7075铝合金搅拌摩擦焊接头在拉伸过程中的裂纹扩展行为  

Behaviors of crack propagation in 7075 aluminum alloy friction stir welded joints during tensile process

作　　者：姜月 朱浩[1,2] 齐芳娟 马泽铭[1,2] 王军 Jiang Yue;Zhu Hao;Qi Fangjuan;Ma Zeming;Wang Jun(Shijiazhuang Tiedao University, Shijiazhuang 050043, China;Hebei Provincial Key Laboratory of Traffic Engineering Materials, Shijiazhuang 050043, China;Suzhou University of Science and Technology, Suzhou 215009, Jiangsu, China;Hebei University of Science and Technology, Shijiazhuang 050018, China)

机构地区：[1]石家庄铁道大学,石家庄050043 [2]河北省交通工程材料重点实验室,石家庄050043 [3]苏州科技大学,江苏苏州215009 [4]河北科技大学,石家庄050018

出　　处：《焊接》2019年第3期28-32,I0025-I0026,共6页Welding & Joining

基　　金：河北省自然科学基金(2016210050);江苏省自然科学基金(BK20141181)

摘　　要：对厚度为6 mm的7075铝合金进行搅拌摩擦焊(FSW)平板对接试验,利用MTS微控电子万能试验机对接头进行不同应变率下平板拉伸试验。分别使用光学显微镜(OM)和扫描电镜(SEM)对接头断裂路径两侧的微观组织和断口形貌进行观察。在此基础上,使用透射电镜(TEM)对接头起裂源处的沉淀相形貌进行观察,研究应变率对接头断裂行为的影响。研究结果表明,随着应变率的增加,接头屈服强度与屈强比略有增大,不同应变率下的微裂纹均形核于接头底部母材(BM)与热影响区(HAZ)交界处。相比于椭圆状Al Cu Mg沉淀相和胶囊状Al_2Cu Mg沉淀相,接头中棒状MgZn_2沉淀相对微裂纹形核起关键作用。应变率较低时,裂纹在扩展过程中发生偏转;随着应变率的增加,接头裂纹走向平直,接头塑性降低,与加载方向的裂纹扩展角减小,断裂方式由以韧窝聚合型断裂为主转变为以剪切断裂为主。The flat butt welding was carried out on 7075 aluminum alloy with the thickness of 6 mm by friction stir welding. The flat tensile test of joints at different strain rates were measured by the MTS. The microstructure of both sides of the fracture path in joints and the fracture morphology were observed by OM and SEM. The precipitated phases at the initiation of crack source were observed by the TEM. The influence of strain rate on fracture behaviors of the joints was studied. The results show that with the increase of strain rate, the yield strength and yield strength ratio of the joint increase slightly. The microcracks nucleate at the bottom of the junction of the base metal (BM) and the heat affected zone (HAZ). The precipitated phase of MgZn 2 with rod shape, compared to AlCuMg with elliptical shape and Al2CuMg with capsule shape, plays a key role in microcrack nucleation. The crack deflects during the propagation process at the low strain rate. With the increase of the strain rate, the crack of joint tends to be straight and the plasticity of joint decreases, simultaneously, the angle of crack propagation decreases with the loading direction. The fracture mode is mainly changed from dimple polymerization fracture to shear fracture.

关 键 词：7075铝合金 搅拌摩擦焊 应变率 断裂机理 

分 类 号：TG457.14[金属学及工艺—焊接]