铝合金搅拌摩擦焊材料流场非对称性的数值模拟研究
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摘要
铝合金搅拌摩擦焊(FSW)过程中,搅拌头附近的材料在高温下发生剧烈的塑性流动。FSW过程中的材料流动直接关系到接头质量。由于运用试验直接观察手段研究固态金属的瞬态塑性流动十分困难,因此数值模拟是研究FSW过程中材料流动行为的重要手段。针对2024铝合金建立了基于计算流体力学(CFD)的材料流动模拟仿真模型,模拟得到了FSW过程中温度、塑性变形等物理量的三维分布。模拟结果与试验结果对比表明,温度场模拟结果与试验结果吻合良好;分析模拟结果发现,搅拌头附近材料应变速率并非对称分布。模拟结果表明,FSW过程中,材料在搅拌针前方分流,在搅拌针后方焊合,分流与焊合位置均位于前进侧;随着焊接速度的提高,焊合难度增大,从而使FSW过程中沟槽缺陷产生的倾向性增大。
Significant plastic flow occurred at high temperature during friction stir welding(FSW). The weld quality related to the material flow pattern closely during FSW process. Owing to the difficulties involved in experimental study on the transient material flow in FSW, numerical simulation became a powerful tool for investigating the material flow pattern during FSW. In this study, numerical simulation based on( CFD) was established to predict the material flow field during friction stir welding of aluminum alloy 2024. The predicted temperature agreed well with the experimental results. It was revealed that the material flow was non-symmetrical. Simulation results showed that the material separates in the front of the FSW pin and re-welds behind the pin. Both the separating and re-welding occurred on the advancing side. The difficulty of re-welding in FSW increased as the increasing of welding speed. As a result, the groove-like void was more likely to be formed.
Significant plastic flow occurred at high temperature during friction stir welding(FSW). The weld quality related to the material flow pattern closely during FSW process. Owing to the difficulties involved in experimental study on the transient material flow in FSW, numerical simulation became a powerful tool for investigating the material flow pattern during FSW. In this study, numerical simulation based on( CFD) was established to predict the material flow field during friction stir welding of aluminum alloy 2024. The predicted temperature agreed well with the experimental results. It was revealed that the material flow was non-symmetrical. Simulation results showed that the material separates in the front of the FSW pin and re-welds behind the pin. Both the separating and re-welding occurred on the advancing side. The difficulty of re-welding in FSW increased as the increasing of welding speed. As a result, the groove-like void was more likely to be formed.
引文
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[18]SHEPPARD T,WRIGHT D S.Determination of flow stress:Part1 constitutive equation for aluminium alloys at elevated temperatures[J].Metal Technol,1979,6:215-23.
[19]TELLO K E,GERLICH A P and MENDEZ P F.Constants for hot deformation constitutive models for recent experimental data[J].Sci Technol Weld Joining,2010,3:260-266.
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[2]DAI Q L,CHEN G Q,MENG L C,et al.Explore the mechanism of high fatigue crack propagation rate in fine microstructure of friction stir welded aluminum alloy[J].Mater Sci Eng A,2013,580:184-190.
[3]YAN D Y,WU A P,Silvanus J,et al.Explore the mechanism of high fatigue crack propagation rate in fine microstructure of friction stir welded aluminum alloy[J].Mater Design,2011,32:2 284-2 291.
[4]关桥.轻金属材料结构制造中的搅拌摩擦焊技术与焊接变形控制[J].航空科学技术,2005,40:13.
[5]陈高强,史清宇.搅拌摩擦焊中材料流动行为数值模拟的研究进展[J].机械工程学报,2015,51(22):11-21.
[6]COLEGROVE P A,SHERCLIFF H R.3-Dimensional CFD modeling of flow round a threaded friction stir welding tool profile[J].J Mater Process Technol,2005,169:320-327.
[7]COLEGRAVE P A,SHERCLIFF H R.CFD modeling of friction stir welding of thick plate 7449 aluminium alloy[J].Sci Technol Weld Joining,2006,11(4):429-441.
[8]ATHARIFAR H,LIN D and KOVACEVIC R.Numerical and experimental investigations on the loads carried by the tool during friction stir welding[J].J Mater Eng Perform,2009,18(4):339-350.
[9]YU Z,ZHANG W,CHOO H,et al.Transient heat and material flow modeling of friction stir processing of magnesium alloy using threaded tool[J].Metall Mater Trans A,2012,43(2):724-737.
[10]NANDAN R,ROY G G,LIENERT T J,et al.Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding[J].Metall Mater Trans,2006,37A:1 247.
[11]COLEGRAVE P A,SHERCLIFF H R.Development of Trivex friction stir welding tool Part 2-three-dimensional flow modelling[J].Sci Technol Weld Joining,2004,9:352.
[12]FLUENT,Release 6.3.26,ANSYS Inc.Modeling and Validation of Repair Grout Flow in Voided Ducts.[M].Lebanon,NH,2006.
[13]SCHMIDT H,HATTEL J and WERT J.An analytical model for the heat generation in friction stir welding[J].Modelling Simul Mater Sci Eng,2004,12:143-157.
[14]CHEN G,FENG Z,ZHU Y,et al.An alternative frictional boundary condition for computational fluid dynamics simulation of friction stir welding[J].Mater Eng Perform,2016.,25(9):4 016-4 023.
[15]QIN X,MICHALERIS.Themo-elasto-viscoplastic modelling of friction stir welding[J].Sci Techn Weld Joining,2009,14:640-649.
[16]ASSIDI M,FOURMENT L,GUERDOUS S,et al.Friction model for friction stir welding process simulation:Calibrations from welding experiments[J].Int J Machine Tool Manuf,2010,50:143-155.
[17]MILLS K C.Recommended values of thermophysical properties for selected commercial alloys[M].Cambridge:Woodhead Publishing Limited,2002:54.
[18]SHEPPARD T,WRIGHT D S.Determination of flow stress:Part1 constitutive equation for aluminium alloys at elevated temperatures[J].Metal Technol,1979,6:215-23.
[19]TELLO K E,GERLICH A P and MENDEZ P F.Constants for hot deformation constitutive models for recent experimental data[J].Sci Technol Weld Joining,2010,3:260-266.
[20]DAVIS J.ASM Specialty Handbook-Aluminum and Aluminum Aloys[M].OH:ASM International,1993:653.