摘要
为改善7A52铝合金VPPA-MIG焊接接头的疲劳性能,本工作通过改变对焊接接头超声冲击的时间延长其疲劳寿命。试验中每条焊接接头各处分别受到2.5 min、5 min、10 min、15 min、30 min和75 min的超声冲击处理。试验利用扫描电镜、透射电镜和X射线衍射仪观察分析焊接接头的表面及晶粒形貌并计算焊接接头的表面晶粒度;利用显微硬度计、X射线应力分析仪和疲劳试验机对焊接接头进行硬度、残余应力及疲劳性能测试,综合分析超声冲击处理对焊接接头疲劳性能的影响。试验结果表明,焊接接头的超声冲击时间为2.5~30 min时,焊接接头处的缺陷明显减少,同时焊接接头表面的晶粒被细化至纳米级,超声冲击时间为30~75 min时,冲击表面出现裂纹;焊接接头经超声冲击处理后,其硬度最大可达140HV,较未处理的焊接接头硬度(100HV)提升40%,同时接头冲击后塑性变形层可达105μm;焊接接头处的残余应力在超声冲击处理后,由残余拉应力转为残余压应力,且在2.5~30 min时残余压应力呈增长趋势,最大可达-329.2 MPa,在超声冲击时间为30~75 min时残余压应力减小;经超声冲击处理的焊接接头的疲劳性能均有提升,在超声冲击处理时间为30 min时接头疲劳强度最优为87.63 MPa,未经处理的焊接构件疲劳强度为48.8 MPa,疲劳强度提升了79.57%。因此,对焊接接头进行超声冲击处理可强化其疲劳性能,延长焊接构件的使用寿命。本工作希望对7A52铝合金VPPA-MIG焊接构件的广泛使用提供理论依据。
To improve the fatigue properties of the 7A52 aluminum alloy VPPA-MIG welded joint,the fatigue life of the welded joint was improved by changing the ultrasonic impact time.In this work,each welded joint was subjected to ultrasonic impact treatment for 2.5 min,5 min,10 min,15 min,30 min and 75 min.The scanning electron microscopy,the transmission electron microscope and the X-ray diffractometer were used to observe and analyze the surface morphology of welded joints and calculate the surface grain size of welded joints.The hardness,the residual stress and the fatigue properties of welded joints were examined via microhardness test,X-ray stress analysis and fatigue test,respectively.The influence of ultrasonic impact treatment on the fatigue properties of welded joints was analyzed comprehensively.The results show that when the ultrasonic impact time is 2.5—30 min,the defects of the welded joint are obviously reduced,with the grain on the surface of the welded joint refined to the nanometer level.When the ultrasonic impact time is 30—75 min,cracks appear on the impact surface.After ultrasonic impact treatment,the hardness of welded joints can reach 140HV,which is 40%higher than that of untreated welding joint,and the plastic deformation layer can reach 105μm.Moreover,after ultrasonic impact treatment,the residual stress of welded joint changes from residual tensile stress to residual compressive stress,and the residual compressive stress increases in 2.5—30 min,with the maximum value of-329.2 MPa.When the ultrasonic impact time is 30—75 min,the residual compressive stress decreases.The fatigue strength of the welded joints treated by ultrasonic impact treatment are significantly improved.When the ultrasonic impact treatment time is 30 min,the maximum fatigue strength of the joints are 87.63 MPa,the fatigue strength of untreated welded members are 48.8 MPa and the fatigue strength are improved by 79.57%.Therefore,ultrasonic impact treatment on welded joint can enhance its fatigue performance and prolong the service life of welded components.Through this work,we hope to provide a theoretical basis for the wide use of 7A52 aluminum alloy VPPA-MIG welding components.
作者
刘成豪
陈芙蓉
LIU Chenghao;CHEN Furong(School of Materials Science and Engineering,Inner Mongolia University of Technology,Hohhot 010000,China)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2022年第15期137-141,共5页
Materials Reports
基金
国家自然科学基金(51165026,51765053)。
