Scaling of coupled heat transfer and plastic deformation around the pin in friction stir welding

This paper presents a coupled phenomenological model of heat transfer and plastic flow around the pin in friction stir welding (FSW). The approach is analogous to the boundary layer analysis in fluid mechanics, and is based on the methodology of scaling. The results are a set of novel closed-form expressions for the maximum temperature reached in the process, the thickness of the shear layer, the shear stress around the pin, the torque and the thermal effect of the shoulder. The model presented focuses on the most common conditions encountered in the practice of FSW, which involve relatively slow translation velocities, relatively high rotation velocities and thin shear layers. The ultimate purpose of this model is to provide simple and accurate expressions useful for providing a temperature and strain rate context for metallurgical analysis of FSW and for the selection of process parameters when using FSW to join novel alloys.     

Friction stir welding of thin DH36 steel plate

Abstract

A series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW). Comparator welds in the same thickness from the same plates were produced using a single sided single pass process submerged arc welds (SAW). This work was carried out to evaluate the mechanical properties of FSW material with a view to its possible application in a shipbuilding production process route.

Overall, the performance of the FSW material was superior to the SAW comparators. Areas such as distortion and fatigue were particularly positive in the FSW material. An 8 mm thick plate was also produced using two FSW passes, one from either side, and it was found to have superior toughness and fatigue performance when compared to the single sided 8 mm FSW material. Some of these benefits are thought to have originated from the internal overlap zone between the two passes.     

Shear localisation modelling of friction stir weld formation process

This paper presents a shear localisation model for studying friction stir welding (FSW) formation process. With this model, shear band (SB) width, SB formation time, and SB propagation speed can be theoretically estimated. The SB propagation speed in this context serves as a theoretical estimate of the maximum welding speed possible for a given material and prescribed welding conditions, such as stir pin rotation speed and torque level. The model is shown to provide reasonable estimates of shear localisation parameters against a set of recent experimental data on FSW of titanium alloy Ti–6Al–4V. With this model, titanium alloy Ti–6Al–4V, high strength low-alloy steel 4340, and aluminium alloy 2024 are compared in terms of shear localisation parameters, such as maximum SB propagation speeds (or welding speeds).     

Correlation Between Crystal Rotation and Redundant Shear Strain in Rolled Single Crystals: A Crystal Plasticity FE Analysis

The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.     

基于SWRXD的5083/6082异种铝合金搅拌摩擦焊接头的残余应力分布规律

以5083铝与6082铝为研究对象,利用搅拌摩擦焊（friction stir welding,FSW）制备了异种材料对接接头.利用短波长X射线衍射（short-wavelength X-ray diffraction,SWRXD）技术,以{311}与{111}为衍射晶面,基于极图最外圈织构参量确定了残余应力测试方向,采用d₀法研究了FSW焊件中心层的残余应力.结果表明,{111}和{311}晶面测试的纵向残余应力分布趋势相近,焊核区为拉应力并出现两个应力峰值;{111}晶面的测试结果更为离散,应力的峰值向前进侧偏移;采用{111}晶面测试的横向的残余应力分布趋势与{311}晶面测试的结果偏差较大.     

7075铝合金搅拌摩擦焊接头变形及失效行为

使用搅拌摩擦焊（FSW）设备对厚度为6mm的7075高强度铝合金平板进行对接试验。设计出双径试样,采用液压伺服试验机对7075铝合金搅拌摩擦焊接头进行拉伸试验,并借助奥林巴斯显微镜和扫描电镜观察接头的变形及失效过程。结果表明,7075铝合金搅拌摩擦焊接头在拉伸过程中出现双颈缩现象,颈缩首先在后退侧出现,随着加载的进行,前进侧也出现颈缩现象。微裂纹在接头中的前进侧和后退侧颈缩区内晶界处由微孔洞聚集产生。随着应变的增加,微孔洞数量明显增加,当应变足够大时,微孔洞连接形成微裂纹。微裂纹沿着与加载方向成45°向焊核区进行扩展,导致接头断裂,断裂位置位于接头中的焊核区,断裂方式为剪切断裂混合着微孔聚集型断裂。     

热暴露下预应变对CMSX-4单晶高温合金的显微组织演变的影响

在室温下,对经完全热处理的第二代单晶高温合金CMSX-4实施压缩和拉伸预应变。压缩和拉伸预应变在单晶CMSX-4中产生了剪切带。单晶CMSX-4在950℃下热暴露10h,沿剪切带产生了γ′粒子择优粗化。剪切带上的γ′粒子逐渐侵入γ通道。最后,γ通道沿着剪切带消失。TCP状粒子伴随着γ通道的消失而出现。然而,热暴露10h的普通单晶CMSX-4没有产生TCP沉淀,也没有γ′粒子择优粗化。热暴露100h的预应变CMSX-4沿剪切带产生了γ′粒子和TCP相粒子择优粗化,基体中也有γ′粒子粗化。     

Investigation of the material flow and texture evolution in friction-stir welded aluminum alloy

The material flow and crystallographic orientation in aluminum alloy sheets joined by friction stir welding (FSW) were investigated by electron back scattered diffraction (EBSD). The microstructure and microtexture of the material near the stir zone was found to be influenced by the rotational behavior of the tool pin. It was found that, during FSW, the forward movement of the tool pin resulted in loose contact between the tool pin and the receding material at the advancing side. This material behavior inside the joined aluminum plates was also observed by an X-ray micrograph by inlaying a gold marker into the plates. As the advancing speed of the tool increases at a given rotation speed, the loose contact region widens. As the microtexture of the material near the stir zone is very close to the simple shear texture on the basis of the frame of the tool pin in the normal and tangent directions, the amount of incompletely rotated material due to the loose contact could be estimated from the tilt angle of the shear texture in the pole figure around the key hole.     

Comparison of single and double pass friction stir welding of skin–stringer aviation aluminium alloy

Abstract

To enhance the strength of the skin–stringer structures used in aircraft, comparative tests between single and double pass friction stir welding (FSW) were performed. Aluminium alloy was used for the skin (2524-T3, 1·8 mm) and stringer (7150-T77511, 2·4 mm). An equilateral right angled structure was used, and perfect joints without internal defects were obtained. Tensile, peel and metallographic tests were also implemented. The results show that the average peel strength of a double pass FSW joint is at least twice that from single pass FSW. Therefore, double pass FSW is an effective way of improving the connection strength of an aircraft skin–stringer structure.     

Comparative study on fatigue properties of friction stir and MIG-pulse welded joints in 5083 Al-Mg alloy

The objective of this investigation was to compare the fatigue properties of friction stir welds with those of MIG-pulse welds. The 5083 Al-Mg alloy was welded by single pass friction stir welding（FSW） and double-sided MIG-pulse welding. The results show that friction stir（FS） welds have a better appearance than MIG-pulse welds for the lack of voids, cracks and distortions. Compared with the parent plate, FSW welds exhibit similar fine grains, while MIG-pulse welds display a different cast microstructure due to the high heat input and the addition of welding wire. The S-N curves of FSW and MIG-pulse joints show that the fatigue life of FS welds is 18 - 26 times longer than that of MIG-pulse welds under the stress ratio of 0.1 and the calculated fatigue characteristic values of each weld increase from 38.67 MPa for MIG-pulse welds to 53.59 MPa for FSW welds.     

Microstructure and Mechanical Properties of Low-Carbon Q235 Steel Welded Using Friction Stir Welding

This study focuses on the microstructure and mechanical properties of the joints of Q235 mild steel, which was formed by the friction stir welding (FSW). The results indicated that, after the FSW, the heat-affected zone (HAZ) of the retreating side (HAZ_RS) and the HAZ of the advancing side (HAZ_AS) recovered under the influence of the heating cycle. The transformation of the phases in the thermo-mechanically affected zone (TMAZ) of the retreating side (TMAZ_RS), the stir zone (SZ) and the TMAZ of the advancing side (TMAZ_AS) generated the pearlite and acicular ferrite. The continuous dynamic recrystallization occurred in all the three zones, whereas the grains were refined. The SZ mainly consisted of D₁, D₂ and F shear textures, while the TMAZ_AS was made up of only the F shear texture. The fine-grained structure, pearlite and the acicular ferrite improved the hardness and tensile strength of the joint. Its ultimate tensile strength was 479 MPa, which was 1.3% higher than that of the base metal. However, the uniform elongation was 16%, which showed a decrease of 33%. The fracture was a ductile fracture with the appearance of dimples. Besides, the joints of the FSW showed an excellent bending performance.     

The application of equal-channel angular pressing to an aluminum single crystal

An investigation was conducted to examine the nature of the deformed microstructure when an aluminum single crystal of known orientation is subjected to equal-channel angular pressing (ECAP). The experiment was performed using a single crystal that was initially oriented within the entrance channel of the die so that the (1 1 1) slip plane was parallel to the theoretical shear plane and the [1 1 0] slip direction lay parallel to the direction of shear. The crystal was subjected to a single pass at room temperature and then examined using various microscopic techniques including orientation imaging microscopy and transmission electron microscopy. It is shown that the detailed experimental observations are fully consistent with the expectations from crystallographic considerations except only in the vicinity of the lower die wall where frictional effects are present.     

带热沉装置的搅拌摩擦焊研究

基于动态控制低应力无变形焊接法原理和搅拌摩擦焊特有的应力应变特点,设计开发了可应用于搅拌摩擦焊的单点式热沉和阵列式射流冲击热沉系统.通过两种不同热沉系统在铝合金搅拌摩擦焊中的对比研究,结果表明,单点式热沉虽然可以减小FSW焊接变形,但此种冷却方式会使接头性能大幅度下降,接头强度仅达到常规FSW的80%左右.经过改进的阵列式射流冲击热沉系统可以主动控制FSW过程中各个区域的温度分布,从而有效控制焊接过程的热弱塑性应力应变场,达到动态控制低应力无变形的焊接效果.焊缝氢含量的测试分析表明,阵列式射流冲击热沉系统可以改善接头的残余应力分布,防止冷却水侵入焊缝.带阵列式射流冲击热沉系统的搅拌摩擦焊技术可以实现低应力无变形焊接,且工艺适用性好,具有广阔的应用前景.     

单晶Al3Ti拉伸与剪切变形的分子动力学模拟

采用分子动力学方法研究单晶Al3Ti模型的拉伸和剪切力学性能。模拟Al3Ti在常温、恒定应变速率下的拉伸和剪切变形过程,讨论了温度和应变速率对体系拉伸和剪切性能的影响。结果表明,Al3Ti室温下很脆,弹性变形阶段结束后在短时间内体系产生的孔洞和位错迅速发展导致材料破坏。温度升高会导致Al3Ti的抗拉强度、杨氏模量、剪切强度和切变模量降低;应变速率增大能提高材料的拉伸和剪切强度,但不影响杨氏模量和切变模量大小。     

A Comparative Analysis of the Impact of Tool Design to Fatigue Behavior of Single-Sided and Double-Sided Welded Butt Joints of EN AW 6082-T6 Alloy

In this paper, the results of fatigue behavior on friction stir welded joints of aluminum alloy EN AW 6082-T6 are reported. In particular, the study presents the influence of the geometry of a welding tool on fatigue strengths and tensile strengths. The test joints were prepared as single side welded and double side welded by FSW. The welding was performed at various linear welding speeds (224, 560, and 900 mm/min) and one rotational speed of 710 rev./min using three different tool shapes. The results of macro examination and tensile test led to the selection of a single set of tool movement parameters at which the test joints for fatigue test were made. Samples were tested in two states of surface condition, i.e., “as-welded” and with mechanically removed marks left by rotating and moving tool during FSW process. Studies have shown that fatigue behavior of FSW joints depends on the tool shape used in the welding process as well as the surface condition of welded joints and manner of joint production.     

MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响

研究了MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响. 结果表明, MIG/FSW叠加焊缝熔合良好,叠加位置未出现气孔等缺陷,FSW焊核区及热影响区组织发生粗化,叠加位置附近微观组织出现明显改变;叠加区域硬度明显降低,尤其是FSW焊缝热力影响区和热影响区. FSW、中心叠加、前进侧热力影响区叠加和后退侧热力影响区叠加MIG焊接头的抗拉强度分别为219.8, 188.0, 195.4和191.4 MPa,MIG焊叠加降低了接头的抗拉强度,断口均表现韧性断裂特征;FSW焊接头及带有MIG叠加焊缝余高的三种接头中值疲劳强度分别为76.7, 65.0, 67.5和65.0 MPa,MIG焊叠加也使FSW接头的疲劳性能有所下降.     

Three-dimensional numerical and experimental investigation on friction stir welding processes of ferritic stainless steel

A three-dimensional thermomechanical simulation of friction stir welding (FSW) processes is carried out for ferritic stainless steel by utilizing an Eulerian finite volume method under the steady state condition, and the simulation result is compared directly with both the measured temperature histories during FSW and the microstructural changes after FSW. Based on a viscoplastic self-consistent approach for polycrystal, the texture development in the FSWed material is determined from the velocity gradients along the streamlines in the material flow field. The simulation results show that the heat is generated mainly near the interface between the tool and the workpiece, and that the viscosity changes drastically in the vicinity of the boundary between the stir zone and the thermomechanically affected zone. From the predicted streamlines, it can be indicated that the strong material flow mainly develops on the retreating side of the tool. Also, the simulation results show that the shear deformation texture is significantly developed in the FSWed region. The measured temperatures and microstructural characteristics agree fairly well with the predicted data.     

Two-dimensional CFD modelling of flow round profiled FSW tooling

Abstract

This paper describes the application of the computational fluid dynamics (CFD) code, FLUENT, to modelling the two-dimensional metal flow in friction stir welding (FSW). The primary goal is to assist in the development of new welding tools, though the models also improve the understanding of the deformation mechanism in FSW, and enable a first order visualisation of the flow round the probe. The paper describes a quantitative method of comparing the flow round different tool shapes. A novel 'slip' model was developed, where the interface conditions were governed by the local shear stresses. This revealed significant differences in behaviour when compared with the common assumption of material stick. The two-dimensional model has demonstrated the viability of the approach for investigating the flow round practical tool shapes, and gives confidence that the development of more computer intensive three-dimensional models will be justified.     

热处理条件对搅拌摩擦镁合金接头各区域抗弹行为的影响

采用搅拌摩擦焊(FSW)工艺制备AZ31B镁合金焊接接头,并在不同条件下进行热处理.研究AZ31B镁合金焊后热处理(PWHT)不同区域的抗弹行为,使用7.62 mm×39 mm穿甲弹,冲击速度为(430±20)m/s.分析热处理前后搅拌摩擦焊接头的显微硬度.结果表明,PWHT工艺(250°C,1 h)能提高热处理后搅拌...     

常规FSW与双轴肩FSW对铝合金接头组织和性能的影响

对采用常规FSW和双轴肩FSW所得到焊接接头性能进行试验研究,测试了两种焊接得到的焊接接头的抗拉强度、屈服强度和断后伸长率,并对接头的微观组织和断口形貌进行了观察和分析.结果表明,双轴肩FSW接头横截面形成了一组由内向外扩张“洋葱环”状的椭圆环;常规FSW焊核区与热力影响区之间组织发生明显变化;硬度的最低处为双轴肩FSW前进侧热力影响区,最高处为双轴肩FSW接头上表面焊核区;常规搅拌摩擦焊接头的综合力学性能最好,双轴肩次之;断口形貌分析表明,接头断裂模式均为韧性断裂,且常规FSW断口韧窝尺寸比双轴肩FSW接头韧窝小而深,表现出更好的塑性.