7075-T6铝合金厚板FSW焊缝沿厚度方向上的显微组织演变规律
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摘要
采用金相显微镜(OM)、扫描电镜(SEM)和背散射电子衍射(EBSD)技术表征7075铝合金厚板搅拌摩擦焊(FSW)焊核中心区的微观结构,研究沿焊缝厚度方向上的显微组织演变规律。结果表明,焊核中心区发生了明显的动态再结晶,由原始粗大的板条状组织转变成了细小的等轴晶;随着距焊缝上表面距离的增加,中心区等轴晶晶粒尺寸呈现逐渐增大的趋势。其中,中心区上部4 mm处的晶粒尺寸最小,仅为7.8μm;底部19 mm处的晶粒尺寸最大,达18.6μm。中心区动态再结晶分数随距离的增大而逐渐减小,从中心区顶部1mm处最大值90.4%减小至底部19mm处最小值57.5%。受动态再结晶影响,焊核中心区主要以大角度晶界(HAGB)分布为主,且中心区大角度晶界随距离的增加呈逐渐降低的趋势;但每一个典型位置处的大角度晶界分布呈现先增大后减小的趋势,且在45°左右时达到最大值;此外,中心区并没有强取向组织产生。同时,焊核中心区主要以细小、弥散的二次析出强化相η相为主,且二次析出强化相颗粒尺寸随距离的增加而呈逐渐增大的趋势,但二次析出强化相颗粒总体数量却呈相反的趋势变化。
In this paper,the microstructure in the nugget zone of friction stir welding(FSW)7075 aluminum alloy thick plate weld is characterized by Optic Microscope(OM),Scanning Electron Microscope(SEM)and Electron Back Scattered Diffraction(EBSD)technology,and the microstructure evolution rule along the thickness direction of thick FSW weld is investigated.The results show that,the dynamic recrystallization occurs in the nugget zone,making the original course lath-shaped structure change to the fine equiaxed grain.With the increasing distance to the weld top surface,the grain size of the equiaxed grain shows an increasing trend.The grain size at 4 mm above the weld top surface is the smallest,being only 7.8μm.However,the size is the biggest at 19 mm,reaching 18.6μm.Moreover,with the increase of the distance,the fraction of the dynamic recrystallization reduces from a maximum value of 90.4% at 1 mm to a minimum value of 57.5% at 19 mm.Meanwhile,a large number of High Angle Grain Boundaries(HAGBs)are mainly distributed in the nugget zone due to the effect of the dynamic recrystallization,and the HAGBs show a decreasing trend with the increase of the distance.But,the HAGBs in each one typical position increase firstly and then decrease,with the largest value of the HAGBs at 45°.Also,no strongly oriented structure is found in the nugget zone.At the same time,many fine and disperse reprecipitated phases are distributed in the nugget zone,and they are mainlyηphase.The particle size of the reprecipitated phases increases with the increase of the distance,while their quantity shows an inverse trend.
In this paper,the microstructure in the nugget zone of friction stir welding(FSW)7075 aluminum alloy thick plate weld is characterized by Optic Microscope(OM),Scanning Electron Microscope(SEM)and Electron Back Scattered Diffraction(EBSD)technology,and the microstructure evolution rule along the thickness direction of thick FSW weld is investigated.The results show that,the dynamic recrystallization occurs in the nugget zone,making the original course lath-shaped structure change to the fine equiaxed grain.With the increasing distance to the weld top surface,the grain size of the equiaxed grain shows an increasing trend.The grain size at 4 mm above the weld top surface is the smallest,being only 7.8μm.However,the size is the biggest at 19 mm,reaching 18.6μm.Moreover,with the increase of the distance,the fraction of the dynamic recrystallization reduces from a maximum value of 90.4% at 1 mm to a minimum value of 57.5% at 19 mm.Meanwhile,a large number of High Angle Grain Boundaries(HAGBs)are mainly distributed in the nugget zone due to the effect of the dynamic recrystallization,and the HAGBs show a decreasing trend with the increase of the distance.But,the HAGBs in each one typical position increase firstly and then decrease,with the largest value of the HAGBs at 45°.Also,no strongly oriented structure is found in the nugget zone.At the same time,many fine and disperse reprecipitated phases are distributed in the nugget zone,and they are mainlyηphase.The particle size of the reprecipitated phases increases with the increase of the distance,while their quantity shows an inverse trend.
引文
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[18]MCWILLIAMS B A,YU J H,YEN C F.Numerical simulation and experimental characterization of friction stir welding on thick aluminum alloy AA2139-T8plates[J].Materials Science and Engineering A,2013,585(11):243-252.
[19]MISHRA R S,MA Z Y.Friction stir welding and processing[J].Materials Science and Engineering R,2005,50(1-2):1-78.
[20]MAO Y Q,KE L M,LIU F C,et al.Investigations on temperature distribution,microstructure evolution,and property variations along thickness in friction stir welded joints for thick AA7075-T6plates[J].International Journal of Advanced Manufacturing Technology,2016,86(1):141-154.
[21]FONDA R W,KNIPLING K E,BINGERT J F.Microstructural evolution ahead of the tool in aluminum friction stir welds[J].Scripta Materialia,2007,58(5):343-348.
[22]DEVINDER Y,RANJIT B.Effect of friction stir processing on microstructure and mechanical properties of aluminium[J].Materials Science and Engineering A,2012,539:85-92.
[23]周俊,张津,计鹏飞.2024/7075异种铝合金搅拌摩擦焊的晶体取向演化[J].焊接学报,2016,37(8):59-62.ZHOU J,ZHANG J,JI P F.Crystal orientation evolution of friction stir welding of 2024/7075dissimilar aluminum alloys[J].Transaction of the China Welding Institution,2016,37(8):59-62(in Chinese).
[24]SU J Q,NELSON T W,MISHRA R,et al.Microstructural investigation of friction stir welded 7050-T651aluminium[J].Acta Materialia,2003,51(3):713-729.
[2]ZHANG Y,SONG X P,CHANG L Y,et al.Fatigue lifetime of laser-MIG hybrid welded joint of 7075-T6aluminum alloy by in-situ observation[J].Rare Metal Materials and Engineering,2017,46(9):2411-2416.
[3]ALATORRE N,AMBRIZ R R,AMROUCHE A,et al.Fatigue crack growth in Al-Zn-Mg(7075-T651)welds obtained by modified indirect and gas metal arc welding techniques[J].Journal of Materials Processing Technology,2017,248:207-217.
[4]KOMARASAMY M,ALAGARSAMY K,ELY L,et al.Characterization of 3″through-thickness friction stir welded 7050-T7451Al alloy[J].Materials Science and Engineering A,2018,731:55-62.
[5]毛育青,柯黎明,刘奋成,等.铝合金厚板FSW焊缝成形及金属流动行为分析[J].航空学报,2016,37(11):3546-3553.MAO Y Q,KE L M,LIU F C,et al.Weld formation and material flow behavior in FSW thick aluminum alloy plates[J].Acta Aeronautica et Astronautica Sinica,2016,37(11):3546-3553(in Chinese).
[6]SHAH P H,BADHEKA V.An experimental investigation of temperature distribution and joint properties of Al7075T651friction stir welded aluminium alloys[J].Procedia Technology,2016,23:543-550.
[7]曹景竹,王祝堂.铝合金在航空航天器中的应用(1)[J].轻合金加工技术,2013,41(2):1-5.CAO J Z,WANG Z T.Application of aluminum alloy in aeronautics and aerospace vehicle(1)[J].Light Alloy Fabrication Technology,2013,41(2):1-5(in Chinese).
[8]曾平.搅拌摩擦焊在船用铝合金结构中的应用[J].船海工程,2010,39(1):55-57ZENG P.The characteristic of friction stir welding and its application in the aluminum alloy structure of ship[J].Ship&Ocean Engineering,2010,39(1):55-57(in Chinese).
[9]党键,庄清.轨道车辆铝合金车体搅拌摩擦焊技术[J].工业技术创新,2017,4(6):79-81.DANG J,ZHUANG Q.Friction stir welding technology for aluminum alloy body of railway vehicles[J].Industrial Technology Innovation,2017,4(6):79-81(in Chinese).
[10]ESMAILY M,MORTAZAVI N,OSILOWICZ W,et al.Bobbin and conventional friction stir welding of thick extruded AA6005-T6 profiles[J].Materials&Design,2016,108:114-125.
[11]KHANDKAR M Z H,KHAN J A,REYNOLDS A P.Prediction of temperature distribution and thermal history during friction stir welding:Input torque based model[J].Science&Technology of Welding&Joining,2003,8(3):165-174.
[12]XU W F,LIU J H,LUAN G H,et al.Temperature evolution,microstructure and mechanical properties of friction stir welded thick 2219-O aluminum alloy joints[J].Materials&Design,2009,30(6):1886-1893.
[13]CANADAY C T,MOORE M A,TAND W,et al.Through thickness property variations in a thick plate AA7050friction stir welded joint[J].Materials Science&Engineering A,2013,559(3):678-682.
[14]董继红,佟建华,郭晓娟,等.30mm 7A05铝合金搅拌摩擦焊接头组织及力学性能[J].焊接学报,2012,33(4):65-68.DONG J H,TONG J H,GUO X J,et al.Microstructure and mechanical properties of friction stir welding joint of7A05aluminum alloy thick-sheet[J].Transaction of the China Welding Institution,2012,33(4):65-68(in Chinese).
[15]MARTINEZ N,KUMAR N,MISHRA R S,et al.Microstructural variation due to heat gradient of a thick friction stir welded aluminum 7449alloy[J].Journal of Alloys and Compounds,2017,713:51-63.
[16]MAO Y Q,KE L M,LIU F C,et al.Effect of tool pin eccentricity on microstructure and mechanical properties in friction stir welded 7075aluminum alloy thick plate[J].Materials&Design,2014,62:334-343.
[17]GUO N,FU Y L,WANG Y Z,et al.Microstructure and mechanical properties in friction stir welded 5A06aluminum alloy thick plate[J].Materials&Design,2017,113:273-283.
[18]MCWILLIAMS B A,YU J H,YEN C F.Numerical simulation and experimental characterization of friction stir welding on thick aluminum alloy AA2139-T8plates[J].Materials Science and Engineering A,2013,585(11):243-252.
[19]MISHRA R S,MA Z Y.Friction stir welding and processing[J].Materials Science and Engineering R,2005,50(1-2):1-78.
[20]MAO Y Q,KE L M,LIU F C,et al.Investigations on temperature distribution,microstructure evolution,and property variations along thickness in friction stir welded joints for thick AA7075-T6plates[J].International Journal of Advanced Manufacturing Technology,2016,86(1):141-154.
[21]FONDA R W,KNIPLING K E,BINGERT J F.Microstructural evolution ahead of the tool in aluminum friction stir welds[J].Scripta Materialia,2007,58(5):343-348.
[22]DEVINDER Y,RANJIT B.Effect of friction stir processing on microstructure and mechanical properties of aluminium[J].Materials Science and Engineering A,2012,539:85-92.
[23]周俊,张津,计鹏飞.2024/7075异种铝合金搅拌摩擦焊的晶体取向演化[J].焊接学报,2016,37(8):59-62.ZHOU J,ZHANG J,JI P F.Crystal orientation evolution of friction stir welding of 2024/7075dissimilar aluminum alloys[J].Transaction of the China Welding Institution,2016,37(8):59-62(in Chinese).
[24]SU J Q,NELSON T W,MISHRA R,et al.Microstructural investigation of friction stir welded 7050-T651aluminium[J].Acta Materialia,2003,51(3):713-729.