Mg-Zn-Y-Zr合金高周疲劳行为研究

发布时间：2018-06-21 14:12

  本文选题：Mg-Zn-Y-Zr合金 + 时效处理　； 参考：《西南交通大学》2017年硕士论文

【摘要】：镁合金作为最轻的金属材料,普遍应用于交通运输、航天装备等领域。目前镁合金受限于其强度而多用于制造非承力部位的零件。重要承力零部件容易在长时间交变载荷作用下发生疲劳断裂,因此开发一款高强度和疲劳性能优异的镁合金成为重要的任务。本课题选取自行开发的稀土镁合金Mg-2.3Zn-0.18Y,通过加入不同含量的Zr(0.03,0.06,0.13 at.%)元素以及热挤压变形方式得到性能优异的Mg-2.3Zn-0.18Y-xZr镁合金。首先,研究挤压态Mg-2.3Zn-0.18Y-xZr镁合金高周疲劳性能和裂纹萌生、扩展机理;其次,选取高周疲劳性能较优的Mg-2.3Zn-0.18Y-0.13Zr合金作为研究对象,分别通过时效处理和喷丸处理提高其高周疲劳性能;最后,分别阐述各工艺下的裂纹萌生、扩展机理和强化机理。得到主要结论如下:(1)随着 Zr 含量的增加,Mg-2.3Zn-0.18Y-xZr(x=0.03、0.06、0.13 at.%)合金的α-Mg平均晶粒尺寸从9.9μm减少到4.8μm;抗拉强度、屈服强度和延伸率都有所提高,其中Mg-2.3Zn-0.18Y-0.13Zr合金的力学性能最好,分别达到346MPa、292MPa和26.7%,其疲劳强度为150MPa。另外,Mg-2.3Zn-0.18Y-0.03Zr合金疲劳断口显微组织的粗大晶粒中发现有孪晶生成,说明孪生变形影响此合金的塑性变形方式。(2)当应力水平较高(180MPa)时,挤压Mg-2.3Zn-0.18Y-xZr合金的高周疲劳裂纹源只有一个。当应力水平较低(160MPa)时,疲劳裂纹源有多个。裂纹萌生于试样表面或表面的第二相颗粒处且沿着解理面进行扩展,呈穿晶断裂模式。(3)Mg-2.3Zn-0.18Y-0.13Zr合金的较佳时效处理工艺参数为180℃、12h。经过此时效工艺参数处理的Mg-2.3Zn-0.18Y-0.13Zr合金的综合力学性能较优,其抗拉强度、屈服强度和延伸率分别达到353±4MPa、323±4MPa和20.3%±2.0%。(4)欠时效态Mg-2.3Zn-0.18Y-0.13Zr合金的疲劳强度为160MPa,比挤压态合金的疲劳强度高6.7%。这是因为时效处理当中析出的MgZn2相颗粒抑制基面上的位错滑移,提高裂纹萌生的最大应力,从而提高合金的疲劳寿命。(5)Mg-2.3Zn-0.18Y-0.13Zr合金较佳喷丸处理的气压强度为0.4MPa,且对喷丸处理的敏感性较大,优化区间较窄。(6)经较佳喷丸工艺处理后的Mg-2.3Zn-0.18Y-0.13Zr合金疲劳强度为173MPa,较挤压态合金的疲劳强度提高了 23MPa,提升幅度为15%。试样经喷丸处理后,裂纹源从试样的表面处转移到试样的亚表面处,变形层组织明显得到细化。裂纹的萌生时间增长,从而延长合金的疲劳寿命。
[Abstract]:As the lightest metal material, magnesium alloy is widely used in transportation, aerospace equipment and other fields. At present, magnesium alloy is limited by its strength and is used to manufacture parts in non-bearing parts. The fatigue fracture of important load-bearing parts is easy to occur under the action of long time alternating load, so it is an important task to develop a magnesium alloy with high strength and excellent fatigue properties. In this paper, Mg-2.3Zn-0.18Y magnesium alloy with excellent properties was obtained by adding different contents of Zr0.03Zn-0.13at.and hot extrusion deformation method. The Mg-2.3Zn-0.18Y-xZr magnesium alloy with excellent properties was obtained by adding different contents of Zr0.03Zn-0.13at.and hot extruding deformation mode of Mg-2.3Zn-0.18Y-xZr magnesium alloy. Firstly, the high cycle fatigue properties and crack initiation and propagation mechanism of extruded Mg-2.3Zn-0.18Y-xZr magnesium alloy were studied. Secondly, Mg-2.3Zn-0.18Y-0.13Zr alloy with high cycle fatigue property was selected as the research object, and the high cycle fatigue property was improved by aging treatment and shot peening respectively. Finally, the crack initiation, propagation mechanism and strengthening mechanism are described respectively. The main conclusions are as follows: (1) with the increase of Zr content, the average grain size of 伪 -Mg decreases from 9.9 渭 m to 4.8 渭 m, and the tensile strength, yield strength and elongation of Mg-2.3Zn-0.18Y-0.13Zr alloy are improved, and the mechanical properties of Mg-2.3Zn-0.18Y-0.13Zr alloy are the best, and the average grain size of the alloy decreases from 9.9 渭 m to 4.8 渭 m, and the mechanical properties of Mg-2.3Zn-0.18Y-0.13Zr alloy are better than that of Mg-2.3Zn-0.18Y-0.13Zr alloy. The fatigue strength is 150 MPA and the fatigue strength is 346 MPA and 26.7 MPA, respectively. In addition, twin formation was found in the coarse grains of fatigue fracture microstructure of Mg-2.3Zn-0.18Y-0.03Zr alloy, indicating that twinning deformation affects the plastic deformation mode of the alloy. When the stress level is high (180MPa), the high cycle fatigue crack source of extruded Mg-2.3Zn-0.18Y-xZr alloy is only one. When the stress level is low (160 MPA), there are many fatigue crack sources. The crack originates at the second phase particle on the surface or surface of the specimen and propagates along the cleavage surface. The best aging process parameter of the alloy is 180 鈩，

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