HDDR-SPS法制备纳米镁合金及其组织与力学性能研究

发布时间：2018-01-07 06:12

本文关键词：HDDR-SPS法制备纳米镁合金及其组织与力学性能研究　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁合金是目前最轻的金属结构材料,具有一系列突出的优点和极广阔的发展及应用前景。然而其较差的力学性能制约了它的广泛应用。晶粒细化是提高镁合金力学性能的最佳途径。通常情况下,金属材料的屈服强度σ(或硬度)与晶粒尺寸d之间遵循Hall-Petch关系:σ=σ0+kd_(-1/2)。对于镁合金而言,其密排六方晶体结构对称性低、滑移系较少,相应的k值非常大,因而细晶强化的效果非常显著。目前细化镁合金晶粒的方法有快速凝固、剧烈塑性变形等,虽然已取得了一些成果,但是这些方法只能将镁合金的晶粒细化到0.5~1μm左右,很难细化到100nm以下并制备出较大尺寸的试样。本文按“商用镁合金粉末→氢化脱氢(HDDR)处理→放电等离子(SPS)烧结→热挤压致密成型→组织分析及力学性能测试”的工艺路线,以商用纯镁及AZ91镁合金切削粉末为原料,利用氢化-脱氢技术制备纳米晶镁及镁合金粉末,通过放电等离子烧结(SPS)制备纳米晶镁及镁合金块体,随后利用合适的挤压工艺得到纳米晶镁合金棒材。利用X-射线衍射、扫描电镜、透射电镜等测试手段,分析了镁合金粉末在氢化脱氢过程中的相转变及组织演变,确定了最佳氢化脱氢工艺,并探究晶粒细化机理;研究了放电等离子烧结的纳米晶镁合金块体材料的组织结构及性能,并探究了镁合金纳米晶粒的组织热稳定性;利用万能试验机,硬度测试仪等仪器设备研究热挤压致密成型的纳米晶镁合金棒材的组织及力学性能。结果表明,采用HDDR,SPS与热挤压相结合的方法,成功制备了纳米镁合金块体材料,其平均晶粒尺寸为15nm。与铸态与粗晶材料相比,屈服强度得到了很大程度的提高。并且采用这种方法制备的纳米晶材料具有超高的热稳定性,为制备高性能纳米晶镁合金材料开辟了新途径。
[Abstract]:Magnesium alloy is the lightest metal structure material at present. It has a series of outstanding advantages and broad development and application prospects. However, its poor mechanical properties restrict its wide application. Grain refinement is the best way to improve the mechanical properties of magnesium alloys. The relationship between yield strength 蟽 (or hardness) and grain size d follows Hall-Petch relation: 蟽 = 蟽 0 KD / 1 / 2 for magnesium alloy. Its dense hexagonal crystal structure has low symmetry, less slip system, the corresponding k value is very large, so the effect of fine grain strengthening is very remarkable. At present, the methods of refining magnesium alloy grain are rapid solidification, severe plastic deformation and so on. Although some achievements have been made, these methods can only refine the grain size of magnesium alloy to about 0.5 渭 m. It is very difficult to refine to below 100 nm and to prepare a large size sample. In this paper, according to the "commercial magnesium alloy powder" 鈫扝ydrogenated dehydrogenation (HDDR) treatment. 鈫扴park plasma sintered. 鈫扝ot extrusion compact forming. 鈫扷sing commercial pure magnesium and AZ91 magnesium alloy cutting powder as raw material, nanocrystalline magnesium and magnesium alloy powder were prepared by hydrogenation-dehydrogenation technology. Nanocrystalline magnesium alloy and magnesium alloy bulk were prepared by spark plasma sintering (SPS), then nanocrystalline magnesium alloy bars were obtained by proper extrusion process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to prepare nanocrystalline magnesium alloy. The phase transition and microstructure evolution of magnesium alloy powder during hydrogenation and dehydrogenation were analyzed by means of transmission electron microscope. The optimum hydrogenation dehydrogenation process was determined and the grain refinement mechanism was explored. The microstructure and properties of nanocrystalline magnesium alloy bulk sintered by spark plasma sintering (SPS) were studied, and the microstructure thermal stability of magnesium alloy nanocrystalline was investigated. The microstructure and mechanical properties of nanocrystalline magnesium alloy bars formed by hot extrusion and densification were studied by means of universal testing machine and hardness tester. The results showed that HDDR was used. Nanocrystalline magnesium alloy bulk materials were successfully prepared by combining SPS with hot extrusion. The average grain size of the bulk materials was 15 nm, which was compared with the as-cast and coarse crystalline materials. The yield strength is greatly improved, and the nanocrystalline materials prepared by this method have super high thermal stability, which opens a new way for the preparation of high performance nanocrystalline magnesium alloy materials.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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