Mechanical properties and microstructure analysis of refilling friction stir welding on 2219 aluminum alloy

The 2219 aluminum alloy under refilling friction stir welding (RF-FSW) was investigated. The micrographs showed that the bead could be divided into six zones, and the grain size and shape were greatly different in these zones. According to the microstructure analysis, the weld nugget zone and the shoulder stirring zone consisted of equiaxed grains, while the grains in the heat affected zone were seriously coarsened. It was obvious that bending deformation occurred in the thermo-mechanically affected zone. According to the microhardness analysis, the lowest hardness of the weld was at the thermo-mechanically affected zone, and the microhardness increased with the retraction of the stir-pin. The tensile strength and elongation of the bead were 70% and 80% of the base metal, respectively. The tensile strength was slightly different for the stable stage and the retraction stage, while the elongation decreased in the retraction stage. The mechanical properties and microstructure responded to different retraction speed were analyzed, and it showed that the elongation decreased with increasing retraction speed.     

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.     

Shear layer modelling for bobbin tool friction stir welding

Abstract

This study presents an approach to model the shear layer in bobbin tool friction stir welding. The proposed CFD model treats the material in the weld zone as a highly viscous non-Newtonian shear thinning liquid. A customised parametric solver is used to solve the highly non-linear Navier–Stokes equations. The contact state between tool and workpiece is determined by coupling the torque within the CFD model to a thermal pseudomechanical model. An existing analytic shear layer model is calibrated using artificial neural networks trained with the predictions of the CFD model. Validation experiments have been carried out using 4 mm thick sheets of AA 2024. The results show that the predicted torque and the shear layer shape are accurate. The combination of numerical and analytical modelling can reduce the computational effort significantly. It allows use of the calibrated analytic model inside an iterative process optimisation procedure.     

Automatic gap detection in friction stir butt welding operations

Friction stir welding (FSW) is a new solid-state welding technology that has been used successfully in many joining applications. A common problem that arises when welding two sheets is the presence of a gap between the sheets. Gaps may be due to improper fixturing, imprecision in the processes used to manufacture the sheets, etc. When the FSW tool encounters a gap, material can possibly escape from the processing zone and the welded part's effective cross-sectional area around the gap will decrease. Both of these effects can possibly cause an unsuitable weld. This paper develops a monitoring algorithm to detect gaps in friction stir butt welding operations in real time (i.e., during the operation). Experimental studies are conducted to determine how the process parameters (e.g., tool rotation rate and tool traverse speed) and the gap width affect the welding process; particularly, the plunge force (i.e., the force acting vertically down on the part). The proposed monitoring algorithm examines the filtered plunge force in the frequency domain to determine the presence of a gap. Several experimental studies are conducted for 2024 aluminum with a variety of process parameters and the monitoring algorithm is shown to be able to reliably detect the presence of gaps in friction stir butt welding operations for tool traverse speeds below 4.233 mm/s and gap sizes above 0.3048 mm.     

Wavelet transform analysis of acoustic emission in monitoring friction stir welding of 6061 aluminum

In this paper, acoustic emission (AE) signals are detected and preliminarily analyzed in order to investigate the possibility of applying the AE technique for the in-process monitoring of an entire friction-stir-welding (FSW) process. Experimental tests are carried out using a high-speed rotating tool traversing on two, butted 6061 aluminum alloy plates with three equally spaced gaps made of two notches aligned along the butting joint of the parts. The wavelet transform (WT) is used to decompose the AE signal into various discrete series of sequences over different frequency bands. There are significant sudden changes in the band energy at the moment when the probe penetrates into and pulls out of the weld joint, as well as when the shoulder makes contact with or detaches from the plates. The band energy variation during the traversing of the tool over the defected region reflects the existence, location, and size of the weld defects. A three-dimensional representation of band energy vs time and scale gives valuable information on the potential weld defects during friction stir welding. Coupled with a contour mapping, the representation can be effectively utilized for monitoring the transient welding state and quickly identifying gap defects.     

汽车制造驶上搅拌摩擦焊之路

新世纪汽车制造轻量化的发展趋势使铝合金、镁合金等轻质合金材料所占的比重越来越大，从而促进了新型搅拌摩擦焊技术在汽车制造中的应用。在简要介绍搅拌摩擦焊技术的基础上，重点一对搅拌摩擦焊技术在汽车稠造业中的应用进行了探讨和综述，并对国内外的搅拌摩擦焊工艺装备进行了简单介绍。     

Temperature and force response characteristics of friction stir welding on Invar 36 alloy

Abstract

The temperature and force response during friction stir welding of Invar 36 alloy were investigated by experimental measurement and numerical simulation. The effect of welding parameters was studied. The temperature and force characteristics were roughly discussed. It is indicated that an elevation rotational speed results in increasing temperature and decreasing axial force, whereas rotational speed has no obvious influence on the longitudinal force. An elevation travelling speed produces increasing axial force and longitudinal force, and a decreased trend of temperature out of stir zone centre. Friction stir welding of Invar 36 alloy produced relatively high peak temperatures, high axial and longitudinal forces, and a narrow temperature distribution compared with those of the other reported high melting temperature materials.     

Development of ceramic backing for friction stir welding and processing

Usually, a workpiece is deformed during friction stir welding due to high applied loads. Consequently, fully and consolidated friction stir-welded joints as well as tool life time can be affected promoting unscheduled manufacturing stops, which favour decreasing the welding productivity. Furthermore, the workforce is dislocated to not predicted maintenance steps. This work proposes the development of a special ceramic backing to joining and processing material using FSW technologies. Four ceramic deposits were tested over a steel plate, which allowed selecting those with less porosity and, thus, better strength. This backing allowed us to obtain full penetration welds for duplex stainless steels, to high forces during engagement for high-strength low-alloy steels and to obtain consolidated aluminium–steel dissimilar joints. For the last one, there was not adherence of the soft material in the workpiece. In addition, the ceramic backing allowed us to confine the heat and plasticized metal, as well as develop established welding parameters.     

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.     

CDRX modelling in friction stir welding of aluminium alloys

In the paper a numerical model aimed to the determination of the average grain size due to continuous dynamic recrystallization phenomena (CDRX) in friction stir welding processes of AA6082 T6 aluminum alloys is presented. In particular, the utilized model takes into account the local effects of strain, strain rate and temperature; an inverse identification approach, based on a linear regression procedure, is utilized in order to develop the proper material characterization.     

Experimental verification of heat input during friction stir welding of Al alloy 5083

Heat input during welding is a basic index for weld quality and service properties associated with the resulting microstructure. In this study, the heat inputs during friction stir welding of Al alloy 5083 at various welding parameters were measured by calorimetry. Multiple regression analysis of the data was conducted to determine an empirical equation to estimate the heat input with the input variables. The effect of the heat input on the grain size of the stir zone was also examined, and a good correlation between the grain size and heat input was obtained. This study obtained a systematic relationship between the input variables, heat input and grain size of the stir zone through experimental measurements.     

High strength lap joint of aluminium and stainless steels fabricated by friction stir welding with cutting pin

Abstract

Dissimilar lap joints of aluminium and stainless steel were first friction stir welded by the tool with a cutting pin. The results showed that sound joints could be obtained by this method. When the pin was inserted into the lower steel sheet, macrointerlocks were formed by the steel flashes plugging into the upper aluminium at both sides of the nugget bottom. At the aluminium/steel interface, a thin intermetallic compound (IMC) layer and the mechanical bonding of microinterlocks were formed. In addition, the aluminium near the interface was also strengthened by grain refinement and IMC particles. Therefore, the beneficial effect of the macrointerlocks provided by the steel flashes was removed, the shear strength of the joint reached 89·7 MPa, which was even higher than that of the base metal of aluminium.     

A simple Eulerian thermomechanical modeling of friction stir welding

A simple three-dimensional thermomechanical model for friction stir welding (FSW) is presented. It is developed from the model proposed by Heurtier et al. (2006) based on a combination of fluid mechanics numerical and analytical velocity fields. Those velocity fields are introduced in a steady state thermal calculation to compute the temperature field during welding. They allow partial sliding between the shoulder and the workpiece, the amount of which is provided as an additional result of the model. The thermal calculation accounts for conduction and convection effects by means of the particular derivative. The complete thermomechanical history of the material during the process can then be accessed by temperature and strain rate contours.The numerical results are compared with a set of experimental test cases carried out on an instrumented laboratory device. The choices for modeling assumptions, especially tribological aspects, are discussed according to agreements or deviations observed between experimental and numerical results. The amount of sliding appears to be significantly influenced by the welding conditions (welding and tool rotational velocities), and physical interpretations are proposed for its evolution.     

Determination of the traverse force in friction stir welding with different tool pin profiles

ABSTRACT

A methodology is developed for the estimation of the traverse force in friction stir welding (FSW) for various pin profiles by combining the results of numerical modelling and experimental monitoring. The effect of pin profiles on the traverse force is evaluated by introducing a modified ratio of the plastic deformation zone, which is obtained by numerical modelling. The formula is validated with the experimental data in the literature and indicates that the traverse force decreases exponentially with increasing ratio of the plastic deformation zone. The proposed methodology provides a concise approach for the estimation of the traverse force for various pin profiles in FSW and can be adopted for the design and assessment of the FSW tool.     

Development of small sized friction stir welding equipment for hand operated welding

Abstract

Friction stir welding (FSW) is widely used in various industrial fields. However, high tiffness is required for FSW equipment which has to withstand high applied load and tool torque and therefore, the equipment becomes large sized. It is difficult to employ FSW for site welding such as repair welding and/or manual welding. The authors made a prototype of FSW apparatus equipped with a counterbalanced tool and a local heating device. The relationship between the applied load and welding parameters was investigated and it was found that the force in the welding direction, Fx is reduced to 70 N or less and that in the transverse direction Fy is to 50 N or less. The combined use of the prototype equipment with a counterbalanced tool and the local heating is very effective to downsize FSW equipment.     

The effect of welding parameters on the corrosion behaviour of friction stir welded AA2024-T351

The effect of welding parameters (rotation speed and travel speed) on the corrosion behaviour of friction stir welds in the high strength aluminium alloy AA2024-T351 was investigated. It was found that rotation speed plays a major role in controlling the location of corrosion attack. Localised intergranular attack was observed in the nugget region for low rotation speed welds, whereas for higher rotation speed welds, attack occurred predominantly in the heat-affected zone. The increase in anodic reactivity in the weld zone was due to the sensitisation of the grain boundaries leading to intergranular attack. Enhancement of cathodic reactivity was also found in the nugget as a result of the precipitation of S-phase. The results were compared with samples of AA2024-T351 that had been heat treated to simulate the thermal cycle associated with welding, and with samples that had been exposed to high temperatures for extended periods to cause significant over-ageing.     

Study of hybrid welding repair process of friction stir welding grove defect

Abstract

Gas tungsten arc welding (GTAW) repair process and GTAW+FSW (friction stir welding) hybrid repair process are studied to remove the large size groove defect formed during FSW. The experimental results indicate that the groove defect can be removed by both the repair processes. The tensile strength of the GTAW repair joint is only 55% of that of the base metal. The tensile fracture occurs at the transition zone between the weld zone and the heat affected zone, and the fracture surface of the repair joint is characterised by clear brittleness. In contrast, the GTAW+FSW hybrid repair joint has a high tensile strength equivalent to 70% of that of the base metal. The tensile fracture occurs at the overlap thermomechanically affected zone between the two FSW nuggets, and the fracture feature of the hybrid repair joint is partially plastic and partially brittle.     

搅拌摩擦焊中的扭矩分析

扭矩的测量对于理解和改进搅拌摩擦焊有很大的帮助.使用扭矩传感器测量了3.5mm厚铝合金5083-H321在不同参数下的扭矩,对扭矩曲线进行了比较,并研究了稳态平均扭矩对接头力学性能的影响.结果发现:焊接速度一定时,稳态平均扭矩随着旋转速度的增加而增加;旋转速度一定时,稳态平均扭矩随着焊接速度的增加而增加.稳态平均扭矩为12 N·m时抗拉强度和伸长率最大,分别达到母材的93.6%和67%.     

Tool eccentricity in friction stir welding: a comprehensive review

ABSTRACT

This paper reviews research on the effect of tool eccentricity in the friction stir welding process. A distinction between pin profile eccentricity and tool eccentricity is addressed, followed by an in-depth review of the research progress in both of the cases, including the mechanism behind the eccentric motion and how it influences the overall joint outcome. Suggestions are made regarding potential future works in this field.