搅拌摩擦焊接技术实现非直线焊缝过程中的材料行为分析

采用基于固体力学的有限元方法建立了搅拌摩擦焊接过程的三维数值模型,研究了搅拌摩擦焊接技术在焊接非直线焊缝时材料的流动行为以及焊接过程中的力学特征。结果显示,搅拌焊接构件后退侧材料的流动较前进侧更为剧烈,且越靠近肩台部分材料的流动速度越大,搅拌头向原焊接构件前进侧移动将导致材料流动速度增加,搅拌头平移方向变化的瞬时会明显改变搅拌头周围材料流动速度的分布规律。搅拌探针-焊接构件接触面上的接触压力分布是比较均匀的。     

搅拌摩擦焊接中的接触界面材料行为分析

通过有限元模型,模拟不同工况下的搅拌摩擦焊接过程发现,焊接构件的中下部搅拌针,与焊接构件接触面上材料流动的速度以及厚度方向上的位置无关,但是靠近上表面的材料流动速度明显增加,而且靠近上表面的材料流动速度与厚度方向上的坐标均呈近似的线性关系。搅拌头轴肩下方的区域是材料流动的主要区域,在轴肩外边缘区域,材料流动速度迅速降低。焊接温度和材料流动速度随搅拌头转速的增加而增加,滑动系数随搅拌头转速的增加而增加。预热时间的变化,对无缺陷搅拌摩擦焊接过程的影响较小。     

焊接参数对搅拌摩擦焊搅拌区材料融合的影响

用率相关本构模型模拟了搅拌摩擦焊接过程,研究了焊接参数的变化对搅拌摩擦焊接构件横截面上材料变形的影响.通过对不同过程参数下等效塑性应变的研究,分析了搅拌区及热力影响区内焊缝中心线两侧材料的融合情况,根据变形分布,从理论上判断焊接参数的变化对焊接质量产生的影响.结果表明,在靠近焊接构件下部材料的融合随着搅拌头转速的增加和焊速的减小趋于良好,但是搅拌头转速过高有可能导致焊接缺陷的产生.     

搅拌摩擦焊接材料流动模型及在缺陷预测中的应用

为了研究搅拌头倾角对搅拌摩擦焊接过程的影响机理,基于DEFORM-3D软件建立了带倾角的FSW三维热-力耦合模型,模拟了搅拌摩擦焊接过程中焊缝区材料的三维运动轨迹,对比分析了有无倾角时FSW过程中材料流动行为的差异. 结果表明,前进侧材料绕搅拌针旋转后大部分沉积于搅拌头后方前进侧区域,返回侧的材料大部分被搅拌头旋推至后方而沉积;采用倾角可以增强搅拌头后方材料从返回侧运动至前进侧区间的流动性,同时还有利于增强材料在厚度方向的运动能力. 根据模拟的材料流动行为对接头缺陷进行了趋势预测,预测结果与试验结果吻合良好.     

三维搅拌摩擦焊接过程数值模拟

将搅拌摩擦焊接过程中材料的流动看作是层流、粘性、非牛顿流体绕过旋转的圆柱体,并基于流体力学理论,建立了三维搅拌摩擦焊缝金属塑性流动的数值分析模型.计算结果表明,在焊缝上部表面附近,由于搅拌头轴肩的影响,材料流动比较混乱,发生多次绕流现象;焊缝下部材料流动规律性较明显:只有很少一部分靠近搅拌头探针的材料在焊接过程中受到探针的作用而发生变形和流动,在大多数的模拟条件下,探针直径范围内的材料仅仅在回撤边一侧沿旋转方向绕过探针.焊缝中部具有底部和上部材料的流动特点,是探针和轴肩共同影响的结果.采用"标记嵌入技术"对焊缝金属流动进行可视化研究,试验结果与模拟结果进行了验证,模拟结果能很好地预测塑性金属流动趋势.     

搅拌摩擦焊接过程中搅拌头转速对材料流动的影响

使用有限元方法模拟了不同搅拌头转速下,搅拌摩擦焊接过程中Al6061～T6材料的三维流动,以及材料流动与搅拌头转速的关系,结果表明,在搅拌摩擦焊接过程中,后退侧的材料流动较前进侧更为剧烈,并且随着搅拌头转速的增加,材料流动也会得到不同程度增强,搅拌头前方的材料在搅拌头的推动作用下向上涌起,被旋推到搅拌头后方并向下运动,该过程的周而复始是促使搅拌摩擦焊接顺利完成的主要原因,等效塑性应变等值线的形状与材料热影响区,热力影响区以及搅拌区的边界形状具有较好的对应关系,随着搅拌头转速的增加,等效塑性应变随之增加。     

厚板双轴肩搅拌摩擦焊温度场及流场数值模拟

针对30 mm厚5A06铝合金双轴肩搅拌摩擦焊的焊接过程,建立温度场及流场的数值模型,计算两种搅拌工具作用下的温度场及流场分布情况。模拟结果发现,双轴肩搅拌摩擦焊接过程中,双轴肩搅拌摩擦焊温度场靠近轴肩区域的温度高,沿板厚中心方向温度逐渐降低,呈哑铃状分布,后退侧温度高于前进侧温度;采用锥形搅拌针焊接时的焊缝温度高于圆柱形搅拌针作用的焊缝。流动场模拟结果表明,工件上、下表面轴肩作用范围内的材料流动最为剧烈,工件内部材料流动相对较弱,采用平行槽结构的搅拌针材料呈横向流动规律,而螺纹结构的搅拌针作用下材料流动较紊乱,材料流动情况与两种搅拌工具作用下的焊缝形貌吻合较好。     

搅拌摩擦焊中动态再结晶及硬度分布的数值模拟

使用率相关弹粘塑性本构模型模拟了搅拌摩擦焊接过程,并着重研究了过程参数对搅拌摩擦焊接动态再结晶过程以及搅拌区内材料硬度的影响．结果表明,在搅拌区内焊接构件上、下表面沿垂直于焊缝方向的硬度分布规律不同．焊接构件顶部材料的硬度分布符合实验得到的结果,即焊缝中心线附近材料硬度较低,热力影响区外材料硬度逐渐升高并最终达到母材的硬度;但是在焊接构件下表面并不显示这一硬度分布规律．搅拌区内材料的硬度与搅拌头转速无明显关系,但随焊速的增加而增加．焊接构件中部材料的晶粒尺寸大于焊接构件底部材料的晶粒尺寸,且搅拌区内晶粒尺寸随搅拌头转速的增加趋于均匀．     

搅拌摩擦焊接产热传热过程与材料流动的数值模拟

搅拌摩擦焊接过程中的产热、传热与塑性材料流动行为直接决定了焊接接头的组织演变及力学性能。对这些物理现象开展数值模拟研究,对于深入理解搅拌摩擦焊接过程的物理机制和优化焊接工艺具有重要意义。本文综述了搅拌摩擦焊接过程产热、传热与材料流动数值模拟的国内外研究现状,指出了存在的主要问题。介绍了作者课题组近年来针对这些问题所开展的研究工作。根据搅拌头-工件界面上的受力特点,研发出了黏着系数和摩擦因数的测试-计算法,为提高数值模拟的精度奠定了基础。建立了针对复杂截面形状搅拌针的搅拌摩擦焊接过程数学模型,数值分析了3种典型搅拌头情况下焊接过程中的产热率、温度分布和塑性流动行为。建立了包含下压、停留、焊接及冷却4个阶段的搅拌摩擦焊接全过程的传热-流动耦合模型,模拟了焊接过程各阶段的产热、温度场和塑性材料流动的演变情况。在此基础上,对搅拌摩擦焊接过程数值模拟领域未来的发展趋势进行了展望,提出了下一步的研究重点。     

轴向载荷变化对搅拌摩擦焊接过程中材料变形和温度分布的影响

采用完全热力耦合模型分析轴向载荷变化对搅拌摩擦焊接过程的影响,发现较低的轴向载荷会导致搅拌摩擦焊接无法完成.搅拌摩擦焊接构件上表面材料由于受到搅拌针和肩台旋转的作用,导致上表面材料变形程度较下表面高,材料沿焊缝中心线的变形并非严格对称,前进侧材料的变形程度较后退侧高,搅拌头轴向载荷的增加会减弱这种不对称性.搅拌摩擦焊接过程中的最高温度随轴向载荷的增加而增加,且搅拌头轴向载荷的增加会促使搅拌区附近的温度分布趋于均匀.     

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.     

Modeling of material flow in friction stir welding process

This paper presents a 3D numerical model to study the material flow in the friction stir welding process. Results indicate that the material in front of the pin moves upwards due to the extrusion of the pin, and then the upward material rotates with the pin. Behind the rotating tool, the material starts to move downwards and to deposit in the wake. This process is the real cause to make friction stir welding process continuing successfully. The tangent movement of the material takes the main contribution to the flow of the material in friction stir welding process. There exists a swirl on the advancing side and with the increase of the translational velocity the inverse flow of the material on the advancing side becomes faster. The shoulder can increase the velocity of material flow in both radial direction and tangent direction near the top surface. The variations of process parameters do have an effect on the velocity field near the pin, especially in the region in which the material flow is faster.     

铝合金搅拌摩擦焊物理场三维数值模拟

基于热物理模拟构建的2024-T3铝合金Arrhenius本构关系,使用Deform-3D软件建立了搅拌摩擦焊三维热-力耦合模型,模拟焊接过程温度、应力、应变等物理场在塑性变形区的分布状态. 结果表明,各物理场受焊速和转速的影响均呈不对称分布,其中材料在前进侧表现为压应力状态,在后退侧出现受拉应力状态;此外,在前进侧材料分别向焊缝表面和根部流动,当材料由后退侧向前进侧的流动速度小于在厚度方向上的流动速度时,在焊缝内产生缺陷,并通过试验验证了这一现象.     

T形接头角接静轴肩搅拌摩擦焊三维流动特征

在T形接头横截面方向预置0.1 mm铜箔作为示踪材料，进行了角接静轴肩搅拌摩擦焊，焊后对T形接头角焊缝进行X-ray 2D透射和X-ray 3D扫描，得到了角焊缝示踪材料的2D流场和3D流场. 在前进侧热塑性材料主要以摩擦剪切为主，材料流动主要向焊接方向流动，并流向前进侧后方，后退侧材料主要以挤压为主，由于T接搅拌针螺纹的存在，使得材料整体向后退侧下方流动. 同时发现，在T接静轴肩后沿附近下方存在示踪材料"堆积区"，表明T接静轴肩对附近的材料塑性流动存在一定的阻碍作用. 根据所获得的观察结果，建立了T形接头角焊缝的三维流动主要特征模型.     

Numerical simulation of effect of rotational tool with screw on material flow behavior of friction stir welding of Ti6A14V alloy

The rotational tool is put forward, which is composed of the one-spiral-flute shoul-der and the rotational pin with screw. Using the turbulent model of the FLUENT software, material plastic flow behavior during the process of friction stir welding of Ti6Al4V alloy is researched by the numerical simulation method and then the effect of rotational tool geometry on material flow during the welding process is attained. The results show that the flow direction of the material near the rotational tool is mainly the same as the rotational direction of the tool while the material near tool flows more violently than the other regions. For the tapered rotational pin, the flow velocity of material inside the workpiece decreases with the increase of the distance away from the workpiece surface because of the change of pin diameter. For the rotational tool, the flute added to the shoulder and the screw added to the pin can greatly increase the flow velocity of material during the welding process while the peak value of the flow velocity of material appears on the flute or the screw. Moreover, the rotational tool with the one-spiral-flute shoulder is better than the tool with the concentric-circles-flute shoulder. Decreasing the width of pin screw and increasing the diameter of pin tip are both good for the increase of flow velocity.     

3D visualization of the material flow in friction stir welding process

0IntroductionThe friction stir welding(FSW),a new solid-statewelding process invented by TWI in1991,is perhaps themost remarkable and potentially useful new welding tech-nique.In the welding process,the base metal doesn’tmelt,so great advantages can be a…