摘要
Micro porosity in aluminum alloys may contribute to fatigue life degradation, which can largely limit the application of alloys. Therefore, the fatigue life of a commercial 7050-T7451 thick plate and an experimental plate with different porosities was compared in this study. The X-ray computed tomography(XCT) was utilized to characterize the size, number density and spatial distribution of porosity inside various samples, and the fracture surface of fatigued specimens was compared by using scanning electron microscope(SEM). The results showed that the fatigue cracks prefer to initiate from constituent particles in the commercial alloy. Whereas the micro porosity is the predominant site for crack nucleation and subsequent failure in the experimental one. The presence of micro porosity in experimental7050-T7451 thick plate may reduce the fatigue life by an order of magnitude or more compared with the defect-free alloy. The pores close to sample surface are the main fatigue crack initiation site, among which larger and deeper pore leads to a shorter fatigue life. The crack initiation is also affected by the pore geometry and direction. Besides, the overall porosity inside the bulk can affect the crack propagation during fatigue tests.
铝合金材料中的显微疏松会导致其疲劳性能的降低,很大程度上限制了合金的应用。本研究针对7050-T7451铝合金厚板进行了分析,对比了不同孔隙率板材之间疲劳性能差异。本研究实验运用了X射线计算机断层成像法(XCT)对材料孔隙率进行了分析,包括孔洞尺寸、数密度以及其尺寸分布,同时运用扫描电镜(SEM)对疲劳断口特征进行了分析。结果表明,对于孔洞较少且尺寸小的样品而言,疲劳裂纹更倾向于从第二相粒子产生,而对于孔洞较大且密度较高的样品而言,裂纹更容易起始于样品表面处的大尺寸孔洞。相比于几乎没有孔洞的样品而言,含有高孔隙率的样品疲劳寿命缩短将近一个数量级,样品疲劳寿命与孔洞大小和深度呈反比关系,且不同形状与朝向的孔洞对疲劳寿命也会造成影响。同时,结果分析可知,样品整体的孔隙率对疲劳长裂纹扩展也会造成一定影响。
作者
XIAO Xiang
ZHANG Qi
JIANG Hui-xue
LIU Cheng
CAO Ling-fei
肖翔;张琪;蒋会学;刘成;曹玲飞(Chinalco Materials Application Research Institute,Beijing 102209,China;International Joint Laboratory for Light Alloys(Ministry of Education),College of Materials Science and Engineering,Chongqing University,Chongqing 400044,China)
基金
Project(2019KJ2X08-4) supported by Chinalco Technology Development Project Fund,China。
作者简介
Corresponding author:LIU Cheng,PhD,Professor,E-mail:liucheng@cmari.com,ORCID:https://orcid.org/0000-0002-5571-0953;Corresponding author:CAO Ling-fei,PhD,Professor,E-mail:caolingfei@cqu.edu.cn,ORCID:https://orcid.org/0000-0002-9255-3491。
