基于数值模拟的搅拌摩擦焊接成形缺陷预测

采用DEFORM-3D软件建立了搅拌摩擦焊三维热-力耦合有限元模型,通过数值模拟研究了不同工艺参数条件下预测搅拌摩擦焊成形缺陷的方法。将数值模拟的缺陷预测结果与实验结果进行对比,验证了本模型进行缺陷预测的可行性。为了研究焊缝成形缺陷产生的原因,对比分析了搅拌倾角、焊速等工艺参数影响搅拌摩擦焊温度及材料流动的规律,结果表明,增大搅拌头倾角可明显增加焊缝前进侧材料的焊接温度,增大焊速会小幅降低前进侧根部材料的焊接温度。同时,增大搅拌头倾角可增大搅拌头后方材料的接触压力,相应地可增大其摩擦驱动力,促使材料产生塑性流动;但增大焊速,会使接触压力降低,使材料因摩擦驱动力不足而流速过小,甚至停止流动形成孔洞型缺陷。     

搅拌摩擦焊专题之搅拌头(上)

搅拌头是搅拌摩擦焊技术的心脏~([TWI]),也是搅拌摩擦焊方法的核心。搅拌摩擦焊过程中搅拌针旋转着插入被焊接材料的结合界面处,使被焊接材料得到热塑化,然后搅拌头沿着待焊接界面向前移动,在搅拌头的作用下,热塑化的被焊接材料从前部向后部转移,并在搅拌头的锻造力作用下形成可靠接头。     

搅拌摩擦焊概述（二）

搅拌摩擦焊是一种纯机械化的固相连接方法。如下图所示，搅拌摩擦焊过程中，一个柱形带特殊轴肩和针凸的搅拌头旋转着缓慢插入被焊工件的待焊接处，被焊工件需要有背部衬垫和被牢固固定，以防止焊接过程搅拌头力的作用从而使工件分离，搅拌头和被焊材料之间的摩擦剪切阻力产生了摩擦热，摩擦热使搅拌头邻近区域的材料受热变软从而得到了热塑化，当搅拌头受到驱动沿着待焊界面向前移动时，热塑化的材料由搅拌头的前部向后部转移，并且在搅拌头轴肩的锻造作用下，实现工件之间的固相连接。     

铝合金搅拌摩擦焊材料流场非对称性的数值模拟研究

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。     

搅拌摩擦焊数值模拟的研究现状

本文论述了国内外搅拌摩擦焊数值模拟的研究现状,重点讨论了国内外研究人员对不同形式的速度场、力场、温度场等的计算机数值模拟,针对不同的搅拌摩擦焊焊接工艺,研究人员提出了不同的数值计算模型,将材料的流动看作是稳态、层流、粘性、非牛顿流体,经实验进行验证能够得到基本符合的数值模拟结果,同时对搅拌类型的数值模拟有较好的指导作用。     

6 mm厚紫铜的搅拌摩擦焊研究

对T2紫铜的搅拌摩擦焊技术进行了试验研究，对其接头组织和力学性能等进行了初步分析，并对紫铜搅拌摩擦焊温度场进行了数值模拟和实验验证。结果表明，用搅拌摩擦焊方法焊接6mm厚的T2紫铜板．可得到成形美观、内部无缺陷的平板对接接头。紫铜搅拌摩擦焊时工件温度较高，焊接区最高温度接近700℃，温度分布以搅拌头为中心，呈放射状向四周逐步降温。     

不锈钢搅拌摩擦焊搅拌头温度场模拟

搅拌头技术是搅拌摩擦焊工艺的关键技术,不绣钢搅拌摩擦焊一个重要的难点是确定不锈钢搅拌摩擦焊搅拌头的材料.此材料要求在1000℃或更高的温度下具有良好的耐磨性和韧性.采用搅拌摩擦焊工艺对3 mm厚0Cr18Ni9不锈钢板进行了对接焊接.利用有限元软件DEFORM-3D初步模拟了在旋转速度600 r/min,焊接速度70 mm/min下焊接不锈钢时搅拌头的温度场分布.结果表明,模拟结果与实测结果基本吻合.     

异种材料及复合热源搅拌摩擦焊

在对接和搭接方式中,异种材料搅拌摩擦焊相较于同种材料分别具有一些额外的焊接参数,并且对搅拌头材料也有更苛刻的使用要求。总结近年来异种材料搅拌摩擦焊的研究现状,介绍异种材料搅拌摩擦焊过程中脆性金属间化合物的生成及其对焊接接头的力学性能产生的影响。从金属流动机理和数值模拟方面,研究金属间化合物的生成和成长规律,给出针对金属间化合物可能的解决方法。针对高熔点焊材,介绍复合热源搅拌摩擦焊技术、常用的辅助热源以及复合热源搅拌摩擦焊在异种材料搅拌摩擦焊方面的优点和研究的不足之处。     

搅拌摩擦焊过程中搅拌头受力与变形的计算方法

提出了搅拌摩擦焊过程中搅拌头受力的计算方法,基于搅拌针的受力情况,对搅拌头在搅拌摩擦焊过程中的变形进行了计算。计算结果表明,搅拌摩擦焊中的温升对改善搅拌头受力具有非常重要的影响,提高焊接温度,将大大降低搅拌头在焊接过程中行进时所受的力,这将极大提高搅拌头的使用寿命。由于变形量很小,因此,可以认为搅拌针在焊接过程中的变形对焊缝形成没有影响。     

火焰辅助加热搅拌摩擦焊数值模拟与试验研究

搅拌摩擦焊(FSW)技术在高熔点材料上的应用仍然受限于搅拌头的寿命。在FSW过程中,搅拌针承受着巨大的剪切力和摩擦磨损。预热工件可以软化被焊材料,是提高搅拌头寿命的方法之一。本文进行了Q235钢氧-丙烷火焰辅助加热FSW数值模拟与试验研究;建立了火焰与搅拌头双热源模型,利用有限元分析软件ANSYS模拟分析了FSW过程中的热量传递过程,获得了被焊材料的温度场分布;进行了Q235钢的火焰辅助加热FSW试验研究,分析了对接焊时FSW接头热影响区、热力影响区和焊核区的显微结构,以及焊缝的显微硬度。计算得到的热影响区形状和尺寸与试验测量的结果基本吻合。     

三维搅拌摩擦焊接传热与塑性流动分析模型

为研究搅拌摩擦焊接过程热流相互作用下的温度场、速度场和粘度场,将材料看成是层流、粘性、非牛顿流体,基于流体力学理论,建立了搅拌摩擦焊接过程的三维热流分析模型.给出了焊接过程热输入与搅拌头的旋转频率、工件运动速度、搅拌头尺寸及材料发生屈服时的剪应力的数学关系式,并将其作为热边界条件加入到了模型中.结果表明,搅拌头前部温度低于后部,温度梯度前部大于后部;受搅拌头周围材料流动的影响,接近搅拌针的区域,后退侧温度高于前进侧;材料上部速度、粘度受轴肩影响较大,下部主要受搅拌针影响;计算得到的热力影响区与试验结果有较好的对应关系.     

Analysis of tool geometry in dissimilar Al alloy friction stir welds using optical microscopy and serial sectioning

Abstract

The influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated. Sheets of Al 2024 and Al 6061 alloys are friction stir welded in lap and butt configurations using different welding conditions. Optical microscopy with serial sectioning is utilised to systematically study material flow when small variations are made to the tool pin. It is shown that three flat features on the pin impose vertical material flow which can promote intermixing. When a threaded tool is used, the material flow and formation of the intermixed region depends on the orientation of the base materials, since the differences in viscosity of material on the advancing versus retreating side of the tool will inhibit intermixing. Decreasing the travel speed will promote intermixing by increasing the residence time to compensate for the differences in material viscosity that otherwise limit intermixing.     

Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding

Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.     

搅拌摩擦焊接过程中材料流动形式

采用完全热力耦合模型对搅拌摩擦焊接过程进行模拟,并详细分析了搅拌摩擦焊接过程中的材料流动形式.结果表明,模型可以成功预测搅拌摩擦焊接过程材料流动和温度分布情况.通过对搅拌头周围材料流动的研究,分析了搅拌摩擦焊接过程中飞边现象形成的主要原因.研究了搅拌摩擦焊接构件不同厚度上材料的三维流动形式,通过与二维情况的比较证实,二维情况下的材料流动数值模拟结果对应于搅拌摩擦焊接构件靠近下表面部分的材料流动情况.从等效塑性应变的分布也能证实搅拌头轴肩对靠近上表面的材料行为具有明显影响,而对下表面附近材料行为影响较弱,从而说明二维情况对应三维情况靠近下表面的部分.     

基于实测小孔的激光深熔焊接三维传热模型

激光深熔焊接的传热过程包括热传导和焊接熔池内熔融材料的对流流动.考虑了熔池的对流和材料热物性参数的温度依存性,建立了激光深熔焊接的三维传热模型,以试验所得小孔为原型;考虑了熔池中流质的轴向流动及轴向的温度变化;采用了"固液同一法",让温度低于液相线的材料粘性系数趋于无限大,而高于液相线的材料则采用实际值.采用有限单元法对模型数值求解的结果表明,激光焊接温度中的等温线为一组类似椭圆的曲线;小孔前沿的温度梯度、速度梯度大;后沿的温度梯度、速度梯度小;焊接熔池中的对流流动是在表面张力驱动下产生的.     

Modeling friction stir welding process of aluminum alloys

The friction stir welding (FSW) process of aluminum alloys has been modeled using a two-dimensional Eulerian formulation. Velocity field and temperature distribution are strongly coupled and solved together using a standard finite element scheme. A scalar state variable for hardening is also integrated using a streamline integration method along streamlines. A viscoplastic constitutive equation to consider plastic flow and strength variations was implemented for the process modeling. Precipitates inside AA6061 alloys are sensitive to elevated temperatures and affect strength evolution with temperature. The overall effects of the precipitate variations with temperature on strength were reflected using temperature-dependent material parameters. The material parameters of constitutive equations were obtained from isothermal compression tests of various temperatures and strain rates. The effects of FSW process conditions on heating and hardening were investigated mainly near the tool pin. The microhardness distribution of the weld zone was compared with the prediction of strength. In addition, crystallographic texture evolutions were also predicted and compared with the experimental results.     

搅拌摩擦焊接偏心挤压流动模型

提出了一种偏心挤压流动模型,该模型认为搅拌头对软化材料的偏心挤压作用是形成接头的主要因素.基于该模型,设计并进行了偏心搅拌摩擦焊接试验.结果表明,搅拌摩擦焊接过程中,接头是由搅拌头偏心挤压材料形成的;搅拌头的偏心量越大,形成的接头核心区也将越大;在搅拌针附近的金属流动将使焊接接头形成在行进方向的层状结构;在接头表面将形成弧形纹,形成的弧形纹不是沿板材对接面对称的,而是偏向后退侧的,弧纹在后退侧形成的弧纹夹角比前进侧形成的弧纹夹角大;行进方向的层状结构和接头表面的弧形纹有对应关系.     

2A14-T6铝合金双轴肩搅拌摩擦焊特征及接头组织性能分析

成功实现了2A14-T6高强铝合金的双轴肩搅拌摩擦焊,获得了表面成形良好,无内部缺陷的优质接头.试验发现,在焊缝的焊核内存在一个由上、下轴肩和搅拌针所驱动的材料塑性流动交汇区,该交汇区靠近焊缝下表面.微观分析表明,焊核上部的晶粒尺寸要小于其中部和下部的晶粒尺寸.焊缝各区的块状第二相在焊接中发生了溶解和粗化,导致接头内出现了宽度近乎轴肩直径二倍的软化区;焊缝各层硬度分布接近,没有出现常规搅拌摩擦焊中常见的接头各层异性现象.经拉伸测试证实,双轴肩焊接接头的强度系数达到了71%,拉伸时断在了焊核内的材料流动交汇区处.     

An integrated model for analysing the effects of ultrasonic vibration on tool torque and thermal processes in friction stir welding

An integrated model of ultrasonic vibration enhanced friction stir welding (UVeFSW) is developed by integrating the thermal-fluid model with the ultrasonic field model and tool torque model. The tool torque and the heat generation rate at tool/workpiece contact interfaces are coupled with the interfacial temperature, strain rate and ultrasonic energy density. The model is used in quantitatively analysing the effects of ultrasonic vibration on tool torque and thermal processes in friction stir welding (FSW). The results show that ultrasonic vibration reduces the flow stress, which results in a decreasing of tool torque, interfacial heat generation rate and interfacial temperature. The complicated interaction of ultrasonic energy with the thermal processes in FSW leads to a gentle thermal gradient and an enhanced plastic material flow in UVeFSW. The model is validated by a comparison of the calculated thermal cycles and tool torque at various welding parameters with the experimentally measured ones.     

Analysis of effect of tool geometry on plastic flow during friction stir spot welding using particle method

The effect of tool geometry on the plastic flow and material mixing during friction stir spot welding (FSSW) is investigated using the particle method approach. For spot welds made with a cylindrical pin tool with flat shoulder, the model predicts the material flow at the pin periphery to be in the upward direction and the material is pushed downward beneath the shoulder giving rise to the resultant hook geometry. Other pin geometries evaluated include tapered pin, inverse tapered pin, triangular pin, convex shoulder, and concave shoulder. With good correlation with experimental trials, this model is then used to predict the material flow for spot welds. The material flow, and thereby the resultant hook formation, is quantified using numerical methods and is expressed as standard deviation of the particle movement. A triangular pin with a concave shoulder is the preferred tool geometry from the current study that results in high strength spot welds.