Numerical simulation of laser preheating of friction stir welding of dissimilar metals

Friction stir welding, FSW, of harder metal alloys is difficult to perform, like here dissimilar welding of titanium alloy to stainless steel in butt joint configuration. One major limitation is tool wear which can be reduced by preheating with a laser beam. A mathematical model to calculate the tool forces during FSW was developed further. The calculations show that the laser beam reduces forces at the pin and shoulder of the FSW-tool, accompanied by reduced heat generation through the tool. Within its operating limits, the process has low sensitivity on the lateral position of the leading laser beam. The model supports the understanding and optimisation of the complex interaction zone of forces and heat around the FSW-tool.     

铜合金与不锈钢搅拌摩擦焊搭接接头组织与性能

采用搅拌摩擦搭接焊对铜合金与不锈钢异种金属进行焊接,得到外观良好、无内部缺陷的搭接接头. 利用金相、扫描电镜、能谱仪、X射线衍射及硬度计等研究了铜–钢搭接焊接头显微组织,分析了接头的物相成分,测试了接头的显微硬度. 结果表明,不锈钢与铜在焊合区形成了“洋葱环”结构,此结构在焊核区的前进侧较后退侧更为均匀;在接头的前进侧、后退侧和底部有明显的热力影响区;在条状结构中形成了新的金属间化合物NiCu₄,这使焊核区不锈钢–铜界面的硬度值明显增大;接头焊核区的硬度值明显高于基体,且焊核区前进侧的硬度值较后退侧更高.     

温度峰值影响6061铝/AZ31B镁异种材料FSW接头成形的规律

以6061-T6铝合金与AZ31B镁合金为研究对象,基于Abaqus软件进行了异种材料搅拌摩擦焊过程的温度场数值模拟,重点分析搅拌针偏置镁侧下的搅拌区温度峰值影响焊缝表面成形的规律。结果表明,当焊接温度峰值高于Al-Mg共晶温度时,搅拌针根部附近区域会出现较明显的黏着现象,其随着焊接速度的降低而加剧,这与焊接温度峰值的升高相关。随着焊接速度的增加,焊缝表面更易避免裂纹缺陷的产生。当搅拌头的转速为1200r/min且焊接速度为40mm/min时,6061铝/AZ31B镁异种材料焊接接头的表面成形良好。     

Fracture toughness and fatigue crack behaviour of A3003/SUS304 lap friction stir welded joints

Friction stir welding (FSW) can weld dissimilar metal joints without a thick and brittle intermetallic compound layer at the weld interface. In this study, the dissimilar lap joint of A3003 aluminium alloy and SUS304 stainless steel was successfully welded by FSW, and the joint obtained was tested to examine the properties of fracture toughness and fatigue crack growth rate. Its fracture toughness was different by the directions of crack propagation. The fracture toughness of advancing side (AS) to retreating side (RS) was stronger than that of RS to AS, and that of cryogenic temperature was stronger than that of room temperature. Its fatigue crack growth rate also showed the same tendency as its fracture toughness. These data were compared with the past data and discussed.     

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.     

Characterization of friction stir welded joint of low nickel austenitic stainless steel and modified ferritic stainless steel

Friction stir welding (FSW) of dissimilar stainless steels, low nickel austenitic stainless steel and 409M ferritic stainless steel, is experimentally investigated. Process responses during FSW and the microstructures of the resultant dissimilar joints are evaluated. Material flow in the stir zone is investigated in detail by elemental mapping. Elemental mapping of the dissimilar joints clearly indicates that the material flow pattern during FSW depends on the process parameter combination. Dynamic recrystallization and recovery are also observed in the dissimilar joints. Among the two different stainless steels selected in the present study, the ferritic stainless steels shows more severe dynamic recrystallization, resulting in a very fine microstructure, probably due to the higher stacking fault energy.     

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.     

搅拌摩擦焊工艺参数对铸态A356铝合金抗拉强度的影响(英文)

A356是一种高强度铝硅铸造态合金,广泛用于食品、化工、船舶、电器和汽车行业。熔焊这种铸造合金时存在许多问题,如孔隙、微裂隙、热裂等。然而,用搅拌摩擦焊(FSW)来焊接这种铸造态合金可以避免上述缺陷发生。研究了搅拌摩擦焊工艺参数对铸造态A356铝合金抗拉强度的影响;对旋转速度、焊接速度和轴向力等工艺参数进行优化;从宏观和微观组织分析角度对焊接区的质量进行分析;对焊接接头的抗拉强度进行了测定,并对抗拉强度与焊缝区硬度和显微组织的相关性进行了研究。在旋转速度1000r/min、焊接速度75mm/min和轴向力5kN的条件下得到的焊接接头具有最高的抗拉强度。     

ODS钢搅拌摩擦焊接头的微观组织及其高温力学性能

采用搅拌摩擦焊(friction stir welding,FSW)技术对氧化物弥散强化(oxide dispersion strengthen,ODS)铁素体钢进行了焊接,并对焊接工艺进行了优化. 当转速为150 r/min,焊接速度为30 mm/min时可以获得无焊接缺陷的ODS钢焊接接头. 结果表明,采用FSW焊接的ODS钢接头的微观组织出现明显的洋葱环结构,搅拌区为等轴再结晶晶粒,前进侧热机影响区表现出明显的塑性流动的特征,热影响区的晶粒较母材也发生了明显改变. 接头的高温拉伸性能偏低,但经过温度1 150 ℃,时间1 h的热处理后,其高温拉伸性能得到大幅提高,与母材拉伸性能接近.     

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium–AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption, weight reduction and emission reduction. However, joining of aluminium (Al) alloys with magnesium (Mg) alloys by fusion welding process is very complicated. Friction stir welding (FSW) is a feasible method to join these two dissimilar alloys. Mixing these two metals together in stir zone (SZ) leads to poor corrosion resistance. In this investigation, an attempt has been made to understand the corrosion resistance of SZ of FSWed dissimilar joints of AA6061 Al alloy and AZ31B Mg alloy. Potentiodynamic polarization test was conducted by varying chloride ion concentration, pH value of the NaCl solution and exposure time. The corroded surfaces were analyzed using optical microscopy, scanning electron microscopy and XRD techniques. Of these three factors investigated, exposure time is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints of Al/Mg alloys.     

铝/钢搅拌摩擦焊金属间化合物调控研究进展

铝/钢异种金属的可靠连接是汽车行业实现轻质节能设计的重要途径. 铝和钢的热物理性能和化学性能差异大,采用固相焊方法连接较为适宜. 搅拌摩擦焊(friction stir welding, FSW)具有热输入低、高温停留时间短和焊接变形小等特点,在连接铝/钢异种金属上具有较大的优势和潜力. 铝/钢异种金属FSW高质量的核心技术之一为界面金属间化合物的调控. 基于铝/钢FSW固相连接机制,文中从焊接参数(焊接速度、焊具转速、偏移量、倾斜角和下压量)、焊具结构(搅拌针形貌、螺纹及锥角)和中间层(铝和锌等)设计等方面对界面金属间化合物调控的研究现状进行了综述,并围绕接头承载能力的提升总结了铝/钢FSW新技术(匙孔填充、自铆接及外源辅助FSW),并进一步展望了铝/钢FSW的发展趋势.     

我国搅拌摩擦焊技术的研究现状与热点分析

从搅拌摩擦焊材料、工艺、焊接机理、有限元数值模拟、接头耐腐蚀性等方面分析了国内对搅拌摩擦焊研究取得的成果与现状,并预测了未来几年国内搅拌摩擦焊研究的热点和重点.分析认为:铝合金仍是未来几年搅拌摩擦焊的主要研究材料,而镁合金、铜合金、不锈钢、碳钢以及异种金属的搅拌摩擦焊将也将成为研究的热点.焊接工艺、有限元数值模拟以及接...     

Microstructures and ion-irradiation behaviour of friction stir welded 12Cr-ODS steel

12Cr oxide dispersion strengthened steel was successfully joined by friction stir welding (FSW), and the joints were irradiated with 3?MeV Au ions at 500°C. The morphology of grains, dislocations, sizes and distributions of nano-sized oxide particles (NPs) in different zones of the FSW joints were analysed. It was found severe plastic deformation occurred and fine equixed grains were formed in stir zone (SZ). The NPs coarsen obviously in thermal-mechanically affected zone (TMAZ) on advancing side (AS) due to the relative movements of plastic materials with high-velocity gradient. The size distributions of the NPs in base metal (BM), heat affected zone (HAZ) and RS-TMAZ are concentrated in a smaller range than those in SZ and AS-TMAZ. Finer grains and high density of dislocations result in hardness increasing obviously in SZ. Irradiation introduced higher hardening in HAZ because of its less grain boundaries and dislocation density compared with SZ and BM.     

Interface shape and microstructure controlled dissimilar friction stir lap welded steels

Abstract

When fusion welding is conducted on the dissimilar materials between a reduced activation ferritic/martensitic steel F82H steel and an austenite stainless steel SUS 316 steel, δ ferrite is generally formed and inevitably deteriorates the weld properties. In this study, dissimilar welding of F82H to SUS 316 steel was successfully achieved by friction stir lap welding technique. It revealed that the shape and microstructure of the joint interface can be controlled by controlling the welding temperature, in another word, by changing the applied load. By controlling the welding temperature at ～710°C, a sound dissimilar joint can be obtained with a smooth joint interface and no mixed microstructure, despite the relative overlapping position of the steel plates. All the dissimilar joints showed high shear tensile strength and fracture in the base metal of F82H steel plate, which has lower strength than the SUS 316 steel plate at room temperature.     

Modelling of electrically enhanced friction stir welding process using finite element method

Abstract

Conventional friction stir welding (FSW) of high strength and high melting point materials, such as steel and titanium, has the disadvantages of a serious tool wear problem and slow welding speed. A new friction stir welding process for such materials called 'electrically enhanced friction stir welding process (EHFSW)' has been suggested and analysed using finite element modelling. The basic idea of EHFSW is that electric current passes from the welding tool into the workpiece through the contact area in the welding region. Thus it results in more localised heating while welding is in progress and is not simply a preheating process. The temperature distribution in the workpiece during the pin plunge stage and the welding stage of the EHFSW process has been determined. The results show that EHFSW can reduce the plunge force significantly with the help of localised electrical heating during the pin plunge stage, which may imply lower tool wear when compared with conventional FSW. At the same time, in the welding stage, the simulation results indicate that the welding speed of the EHFSW process can be at least two times faster than that of the conventional FSW process. Thus, finite element analysis shows that EHFSW is a promising process and could reduce tool wear while improving the welding speed, especially for high melting/O point materials.     

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).     

铸铁冷焊的氧化铁系低碳钢焊条的研制

针对采用低碳铜焊条在冷焊铸铁时极易出现白口屡、抗裂性差的问题,本文利用氧化铁皮和石墨,研制了铸铁冷焊用氧化铁系低碳钢焊条,在半熔化区和焊缝区降低了白口层和裂纹的发生.     

Friction stir welding of 304 stainless steel using Ir based alloy tool

Abstract

In order to investigate the durability of an Ir based alloy tool, friction stir welding (FSW) of 304 stainless steel plates was performed under various welding conditions, and the mechanical properties of the joints were measured. Defect free joints are possible under certain conditions, and the mechanical properties of the joints are the same as the base material. When the rotation pitch is ～0·3, the degree of wear of the Ir based alloy tool with 1·4 mm probe height, which was used for the FSW of a 304 stainless steel plate with 2 mm thickness, was less than or equal to that of the polycrystalline cubic boron nitride tool with 2 mm probe height, which was used for the FSW of a 304 stainless steel plate with 9 mm thickness. The result of the tool life test in this study showed that the Ir based alloy tool enabled the FSW of 304 stainless steel over a 75 m length.     

Optimization of microstructure at Ni-C steel joint by friction stir welding with CO2 cooling

The effect of additional cooling by splaying liquid CO₂ during friction stir welding (FSW) on the microstructure change in the stir zone of Fe – 24 wt%Ni – 0.1%C alloy steel was investigated. When the cooling rate after the stirring increased by the adoption of a faster welding speed and the use of CO₂ cooling, a larger amount of retained austenite with lath martensite was present in the stir zone. The room temperature tensile test clarified that the retained austenite contributes to the high strength without loss of elongation due to the transformation-induced plasticity (TRIP) effect.     

搅拌摩擦焊修复ZL210铸造铝合金组织与性能分析

鉴于铸件中存在不可避免的缺陷,以ZL210合金为研究对象,对搅拌摩擦焊修复技术进行试验研究,重点分析转速对修复接头微观形貌和力学性能的影响. 结果表明,当转速过低时,修复区容易出现孔洞缺陷;在合理的焊接参数组合下可得到无缺陷的焊核区,其由细小的等轴晶组成. 修复区的显微硬度呈“W”分布,热影响区的宽度随转速增加而增加. 另外,随着转速的增加,修复区的抗拉强度先增加后减小;当转速为1 500 r/min,修复区的抗拉强度和断后伸长率达到最大值,分别为318 MPa和11.8%. 断裂形貌表明修复后材料呈现典型的韧性断裂.