Establishing relationships between mechanical properties of aluminium alloys and optimised friction stir welding process parameters

Friction stir welding (FSW) is a solid state welding process for joining aluminium alloys and is employed in aerospace, rail, automotive and marine industries. In FSW, the base metal properties such as yield strength, hardness and ductility control the plastic flow of the material under the action of a rotating non-consumable tool. The FSW process parameters such as, the tool rotational speed, the welding speed and the axial force play a major role in deciding the weld quality. In this investigation, FSW joints were made using six different grades of aluminium alloys (AA1100, AA2219, AA2024, AA6061, AA7039, and AA7075) using different levels of process parameters. Macrostructural analysis was carried out to identify the feasible working range of process parameters. The optimal welding conditions to attain maximum strength for each alloy were identified using Response Surface Methodology (RSM). Empirical relationships were established between the base metal mechanical properties of aluminium alloys and optimised FSW process parameters. These relationships can be effectively used to predict the optimised FSW process parameters from the known base metal properties (yield strength, elongation and hardness).     

Establishing relationship between the base metal properties and friction stir welding process parameters of cast aluminium alloys

In friction stir welding (FSW), the material under the rotating action of non-consumable tool has to be stirred properly to get defect free welds in turn it will improve the strength of the welded joints. The welding conditions and parameters are differing based on the mechanical properties of base materials such as tensile strength, ductility and hardness which control the plastic deformation during friction stir welding. The FSW process parameters such as tool rotation speed, welding speed and axial force, etc. play a major role in deciding the weld quality. FSW Joints of cast aluminium alloys A319, A356, and A413 were made by varying the FSW process parameters and the optimum values were obtained. In this investigation, empirical relationships are established and they can be effectively used to predict the optimum FSW process parameters to fabricate defect free joints with high tensile strength from the known base metal properties of cast aluminium alloys.     

Effect of Tool Pin Profile and Tool Rotational Speed on Mechanical Properties of Friction Stir Welded 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 many of 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 nonconsumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force, etc., and tool pin profile play a major role in deciding the joint properties. In this investigation, an attempt has been made to study the effect of rotational speed and tool pin profile on mechanical properties of 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 five different tool rotational speeds (800-1600 RPM). Tensile properties, microhardness, and microstructure of the joints have been evaluated. From this investigation it is found that the joints fabricated using square pin profiled tool with a tool rotational speed of 1200 RPM exhibited superior mechanical properties compared to other joints.     

Tensile behavior of dissimilar friction stir welded joints of aluminium alloys

The heat treatable aluminium alloy AA2024 is used extensively in the aircraft industry because of its high strength to weight ratio and good ductility. The non-heat treatable aluminium alloy AA5083 possesses medium strength and high ductility and used typically in structural applications, marine, and automotive industries. When compared to fusion welding processes, friction stir welding (FSW) process is an emerging solid state joining process which is best suitable for joining these alloys. The friction stir welding parameters such as tool pin profile, tool rotational speed, welding speed, and tool axial force influence the mechanical properties of the FS welded joints significantly. Dissimilar FS welded joints are fabricated using five different tool pin profiles. Central composite design with four parameters, five levels, and 31 runs is used to conduct the experiments and response surface method (RSM) is employed to develop the model. Mathematical regression models are developed to predict the ultimate tensile strength (UTS) and tensile elongation (TE) of the dissimilar friction stir welded joints of aluminium alloys 2024-T6 and 5083-H321, and they are validated. The effects of the above process parameters and tool pin profile on tensile strength and tensile elongation of dissimilar friction stir welded joints are analysed in detail. Joints fabricated using Tapered Hexagon tool pin profile have the highest tensile strength and tensile elongation, whereas the Straight Cylinder tool pin profile have the lowest tensile strength and tensile elongation. The results are useful to have a better understanding of the effects of process parameters, to fabricate the joints with desired tensile properties, and to automate the FS welding process.     

Mechanical and fracture properties of aluminium cylinders manufactured by orbital friction stir welding

Butt welding of AA6063 aluminium cylindrical shells was performed using the orbital friction stir welding (FSW) method. Tool rotation speed and orbital speed (i.e., traverse speed of rotating cylinder during welding) were considered as variable, and the strength and the mechanical properties including tensile strength, microhardness, mode I fracture energy and mode I crack growth behaviour of manufactured cylinders were investigated experimentally. A novel and subsized test specimen was designed and manufactured for fracture testing of specimens extracted from both base metal and weld zone region of cylinders. The initial precrack was introduced along (i) the tool penetration through the pipe thickness (i.e., T‐direction) and (ii) along the tool travelling direction (i.e., L‐direction). It was found that the crack growth resistance and fracture energy values of FSW samples are greater than the corresponding values of base aluminium material along both “L”‐ and “T”‐directions. Also, the fracture resistance value in T‐direction was higher than the L‐direction for the whole tested FSW samples with different welding speeds.     

TEM study of the FSW nugget in AA2195-T81

During friction stir welding (FSW) the material being joined is subjected to a thermal-mechanical process in which the temperature, strain and strain rates are not completely understood. To produce a defect free weld, process parameters for the weld and tool pin design must be chosen carefully. The ability to select the weld parameters based on the thermal processing requirements of the material, would allow optimization of mechanical properties in the weld region. In this study, an attempt is made to correlate the microstructure with the variation in thermal history the material experiences during the FSW process.     

Microstructure and mechanical properties of friction stir welded copper

The main objective of this investigation was to apply friction stir welding technique (FSW) for joining of 2 mm thick copper sheet. The defect free weld was obtained at a tool rotational and travel speed of 1,000 rpm and 30 mm/min, respectively. Mechanical and microstructural analysis has been performed to evaluate the characteristics of friction stir welded copper. The microstructure of the weld nugget (WN) consists of fine equiaxed grains. Similarly, the elongated grains in the thermomechanically affected zone (TMAZ) and coarse grains in the heat-affected zone (HAZ) were observed. The hardness values in the WN were higher than the base material. Eventually HAZ shows lowest hardness values because of few coarse grains presence. Friction stir welded copper joints passes 85% weld efficiency as compared to the parent metal.     

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding(FSW)process parameters on tensile strength of cast LM6 aluminium alloy.Joints were made by using dierent combinations of tool rotation speed,welding speed and axial force each at four levels.The quality of weld zone was investigated using macrostructure and microstructure analysis.Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure.The joint fabricated using a rotational speed of 900 r/min,a weldin...     

Joint properties of friction stir welded AZ31B– H24 magnesium alloy

Abstract

The weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed. Sound welding conditions depended mainly on sufficient heat input during the welding process. Insufficient heat input, which was generated in the case of higher travel speed and lower rotation speed, caused an inner void or lack of bonding in the stir zone. The microstructure of the weld zone was composed of five regions: base metal, heat affected zone, thermomechanically affected zone, stir zone I and stir zone II. Unlike the general feature of friction stir welded aluminium alloys, the grain size of the weld zone was larger than that of the base metal. Stir zones I and II were characterised by partial dynamic recrystallisation and full dynamic recrystallisation, respectively. The hardness of the weld zone was lower than that of the base metal owing to grain growth. A wider range of defect free welding conditions was acquired at higher tool rotation speed and lower welding speed. The maximum tensile strengh was 240 MPa, which was ~85% of the base metal value of 293 MPa. The fracture location was close to the stir zone.     

Process optimization in the self-reacting friction stir welding of aluminum 6061-T6

Self-reacting friction stir welding (SR-FSW), also called bobbin-tool friction stir welding (BT-FSW), is a solid state welding process similar to friction stir welding (FSW) except that the tool has two opposing shoulders instead of the shoulder and a backing plate found in FSW. The tool configuration results in greater heat input and a symmetrical weld macrostructure. A significant amount of information has been published in the literature concerning traditional FSW while little has been published about SR-FSW. An optimization experiment was performed using a factorial design to evaluate the effect of process parameters on the weld temperature, surface and internal quality, and mechanical properties of self-reacting friction stir welded aluminum alloy 6061-T6 butt joints. The parameters evaluated were tool rotational speed, traverse speed, and tool plunge force. A correlation between weld temperature, defect formation (specifically galling and void formation), and mechanical properties was found. Optimum parameters were determined for the welding of 8-mm-thick 6061-T6 plate.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of AA7039 aluminum alloy

A high strength Al–Zn–Mg alloy AA7039 was friction stir welded by varying welding and rotary speed of the tool in order to investigate the effect of varying welding parameters on microstructure and mechanical properties. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld, hence on temperature profile which in turn governs the microstructure and mechanical properties of welded joints. There exits an optimum combination of welding and rotary speed to produce a sound and defect free joint with microstructure that yields maximum mechanical properties. The mechanical properties increase with decreasing welding speed/ increasing rotary speed i.e. with increasing heat input per unit length of welded joint. The high heat input joints fractured from heat affected zone (HAZ) adjacent to thermo-mechanically affected zone (TMAZ) on advancing side while low heat input joints fractured from weld nugget along zigzag line on advancing side.     

Influence of a non-rotating shoulder on heat generation,microstructure and mechanical properties of dissimilar AA2024/AA7050 FSW joints

Friction stir welding (FSW) and stationary shoulder friction stir welding (SSFSW) were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A comparison between the two processes was performed by varying the welding speed while keeping the rotational speed constant. Through the analysis of the force and torque produced during welding and a simple analytical model, it was possible to show that in SSFSW there is more effective coupling with the tool and the heat produced is more efficiently distributed. This process decreases both the welding area and the diffusion at the interface of the two alloys compared with FSW. The minimum microhardness occurred at the advancing side (AS) at the interface between the thermo-mechanically affected zone (TMAZ) and the stir zone (SZ) in both processes, although the decrease was more gradual in SSFSW. This interface is also where all specimens failed for both welding technologies. An increase in tensile strength was measured in SSFSW compared with standard FSW. Furthermore, it was possible to establish the mechanical performance of the material in the fracture zone using digital image correlation.     

Friction stir welding for the transportation industries

This paper will focus on the relatively new joining technology—friction stir welding (FSW). Like all friction welding variants, the FSW process is carried out in the solid-phase. Generically solid-phase welding is one of the oldest forms of metallurgical joining processes known to man. Friction stir welding is a continuous hot shear autogenous process involving a non-consumable rotating probe of harder material than the substrate itself. In addition, FSW produces solid-phase, low distortion, good appearance welds at relatively low cost. Essentially, a portion of a specially shaped rotating tool is plunged between the abutting faces of the joint. Once entered into the weld, relative motion between the rotating tool and the substrate generates frictional heat that creates a plasticised region around the immersed portion of the tool. The contacting surface of the shouldered region of the tool and the workpiece top contacting surface also generates frictional heat. The shouldered region provides additional friction treatment to the weld region as well as preventing plasticised material being expelled. The tool is then translated with respect to the workpiece along the joint line, with the plasticised material coalescing behind the tool to form a solid-phase joint as the tool moves forward. Although the workpiece does heat up during FSW, the temperature does not reach the melting point. Friction stir welding can be used to join most aluminium alloys, and surface oxide presents no difficulty to the process. Trials undertaken up to the present time show that a number of light weight materials suitable for the automotive, rail, marine, and aerospace transportation industries can be fabricated by FSW.     

Dissimilar friction stir lap welding of AA 5754-H22/AA 6082-T6 aluminium alloys: Influence of material properties and tool geometry on weld strength

Dissimilar friction stir welding (FSW) of heat (AA 6082-T6) and non-heat (AA 5754-H22) treatable aluminium alloys, in lap joint configuration, was performed in this work. The base material plates were 1 mm thick. Welds were performed combining different plates positioning, relative to the tool shoulder, in order to assess the influence of base materials properties on welds strength. Three different tools were tested, one cylindrical and two conical, with different taper angles. Welds strength was characterized by performing transverse and tensile–shear tests. Strain data acquisition by Digital Image Correlation (DIC) was used to determine local weld properties. The results obtained enabled to conclude that the dissimilar welds strength is strongly dependent on the presence of the well-known hooking defect and that the hooking characteristics are strongly conditioned by base materials properties/positioning. By placing the AA 6082-T6 alloy, as top plate, in contact with the tool shoulder, superior weld properties are achieved independently of the tool geometry. It is also concluded that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the most suitable solution for the production of welds with similar strengths for advancing and retreating sides.     

A356Al/TiB2颗粒增强铝基复合材料的搅拌摩擦焊

采用纯机械化的固相连接技术--搅拌摩擦焊成功地焊接了应用原位反应合成法制造的铸态A356Al/6.5%TiB2(体积分数)颗粒增强铝基复合材料,与铝合金相比,铝基复合材料搅拌摩擦焊的焊缝质量对焊接参数更为敏感.该连接方法在较低温度下实现铝基复合材料的焊接,避免了基体铝合金与增强相之间的化学反应,同时在搅拌头机械搅拌、挤压和摩擦热的共同作用下,焊缝区基体材料的晶粒和增强相被破碎并形成再结晶晶核,细化了组织结构,增强相分布也更加弥散.焊缝区的硬度值波动范围很小,抗拉强度比母材增加约20%.研究表明,搅拌摩擦焊用于连接颗粒增强铝基复合材料具有明显的优势.     

Optimization of friction stir welding process parameters to maximize tensile strength of stir cast AA6061-T6/AlNp composite

Aluminium Matrix Composites (AMCs) reinforced with particulate form of reinforcement has replaced monolithic alloys in many engineering industries due to its superior mechanical properties and tailorable thermal and electrical properties. As aluminium nitride (AlN) has high specific strength, high thermal conductivity, high electrical resistivity, low dielectric constant, low coefficient of thermal expansion and good compatibility with aluminium alloy, Al/AlN composite is extensively used in electronic packaging industries. Joining of AMCs is unavoidable in many engineering applications. Friction Stir Welding (FSW) is one of the most suitable welding process to weld the AMCs reinforced with particulate form of ceramics without deteriorating its superior mechanical properties. An attempt has been made to develop regression models to predict the Ultimate Tensile Strength (UTS) and Percent Elongation (PE) of the friction stir welded AA6061 matrix composite reinforced with aluminium nitride particles (AlN_p) by correlating the significant parameters such as tool rotational speed, welding speed, axial force and percentage of AlN_p reinforcement in the AA6061 matrix. Statistical software SYSTAT 12 and statistical tools such as analysis of variance (ANOVA) and student’s t test, have been used to validate the developed models. It was observed from the investigation that these factors independently influenced the UTS and PE of the friction stir welded composite joints. The developed regression models were optimized to maximize UTS of friction stir welded AA6061/AlN_p composite joints.     

Joining of metal matrix composites using friction stir welding: a review

The application of fusion welding process is restricted to certain grades of alloys and materials. Solid-state joining process offers greater advantages over fusion welding process such as fumeless and effective joining, minimum or no preparation time, environment friendly, etc. One such solid-state joining process is friction stir welding (FSW), which uses a non-consumable rotating tool. This rotating tool joins the two faying surfaces of the workpiece by forging them. This joining technique successfully joins metals, alloys and metal matrix composite (MMC), which are considered as difficult to join using conventional processes. The present study is an endeavor to review a specific domain of FSW, i.e. joining of MMCs. The initial part of the study provides a detailed introduction about the FSW process, and along with it, an overview of the published literature related to FSW of alloys has been presented. The later part of the study pays specific attention to macrostructure, microstructure, joint properties and residual stresses in welded joints along with wearing of tool during welding of MMC. The observations of this study provide a basis for future research in the specified domain.     

Friction stir welding of dissimilar aluminum alloys AA2219 to AA5083 – Optimization of process parameters using Taguchi technique

The joining of dissimilar Al–Cu alloy AA2219-T87 and Al–Mg alloy AA5083-H321 plates was carried out using friction stir welding (FSW) technique and the process parameters were optimized using Taguchi L₁₆ orthogonal design of experiments. The rotational speed, transverse speed, tool geometry and ratio between tool shoulder diameter and pin diameter were the parameters taken into consideration. The optimum process parameters were determined with reference to tensile strength of the joint. The predicted optimal value of tensile strength was confirmed by conducting the confirmation run using optimum parameters. This study shows that defect free, high efficiency welded joints can be produced using a wide range of process parameters and recommends parameters for producing best joint tensile properties. Analysis of variance showed that the ratio between tool shoulder diameter and pin diameter is the most dominant factor in deciding the joint soundness while pin geometry and welding speed also played significant roles. Microstructural studies revealed that the material placed on the advancing side dominates the nugget region. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy of 5083 side, where tensile failures were observed to take place.     

Recent advances in friction-stir welding - Process, weldment structure and properties

Friction-stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, the reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.     

Predicting tensile strength,hardness and corrosion rate of friction stir welded AA6061-T6 aluminium alloy joints

AA6061-T₆ aluminium alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio and good corrosion resistance. The friction stir welding (FSW) process and tool parameters play major role in deciding the joint characteristics. In this research, the tensile strength and hardness along with the corrosion rate of friction-stir-butt welded joints of AA6061-T₆ aluminium alloy were investigated. The relationships between the FSW parameters (rotational speed, welding speed, axial force, shoulder diameter, pin diameter and tool hardness) and the responses (tensile strength, hardness and corrosion rate) were established. The optimal welding conditions to maximize the tensile strength and minimize the corrosion rate were identified and reported here.