不同过程参数对搅拌摩擦焊接中材料流动以及残余应力分布的影响

通过有限元法建立了搅拌摩擦焊接的二维模型,并研究了不同工艺参数下搅拌摩擦焊接过程中材料的流动以及残余应力的分布。在搅拌摩擦焊接过程中,切向流动构成了材料流动的主要形式,并且材料流动最为剧烈的区域发生在后退侧。在材料的切向流动中,材料的流动方向不是单一的,可能会形成漩涡。搅拌头平移速度和转速的增加,都能使材料在后退侧的流动变得更为剧烈,但是在材料流动速度较小的区域,参数的改变对材料流动的影响很小。纵向残余应力的最大值始终发生在热影响区的边界,并且纵向残余应力在靠近焊缝中心线的附近一般为正值,而在靠近焊接构件边界的地方,残余应力则表现为负值。纵向残余应力的最大值随着搅拌头平移速度的增加而有所增加,但是搅拌头转速的变化对纵向残余应力的分布影响不大。     

搅拌摩擦焊接过程中材料的三维流动分析

通过有限元方法对搅拌摩擦焊接过程中焊接构件材料的三维流动进行了研究，结果显示，在搅拌摩擦焊接工艺中，材料的等效塑性应变云图与焊接构件显微结构分布图有一定联系。在后退侧搅拌头的后方是材料流动较弱的区域，在后退侧搅拌头的前方则是材料流动最为剧烈的区域，材料越靠近焊接构件的上表面，其流动性越强。搅拌头前方的材料在搅拌头的推动下向上涌起，同时被旋推到搅拌头的后方，在肩台的作用下，这部分材料将会被压向下方以填充由于搅拌头的移动而留下的空间，这个过程周而复始，从而使搅拌摩擦焊接可以顺利进行。     

Simulation of heat transfer and analysis of impact of tool pin geometry and tool speed during friction stir welding of AZ80A Mg alloy plates

Peak temperature arising during the joining of metals by friction stir welding (FSW) needs to be investigated along with other process parameters of FSW to understand their inevitable impact on joint quality. This investigational and experimental analysis aims to determine the impact of pin geometry and its rotational speed by formulating thermic mechanical process-based models to anticipate peak temperature and to compare it with actual values. Three distinctive pin geometries rotated at three speeds were used while other parameters were unchanged. The fitness and suitability of the model were verified by comparing the anticipated values with the experimental values. Macrographic and micrographic observations revealed that flawless joints with improved mechanical properties were fabricated at a peak temperature of 616 K (80 % melting temperature) when a taper cylindrical pin with a rotational speed of 818 rpm was employed. In addition, SEM analysis of the fractured specimen confirmed that failure of the defect free weldment occurred in brittle mode, indicating that preferred fusion of grains and their constituents occurred during the joining process.

     

焊接工艺参数对FGH96合金惯性摩擦焊过程材料塑性流动行为的影响

采用数值模拟方法对FGH96合金惯性摩擦焊过程进行分析,获得温度、轴向缩短量、材料流动与飞边四者之间的关系,着重研究初始转速与轴向压力等焊接工艺参数对材料塑性流动行为的影响规律。研究结果表明:在惯性摩擦焊初始阶段,材料温度与流动速度较低,无飞边产生;随着焊接过程的进行,材料的温度与流动速度呈现先升高后降低的规律;在焊接过程进入稳态后,摩擦面中心区域的材料主要沿试件的旋转方向流动,而摩擦面上两边界附近的材料向面外流动并形成飞边,飞边尺寸与弯曲程度随焊接时间的增加而增加。同时,随到摩擦面距离的增加,材料的流动速度逐渐降低且材料沿轴向流动的速度分量增大。结合FGH96合金惯性摩擦焊轴向缩短量的数值模拟结果,解释了从提高材料流动速度的幅度上看增加轴向压力优于初始转速的原因。     

Influences of tool pin profile and axial force on the formation of friction stir processing zone in AA6061 aluminium alloy

AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance. Compared to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile plays a major role in deciding the weld quality. In this investigation an attempt has been made to understand the effect of axial force and tool pin profiles on FSP zone formation in AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different axial force levels. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.     

搅拌摩擦焊接中搅拌头的受力分析

采用基于固体力学的有限元方法研究搅拌摩擦焊接过程中,不同过程参数情况下搅拌头的受力情况.研究发现,搅拌摩擦焊接过程中搅拌头上应力的最大值发生在搅拌头前进方向上搅拌头与焊缝中心线接触点的附近,且von Mises应力的最大值随搅拌头平移速度的增加而增加,随搅拌头转速的增加而较小.搅拌头前方的接触压力较大,后方接触压力较小,后退侧的接触压力较前进侧大.搅拌头的不停旋转决定了搅拌头受到交变载荷作用,导致疲劳成为搅拌头破坏的原因之一.焊缝中心线附近的等效塑性应变和结构纹理呈现洋葱状结构.     

搅拌摩擦焊工艺参数对LY12铝合金焊缝金属流动形态的影响

采用铝箔作为标示材料,研究了旋转速度、焊接速度、下压量等工艺参数对LY12铝合金搅拌摩擦焊焊缝金属流动形态的影响.结果表明:焊缝金属的流动形态由4个特征区域组成,即水平流动区、紊流区、"洋葱环"区和刚塑性迁移区;搅拌摩擦焊的焊缝关于中心不对称,返回边标示材料的变形程度比前进边的大;随着旋转速度的提高,金属在焊缝厚度方向向上的迁移量先增大后减小;随着焊接速度的提高,金属向上迁移的最大位移减小;增大下压量,有利于金属的流动和焊缝致密度的提高.     

无针搅拌摩擦点焊材料流动行为及其与接头宏观形貌、晶粒特征的相关性

搅拌摩擦焊接头材料流动行为是优化焊接工艺的根本所在,目前关于无针搅拌摩擦点焊流动行为尚未形成统一的认识。以0.02 mm镍箔为示踪材料,采用轴肩端面具有渐开线凹槽的无针搅拌头,改变旋转速度和焊接时间进行1.8 mm厚2198-T8铝锂合金搭接搅拌摩擦点焊试验,借助微焦点锥束三维CT设备、扫描电镜等测试手段,研究材料流动行为及其对接头宏观形貌、晶粒特征的影响。结果表明,轴肩下方的金属在轴肩挤压和摩擦热作用下先软化,以螺旋形向下向内流动形成搅拌区;随着焊接时间的延长,搅拌区金属向上和向外流动增强,致使搅拌区外缘界面翘曲,形成Hook缺陷。随旋转速度或焊接时间增大,搅拌区金属向下和向上向外流动加剧,焊核的深度和直径增大、晶粒更细小;下板金属软化程度加强,搅拌区外缘下板更多的塑化金属向上向外流动,致使Hook更翘曲。研究结果为深入了解无针搅拌摩擦点焊材料流动行为和优化焊接工艺提供了理论基础。     

A fully coupled thermo-mechanical model of friction stir welding

This paper presents a new developed fully coupled thermo-mechanical model of the friction stir welding process. Results indicate that the rotation of the shoulder can accelerate the material flow behavior near the top surface. The material deformation and the temperature field can have relations with the microstructural evolution. The texture of the appearance of the friction stir welds can correlate well with the equivalent plastic strain distributions on the top surface. The temperature field in the friction stir welding process is approximately symmetric to the welding line. The material flows in different thicknesses are different. The shoulder can have a significant effect on material behaviors on the top surface, but this effect is greatly weakened when the material gets closer to the bottom surface of the welding plate.     

2A14厚板铝合金SSFSW角焊缝接头组织及性能

采用自主研制搅拌针长度为8.5mm的静止轴肩搅拌工具和2A14-T4厚板铝合金进行150°角焊缝接头静止轴肩搅拌摩擦焊工艺试验,探讨焊接工艺参数对接头组织和力学性能的影响规律。结果表明:在500~700r/min主轴转速与40~100mm/min焊接速度范围内均可获得表面光滑无内部缺陷的角焊缝接头,其外观尺寸可精确控制基本无残余焊接角变形。焊缝区主要由焊核(Stir zone,SZ)组成,SZ形状类似搅拌针圆锥台状或椭圆状、其宽度沿厚度方向分布比较均匀;热力影响区(Thermal mechanical affected zone,TMAZ)及热影响区(Heat affected zone,HAZ)宽度明显较小。焊缝区硬度分布具有明显不均匀特征,最薄弱区位于TMAZ与HAZ的交界处。主轴转速变化对焊缝区平均硬度影响较小,但随着焊接速度增加其平均硬度明显增大。角焊缝前进侧等效拉伸强度大于后退侧,等效拉伸强度随转速增加而减小,焊速的增大而增大。在500r/min-100mm/min焊接工艺下所得到的接头等效拉伸强度最高,可达到母材的79.24%。在拉-剪复合承载模式下,角焊缝拉伸试样宏观塑性变形很小呈现脆性断裂特征。     

基于DEFORM的搅拌摩擦焊接过程数值模拟及流动分析

以塑性力学的基本理论为依据,通过Arbitrary Lagrangian-Eulerian（ALE）有限元方法,使用动态适应性网格建立焊接过程塑性金属流动有限元模型,利用金属塑性成形有限元软件Deform-3D模拟搅拌摩擦焊成形过程,得到了搅拌摩擦焊过程中的温度场分布以及焊缝区金属的流动。通过有限元模拟发现：焊接过程中由于搅拌针不断前进而在其后面形成空腔,搅拌摩擦焊的过程即为金属填充空腔的过程,FSW中常见的洋葱圆环结构就是涡旋状速度场造成的;通过模拟发现前进侧与返回侧的温度场关于焊缝分布不对称,呈倒三角形分布,且前进边温度低于返回侧,并因材料在不同温度下的剪切强度的差别而对焊缝流场产生影响,并与实际焊缝区形状相符;模拟采用点追踪技术结合嵌入性实验发现焊缝水平面内前进侧与返回侧塑性金属流动趋势不同,前进侧大量金属流向返回侧并在轴肩的下压力作用下向焊缝内部运动。     

基于仿真的搅拌摩擦焊连接AA2024-T3不同板厚过程对比

采用完全热力耦合模型以及修正的库仑模型,分别模拟AA2024-T3铝合金中厚板和薄板的搅拌摩擦焊接过程,通过对比发现搅拌摩擦焊接中材料流动速度的最大值发生在上表面搅拌针前方靠近后退侧,焊接构件上表面材料流动速度明显高于下表面,这说明搅拌头轴肩的旋转对材料流动具有明显影响。相同的焊接参数下,焊接中厚板需要更高的外输入功率以完成搅拌摩擦焊接过程,摩擦能耗在搅拌摩擦焊接中占据主要成分,是温度场形成的主要热源。在焊接薄板时,摩擦能耗占据更高的比例,说明此时的热转换率更高。塑性变形和温度是决定焊接微观结构的主要指标,中厚板搅拌摩擦焊接产生的改善晶粒大小的效果和有效利用外输入能量方面较薄板稍差。因此,无论从能量利用的角度还是对微观结构的推断均发现薄板的搅拌摩擦焊接过程具有更高的效率。     

Friction stir welding of AZ61A magnesium alloy

This paper deals with the development of an empirical relationship to predict tensile strength of friction stir welded AZ61A magnesium alloy. The process parameters such as tool rotational speed, welding speed, axial force and tool pin profile play a major role in deciding the tensile strength. The response surface method (RSM) was used to develop the empirical relationship. The four-factor, five-level central composite design was used to minimize the number of experimental conditions. The developed empirical relationship can be effectively used to predict tensile strength of friction stir welded AZ61A magnesium alloy joints at 95 % confidence level.     

Effects of tool rotation and pin diameter on fatigue properties of friction stir welded lap joints

The objective of this study was to determine the effects of the tool pin diameter and tool rotation on the fatigue behaviour of friction stir welded (FSW) lap joints. FSW lap joints of AA 5754 aluminium alloy plates were produced by means of a conventional semiautomatic milling machine. Consequently, defect free FSW lap joints were produced on alloy plates at a constant traverse speed but with different tool pin diameter and tool rotation. Therefore, within this study, tool rotation and the tool pin diameter were accepted as variable parameters, while others held fixed. The results of the tests performed, indicate that an optimisation is required for the studied parameters, in order to obtain reasonable fatigue strength. An index, related to tool rotation, traverse speed, pin diameter, and pin height can be identified and used to select optimum parameters for FSW applications.     

Multi-layered metal flow and formation of onion rings in friction stir welds

The friction stir welding (FSW) is achieved with an external tool consisting of a shoulder and pin. The shoulder and pin transfer the metal from the front side to the rear side in two distinct modes; the first and second modes of metal transfer, respectively. In the present study, the pin in the form of a cylindrical tool is used to analyse the metal flow during FSW in the second mode of metal transfer. Movement of the cylindrical tool transfers the metal from the front side to the rear side layer by layer. The longitudinal and transverse forces during the metal transfer are measured and the layered metal flow phenomenon has been proposed, due to stick and slip conditions. Based on the results obtained, the two modes of metal transfer as well as the formation of onion rings in friction stir welds have been explained. The present work can be used to model the process for improving tool and fixture design.     

铝合金液冷冷板窄台阶搭接搅拌摩擦焊工艺研究

文中研究了铝合金液冷冷板窄台阶搭接搅拌摩擦焊工艺。冷板基底材料为6063 铝合金,盖板材料为3A21 铝合金。设计了窄搭接搅拌头,减小了轴肩宽度和焊接压力,增加了接头焊接时材料的流动性,针对不同焊深窄台阶冷板进行了窄搭接焊接工艺试验。研究表明,通过优化搅拌头形貌尺寸和工艺参数能够实现4-2（焊缝深度–台阶宽度,mm）、6-4 和9-6 的窄搭接搅拌摩擦焊焊接,焊接过程中进行定位预焊能有效避免产生焊缝S 型曲线,前进侧为6063 或3A21 时均能形成良好的焊缝。     

Load bearing capacity of tool pin during friction stir welding

Although friction stir welding (FSW) is now widely used for the welding of aluminum and other soft alloys, premature tool failure limits its application to hard alloys such as steels and titanium alloys. The tool pin, the weakest component of the tool, experiences severe stresses at high temperatures due to both bending moment and torsion. It is shown that the optimum tool pin geometry can be determined from its load bearing capacity for a given set of welding variables and tool and work-piece materials. The traverse force and torque during friction stir welding are computed using a three-dimensional heat transfer and viscoplastic material flow model considering temperature and strain rate-dependent flow stress of the work-piece material. These computed values are used to determine the maximum shear stress experienced by the tool pin due to bending moment and torsion for various welding variables and tool pin dimensions. It is shown that a tool pin with smaller length and larger diameter will be able to sustain more stress than a longer pin with smaller diameter. The proposed methodology is used to explain the failure and deformation of the tool pin in independent experiments for the welding of both L80 steel and AA7075 alloy. The results demonstrate that the short tool life in a typical FSW of steels is contributed by low values of factor of safety in an environment of high temperature and severe stress.     

搅拌摩擦焊焊缝金属塑性流动的抽吸—挤压理论

通过镶嵌多层铜箔作为标识材料,利用带螺纹和表面光滑的圆柱形搅拌针进行搅拌摩擦焊试验,确定了焊接时金属在焊缝厚度方向存在剧烈的塑性流动,搅拌针表面的螺纹是驱动焊缝塑化金属在焊缝厚度方向流动的主要因素.在试验基础上提出了焊缝塑化金属厚度方向流动的"抽吸-挤压"理论,认为当搅拌头旋转引起塑化金属沿螺纹表面轴向流动时,在螺纹的一端形成一瞬时空腔,周围塑化金属将被吸向此空腔,形成所谓抽吸效应;在螺纹的另一端,塑化金属将改变流向并挤压周边金属,形成所谓挤压效应:正是由于空腔对塑化金属朝焊缝中心的抽吸作用和挤压区往外对塑化金属的挤压作用,使高温塑化金属在焊缝厚度方向形成剧烈的环形迁移运动.用抽吸-挤压理论分析了焊缝中洋葱瓣花纹的形成,洋葱瓣中心的位置及隧道型缺陷的位置与由此理论分析的结果一致.通过工艺试验观察洋葱瓣花纹尺寸变化及他人的试验结果,验证了用"抽吸-挤压"理论预测焊缝成形的正确性.     

干摩擦工况下Si3N4/PTFE配副材料摩擦磨损特性与转移膜形成分析

为使全陶瓷轴承在干摩擦工况下可靠运转,选用四氟乙烯(PTFE)材质的保持架为全陶瓷轴承提供润滑.利用Rtec销/盘摩擦磨损试验机,以PTFE盘与氮化硅(Si3 N4)销为摩擦副,研究Si3 N4/PTFE在不同载荷和转速条件下的摩擦磨损性能,通过SEM对Si3 N4表面的转移膜形貌进行观察,分析转移膜形成原因.结果表明...     

Improving joint features and tensile shear properties of friction stir lap welded joint by an optimized bottom-half-threaded pin tool

To increase the lap shear failure load of friction stir lap welding (FSLW) joint, a tool with a bottom-half-threaded pin was designed in the present study. Using 7N01-T4 aluminum alloy as the research object, tools with the bottom-half-threaded pin and the traditional full-threaded pin were used to fabricate lap joints. Results showed that the thread end position on the pin greatly influenced the material flow behavior. The material concentrated zone using the bottom-half-threaded pin mainly located above the lap interface, which is beneficial to suppress the hook and cold lap. The lap shear failure load of the FSLW joint using the bottom-half-threaded pin was 17,644.7 N, which is equal to 122.8 % of the joint using the full-threaded pin.