A thermal model of friction stir welding in aluminum alloys

A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.     

搅拌头机械载荷在搅拌摩擦焊接中的作用的数值分析

利用数值模拟技术分析搅拌头机械载荷在焊接过程中的作用,通过对比只考虑热载荷,考虑热载荷和搅拌头的下压力,综合考虑热载荷、搅拌头下压力和工作扭矩三种条件下的应力,应变和变形,结果发现,搅拌头下压力使焊后残余应力值大幅下降;搅拌头的工作扭矩是焊后残余应力、应变不对称分布的重要影响因素;并且搅拌头机械载荷使得薄板焊后残余变形的模式发生了完全相反的变化,由不考虑搅拌头载荷时的马鞍状变成了反马鞍状.     

Modelling of 7050 aluminium alloy friction stir welding

Abstract

A thermal model combined with a microstructural and yield strength model has been developed to give a prediction of precipitate evolution and strength in the as welded and post-weld heat treated condition for friction stir welding of 7xxx aerospace aluminium alloys. This fully coupled model is applied to an overaged high strength 7050 aluminium alloy friction stir welded using a range of welding rotation and translation speeds. The evolution of the microstructure has been predicted as a function of the process parameters. The resulting microstructural evolution is shown to be a complex function of both peak temperature observed during the weld cycle and heating/cooling rates. Yield strength has been calculated from the microstructural predictions and a comparison between predicted yield strength and measured hardness has been used to test the modelling approach. Reasonably good agreement between model and experiment is found over the wide range of process parameters investigated.     

Microstructure,mechanical properties and residual stresses as a function of welding speed in aluminium AA5083 friction stir welds

Friction stir welding (FSW), like other friction welding techniques, has the advantage that many of the welding parameters, e.g. tool design, rotation speed and translation speed, can be controlled in a precise manner, thus controlling the energy input into the system. However, the effect of different welding speeds on the weld properties remains an area of uncertainty. In this paper, we report the results of microstructural, mechanical property and residual stress investigations of four aluminium AA5083 friction stir welds produced under varying conditions. It was found that the weld properties were dominated by the thermal input rather than the mechanical deformation by the tool.     

Thermal history in UNS S32205 duplex stainless steel friction stir welds

Consolidated UNS S32205 duplex stainless steel joints welds were performed using a friction stir welding (FSW) process. An experimental set-up was used to record the thermal history of duplex stainless steel FSW joint. For points at equal distance from the weld centreline, temperature measured near the beginning of the weld was lower than that measured in the middle of the welded joint. This was attributed to a non-stationary transfer condition. FSW thermal cycle showed shorter time spent at elevated temperature compared that presented by fusion welding, indicating less propensity to detrimental second phase precipitation. To support temperature measurements with thermocouples, a three-dimensional finite element thermal model of FSW was implemented, which provided a good agreement with experimental data.     

A Fully Coupled Thermomechanical Model of Friction Stir Welding(FSW) and Numerical Studies on Process Parameters of Lightweight Aluminum Alloy Joints

This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding(FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson–Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules(i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.     

Microstructural investigation of friction stir welded 7050-T651 aluminium

The grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal. The various regions were studied in detail to better understand the microstructural evolution during friction stir welding (FSW). The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Using the combination of structural characteristics observed in each weld region, a new dynamic recrystallization model has been proposed. The precipitation phenomena in different weld regions are also discussed.     

Enhancing metallurgical and mechanical properties of friction stir lap welding of Al–Cu using intermediate layer

Abstract

In this paper, the material behaviour and mechanical characteristics of lap joint friction stir welding (FSW) between dissimilar alloys, namely, Cu and Al, is investigated. In order to produce welds of a higher quality, a layer of Cu is anodised on the aluminium alloy. The mechanical and the microstructural characterisations are performed on the welds, which are produced using various welding parameters. Scanning electron microscope with energy dispersive X-ray spectroscopy is used to identify the elemental compositions of phases that are formed. The results reveal that the use of the copper anodised layer prevented formation of brittle intermetallic compounds due to the direct FSW of 6061 aluminium alloy to copper and, as a result, enhanced the weld metallurgical and mechanical properties.     

Finite element modeling of friction stir welding—thermal and thermomechanical analysis

Friction stir welding (FSW) is a relatively new welding process that may have significant advantages compared to the fusion processes as follow: joining of conventionally non-fusion weldable alloys, reduced distortion and improved mechanical properties of weldable alloys joints due to the pure solid-state joining of metals. In this paper, a three-dimensional model based on finite element analysis is used to study the thermal history and thermomechanical process in the butt-welding of aluminum alloy 6061-T6. The model incorporates the mechanical reaction of the tool and thermomechanical process of the welded material. The heat source incorporated in the model involves the friction between the material and the probe and the shoulder. In order to provide a quantitative framework for understanding the dynamics of the FSW thermomechanical process, the thermal history and the evolution of longitudinal, lateral, and through-thickness stress in the friction stirred weld are simulated numerically. The X-ray diffraction (XRD) technique is used to measure the residual stress of the welded plate, and the measured results are used to validate the efficiency of the proposed model. The relationship between the calculated residual stresses of the weld and the process parameters such as tool traverse speed is presented. It is anticipated that the model can be extended to optimize the FSW process in order to minimize the residual stress of the weld.     

铝合金超声搅拌复合焊接

铝合金的搅拌摩擦焊（FSW）通常在焊接区形成上高下低”浅漏斗状”的温度场,使焊缝厚度方向的组织性能差异较大．为了得到更好的焊接效果,文中提出超声搅拌复合焊思想,将超声波通过搅拌头导入焊缝纵深处,以改善焊缝组织性能．试验采用2．5mm厚的2219铝合金分别用上述两种方法进行焊接,并对焊缝的微观组织和力学性能进行了分析比较...     

Developing predictive tools for friction stir weld quality assessment

Abstract

This research programme explores predictive tools that assess friction stir weld quality in aluminium alloys through dynamic characterisation. The study focuses on the correlations between dynamic interrogations measures of friction stir welded panels with the weld energy, as welded mechanical properties and the microstructure. 7136-T76 aluminium extrusions were joined at unique weld energies, and to characterise and identify the friction stir welds through non-destructive techniques, theoretical modelling and lab scale dynamic testing were conducted to establish the correlation between the weld energy and the associated spectral characteristics of the beam (natural frequencies/mode shapes). In this non-destructive evaluation study, the modal parameters were measured and were correlated with the friction stir weld microstructure and the physical parameters of the welded components, such as axial and flexural rigidities. The viability of weld parameter identification and weld quality assessment of friction stir welding beams using dynamic interrogation techniques is demonstrated.     

超声功率对2219-T351铝合金搅拌摩擦焊接头组织与性能的影响

采用搅拌摩擦焊和不同功率的超声辅助搅拌摩擦焊对2219-T351铝合金进行焊接试验，测量焊接温度和焊接压力，对焊接接头的微观组织、显微硬度和力学性能进行分析，研究了加入不同超声功率后焊缝的组织性能和材料流动性. 结果表明，超声能降低焊接温度，随着超声功率增加减小的幅度越大. 加入了超声后，焊缝微观组织更加均匀，底部材料的流动情况得到改善，焊缝区有更多的强化相残留，焊接接头的显微硬度、抗拉强度及断后伸长率在加入超声后均有提高，在加入2.25 kW的超声功率时达到最高，最高拉伸强度为331 MPa，可达到母材的80%左右.     

20mm厚2219铝合金可回抽搅拌摩擦焊接及接头组织和性能分析

为了解决封闭环缝的焊接匙孔问题,研究了采用可回抽搅拌摩擦焊接进行匙孔消除的焊接工艺. 在厚板可回抽焊接过程中,搅拌针末端的瞬时空腔问题受体积效应影响将更为显著且更难控制. 研究了不同回抽焊接长度下20 mm中厚板2219铝合金可回抽焊接接头的内部质量、组织形貌和力学性能. 结果表明,在焊接速度100 mm/min、搅拌头转速400 r/min的参数组合下,回抽焊接区长度为200 ~ 500 mm时,可获得无内部缺陷的可回抽搅拌摩擦焊焊缝;回抽焊接区接头横截面上存在2个焊核,靠近焊缝上表面的焊核大小随着回抽过程不断减小;一次焊接、重复焊接和可回抽焊接接头的拉伸性能依次降低,且可回抽焊接接头的力学性能随着回抽距离的增长而有所提升;在实际工程应用中回抽距离500 mm为较优的参数选择.     

Characteristics of Laser Beam and Friction Stir Welded AISI 409M Ferritic Stainless Steel Joints

This article presents the comparative evaluation of microstructural features and mechanical properties of friction stir welded (solid-state) and laser beam welded (high energy density fusion welding) AISI 409M grade ferritic stainless steel joints. Optical microscopy, microhardness testing, transverse tensile, and impact tests were performed. The coarse ferrite grains in the base material were changed to fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. On the other hand, columnar dendritic grain structure was observed in fusion zone of laser beam welded joints. Tensile testing indicates overmatching of the weld metal relative to the base metal irrespective of the welding processes used. The LBW joint exhibited superior impact toughness compared to the FSW joint.     

高熔点材料的搅拌摩擦焊接技术

通过焊具设计、接头微观组织与性能、焊接温度场和残余应力、热源辅助的搅拌摩擦焊(FSW)几个方面,全面介绍了高熔点材料搅拌摩擦焊技术的研究现状.结果表明,合适的搅拌头材料为钨铼(W-Re)合金和多晶立方氮化硼(PCBN);采用合适的焊具设计和工艺参数,可以得到具有良好微观组织、高强度的FSW接头;在模拟搅拌摩擦焊温度场和接头残余应力时,应依据焊接过程实际进一步完善物理模型;引入辅助热源有利于高熔点材料焊缝成形并提高焊具使用寿命.     

Two modes of metal flow phenomenon in friction stir welding process

Abstract

It has been widely recognised that the fundamental mechanism of weld formation in friction stir welding (FSW) is too complex, a phenomenon to be understood completely. In the present study two modes of metal transfer phenomenon in FSW have been discussed with the help of three FSW techniques. In the first technique a strip is welded to the plate by the process, in the second one the brass sheet is inserted perpendicular to the welding direction and in the third one the process is performed with tools having different pin lengths. The results suggest a strategy to model the process particularly for predicting welding tool performance.     

Properties and structure of friction stir welded joints in 1424 and V-1461 (Al–Li) alloys*

The effect of the friction stir welding (FSW) conditions on the structure of welded joint and mechanical properties of 1424 and V-1461 alloys is investigated. FSW is accompanied by the formation of a recrystallized fine-grain microstructure in the welded joint. It is shown that the increase of the heat input to the welded sheets does not increase the average grain size in the weld zone (the average grain size is 1.5–2.2 μm). The tensile strength of the welded joints depends on the welding conditions for both alloys. Special features of the microstructure formed in the zone of the welded joint are discussed and the effect of the microstructure on the mechanical properties of the welded joints and evolution under the effect of heat treatment after FSW are determined.     

Themo-mechanical and microstructural modeling of friction stir welding of 6111-T4 aluminum alloys

Plastic deformation and thermal history as well as microstructure evolution of friction stir welded 6111-T4 aluminum alloys were numerically simulated. Material and heat flow during friction stir welding were calculated considering the momentum balance equation and energy balance equation under the steady state condition. Based on the calculated temperature history, the coupled nucleation, growth, and coarsening of precipitates were simulated using microstructural modeling, as proposed by Myhr et al. [7,8]. Finally, the distribution of precipitates was used to calculate the mechanical properties of the weld zone, particularly the yield stress, based on the dislocation theory. The results compared well with the measurements, suggesting that the method can be applicable to predict yield stress.     

Development of Ir based tool for friction stir welding of high temperature materials

Abstract

A friction stir welding (FSW) tool with high strength and high wear resistance at elevated temperature is needed to perform FSW of high temperature materials. The purpose of this study is to develop a welding tool suited for FSW of high temperature materials. It has been clarified that Ir is little oxidised at elevated temperatures and that the addition of Re within the solubility limit to Ir increases the recrystallisation temperature, the high temperature strength and the high temperature hardness of the Ir alloy. SUS304 stainless steel was successfully friction stir welded by an Ir–10?at‐%Re welding tool without significant wear.     

工艺参数对搅拌摩擦焊洋葱圆环形成的影响

搅拌摩擦焊中焊缝材料的流动对焊件性能有很大影响，洋葱圆环是搅拌摩擦焊焊焊核区中材料流动的集中体现，文中对5mm厚的1060、3003铝合金板材进行了搅拌摩擦焊连接，通过对其焊核区腐蚀后的形貌观察分析研究了不同工艺参数下材料的流动形态，结果表明，工艺参数对搅拌摩擦焊焊核区洋葱圆环的形成有很大影响，采用较高的搅拌头转速和合适的焊接速度可获得稳定，质量良好的搅拌摩擦焊接头。