超声冲击强化铝合金小孔构件的试验研究
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摘要
目的提升铝合金小孔构件的疲劳寿命,改善表面性能。方法采用超声冲击强化工艺对铝合金小孔构件进行试验研究,利用MHV2000显微硬度测量仪、XRD射线应力测定仪、疲劳试验机分别测量试件的显微硬度、残余应力、疲劳寿命。利用扫描电镜拍摄试件强化加工前后的显微照片。针对不同阻抗阈值条件,考察主要工艺参数对小孔构件强化效果的影响。结果研究表明,采用基于等效阻抗控制的超声冲击强化工艺,阻抗阈值设定为75Ω时,孔边的平均残余应力值出现极大值,距离孔壁的残余应力分布呈现先增大后减小的规律。孔壁的显微硬度趋势保持一致,阻抗阈值越大时,其平均值也越大。微观组织反映孔被强化后的痕迹,被强化试件疲劳断口齐整,组织均匀,有明显被压实的现象。结论超声冲击强化工艺适合小孔构件强化,疲劳寿命最大提高3.1倍,孔口表面形成了有效的残余压应力场,孔内表面显微硬度提高了1倍。
The work aims to improve the fatigue life and the surface performance of aluminium alloy hole test specimen.Ultrasonic impact strengthening technology was adopted to study the aluminium alloy hole test specimen through experiment and MHV2000 microhardness tester, X ray stress tester and fatigue testing machine were used to measure the microhardness, residual stress and fatigue life of the specimen. Then, SEM was applied to take the microphotos of specimen before and after the reinforcement. According to different impemdance thresholds, the strengthened effects on the hole specimens by main parameters were studied. Through the experiment, the ultrasonic shock processing based on the equivalent impedance control was adopted. If the impedance threshold was 75 ?, the average residual stress of the hole was maximum and the distribution of residual stress from the distance of hole increased first and then decreased. The trend of microhardness of hole wall was consistent and the average increased as the impemdance threshold grew. The reinforced trace was obvious through microstructure and the fatigue fracture of strenthened specimen was neat and uniform with obvious trace of compression. Ultrasonic impact strengthening technology is suitable for small hole component and can improve the fatigue life by 3.1 times. The effective residual compressive stress field can be obtained on the hole surface and the surface microhardness inside the hole doubles.
The work aims to improve the fatigue life and the surface performance of aluminium alloy hole test specimen.Ultrasonic impact strengthening technology was adopted to study the aluminium alloy hole test specimen through experiment and MHV2000 microhardness tester, X ray stress tester and fatigue testing machine were used to measure the microhardness, residual stress and fatigue life of the specimen. Then, SEM was applied to take the microphotos of specimen before and after the reinforcement. According to different impemdance thresholds, the strengthened effects on the hole specimens by main parameters were studied. Through the experiment, the ultrasonic shock processing based on the equivalent impedance control was adopted. If the impedance threshold was 75 ?, the average residual stress of the hole was maximum and the distribution of residual stress from the distance of hole increased first and then decreased. The trend of microhardness of hole wall was consistent and the average increased as the impemdance threshold grew. The reinforced trace was obvious through microstructure and the fatigue fracture of strenthened specimen was neat and uniform with obvious trace of compression. Ultrasonic impact strengthening technology is suitable for small hole component and can improve the fatigue life by 3.1 times. The effective residual compressive stress field can be obtained on the hole surface and the surface microhardness inside the hole doubles.
引文
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[13]王亮,汝继刚,李惠曲,等.孔挤压强化工艺对7A12铝合金组织及疲劳性能影响的研究[J].新技术新工艺,2014(11):14-17.WANG Liang,RU Ji-gang,LI Hui-qu,et al.Research on effects of cold holes expansion on microstructure and fatigue property of 7A12 aluminum alloy[J].New technology&new process,2014(11):14-17.
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[15]徐春阳,陈文婷,王晓栋,等.微波布拉格衍射中立方晶体晶面衍射测量与模型选取讨论[J].物理实验,2014,34(10):45-48.XU Chun-yang,CHEN Wen-ting,WANG Xiao-dong,et al.Measuring cubic crystal diffraction and choosing cubic model crystal in microwave bragg diffraction[J].Physics experimentation,2014,34(10):45-48.
[2]XUE Y,MCDOWELL D L,HORSTEMEYER M F,et al.Microstructure-based multistage fatigue modeling of aluminum alloy7075-t651[J].Engineering fracture mechanics,2007,74(17):2810-2823.
[3]CAMPBELL C E,BENDERSKY L A,BOETTINGERW J,et al.Microstructural characterization of al-7075-t651chips and workpieces produced by high-speed machining[J].Materials science and engineering A,2006,430(1):15-26.
[4]张全纯.先进飞机机械连接技术[M].北京:兵器工业出版社,2000.ZHANG Quan-chun.Advanced aircraftmechanical joint technology[M].Beijing:Publishing House of Ordnance Industry,2000.
[5]ZHANG Y,FITZPATRICK M E,EDWARDS L.Analysis of the residual stress around a cold-expanded fastener hole in a finite plate[J].Strain,2005,41(2):59-70.
[6]NADAI A.Theory of the expanding of boiler and condenser tube joints through rolling[J].Trans.ASME,1943,65:865-880.
[7]艾莹珺,王欣,宋颖刚,等.挤压强化对TC17钛合金孔结构疲劳寿命的影响[J].航空材料学报,2017,37(6):82-87.AI Ying-jun,WANG Xin,SONG Ying-gang,et al.Effect of cold expansion on fatigue life of hole structure of TC17titanium alloy[J].Journal of aeronautical materials,2017,37(6):82-87.
[8]伊琳娜,汝继刚,黄敏,等.孔挤压强化对2124铝合金疲劳寿命及微观组织的影响[J].航空材料学报,2016,36(5):31-37.YI Lin-na,RU Ji-gang,HUANG Min,et al.Influence of hole cold expansion on microstructure and fatigue life of2124 aluminum alloy[J].Journal of aeronautical materials,2016,36(5):31-37.
[9]王智,李京珊.影响冷挤压强化效果的因素[J].机械强度,2002,24(2):302-304.WANG Zhi,LI Jing-shan.Factors of influencing the beneficial effect of cold expansion[J].Journal of mechanical strength,2002,24(2):302-304.
[10]刘晓龙,高玉魁,刘蕴韬,等.孔挤压强化残余应力场的三维有限元模拟和实验研究[J].航空材料学报,2011,31(2):24-27.LIU Xiao-long,GAO Yu-kui,LIU Yun-tao,et al.3D finite element simulation and experimental test on residual stress field by hole cold expansion[J].Journal of aeronautical materials,2011,31(2):24-27.
[11]王洪达,苏宏华.TC4开缝衬套冷挤压残余应力分布有限元仿真[J].机械制造与自动化,2010,39(3):98-100.WANG Hong-da,SU Hong-hua.Finite element simulation of split-sleeve cold expansion process in TC4 titanium alloy[J].Jiangsu machinebuilding&automation,2010,39(3):98-100.
[12]李进一,凌祥,周建新.超声冲击残余应力场的有限元模拟[J].航空材料学报,2012,32(1):84-88.LI Jin-yi,LING Xiang,ZHOU Jian-xin.Finite element simulation of residual stress field induced by ultrasonic impact treatment[J].Journal of aeronautical materials,2012,32(1):84-88.
[13]王亮,汝继刚,李惠曲,等.孔挤压强化工艺对7A12铝合金组织及疲劳性能影响的研究[J].新技术新工艺,2014(11):14-17.WANG Liang,RU Ji-gang,LI Hui-qu,et al.Research on effects of cold holes expansion on microstructure and fatigue property of 7A12 aluminum alloy[J].New technology&new process,2014(11):14-17.
[14]丁瑞翔.基于等效阻抗的超声加工自动进给系统设计研究[D].南京:南京航空航天大学,2016.DING Rui-xiang.Research on the equivalent impedance of the ultrasonic machining automatically feed system[D].Nanjing:Nanjing University of Aeronautics and Astronautics,2016.
[15]徐春阳,陈文婷,王晓栋,等.微波布拉格衍射中立方晶体晶面衍射测量与模型选取讨论[J].物理实验,2014,34(10):45-48.XU Chun-yang,CHEN Wen-ting,WANG Xiao-dong,et al.Measuring cubic crystal diffraction and choosing cubic model crystal in microwave bragg diffraction[J].Physics experimentation,2014,34(10):45-48.