Influence of FSP on the microstructure,microhardness, intergranular corrosion susceptibility and wear resistance of AA5083 alloy

This article investigates the role of friction stir processing (FSP) process parameters on the evolution of microstructure, hardness, intergranular corrosion resistance and wear resistance of aluminium alloy AA5083. The FSP trials are performed by changing the process parameters as per face-centered central composite design. The friction stir processed (FSPed) specimens subjected to intergranular corrosion test and wear test are characterized using field emission scanning electron microscope, energy dispersive x-ray spectroscopy and X-ray diffraction. Outcomes suggest that grain refinement, dispersion and partial dissolution of secondary phase has simultaneously increased the hardness, intergranular corrosion resistance and wear resistance of the FSPed specimens. The study found that tool rotation speed of 700?rpm, tool traverse speed of 60?mm?min^?1 and shoulder diameter of 15?mm results in maximum hardness, wear resistance and intergranular corrosion resistance.     

Effect of friction stir processing parameters on the microstructural and electrical properties of copper

Friction stir processing (FSP) is an innovative technology, based on friction stir welding (FSW) operative principles, which can be used for changing locally the microstructure and the mechanical properties of conventional materials. In this work, the copper alloy C12200 was friction stir processed using two distinct tools, i.e. a scrolled and a conical shoulder tool, in order to promote different thermomechanical conditions inside the stirred volume, and consequently, varied post-processed microstructures. The influence of the tool geometry and tool rotation and traverse speeds on the microstructural and electrical properties of the processed copper alloy was analysed. The processing conditions were found to have an important influence on the electrical conductivity of the processed material. The differences in electrical conductivity were explained based on dislocations density effects. The effect of the dislocations density on electrical conductivity of the processed material was found to prevail over the effect of the grain boundaries.     

搅拌摩擦点焊技术在汽车行业的应用

随着汽车行业产品的轻量化发展,镁、铝等轻质合金被大量运用,其焊接技术亦为越来越多的工业制造商所关注,搅拌摩擦点焊技术是在搅拌摩擦焊技术的基础上衍生而来的一种适用于轻金属合金连接的新型的固相点焊技术。可以代替熔焊、激光焊、电阻点焊等多种焊接方法,而成为一种新型的搅拌摩擦焊方法。本文将对搅拌摩擦点焊的产生背景、基本原理以及在汽车行业的应用进行简述。     

Influences of tool pin profile and axial force on the formation of friction stir processing zone in AA6061 aluminium alloy

AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance. Compared to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile plays a major role in deciding the weld quality. In this investigation an attempt has been made to understand the effect of axial force and tool pin profiles on FSP zone formation in AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different axial force levels. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.     

钢搅拌摩擦焊接及加工研究进展

自搅拌摩擦焊发明至今,国内外开展了大量的有关搅拌摩擦焊(Friction stir welding, FSW)技术的研究与开发工作,并且已在轻合金结构制造领域得到大量实际应用。此外,基于搅拌摩擦焊原理发展而来的另一项技术--搅拌摩擦加工也得到广泛关注,并且在金属材料组织改性及复合材料制备方面显示了独特的优势。然而,由于受到高温搅拌头材料的限制,对钢铁材料搅拌摩擦焊接及加工的研究相比铝合金要少了很多。本研究对钢铁材料搅拌摩擦焊接及加工的研究进展进行简要概述,总结同质钢铁材料搅拌摩擦焊接、异质钢铁材料搅拌摩擦焊接、钢铁材料搅拌摩擦加工以及高温焊接工具材料等几方面的研究成果,指出其中存在的重要科学及技术问题,并对钢铁材料搅拌摩擦焊接以及搅拌摩擦加工的发展趋势及值得关注的问题进行展望。     

搅拌摩擦加工制备金属基复合材料的研究现状

搅拌摩擦加工技术是源于搅拌摩擦焊接技术的一种加工技术,目前已经被用于各种复合材料制备的研究中.本文主要介绍了搅拌摩擦加工技术制备复合材料的原理,概述了目前采用搅拌摩擦加工技术制备复合材料的研究进展,简要分析了搅拌摩擦加工制备复合材料的应用前景.     

Composite fabrication using friction stir processing—a review

Composite manufacturing is one of the most imperative advances in the history of materials. Nanoparticles have been attracting increasing attention in the composite community because of their capability of improving the mechanical and physical properties of traditional fiber-reinforced composites. Friction stir processing (FSP) has successfully evolved as an alternative technique of fabricating metal matrix composites. The FSP technology has recently shown a significant presence in generation of ex situ and in situ nanocomposites. This review article essentially describes the current status of the FSP technology in the field of composite fabrication with the main impetus on aluminum and magnesium alloys.     

In situ formation of Al–Al3Ni composites on commercially pure aluminium by friction stir processing

Possibility of the formation of Al–Al₃Ni composite layers on commercial pure aluminium plates by friction stir processing (FSP) has been studied. It is believed that the hot working nature of FSP can effectively promote the exothermic reaction between Al and added Ni powder to produce Al₃Ni intermetallic compounds in the aluminium matrix. In this study, the effects of the rotational and traverse speed of the tool as well as the number of FSP passes on the in situ formation of Al₃Ni in aluminum matrix were examined. Besides, the microstructure and microhardness of the fabricated surface layers were also studied. The results showed that the ratio of tool rotational speed to traverse speed (ω/υ) is the main controlling parameter of the heat generated during FSP and hence the reaction between aluminium and nickel. Increasing the number of FSP passes also promoted the reaction between Ni and Al and improved the distribution of Al₃Ni compounds, too. The composite layer achieved by six passes of FSP showed the highest hardness, which was almost twice of that of the base metal.     

Electrical Conductivity and Friction Force Estimation in Compliant Electrical Connectors

The electrical conductivity and friction force of a compliant curved beam loaded by a rigid flat surface which simulate electrical connectors in high-tech applications is analyzed. Both the elastic deformation of the curved beam and elastic-plastic deformation of the asperities are considered. The effects of the applied load, the surface hardness and roughness as well as the beam geometry on the electrical conductivity and friction are investigated. It is found that the electrical conductivity is insensitive to changes in the beamís geometry like its angular span and slender ratio. Surface roughness and hardness affect both electrical conductivity and friction.     

Predicting the grain size and hardness of AZ91/SiC nanocomposite by artificial neural networks

In the present study, SiC nanoparticles were added to as-cast AZ91 magnesium alloy through friction stir processing (FSP) and an AZ91/SiC surface nanocomposite layer was produced. A relation between the FSP parameters and grain size and hardness of nanocomposite using artificial neural network (ANN) was established. Experimental results showed that distribution of nanoparticles in the stirred zone (SZ) was not uniform and SZ was divided into two regions. In the ANN modeling, the inputs included traverse speed, rotational speed, and region types. Outputs were hardness and grain size. The model can be used to predict hardness and grain size as functions of rotational and traverse speeds and region types. To check the adequacy of the ANN model, the linear regression analyses were carried out to compute the correlation coefficients. The calculated results were in good agreement with experimental data. Additionally, a sensitivity analysis was conducted to determine the parametric impact on the model outputs.     

Weld temperature effects during friction stir welding of dissimilar aluminum alloys 6061-t6 and 7075-t6

The objective of this work is to establish nominal friction stir [butt] welding process parameters for joining 4.76-mm-thick aluminum alloys 6061-T6 and 7075-T6 and to improve the joint quality via programmed tool offsets. In addition, dynamic tool–workpiece interface temperatures are measured during welding and used to explain the effects of alloy placement and weld tool offset from the joint. Weld tool offsets into the retreating side AA7075 increase the measured tensile strength of the dissimilar joint. The increased joint strength is facilitated by lower average weld temperatures with increasing amount of AA7075 stirred into the nugget.     

Computational investigations on reliable finite element-based thermomechanical-coupled simulations of friction stir welding

The finite element method was used in the current work to study the selection of the constitutive models, the selection of the frictional coefficients, the selection of the contact models and the selection of the physical parameters. Numerical results show that the shape of the shoulder can affect the material flows obviously and a total of about 54.3% energy can be transformed into heat in friction stir welding/friction stir processing (FSW/FSP). When the physical parameters are further considered to be functions of temperature, the predicted temperature is lower than the one in which the physical parameters are constant. When strain-hardening effect is considered, the equivalent plastic strain is decreased and the corresponding energy dissipated by plastic deformation is decreased. The effect of the frictional coefficient on the prediction of the temperature field in FSW/FSP is small when the selection of the frictional coefficient is located in a reasonable small extent. The computational costs in the simulation of FSW/FSP are not only affected by the mesh sizes and wave speed but also affected by the mesh distortions. So, mesh distortions should be considered to be minimized in the numerical modeling of FSW/FSP to reduce the computational costs.     

SIMOTION D435在搅拌摩擦焊接机中的应用

针对目前我国搅拌摩擦焊设备的自主研发水平不高,大部分只能焊接一维直线或者无法恒压力控制的问题,设计了一套既能焊接二维曲线又可恒压力控制的搅拌摩擦焊设备.通过对搅拌摩擦焊接的焊接原理和控制要素的分析,在综合比较了各种控制方案后,选用了以SIMOTION D435为核心的控制方案;在对所需功能进行分析的基础上,控制程序采用模块式的编程方法,综合运用LAD语言和MCC语言,实现了搅拌摩擦焊接时的二维轨迹插补和压力PID控制,并对压力的控制精度和进给轴的定位精度进行了实验分析.研究结果表明,该系统运行稳定,压力控制精度高,适合于铝合金、镁合金等轻合金的二维平面的搅拌摩擦焊接.     

Effect of tool pin design on the microstructural evolutions and tribological characteristics of friction stir processed structural steel

In this research, friction stir processing (FSP) technique is applied for the surface modification of ST14 structural steel. Tungsten carbide tools with cylindrical, conical, square and triangular pin designs are used for surface modification at rotational speed of 400 rpm, normal force of 5 KN and traverse speed of 100 mm min⁻¹. Mechanical and tribological properties of the processed surfaces including microhardness and wear characteristics are studied in detail. Furthermore, microstructural evolutions and worn surfaces are investigated by optical and scanning electron microscopes. Based on the achievements, all designed pins were successfully applicable for low carbon steel to produce defect-free processed material. By the microstructural changes within the stirred zone, the processed specimen is obtained higher mechanical properties. This is due to the formation of fine grains as the consequence of imposing intensive plastic deformation during FSP; however, this issue is highlighted by using square pin design. In this case, minimum grain size of 5 μm and maximum hardness of 320 VHN, as well as, maximum wear resistance are all examined for the specimen modified by square pin.     

搅拌摩擦加工原位合成Al-Ti颗粒增强铝基复合材料的微观结构

采用搅拌摩擦加工法进行了原位合成Al-Ti金属间化合物颗粒增强铝基复合材料的试验,研究了复合材料的微观组织和精细结构。结果表明,以纯Ti粉和纯铝板为原材料,采用搅拌摩擦加工的方法可以原位合成TiAl3金属间化合物颗粒增强铝基复合材料。在复合材料铝基体上,除了生成的TiAl3金属间化合物外,还存在一些纯Ti颗粒以及纯铝基体上的固溶体。经旋转摩擦挤压后,纯铝基体的晶粒得到细化,尺寸为200nm左右,生成的TiAl3晶粒尺寸约为200~300nm。     

A study on natural aging behavior and mechanical properties of friction stir-welded AA6061-T6 plates

Mechanical properties, microstructural events, residual stresses, and aging behavior of friction stir-welded AA6061-T6 were investigated in this work. Microstructural and mechanical characterizations of the friction stir-welded joints in as-welded and post-welded conditions were made by means of optical metallography, transmission electron microscopy, X-ray diffraction for determination of residual stresses, tensile testing, and hardness measurements. It was found that weld strength and hardness variations after welding are mainly dependent on the imposed heat input per unit length. Besides, the kinetics of natural aging in the welded samples was found to be noticeable within the first 14 days, and its effect decreases considerably in longer aging durations. The residual stress measurements show that subsequent natural aging leads to considerable relaxation of residual stress of about 22 MPa, while this effect is particularly significant in the stir zone and the thermomechanically affected zone.     

Exploring the hybrid metal extrusion and bonding process for butt welding of Al–Mg–Si alloys

The hybrid metal extrusion and bonding (HYB) process is a new solid-state joining technique developed for aluminum alloys. By the use of filler material addition and plastic deformation sound joints can be produced at operating temperatures below 400 °C. The HYB process has the potential to compete with commonplace welding technologies, but its comparative advantages have not yet been fully explored. Here, we present for the first time the results from an exploratory investigation of the mechanical integrity of a 4-mm AA6082-T6 HYB joint, covering both hardness, tensile and Charpy V-notch testing. The joint is found to be free from defects like pores, internal cavities and kissing bonds, yet a soft heat-affected zone (HAZ) is still present. The joint yield strength is 54% of that of the base material, while the corresponding joint efficiency is 66%. The indications are that the HYB process may compete or even outperform conventional welding techniques for aluminum in the future after it has been fully developed and optimized.     

Load bearing capacity of tool pin during friction stir welding

Although friction stir welding (FSW) is now widely used for the welding of aluminum and other soft alloys, premature tool failure limits its application to hard alloys such as steels and titanium alloys. The tool pin, the weakest component of the tool, experiences severe stresses at high temperatures due to both bending moment and torsion. It is shown that the optimum tool pin geometry can be determined from its load bearing capacity for a given set of welding variables and tool and work-piece materials. The traverse force and torque during friction stir welding are computed using a three-dimensional heat transfer and viscoplastic material flow model considering temperature and strain rate-dependent flow stress of the work-piece material. These computed values are used to determine the maximum shear stress experienced by the tool pin due to bending moment and torsion for various welding variables and tool pin dimensions. It is shown that a tool pin with smaller length and larger diameter will be able to sustain more stress than a longer pin with smaller diameter. The proposed methodology is used to explain the failure and deformation of the tool pin in independent experiments for the welding of both L80 steel and AA7075 alloy. The results demonstrate that the short tool life in a typical FSW of steels is contributed by low values of factor of safety in an environment of high temperature and severe stress.     

温度对搅拌摩擦焊接接头摩擦磨损性能的影响

通过对搅拌摩擦焊过程中铝合金板上各特征点在不同焊接参数的温度变化规律的检测,研究搅拌摩擦焊接参数对焊接过程温度场的影响,搅拌摩擦焊焊接接头的摩擦磨损行为,以及搅拌摩擦焊接头的摩擦磨损性能随温度的变化趋势。结果表明:在搅拌头旋转速度一定时,各特征点的温度峰值会随焊接速度的增加而降低,在焊接速度一定时,特征点的温度峰值会随搅拌头旋转速度的增加而升高;搅拌摩擦焊接头磨损表面呈现轻微的疲劳磨损特征,无明显的表层剥落开裂迹象;试样的磨损量与接头区域的焊缝成型有密切关系,而焊缝的成型质量与温度场的分布有密切联系,试验表明温度场梯度越小,磨损量越小。     

搅拌摩擦焊和钨极氩弧焊焊接接头的残余应力

利用X射线衍射法测量了铝合金搅拌摩擦焊和钨极氩弧焊(TIG)焊接接头表面的残余应力分布.结果表明:两种接头在焊缝区及其周围的残余应力存在着明显的变化,在平行于焊缝方向,应力呈"W"型的分布,焊缝外残余应力值迅速下降;钨极氩弧焊焊接接头残余应力的最大值位于热影响区;在热影响区,搅拌摩擦焊接接头残余应力平均值比TIG焊接接头的约低15%～25%.