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金属学报  2018, Vol. 54 Issue (8): 1131-1140    DOI: 10.11900/0412.1961.2017.00448
  本期目录 | 过刊浏览 |
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 wordssynchrotron 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

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
Specimen Cracking source A / μm σmax / MPa R Nf / cyc
ESRF-1 Sub-surface pore 130.31 167 0.1 6700
SSRF-3 Surface pore 75.52 188 0.2 7400
SSRF-2 Sub-surface pore 67.71 214 0.2 22000
ESRF-3 Surface pore 121.26 173 0.1 24800
SSRF-5 Surface pore 80.67 217 0.2 26000
SSRF-1 Sub-surface pore 84.11 237 0.2 30000
ESRF-5 Sub-surface pore 78.43 137 0.1 40900
ESRF-4 Surface pore 109.60 148 0.1 47200
SSRF-4 Surface pore 132.77 144 0.2 77340
ESRF-2 Surface pore 57.81 143 0.1 88000
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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