冶金型气孔对熔化焊接7020铝合金疲劳行为的影响

doi:10.11900/0412.1961.2017.00448

金属学报

2018, Vol. 54

Issue (8): 1131-1140 DOI: 10.11900/0412.1961.2017.00448

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冶金型气孔对熔化焊接7020铝合金疲劳行为的影响

宋哲¹, 吴圣川¹(

), 胡雅楠¹, 康国政¹, 付亚楠², 肖体乔²

1 西南交通大学牵引动力国家重点实验室成都 610031
2 中国科学院上海应用物理研究所上海同步辐射光源上海 201204

The Influence of Metallurgical Pores on Fatigue Behaviors of Fusion Welded AA7020 Joints

Zhe SONG¹, Shengchuan WU¹(

), Yanan HU¹, Guozheng KANG¹, Yanan FU², Tiqiao XIAO²

1 State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China
2 Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China

引用本文:

宋哲, 吴圣川, 胡雅楠, 康国政, 付亚楠, 肖体乔. 冶金型气孔对熔化焊接7020铝合金疲劳行为的影响[J]. 金属学报, 2018, 54(8): 1131-1140.
Zhe SONG, Shengchuan WU, Yanan HU, Guozheng KANG, Yanan FU, Tiqiao XIAO. The Influence of Metallurgical Pores on Fatigue Behaviors of Fusion Welded AA7020 Joints[J]. Acta Metall Sin, 2018, 54(8): 1131-1140.

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摘要:

基于同步辐射X射线三维高精度原位成像技术,识别和统计出工艺稳定的激光复合焊接7020铝合金接头中的气孔数量、形貌、尺寸和空间分布特征,结合气孔统计数据结果和焊缝晶粒大小,定义了7020铝合金激光复合焊接头中影响接头疲劳性能的气孔临界尺寸。利用同步辐射X射线三维原位疲劳实验数据和疲劳断口形貌,探讨了疲劳试样裂纹源处气孔尺寸、应力和疲劳寿命之间的定量关系。同时,基于有限元仿真分析,研究了不同位置下气孔处的应力场状态。最后,通过疲劳裂纹扩展速率实验,揭示了气孔对疲劳裂纹萌生、扩展和试样瞬断的影响。研究结果表明,激光复合焊接头临界气孔尺寸可定为30 μm;同步辐射X射线成像和疲劳断口显示,较大的表面气孔和近表面的气孔较容易萌生疲劳裂纹。仿真研究也表明,气孔周围的应力集中程度随着气孔位置由表面向内部移动呈现出先增大后减小最后趋于稳定的趋势;疲劳裂纹扩展速率数据分布趋势表明,气孔对长裂纹扩展过程的影响较小,可忽略不计,但一般认为对裂纹前缘形貌有较大影响。

关键词 ：同步辐射X射线成像, 焊接缺陷, 疲劳寿命评价, 激光复合焊接, 高速列车

Abstract：

With the rapid development of Chinese high-speed railway system, the urgent demand for lighter weight structures is increasing, and aluminum alloys are widely applied into manufacturing the railway train and critical safety components. As a medium strength aluminum alloy, the 7020 aluminum alloy shows a great potential. Hybrid laser welding has currently become one of the most important welding techniques for medium and high strength aluminum alloys. Nevertheless, intrinsic defects such as pores and shrinkages physically determine the fatigue resistance of the welded joint. Based on in situ synchrotron radiation X-ray computed microtomography (SR-μCT), the population, location and size of gas pores within AA7020 hybrid welded joints are firstly identified and counted. The critical size of gas pores, affecting the fatigue properties of welded joints, is acquired by combining the statistical results of the pores and the average grain size of the hybrid weld. Meanwhile, the qualitative relationship between pore size, effective stress and fatigue life is discussed through in situ fatigue life data via SR-μCT and fracture morphology. By using the finite element analysis, detailed works have been performed on the stress state near the pores of different positions inside the joint. Through the simulation analysis, the stress concentration coefficient around the pores firstly increases, then decreases, and finally tends to a stable trend as the location of the pore-like defect is transferred from the surface to the inside. Besides, the influence of porosity on fatigue crack initiation, fatigue crack growth and sudden breaking process is also analyzed using fatigue crack growth experiment. In conclusion, the results show that the critical pore size of hybrid laser welded joint can be qualitatively identified as 30 μm; the SR-μCT and fracture analysis show that larger surface and sub-surface pores are more likely to initiate fatigue cracks, and the fatigue crack propagation experiment further shows that the porosity has very little effect on the long crack growth but significant influence on the crack front.

Key words： synchrotron radiation X-ray microtomography welding defect fatigue life assessment laser hybrid welding high-speed railway train

收稿日期: 2017-10-26

ZTFLH:

TG405

基金资助:国家自然科学基金项目No.11572267,四川省科学技术计划项目No.2017JY0216,西安交通大学机械结构强度与振动国家重点实验室开放项目No.SV2016-KF-21

作者简介:

作者简介宋哲,男,1992年生,硕士

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https://www.ams.org.cn/CN/10.11900/0412.1961.2017.00448 或 https://www.ams.org.cn/CN/Y2018/V54/I8/1131

图1 同步辐射X射线原位成像实验工作原理及原位疲劳试样尺寸示意图

图2 上海光源与欧洲光源10个原位成像疲劳试样中气孔的统计结果

图3 上海光源与欧洲光源原位成像疲劳试样中不同尺寸的气孔在焊缝中的位置分布

图4 典型激光复合焊接7020铝合金接头的同步辐射X射线气孔分布

图5 激光复合焊接7020铝合金焊接接头中的工艺型气孔同步辐射X射线成像结果

图6 焊接接头中气孔缺陷位置的分类示意图

表1 上海光源与欧洲光源原位疲劳实验疲劳寿命、缺陷位置和影响面积结果统计

图7 表面气孔萌生疲劳裂纹且寿命为77340 cyc的试样的断口形貌

图8 疲劳实验和同步辐射X射线原位疲劳实验最大等效应力与循环周次的S-N关系

图9 仿真模型中气孔与焊缝上表面的位置关系示意图及焊缝有限元仿真边界约束条件的施加

图10 平面X-Z上的主应力分布

图11 弹性和弹塑性仿真模拟不同位置时气孔周围应力集中系数的变化曲线

图12 3个激光复合焊7020铝合金的裂纹扩展速率

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