氢化—脱氢处理制备ZK60镁合金纳米晶材料

发布时间：2018-05-26 17:04

  本文选题：镁合金 + 纳米晶　； 参考：《太原理工大学》2015年硕士论文

【摘要】：镁及镁合金凭借自身突出的性能优点，，一直被航空航天、汽车工业和电子通讯等领域视为替代铝合金、钢铁材料的理想选择。然而，镁合金强度偏低且塑性变形能力差，使得它在工业中的应用受到限制。由于镁合金的机械性能受晶粒尺寸的影响较大，所以可以利用细化晶粒的方式来提高镁合金的强度和塑性。尽管晶粒细化的方法很多，但都难以真正将镁合金晶粒细化到纳米尺寸。本文中采用了氢化-脱氢法(HDDR)对ZK60镁合金粉末进行晶粒细化处理，最终获得镁合金纳米晶粉末材料。 本文首先探究了利用氢化-脱氢法对铸态ZK60镁合金粉末进行晶粒细化处理的氢化、脱氢工艺的参数路线。然后利用XRD分别测试了氢化、脱氢过程中温度、氢压和保温时间对相组成的影响，利用OM、SEM和TEM观察了ZK60镁合金粉末显微组织的演化规律，并分析了ZK60镁合金在氢化、脱氢过程中实现晶粒细化的机理。最后，对比在相同工艺参数下对纯镁进行氢化-脱氢处理的结果，讨论了歧化反应对镁合金晶粒细化过程的影响。 结果显示：在氢化过程中，温度是对反应过程影响最大的因素，温度越高，反应进程越快，氢化程度越大。延长保温时间同样可以起到提到氢化程度的效果。氢压对氢化过程的影响相对较小，呈现出随氢压增大，对氢化程度先抑制后促进的趋势。脱氢过程中，温度和保温时间的影响与氢化过程一致，但脱氢时间不宜选择过长，避免细化后的晶粒再次长大。综合考虑，确定了铸态ZK60镁合金晶粒细化的最优工艺参数路线：450℃、2MPa下氢化保温12h，再在350℃真空下脱氢3h。 采用已确定的最优工艺参数对ZK60镁合金粉末进行氢化-脱氢处理，由微观组织的演变过程表明，氢化处理使粉末颗粒发生应力断裂而产生许多碎小颗粒，再进行脱氢处理，粉末的颗粒尺寸变化不大，而ZK60镁合金的晶粒从150~200μm被细化至30nm左右，且大小较为均匀。由纯镁的氢化-脱氢处理结果，证明对于ZK60镁合金，可以忽略Zn、Zr元素对反应过程的影响，晶粒被细化主要是在脱氢重组过程中实现的，歧化反应对晶粒的细化帮助不大。
[Abstract]:Magnesium and magnesium alloys have been regarded as an ideal alternative to aluminum alloy and steel due to their outstanding performance advantages in the fields of aerospace, automotive industry and electronic communication. However, the low strength and poor plastic deformation ability of magnesium alloy limit its application in industry. Because the mechanical properties of magnesium alloys are greatly affected by grain size, the strength and plasticity of magnesium alloys can be improved by means of grain refinement. Although there are many methods of grain refinement, it is difficult to refine magnesium alloy grain to nanometer size. In this paper, the ZK60 magnesium alloy powder was refined by hydrogenation and dehydrogenation method, and the nanocrystalline magnesium alloy powder material was obtained. In this paper, the hydrogenation and dehydrogenation of as-cast ZK60 magnesium alloy powders by hydrogenation and dehydrogenation were studied. Then the effects of temperature, pressure and holding time on the phase composition during hydrogenation and dehydrogenation were measured by XRD. The microstructure evolution of ZK60 magnesium alloy powder was observed by OMSEM and TEM, and the hydrogenation of ZK60 magnesium alloy was analyzed. Mechanism of grain refinement in dehydrogenation process. Finally, the effect of the disproportionation reaction on the grain refinement process of magnesium alloy was discussed by comparing the results of hydrogenation and dehydrogenation of pure magnesium under the same process parameters. The results show that temperature is the most important factor in the process of hydrogenation. The higher the temperature, the faster the reaction process and the greater the degree of hydrogenation. Prolonging the heat preservation time can also have the effect of mentioning the degree of hydrogenation. The effect of hydrogen pressure on the hydrogenation process is relatively small, showing the trend that with the increase of hydrogen pressure, the hydrogenation degree is inhibited first and then promoted. In the dehydrogenation process, the effects of temperature and holding time are consistent with the hydrogenation process, but the dehydrogenation time should not be chosen for too long to avoid the grain growth after refinement. The optimum process parameters for grain refinement of as-cast ZK60 magnesium alloy were determined, which were hydrogenated for 12 h at 1: 450 鈩

本文编号：1938114