摘要
以7075-T6铝合金搅拌摩擦焊接头为研究对象,对其显微组织结构、3.5%NaCl(质量分数)溶液腐蚀疲劳寿命和腐蚀疲劳断裂特征进行了研究,分析了7075铝合金搅拌摩擦焊接头的腐蚀疲劳性能及断裂过程.结果表明,7075-T6铝合金搅拌摩擦焊接头腐蚀疲劳S-N曲线方程为lgN=5.845-0.014S,随着应力幅增大,腐蚀疲劳寿命大幅度降低;腐蚀疲劳裂纹起源于接头的热影响区,逐渐扩展最终断裂于接头的焊核区.腐蚀疲劳断口存在多个裂纹源,且受到应力集中作用的影响,裂纹源萌生于腐蚀坑处.高应力作用加剧了试样边角部分的腐蚀损伤,导致边角比平面位置腐蚀程度更严重.裂纹扩展区出现了明显的晶间断裂和疲劳辉纹;在腐蚀介质和交变载荷的共同作用下,裂纹扩展区腐蚀程度最重,晶界处产生了阳极溶解现象并产生了“冰糖块状”和“蚁巢状”的形貌特征;瞬断区产生了大量解理台阶和二次裂纹,为脆性断裂,在第二相粒子分布区域存在孔洞形貌特征.
Taking 7075-T6 aluminum alloy friction stir welding joint as the research object,the microstructure,3.5 wt%NaCl solution corrosion fatigue life and corrosion fatigue fracture characteristics were studied,and the corrosion fatigue performance and fracture process of 7075 aluminum alloy friction stir welding joint were analyzed.The results showed that:the S-N curve equation of corrosion fatigue of 7075-T6 aluminum alloy friction stir welded joint is lgN=5.845-0.014S,With the increasing of stress amplitude,the corrosion fatigue life decreased greatly.The corrosion fatigue crack originated in the thermal affected zone of the joint,gradually expanded and finally broke in the welded core zone of the joint.There were multiple crack sources in the corrosion fatigue fracture,and with the influence of stress concentration,the crack source originated in the corrosion pit.The high stress aggravated the corrosion damage of the corner part of the sample,led to more serious corrosion than that of the plane position.Obvious intergranular fracture and fatigue striation appeared in the crack growth zone.Under the combined action of corrosive medium and alternating load,the crack growth zone suffered the most serious corrosion,and the anodic dissolution occurred at the grain boundary,resulting in the morphology characteristics of“rock candy”and“ant nest”.Instantaneous fault zone was brittle fault,and there were a lot of cleavage steps and secondary cracks in this zone,the pore morphology appeared in the second phase particle distribution region.
作者
马青娜
邵飞
白林越
徐倩
MA Qingna;SHAO Fei;BAI Linyue;XU Qian(Army Engineering University of PLA,Nanjing,210037,China)
出处
《焊接学报》
EI
CAS
CSCD
北大核心
2020年第6期72-77,I0005,共7页
Transactions of The China Welding Institution
基金
中国博士后科学基金(2018M643852)
十三五装备预研项目(30110010403,30110030103).
关键词
7075铝合金
FSW接头
腐蚀疲劳
断口特征
7075 aluminium alloy
friction stir welding joint
corrosion fatigue
fracture characteristics
