Numerical analysis of friction stir welding process

Friction stir welding (FSW), which has several advantages over the conventional welding processes, is a solid-state welding process where no gross melting of the material being welded takes place. Despite significant advances over the last decade, the fundamental knowledge of thermomechanical processes during FSW is still not completely understood. To gain physical insight into the FSW process and the evaluation of the critical parameters, the development of models and simulation techniques is a necessity. In this article, the available literature on modeling of FSW has been reviewed followed by details of an attempt to understand the interaction between process parameters from a simulation study, performed using commercially available nonlinear finite element (FE) code DEFORM. The distributions of temperature, residual stress, strain, and strain rates were analyzed across various regions of the weld apart from material flow as a means of evaluating process efficiency and the quality of the weld. The distribution of process parameters is of importance in the prediction of the occurrence of welding defects, and to locate areas of concern for the metallurgist. The suitability of this modeling tool to simulate the FSW process has been discussed. The lack of the detailed material constitutive information and other thermal and physical properties at conditions such as very high strain rates and elevated temperatures seems to be the limiting factor while modeling the FSW process.     

铝合金搅拌摩擦焊接参数对温度场的影响

检测搅拌摩擦焊过程中铝合金薄板上各特征点在不同焊接参数下的温度变化规律，研究搅拌摩擦焊接参数对焊接过程温度场的影响。试验结果表明，在搅拌头旋转速度一定时，各特征点的温度峰值随焊接速度的增加而降低；在焊接速度一定时，特征点的温度峰值随搅拌头旋转速度的增加而升高。     

5052与6061异种铝合金搅拌摩擦焊接头的组织和力学性能

采用搅拌摩擦焊(FSW)方法对6 mm厚的5052和6061异种铝合金进行了焊接,采用光学显微镜(OM)、扫描电镜(SEM)分析母材和焊接接头的显微组织和断口形貌,利用XRD分析了搅拌区域的物相组成,并测试了室温拉伸性能和显微硬度。结果表明,5052合金置于前进侧时更有利于材料在焊核区域的相互混合,焊接接头的最低硬度在5052合金一侧热影响区(HAZ),并在这个区域发生了断裂,断裂特征为韧性断裂。焊接接头的最大抗拉强度为225 MPa,伸长率为5.77%。     

基于网格重剖分的搅拌摩擦焊接数值模拟及搅拌头受力分析

采用自适应网格方法,建立搅拌摩擦焊接过程的完全热力耦合热刚粘塑性有限元模型,模拟搅拌摩擦焊接过程中工件的温度场、变形场和搅拌头的受力。计算结果表明,温度场关于搅拌头的分布为非对称,焊接在前行侧的有效应变高于其返回侧;沿焊缝区域的温度场、应变场分布是由工件的上表面至底面,呈自上而下的顺序递减。对搅拌头反力曲线的研究表明,在相同的转速下,焊接速度越快,其反力越大;在相同的焊接速度下,转速越大,其反力越小;搅拌头的受力峰值产生在预热阶段结束和搅拌头开始移动的时刻,在给定搅拌头倾角的情况下,搅拌头的最高温度产生在搅拌头的后侧。     

Comparison of 2A12 aluminium alloy joint by ultrasonic assisted friction stir welding and friction stir welding

Ultrasonic assisted friction stir welding （UAFSW） is a recent modification of conventional friction stir welding, which adds ultrasonic energy directly into the friction stir welding area by the pin. In this study, 2A12 aluminum alloy was welded by this process and conventional, respectively. The tensile tests, microstructure and fracture surface of FSW joint and UAFSW joint were analyzed. The research results show that the surface forming texture of ultrasonic assisted friction stir welding joint, compared with conventional, is finer and more uniform, showing metallic matte color. The grains are much finer in weld nugget zone, thermo-mechanically affected zone and heat-affected zone; S-phase particles size is much smaller and distribution is more homogeneous in the matrix. The tensile strength of UAFSW joint is 94. 13% of base metal, and the elongation is 11.77%. The tensile strength of FSW joint is 83.15% of base metal, and the elongation is 8.81%. The tests results reveal that ultrasonic vibration can improve the tensile strength and the elongation of welded joints.     

5083铝合金搅拌摩擦焊与MIG焊缝腐蚀性能对比

对5083铝合金FSW（搅拌摩擦焊）和MIG（熔化极氩弧焊）焊缝的微观显微组织和腐蚀性能进行了分析.结果表明,FSW焊缝由细小的等轴再结晶组织构成,而MIG焊缝晶粒粗大,组织不均匀.电化学腐蚀试验表明,主轴旋转频率为300 r/min,焊接速度为160 mm/min,搅拌头倾角为3°的FSW焊缝与MIG焊缝相比,腐蚀电...     

Fatigue behaviour of dissimilar friction stir welds between wrought and cast aluminium alloys

Wrought aluminium alloy, A6016-T4, was welded to cast one ADC12 by a friction stir welding technique. A6016 was set on the advancing side, while ADC12 was on the retreating side based on the pre-tensile test results. The dissimilar welds exhibited lower fatigue strengths than A6016 but higher than that of ADC12. Fatigue strengths increased when the tool was offset into ADC12, which could be explained based on the risk volume concept. When ADC12 was set on the advancing side, the fatigue strengths decreased. Microstructural observation revealed that the macroscopic structure in the stir zone drastically changed by putting ADC12 on the advancing side, and insufficient mixing of dissimilar alloys resulted in the lower fatigue strengths.     

6061-T5铝合金水平补偿搅拌摩擦焊接头力学性能研究

采用水平补偿搅拌摩擦焊技术对4 mm厚6061-T5铝合金板进行焊接,设计了水平补偿搅拌摩擦焊对接接头结构,测试焊接接头的强度、延伸率和硬度,分析接头的断裂形式。结果表明,对于4 mm厚的6061-T5铝合金,在搅拌头旋转速度为1 500 r/min、搅拌头轴肩压入量为0.2 mm、补偿凸台高为0.3 mm的条件下,焊速为400 mm/min时可获得抗拉强度为227 MPa且弯曲性能良好的接头。焊接接头断口存在明显的分层,有韧性撕裂的痕迹。接头硬度大致呈"W"型分布,后退侧的硬度高于前进侧,显微硬度的最大值出现在接头后退侧。     

6061-T6铝合金双轴肩搅拌摩擦焊接头组织与力学性能

针对6 mm厚6061-T6铝合金板材,在主轴转速800 r/min,焊接速度150 mm/min参数下实现双轴肩搅拌摩擦焊接,并对一部分试件进行焊后热处理。对焊态试件和焊后热处理试件同时进行金相试验、拉伸试验和显微硬度试验对比分析。在焊态下,接头平均抗拉强度为203 MPa,达到母材的64%,接头在焊缝区32 mm的宽度区域内显微硬度出现不同程度的下降,显微硬度分布呈"W"型;接头经焊后热处理后,焊态下溶解消失的强化相重新析出,使接头组织重新得到强化,热处理态接头平均抗拉强度为292 MPa,达到母材的92%,整个焊缝区显微硬度均得到提高,焊态下"W"型显微硬度分布规律消除。     

异种铝合金摩擦焊接移动速度和旋转速度的优化(英文)

在摩擦焊接过程中的热效应导致的高模量使铝合金容易变形、强度降低。对船用异种铝合金进行了搅拌摩擦焊接。确定5052-0和6061-T6铝合金在焊接时移动速度和旋转速度的最优条件。得到铝合金最佳焊接条件为移动速度61mm/min和旋转速度1600r/min。     

基于DFR法的2524铝合金搅拌摩擦焊疲劳可靠性分析

基于细节疲劳额定值(DFR)法,对2524-T3铝合金搅拌摩擦焊对接接头的疲劳性能进行研究,并采用光学显微镜和扫描电镜分析焊接接头组织形貌和疲劳断口。结果表明,2524-T3铝合金搅拌摩擦焊对接接头具有良好的疲劳性能,其DFR值为180.9 MPa;断口分析表明疲劳源位于焊缝根部,此处存在的弱连接缺陷对搅拌摩擦焊接头疲劳性能有重要影响。     

铝合金搅拌摩擦焊技术研究存在的问题及趋势

搅拌摩擦焊(Friction Stir Welding-FSW)是目前铝、镁、铜及有色金属等轻合金连接的最先进连接技术之一,FSW与传统熔焊相比,在工艺过程、接头性能等方面具有许多优势.在讨论FSW技术特征、工艺特点及应用研究的基础上,对目前国内外有关FSW技术的研究现状、发展趋势及存在问题进行了详细综述,所涉及的问题是在工业化铝合金结构制造领域(如飞机机身结构、高速客车及汽车车体结构等)大规模推广应用FSW技术必须解决的基础性问题;其次讨论基于FSW研究开发的新思路及新工艺,尤其是搅拌摩擦点焊技术(Friction Stir Spot Welding-FSSW)的原理、特点及在汽车车体轻量化开发中的巨大应用前景.     

Macrostructures and mechanical properties of ultrasonic-assisted friction stir welding joint of 2024-T3 aluminium alloy

In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection of friction stir welding tool and process parameters. Ultimately, such defects degrade the properties of weld and may pose serious concerns towards the integrity and safety of the weld component. In order to improve the properties of weld joints, an ultrasonic-assisted friction stir welding device has been configured where ultrasonic energy is transferred from an ultrasonic unit directly into one of the workpieces near the tool. Using this configuration, ultrasonic-assisted friction stir welding was conducted on 6 mm thick 2024-T3 aluminum alloy sheets. The macrostructure and mechanical properties of these welds were compared with the welds of this alloy prepared by conventional friction stir welding using identical process parameters. The results show that the welding speed can be increased while satisfactory weld quality is still ensured. The ultrasonic energy transferred in this configuration could enlarge the volume of weld nugget zone. Also, the influence of ultrasonic energy on the suppression or elimination of the tunnel defect is quite apparent. However, any beneficial effects of ultrasonic vibration on the tensile strength and the elongation of the joint were less obvious in this configuration.     

Investigation of weld defects in dissimilar friction stir welding of aluminium to brass by radiography

Abstract

The present study was focused on detecting weld defects in dissimilar joints made by friction stir welding. Radiography test and optical microscopy were used to evaluate the main defects. Coarse and continuous fragments of brass in aluminium matrix, tunnelling and void defects in vicinity of fragments were the main observed defects.     

Equations of heat generation during friction stir welding for tapered polygonal tools

ABSTRACT

Owing to the complex nature of heat generation in friction stir welding, equations are required to understand the effect of process parameters and tool geometry on heat generation. In this study, simplified equations for straight tool profiles have been extended to treat tapered tool profiles for triangular, square, pentagonal and hexagonal geometries. New equations have been implemented to model heat generation in a finite element software package for welding aluminium alloy. The calculated thermal profiles agree better with experimental data than those calculated using the simplified equations. It was also demonstrated that the amount of heat generation increases with increasing number of flats on the tapered tool profile, with a hexagonal tapered tool profile generating the highest temperature.     

Microstructural analysis of the stir zone of Al alloy produced by friction stir spot welding

The present study applied friction spot joining (FSJ), which was recently developed as a lap joining technique of Al alloys, to two sheets of Al alloy 6061, 1 mm in thickness, and then examined the microstructural feature in the weld. The weld had the nugget-shaped stir zone around the exit hole of the probe, and the stir zone exhibited the equiaxed grain structure having finer grain size than that of the base material. The crystallographic texture analysis using electron backscattered diffraction method suggested that the material movement occurred along the rotating direction of the welding tool in the wide region including the stir zone. In the periphery of the nugget-shaped stir zone, which was characterized as the region having the finer grain size than that of the stir zone interior, any inclusions and precipitates were not found in the SEM scale. The weld was softened around the weld centre. The softening could be explained by dissolution and/or growth of the strengthening precipitates due to thermal cycle of FSJ.     

35mm厚板铝合金搅拌摩擦焊接头组织和性能

采用搅拌摩擦焊双面焊工艺,对35 mm厚板6005A-T6铝合金型材进行了搅拌摩擦焊接,获得成形良好、表面光滑、无隧道孔和沟槽缺陷的焊接接头.应用光学显微镜、扫描电镜、显微硬度仪及电子拉伸试验机等对搅拌摩擦焊接头组织与性能进行研究.结果表明,接头焊核区组织为细小等轴晶;前进侧出现明显的螺旋纹及清晰的结合线,热力影响区晶粒被明显拉长呈条状组织,热影响区受热晶粒粗大;后退侧未见螺旋纹,晶粒比前进侧细小,过渡区较前进侧宽.在搅拌头旋转频率为650 r/min,焊接速度为200 mm/min工艺条件下接头抗拉强度为213 MPa,达到母材强度的84.8%,断裂起始于焊缝前进侧的热影响区,扩展至双面焊接重合区时,沿着焊缝后退侧热影响区直至断裂;接头显微硬度最低值出现在前进侧热影响区,最低值为50 HV.     

铝合金搅拌摩擦焊的研究现状与展望

在介绍搅拌摩擦焊技术的基本原理及影响因素的基础上,综述了铝合金搅拌摩擦焊在接头金属塑性流动、显微组织以及性能等方面的国内外研究现状.研究现状表明,搅拌头形状和工艺参数对接头组织和性能具有重要影响,在合适的工艺参数下可获得综合性能良好的铝合金搅拌摩擦焊接头,并取得了一定规模的应用.此外,指出了搅拌摩擦焊技术的不足和接头性...     

Microstructure and microhardness of aluminium alloy friction stir welds with heat treatment

In this study, the Al–Mg–Si aluminium alloy with a T6 temper is self-support friction stir welded, and the effect of post-weld heat treatment on joints is investigated by detailed microstructural investigations and microhardness measurements. The hardness decreases from average 59 to 52?HV with holding time ranging from 10 to 60 minutes at temperature 723?K. With increasing holding temperature, the microhardness becomes more uniform and increases. Microhardness profiles are explained by precipitate distributions and precipitation sequences. The fine grain structure undergoes abnormal grain growth, and the degree of which depends on holding temperature and intense plastic deformation, and the biggest size is more than 1?mm.     

6082铝合金双轴肩FSW接头组织及腐蚀性能

利用光学显微镜及动电位极化曲线技术,研究了12mm厚6082一T6铝合金双轴肩搅拌摩擦焊接头组织形貌及其电化学性能．结果表明,主轴转速600r／min,焊接速度为300mm／min,搅拌头倾角为0°的焊缝组织出现了明显的变化,焊合区组织发生了动态再结晶,形成细小的等轴晶结构;母材的腐蚀形貌比较粗糙,表面有较深的点蚀坑,而接头焊核区表面腐蚀形貌均一,点蚀现象较轻;动电位极化测试表明双轴肩搅拌摩擦焊接头焊核区的腐蚀电压比母材高,耐腐蚀性能比母材好．