过熔化与凝固的过程,能减少或避免类似于熔化焊中产生的缺陷,更容易实现同母材组织性能一致的高质量连接。并且连接后的焊件精度高、变形小,可以实现精密结合,一般不需要再进行机加工,经济效益明显。因此研究镁合金的扩散焊接有十分重要的理论意义和实际意义。目前,AZ31B是应用最为广泛的变形镁合金,同时还是一种非常重要的商用镁合金。因此本文对工业挤压态AZ31B变形镁合金的热处理工艺和真空扩散焊接工艺进行了研究。热处理的实验结果表明在温度为300℃、时间为30min时,晶粒尺寸达到最小,为14.1μm；然后在合理的连接温度、保温时间、压力等参数下对AZ31B镁合金进行扩散焊接实验研究,实验结果表明,在温度为420℃,压力8MPa,保温时间为90min时,获得的扩散焊接接头的显微组织最好；杂质对扩散焊接接头质量的影响也不容忽视,需要通过调节连接温度、时间来避免杂质在连接界面聚集,从而提高接头的质量。然后对扩散焊接接头进行显微硬度测定,发现焊缝处显微硬度值最大,为81.8HV0.05,距焊缝越远,显微硬度值也越低。最后利用万能实验机对焊接接头进行剪切实验,实验结果表明,温度为420℃,压力8MPa,保温时间为90min时扩散焊接接头的剪切强度值最大,达到49.9MPa。更多还原

【Abstract】 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.更多还原