转速对搅拌摩擦焊接搅拌区晶粒尺寸影响

基于搅拌摩擦焊接的完全热力耦合模型,跟踪材料物质点运动轨迹,划分出不同搅拌头转速下搅拌区域边界。沿材料物质点迹线提取出真实应变与温度历程,可进一步计算Zener-Hollomon参数并利用经验公式预测搅拌区晶粒尺寸。经计算发现较大转速工况下,搅拌区尺寸较大。搅拌区晶粒尺寸随焊接温度的增加而增加,随应变率的增加而减小。随着搅拌头转速的增加,焊接区材料温度与等效应变率均有明显增长,但是温度影响更为明显,平均晶粒尺寸随搅拌头转速的增加而增加。     

6061铝合金无倾角搅拌摩擦焊工艺及性能

目的 为了适应空间曲面构件的搅拌摩擦焊,开展6061铝合金无倾角搅拌摩擦焊工艺及性能的研究。方法 采用无倾角搅拌摩擦焊用的搅拌头,对5 mm厚6061-T6铝合金板材进行试验,研究焊缝成形及接头力学性能,并分析接头组织特征。结果 零倾角搅拌摩擦焊接头从组织上可区分为5个不同区域：焊核区(WNZ)、热力影响区(TMAZ)、热影响区(HAZ)、轴肩影响区(SAZ)和母材(BM);随着搅拌头转速增加,焊缝宽度和焊核尺寸均先变大后变小;随焊接速度增加,焊缝宽度和焊核尺寸均逐渐变小;当焊接速度固定时,随搅拌头转速增加,接头拉伸强度先增加后减小;当搅拌头转速固定时,随焊接速度增加,接头拉伸强度逐渐增大。结论 采用无倾角搅拌摩擦焊接方法,能够实现对5 mm厚6061-T6铝合金板材的有效焊接。     

7075铝合金高速搅拌摩擦焊材料流动行为及性能研究

目的 针对7075–O铝合金高焊速、高转速搅拌摩擦焊接缺陷多、质量差等问题,研究焊接接头材料流动对焊缝性能的影响。方法 选用焊接速度1 000 mm/min,搅拌转速分别为1 000、1 200、1 600、1 700 r/min的条件对7075–O铝合金板进行搅拌摩擦焊接,分析不同焊接工艺参数下焊接接头的显微组织及力学性能。同时,利用Fluent软件模拟7075–O铝合金搅拌摩擦焊接过程中的材料流动场分布,分析焊接材料流动与缺陷形成的关系。结果 利用7075–O铝合金三维流动模型,预测出高焊速条件下焊缝前进侧形成一个低压区,孔洞等缺陷易出现在此区域,数值模拟预测与试验结果吻合。在高焊接速度1 000 mm/min、焊接转速1 200 r/min时,焊缝表面光滑平整,焊核区域的硬度分布更加均匀。结论 随着搅拌转速从1 000 r/min增大到1 700 r/min,热输入量逐渐增大,孔洞缺陷由隧道型孔洞转变为不连续的小孔。同时,随着搅拌转速的增大,焊缝高硬度区域的宽度先增大而后降低。当搅拌转速为1 200 r/min时得到了优质的焊接接头,焊缝焊核区硬度分布均匀,硬度值最高为176HV。     

工艺参数对AZ31镁合金往复挤压过程的影响

运用刚黏塑性有限元法对不同工艺参数下的AZ31镁合金往复挤压过程进行了热力耦合数值模拟,研究了不同初始坯料温度、挤压速率和摩擦因数对往复挤压过程中等效应变、等效应力及温度场的影响。结果表明:在往复挤压过程中,挤压速率对等效应变峰值影响不大,随着挤压速率的增大,工件内温度峰值直线上升,温度分布不均匀程度增大,应力峰值先增加后减小;随着初始坯料温度升高,等效应力峰值呈直线趋势减小;摩擦因数对温度峰值的影响很小,随着摩擦因数的增大,等效应变峰值先增大然后趋于平稳,等效应力峰值增大,其增大幅度减小。     

6061铝合金搅拌摩擦焊工艺窗口的研究

目的提高6061铝合金搅拌摩擦焊接头的质量,确定合适的工艺参数范围。方法设计3种不同的搅拌头进行焊接,分析接头拉伸强度与组织性能,并根据试验结果建立工艺窗口,选择合适的轴肩尺寸及工艺参数范围。结果随着轴肩尺寸减小,焊缝宽度、金属流动性、热力影响区面积均减小,在较大的焊接速度及较小的搅拌头转速下,焊缝底部出现缺陷;采用轴肩直径小的搅拌头进行焊接,在一定焊接参数范围内,焊接接头的拉伸强度得到提高;随着轴肩直径减小,焊核区晶粒组织细化,材料变形程度减小;由建立的工艺窗口可知,当轴肩尺为9 mm时,可选择的参数范围最大。结论焊接时采用小尺寸轴肩,可以在搅拌头行走速度更低、转速更大的情况下,仍然可以保持合理产热量,使接头性能得到提高。     

冷-热源辅助对FSW残余应力影响的数值模拟

目的采用焊接中施加冷热源辅助的方式对焊接应力进行控制,以减小焊后残余应力。方法采用热机耦合数值模拟的方式对2024铝合金搅拌摩擦焊接过程进行仿真,研究采用焊缝两侧加热且底部激冷的温差拉伸辅助工艺降低残余应力的效果。结果与常规工艺相比,温差拉伸时焊缝附近区域的温度梯度明显减小,焊缝区域温度峰值降低了75.3℃;搅拌头后方形成一个焊缝两侧温度高中间温度低的马鞍形温度场。两种工艺下的纵向残余应力峰值均位于焊缝边缘;相比于常规工艺,温差拉伸工艺下的残余应力峰值降低了23.4%。结论冷热源辅助可以有效减小搅拌摩擦焊接头的残余应力峰值。     

厚板7022铝合金搅拌摩擦焊接实验研究

对10mm厚度的7022铝合金进行了搅拌摩擦焊接,获得表面光滑的焊接接头,并通过X射线检测焊缝无裂纹和气孔。研究该搅拌摩擦焊接头不同区域的显微组织特征,并通过拉伸、冲击和硬度试验分析了焊接接头的力学性能。结果表明,焊缝处组织为细小均匀的等轴晶粒;在搅拌头转速为400r/min,焊接速度为100mm/min时焊接接头的抗拉强度、屈服强度均比母材高;焊接接头的冲击韧性比母材高;焊接接头显微硬度比母材稍低,焊接接头具有良好的力学性能。     

基于CEL方法的搅拌摩擦焊6061铝合金温度场研究

目的研究搅拌摩擦焊接过程中焊接件温度场分布规律及工具头旋转速度对焊接件温度升高和温度场分布的影响规律。方法基于耦合欧拉–拉格朗日（CEL）方法,采用Johnson–Cook本构模型、温度相关的热机械物理参数、经典库仑定律和质量缩放技术,建立搅拌摩擦焊三维热力耦合有限元模型,模拟6061铝合金在不同旋转速度下的搅拌摩擦焊接过程,并进行分析比较。通过侧边打孔将热电偶埋入焊件,从而获取工件特定采样点的温度数据,对模拟结果的准确性进行验证。结果 焊缝返回侧的温度高于前进侧,工具头后方温度高于前方;焊接区域的温度随着下扎深度的增加而升高;最高温度出现在下扎结束阶段,而焊接阶段最高温度略有下降并且保持稳定;当转速从500 r/min增大到1 000 r/min时,焊缝中心峰值温度从337.4℃升高到496.5℃。特定测温点的模拟温度与热电偶实测数据吻合较好,最大误差不超过20%。模拟焊缝与实际焊缝宏观相貌吻合良好,特别是焊缝返回侧的飞边。结论 高温区域主要分布在焊缝返回侧的工具头后方;工具头转速控制温度的变化,所有焊接阶段的温度随转速的增大而升高,且高温区域扩大。     

搅拌摩擦焊焊缝塑性流动规律的数值模拟

使用FLUENT流体工程仿真软件对搅拌摩擦焊缝金属的塑性流动进行了数值模拟;初步得出了搅拌摩擦焊焊缝塑性流体流动规律.实验结果表明:随着距轴肩和搅拌针距离的增大,速度场开始减弱,焊缝金属由顶面向底面、由搅拌区向旋转区的流动也随之减弱.     

率相关材料在搅拌摩擦焊接过程中的行为分析

为研究金属粘性效应时的搅拌摩擦焊接材料流动行为,采用率相关本构描述搅拌摩擦焊接过程中的材料行为,并与非率相关材料模型的计算结果进行了对比.结果显示,由于考虑了金属的粘性效应.用率相关材料模型模拟搅拌摩擦焊接过程能更好地反映材料流动行为的本质.在搅拌摩擦焊接中,材料沿搅拌头切向方向的运动构成了搅拌摩擦焊接构件材料流动的主要形式.焊接构件-搅拌头接触面上的接触压力在搅拌头前方较大,在搅拌头后方较小,这一规律在率相关模型中更为明显.搅拌头前方材料在搅拌头的挤压之下向远离搅拌头的方向运动,而搅拌头后方的材料要填充由于搅拌头的移动而留下的空间,这一过程是保证搅拌摩擦焊接顺利完成的一个主要因素.因此,用率相关模型模拟搅拌摩擦焊接过程中的材料力学行为更为接近真实情况.     

The simulation of material behaviors in friction stir welding process by using rate-dependent constitutive model

Friction stir welding is a new solid state joining technology, which is suitable for joining some hard-to-weld materials, such as aluminum alloy, magnesium alloy, etc. The modeling of material flows can provide an efficient method for the investigation on the mechanism of friction stir welding. So, 3D material flows under different process parameters in the FSW process of 1018 steel are studied by using rate-dependent constitutive model. Numerical results indicate that the border of the shoulder can affect the material flow near the shoulder–plate interface. The mixture of the material in the lower half of the friction stir weld can benefit from the increase in the angular velocity or the decrease in the welding speed. But flaws may occur when the angular velocity is very high or the translational velocity is very small. When the angular velocity applied on the pin is small or the welding speed is high, the role of the extrusion of pin on transport of the material in FSW becomes more important. Swirl or vortex occurs in the tangent material flow and may be easier to be observed with the increase in the angular velocity of the pin.     

Effect of Traverse/Rotational Speed on Material Deformations and Temperature Distributions in Friction Stir Welding

A fully coupled thermo-mechanical model was developed to study the temperature fields and the plastic deformations of alloy AL6061-T6 under different process parameters during the friction stir welding （FSW） process. Three-dimensional results under different process parameters were presented. Results indicate that the maximum temperature is lower than the melting point of the welding material. The higher temperature gradient occurs in the leading side of the workpiece. The calculated temperature field can be fitted well with the one from the experimental test. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface, which is formed by the specific material flow patterns in FSW. The maximum temperature can be increased with increasing the welding speed and the angular velocity in the current numerical modelling.     

Comparison of two contact models in the simulation of friction stir welding process

Two contact models are used to simulate the thermo-mechanical interaction process in friction stir welding. Comparison shows that the classical Coulomb friction model can be accurate enough for the simulation of friction stir welding in lower angular velocity. But in higher angular velocity, the classical Coulomb friction model fails to work due to the increase of the dynamic effect of the welding tool. Because the shear failure of material is considered in modified Coulomb friction model, the increase of the frictional stress on the tool–plate interface is limited by the shear failure. So, this model can keep valid even when the angular velocity of the welding tool is increased to a high level.     

Modeling of friction stir welding process for tools design

A three-dimensional friction stir welding (FSW) process model has been developed based on fluid mechanics. The material transport in the welding process has been regarded as a laminar, viscous, and non-Newtonian liquid that flows past a rotating pin. A criterion to divide the weld zone has been given on the basis of cooperation of velocity field and viscosity field. That is, the η₀-easy-flow zone that existed near the tool pin corresponded to the weld nugget zone; the area between the η₀-easy-flow zone and η₁-viscosity band is corresponded to the thermal-mechanical affected zone (TMAZ). The model gives some useful information to improve the understanding of material flow in FSW through the simulation result of velocity distribution. In order to appraise the friction stir pin design, three kinds of pin geometry, one is column pin, the second is taper pin, and the last one is screw threaded taper pin, were used in the model. The pin geometry seriously affected the simulation result of velocity distribution in the η₀-easy-flow zone. The velocity distribution in the η₀-easy-flow zone can be considered as the criterion of optimizing friction stir tool design. This study will benefit to direct the friction stir tool design.     

Joint formation mechanism of high depth-to-width ratio friction stir welding

High depth-to-width ratio friction stir welding is an attractive method for the joining demands of aluminum profiles, which is sparked with its extremely low heat input and high mechanical performance. In this study, the joint formation mechanism was studied by a numerical model of plastic flow combined with experimental approaches. A fluid-solid-interaction algorithm was proposed to establish the coupling model, and the material to be welded was treated as non-Newtonian fluid. The thread structure and the milling facets on tool pin promoted drastic turbulence of material. The thread structure converged the plasticized material by its inclined plane, and then drove the attached material to refill the welds. The milling facets brought about the periodic dynamic material flow. The thread structure and the milling facets increased the strain rate greatly under the extremely low heat input, which avoided the welding defects. The condition of the peak temperature of 648 K and the strain rate of 151 s⁻¹ attributed to the lowest coarsening degree of precipitate. The tensile strength of the joint reached 265 MPa, equivalent to 86% of base material. The amelioration via the material flow model inhibits the welding defects and optimizes the parameter intervals, providing references to extracting process-structure-property linkages for friction stir welding.     

Numerical Modeling of Friction Stir Welding Process by Using Rate-dependent Constitutive Model

Rate-dependent constitutive model was used to simulate the friction stir welding process. The effect of the viscosity coefficient and the process parameters on the material behaviors and the stress distributions around the pin were studied. Results indicate that the stress in front of the pin is larger than that behind the pin. The difference between the radial/circumferential stress in front of the pin and that behind it becomes smaller when the material gets closer to the top surface. This difference increases with increasing the viscosity coefficient and becomes smaller when the welding speed decreases. The variation of the angular velocity does not significantly affect the difference.     

铝合金搅拌摩擦焊接头隧道型缺陷研究

焊接热输入不足导致铝合金搅拌摩擦焊接头中常出现隧道型缺陷，本文通过产热分析发现：选择与被焊材料摩擦系数斗较大的材料作为搅拌头制造材料；在圆柱体搅拌头的指头上制造螺纹提高焊接产热；提高旋转速度或者降低焊接速度来提高焊接线能量；减小搅拌指头半径r1是改善和消除隧道型缺陷的4种有效途径。     

2024铝合金水下搅拌摩擦焊热力耦合仿真分析

目的 优化搅拌摩擦焊接工艺参数,以提高接头的力学性能。方法 基于ABAQUS软件建立了热力耦合有限元模型,使用耦合欧拉-拉格朗日方法对典型的航空航天用板材2024铝合金的水下搅拌摩擦焊接过程进行了仿真研究。分析了搅拌摩擦焊接过程中板材的温度场分布和材料变形情况,同时研究了前进侧和后退侧相应位置材料的流动特征,进一步讨论了搅拌头冷却速度和摩擦因数对焊接温度和材料流变场的影响。结果 当摩擦因数较小时,针对焊接过程的有限元模拟将会失败;前进侧和后退侧材料变形和流动差异显著;焊接温度和等效应变随摩擦因数的增大而升高,随冷却速度的增大而降低。结论 当摩擦因数为0.8时,能较好地完成焊接。相对于空冷,水冷能明显缩短高温持续时间。     

铝合金薄板搭接高速 FSW 缺陷及断裂行为

目的 为了拓展搅拌摩擦焊技术应用,对薄板搭接结构高速搅拌摩擦焊工艺优化与工程应用提供 借鉴与指导。方法 采用圆锥无螺纹搅拌针,进行了 6061 铝合金薄板搭接高速搅拌摩擦焊接,对接头界 面缺陷及其断裂模式进行分析,探讨了转速对 6061 铝合金薄板搭接接头成形及性能的影响规律。结果 发现在无螺纹圆锥搅拌针、高转速（6000~9000 r/min）条件下,接头塑性金属在后退侧易形成飞边流出, 导致下板前进侧出现孔洞缺陷,且随转速增大,界面缺陷尺寸逐渐增大,当转速达到 10 000 r/min 时, 孔洞尺寸有所减小,此时接头拉剪强度最高,为 123 MPa。对试样拉剪断裂位置分析发现,高速搭接接 头断裂位置主要有两种,分别断裂在结合界面处或在前进侧下板,且转速在 9000 r/min 以上越趋向于在 结合界面断裂。结论 高转速搭接焊接必须协调轴肩相貌、焊接工装约束等条件,保证接头塑性金属充 分流动而不流失,才能获得成形良好无缺陷的接头。