挤压成形7A04合金轮圈轴向和周向力学性能研究

发布时间：2018-01-16 10:22

本文关键词：挤压成形7A04合金轮圈轴向和周向力学性能研究　出处：《中北大学》2017年硕士论文　论文类型：学位论文

【摘要】：在能源和环保的双重要求下,轻量化已成为交通运输车辆节能减排的重要手段之一。为此人们通过挤压成形开发了重型车辆用铝合金轮辋,并取得良好效果。为改善挤压铝合金轮辋组织,进一步提高其性能,本文借助拉伸试验、冲击试验、疲劳试验和SEM等方法分别对轮圈轴向和周向的力学性能进行分析,并从轮圈挤压后的组织来分析引起各向异性的原因,为改进铝合金轮辋成形工艺提供了参考依据。主要结论如下:(1)挤压成形7A04合金轮圈轴向与周向的拉伸性能相差不大,屈服强度和抗拉强度基本相同。但由于轮圈表面组织中被拉长的晶粒及第二相粒子沿轴向分布,更多的抑制了周向的变形,使其延伸率和断面收缩率都低于轴向,因此轴向的塑韧性比周向好。(2)轮圈轴向与周向(两个方向上缺口都在轮圈表面)的冲击性能也相差不大,这是由于本试验中冲击功主要为裂纹扩展功,缺口都在轮圈表面时,轴向与周向的裂纹扩展路径基本相同,而轮圈表面组织结构对其影响较小,故轴向冲击功比周向仅大约2%;由于挤压后的轮圈组织沿厚度方向逐层堆积,缺口在轮圈表面的试样比缺口在轮圈侧切面的试样在冲击断裂过程中所消耗的能量大,冲击功高约17.6%,且断面也更曲折。(3)轮圈轴向与周向的疲劳性能存在差异:周向S-N曲线为S12.658N=6.639×1036,轴向S-N曲线为S12.987N=7.640×1037。轴向的疲劳性能优于周向,其中高应力时两个方向上疲劳寿命相差偏小,低应力时相差偏大。这是由于轮圈表面上晶粒与第二相沿轴向分布,使得周向上裂纹更容易扩展,而轴向裂纹扩展时需切断纤维组织,有明显的扭曲现象,不易扩展,且轴向疲劳裂纹形核粒子较大,微裂纹孕育成核阶段寿命较高;另外在周向解理台阶上分布有脆性疲劳条带,具有更明显的脆性断裂特征,且相同应力下周向的疲劳条带间距要大于轴向,应力越小差值越大,故周向的裂纹扩展速率比轴向快,且低应力下相差较多。
[Abstract]:With the requirement of both energy and environmental protection, lightweight has become one of the important means of energy saving and emission reduction of transportation vehicles. So people through the extrusion is developed with Aluminum Alloy rim heavy vehicle, and achieved good results. Aluminum Alloy extrusion and rim organization to improve, improve its performance by means of tensile test, impact test analysis of fatigue test and SEM method respectively on the mechanical properties of the axial and circumferential rim, and extruded from the rim to analyze the cause of anisotropy, in order to improve the Aluminum Alloy forming process provides the reference. The main conclusions are as follows: (1) the tensile properties of 7A04 alloy rim of the axial and circumferential direction difference little extrusion, yield strength and tensile strength are basically the same. But the organization is in the rim surface grain and second phase particles elongated along the axial direction, more circumferential suppression The deformation, the elongation and contraction rates are lower than the axial, so the axial ductility than week for the better. (2) the axial and circumferential rim (two direction of the gap in the rim surface) the impact performance is less, this is due to the impact of the experiment work mainly for crack propagation work the gap in the rim surface, axial and circumferential crack propagation path is basically the same, but the organization structure has little influence on the wheel surface, so the axial impact power ratio is only about 2% weeks to the rim after extrusion; microstructure along the thickness direction of each layer accumulation, notch on the specimen surface than the gap in the circle of wheel rim the side section consumed during impact fracture energy, the impact is too high about 17.6%, and the section is more tortuous. (3) the fatigue performance of axial and circumferential rim difference: circumferential S-N curve for the S12.658N=6.639 * 1036, axial S-N curve was S12.987N=7.640 * 1037. axial fatigue properties than circumferential, including high stress in two directions is the fatigue life of small, low stress is too large. This is because the rim on the surface of grains and second phase axial distribution, makes the circumferential cracks propagate more easily, and the axial crack extension need to cut off the fibrous tissue there are obvious distortions, and not easy to expand, and the axial fatigue crack nucleation for larger particles, the micro crack develops into a higher stage in the life of nuclear; circumferential cleavage steps on the distribution of brittle fatigue striations, brittle fracture has more obvious characteristics, and the same stress next week to the fatigue striation spacing to greater than the axial stress, the smaller the difference is large, so the circumferential crack growth rate is faster than the axial, and low stress are different.

【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21;TG379

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