Formation of interfacial microstructure in a friction stir welded lap joint between aluminium alloy and stainless steel

The interfacial microstructure produced through tool transit of a friction stir welded lap joint between an aluminium alloy and stainless steel was studied by transmission electron microscopy in order to clarify its early stages of formation. Transmission electron microscopy studies of the bottom surface of the exit hole revealed the presence of several mixed layers of an ultrafine intermetallic compound (IMC) and stainless steel. The joining between dissimilar materials was achieved through a continuous flow of the stirred aluminium alloy into the mixed layers and the resultant growth of the ultrafine IMCs due to the heat induced by the friction between the tool and the specimen. The continuous thin reaction layer finally produced at the interface was found to be stronger than the base aluminium alloy.     

Numerical and experimental investigation on friction stir lap welding of aluminium to steel

Use of multimaterial fabrication such as aluminium to steel to reduce overall vehicular body weight has gained significant attention in the automotive industries. Since fusion welding of aluminium to steel is difficult, friction stir welding of the same is considered as an effective recourse. Quantitative studies on friction stir welding of aluminium to steel are thus important but scarce in the literature. We present here a numerical and experimental study on friction stir lap welding of AA6061 to high strength interstitial free coated steel sheets under different combinations of tool rotational speed and welding speed. The computed values of thermal cycle, torque and traverse force are found to be in good agreement with the corresponding experimentally measured values. The computed thermal cycles along the AA6061 to steel interfaces are related qualitatively with the experimentally measured trend and distribution in Fe–Al intermetallics along the weld joint interface.     

异种铝合金单层板与双层板对搭接搅拌摩擦焊

将一块厚4 mm的LF5铝板与两块厚2 mm的6063铝板组成并种铝合金对搭接复合接头,进行搅拌摩擦焊工艺试验并优化焊接参数,获得优质焊缝.重点研究搅拌头转速、搅拌针偏移量对复合接头抗拉强度的影响,并对焊缝表面及横截面宏观形貌、焊缝“洋葱环”组织形貌、焊缝缺陷等进行观察.分析在搅拌针选取不同偏移量的条件下,双层板一侧的...     

Characterization of aluminum/steel lap joint by friction stir welding

The welding of a lap joint of a commercially pure aluminum plate to a low carbon steel plate (i.e., Al plate top, and steel plate bottom) was produced by friction stir welding using various rotations and traveling speeds of the tool to investigate the effects of the welding parameters on the joint strength. The joint strength depended strongly on the depth of the pin tip relative to the steel surface; when the pin depth did not reach the steel surface, the joint failed under low applied loads. Meanwhile, slight penetration of the pin tip to the steel surface significantly increased the joint strength. The joint strength tended to increase with rotationspeed and slightly decrease with the increase in the traveling speed, although the results were quite scattered. The effects of the welding parameters were discussed metallographically based on observations with optical and scanning electron microscopes.     

Friction stir welding of aluminium lap joint by tool without probe

A friction stir welding process, with a rotating tool without a probe, was employed and applied to a lap joint of aluminium plate. The thickness of the aluminium plates was 0.5 mm. New tool shapes were developed. The tops of the tool were dome shaped. In this process, the rotating tool was plunged into the aluminium plate. The tool-rotating axis was vertical to the specimen surface, and then moved in the welding direction at a speed of 20 mm/s. Tool rotation speed was 18,000 rpm.

At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. At tool plunge depth of 0.1 mm, its joint was fractured at the weld interface. At tool plunge depth of 0.2 mm or over, the joints were fractured at the stir zone of the upper plate or the heat affected zone of the lower plate. Based on observation of the hardness profiles and the thickness change of the weld area, controlling factors of the joint strength are discussed.     

Microscale evaluation of mechanical properties of friction stir welded A6061 aluminium alloy/304 stainless steel dissimilar lap joint

Abstract

Microscale evaluation of the mechanical properties of a friction stir welded A6061/SUS 304 grooved lap joint was performed using a microtensile test and transmission electron microscopy. The microtensile test revealed that ～62% of the area along which the rotating tool passed the specimen was regarded as the bonded region and that the joint was fractured at the A6061 matrix owing to the formation of very thin interfacial reaction layers. Equiaxed aluminium grains were observed at the interface of the specimen after it was fractured, indicating that the interface deformed only slightly during the microtensile test. It should be noted that although the maximum tensile strength of the joint was approximately the same as that of the base alloy, the proof stress of the joint decreased with the dissolution of the β″ phase in the A6061 aluminium alloy.     

Filling exit holes of friction stir welding lap joints using consumable pin tools

Abstract

In this study, filling friction stir welding was used to remove the exit hole of friction stir welding lap joints made from AA5456 sheets. For this purpose, the exit holes were filled by consumable pins with various geometries and different pin applying methods. Then, the structures and mechanical properties of the resulting joints were investigated. Results showed that the strength of 7% higher than the strength of the joint with the non-filled exit hole, ～91% of the corresponding defect free joints, is obtainable with this technique. The best results were found by a pin with 11° cone angle, 8?mm diameter and 7?mm length, and with a 6?mm plunge without rotation.     

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.     

Influence of aluminium alloy type on dissimilar friction stir lap welding of aluminium to copper

A heat-treatable (AA 6082) and a non-heat treatable (AA 5083) aluminium alloys were friction stir lap welded to copper using the same welding parameters. Macro and microscopic analysis of the welds enabled to detect important differences in welding results, according to the aluminium alloy type. Whereas important internal defects, resulting from ineffective materials mixing, were detected for the AA 5083/copper welds, a relatively uniform material mixing was detected in the AA 6082/copper welds. Micro-hardness testing and XRD analysis also showed important differences in microstructural evolution for both types of welds. TEM and EBSD-based study of the AA 5083/copper welds revealed the formation of submicron-sized microstructures in the stirred aluminium region, for which untypically high hardness values were registered.     

Achieving high property friction stir welded aluminium/copper lap joint at low heat input

Abstract

Aluminium and copper plates with 3 mm thickness were successfully friction stir lap welded at a lower rotation rate of 600 rev min^?1 using a larger pin 8 mm in diameter. Good metallurgical bonding on the Al/Cuinterface was achieved due to the formation of a thin, continuous and uniform Al–Cu intermetallic compound layer. Furthermore, many Cu particles consisting of pure Cu and intermetallic compound layers were generated at the lower part of the nugget zone, forming a composite structure with increased hardness. A lower rotation rate resulted in a decrease in annealing softening in the heat affected zone (HAZ), and a larger diameter pin increased the Al–Cu bonding area. These factors resulted in that the friction stir welded lap joint exhibited a high failure load of 2680 N with failure in the HAZ on the aluminium side.     

Friction stir lap joining of aluminium alloy to polypropylene sheets

Joining feasibility of aluminium alloy to polypropylene sheets via friction stir lap joining was examined. Effects of heat-input on microstructure and mechanical behaviour of the joints were investigated. A covering plate was used to confine flow of molten polymer. The results showed a distinctive interaction layer at polymer/aluminium interface, consisted mainly of C, O and Al. Shear strength of the joints decreased by enhancement of the heat-input due to increase in the thickness of the interaction layer as well as the gap width between this layer and both aluminium and polymer matrices. Maximum shear-tensile strength of 5.1?MPa (～20% of polymer shear strength) was obtained, which was higher than or comparable to that of the joints produced by other processes.     

Towards attaining dissimilar lap joint of CuCrZr alloy and 316L stainless steel using friction stir welding

CuCrZr alloy (Cu-0.8wt-%Cr-0.1wt-%Zr) and 316L stainless steel (Fe-0.03wt-%C-16wt-%Cr-10wt-%Ni) plates were successfully friction stir lap welded resulting in significant mechanical mixing of the two matrix elements, Cu and Fe, in the stir zone. The severe mixing not only led to improved load bearing response but also leads to form Cu-rich and Fe-rich regions in the weld nugget. The formation of these phases governs the failure mechanism of the joint. Tensile properties of the weld showed promising response when compared with joints made for the similar alloy pair by other welding techniques. This suggests strong feasibility of applying FSW for joining Cu and steel for nuclear applications.     

Friction stir welding of duplex stainless steels

Duplex stainless steels are successful in a variety of applications such as the food industry, petrochemicals and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may change during fusion welding steps, and it can compromise the performance of these materials. Friction stir welding is a solid-state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. Superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat-affected zone. Consolidated friction stir welded joints with full penetration 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints, showing increased yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding grain refinement was observed in the welded joint, achieving grain sizes as small as 1 μm. This refinement was associated with the combination of microstructural restoration mechanisms in the dual-phase microstructure promoted by severe deformation associated with a high temperature during the welding process.     

Influence of zinc on intermetallic compounds formed in friction stir welding of AA5754 aluminium alloy to galvanised ultra-high strength steel

In this study, lap joints between AA5754 and DP1000 ultra-high strength steels were produced by friction stir welding. In order to investigate the roles of zinc on intermetallic phase formation and joint properties, steel substrates were used, two being galvanised coated and one uncoated. Joint performance has been evaluated in term of maximum tensile shear loading. The effects of the process parameter, translational speed; chemical compositions; and intermetallic phase formation on the mechanical properties have been investigated. The results show that joints with a galvanised layer exhibit higher strength as compared to the non-coated steel. A thicker galvanised layer promotes the presence of zinc in the aluminium matrix, resulting in better joint properties. The level of zinc contents in the aluminium matrix depends on process temperature and material circulation characteristics. Two stable Al-rich intermetallic phases, Al₅Fe₂ and Al₁₃Fe₄, were detected at the interface regardless of the coating conditions.     

Evaluation of heat input during friction stir welding of aluminium alloys

Heat input is one of the key parameters governing the quality and service properties of friction stir welds. By using a calorimetric technique, the heat inputs generated during the friction stir welding of the aluminium alloys, 1100 and 5083, were measured over a wide range of welding parameters. An empirical equation to estimate the heat input using the welding parameters was established based on a multiple regression analysis of the results. The effect of the heat input on the final grain size of the stir zone was also investigated by the electron backscatter diffraction method. The quantitative relationships between the input variables, heat inputs, and final grain sizes in the stir zone were derived.     

Process and joint quality of ultrasonic vibration enhanced friction stir lap welding

In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects.     

Effect of pin rotating speed on lap shear strength of stationary shoulder friction stir lap welded 6005A-T6 aluminum alloy

Stationary shoulder friction stir lap welding (SSFSLW) was successfully used to weld 6005A-T6 aluminum alloy in this paper.Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed.Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder.Cross section of the SSFSLW joint presents a basin-like morphology and little material loss.By increasing the rotating speed from 1 000 rpm to 1 600 rpm,both effective sheet thickness and lap width increase,while lap shear failure load firstly decreases and then increases.The maximum failure load of 14.05 kN is attained when 1 000 rpm is used.All SSFSLW joints present shear fracture mode.     

Orbital friction stir lap welding in tubular parts of aluminium alloy AA5083

In this study, orbital friction stir lap welding of 360?mm diameter AA5083-H321 tube to 350?mm diameter AA5083-O flange was investigated. The influence of rotational and travel speed of tool with triangular frustum pin on the metallurgical structure and mechanical properties of orbital friction stir lap welded samples were studied. The results indicated that defect free orbital lap joints are successfully obtained using tool rotational speed of 650 and 800?rev?min^?1 with a constant travel speed of 40?mm?min^?1. The strengthening mechanism in the stir zone is solid solution strengthening and dislocation looping. The maximum joint strength was achieved at a welding speed of 650?rev?min^?1 and 40?mm?min^?1. Failure of tensile shear test samples occurred far from the friction stir welding zone.     

搅拌摩擦焊搭接接头的研究现状与展望

搅拌摩擦焊由于其固相连接的特点,在进行铝合金的搭接焊接时,原始搭接界面会随着金属流动而形成迁移界面,从而对焊缝性能造成影响。在此通过对现有文献中搅拌摩擦焊搭接接头的研究内容进行分析,对搅拌摩擦焊搭接接头性能的影响因素及其影响原因进行了综述,并在此基础上展望了搅拌摩擦焊搭接焊的研究方向。