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中文摘要：
为了细化AZ91镁合金晶粒，采用氢化-歧化-脱氢-重组（HDDR）处理了镁合金粉末。研究了不同氢化温度、氢压和氢化时间对AZ91镁合金粉末HDDR过程的影响，探讨了AZ91镁合金HDDR过程的晶粒细化机制。分别用粉末X射线衍射、光镜、扫描电镜和透射电子显微镜来表征粉末的微观结构转变。结果表明，AZ91镁合金粉末最低的氢化温度是350℃，随着温度的增加、氢压的提高和氢化时间的延长，氢化反应的程度不断增加，直到粉末完全氢化，粉末最佳的HDDR过程参数是在450c、4MPa氢压下氢化12h后，在350℃真空中脱氢4h；氢化脱氢后的粉末形貌为薄片状，大小与原始粉末相当；在最佳HDDR参数下，AZ91镁合金粉末的晶粒大小从100um细化到了20nm。晶粒细化的过程表明，在HDDR的全过程中都有晶粒细化发生，其中较大程度的细化发生在脱氢重组过程中。
英文摘要：
The grain sizes of AZ91 magnesium alloy powders were refined by using hydrogenation-disproportionation-desorption-reeombination （HDDR） processing. The effect of the hydrogenation temperature, hydrogen pressure and hydrogenation time in the HDDR process on the phase transition of AZ91 alloy was studied. The mechanism of grain refining in HDDR processing was also discussed. The microstructure evolution of the alloy was characterized by powder X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that the lowest hydrogenation temperature was 350℃ and the degree of hydrogenation increased with the increase of hydrogenation temperature, hydrogen pressure and hydrogenation time until the powders were fully hydrogenated. The optimal HDDR technique was that the AZ91 powders are hydrogenated at 450℃ under 4 MPa for 12 h and then dehydrogenated at 350 ℃ for 4 h in vacuum. The morphology of the HDDR-treated Mg alloy powders is plate shaped and the size of the HDDR-treated Mg alloy powders is similar to that of the untreated powders. Under the optimal condition the grain size of the AZ91 Mg alloy powders can be immensely reduced from 100 um to 20 nm. The evolution of the grain size of the powders in HDDR process demonstrates that the process of grain refinement was continued throughout the HDDR treatment and the major grain refinement happened in dehydrogenation process.
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