The volume of fluid (VOF) modeling method was implemented to simulate the underwater friction-stir welding (FSW) process for dissimilar joining between aluminum and steel. Temperature profile, ...materials flow, and intermixing during dissimilar bonding under the cooling medium were monitored via VOF modeling and verified according to experimental data. The effects of processing parameters on the formation of intermetallic compounds (IMCs) at the Al/St interface, microstructural characteristics, and mechanical property of dissimilar weldments were studied and addressed. By decreasing tool rotational speed (w), increasing traverse velocity (v), and employing cooling medium, peak temperature continuously reduced (down to ∼473 and 573 K for the aluminum and steel sides, respectively) led to substantial refining the grain structure and formation of a thinner IMC layer. The average grain size in the aluminum and steel sides of SZ is refined down to ∼4 and 12 µm, respectively. The thickness of the IMC layer varied depending on the processing parameters with the lowest value of ∼0.2 µm. The formation of a curved interface due to enhanced materials mixing at the advancing side is noted with a linear hardness gradient across the dissimilar weldment. Superior mechanical strength of ∼80 MPa attained at an optimized submerged condition of w = 1650 rpm/v = 40 mm/min showed combined ductile-brittle fractographic aspects on the fracture surface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, the development of the microstructure and crystallographic texture during friction stir welding (FSW) of AA2024 and AA6061 dissimilar joint was investigated. Electron backscattered ...diffraction (EBSD) technique was employed to characterize the textures and revealed the evolution of microstructures during friction stir welding. Experimental results showed the grain refinement in the stirred zone through continuous and discontinuous recrystallization. The fraction of precipitates in the stirred zone of the retreating side was much higher than that of the advancing side. On the other hand, the extent of continuous dynamic recrystallization in the thermomechanically affected zone (TMAZ) of the advancing side was lower than that of the retreating side and the recrystallized grains were rarely seen on the advancing side. The initial texture components of the sheets mainly consisted of {001}〈100〉 Cube and {011}〈011〉 Rotated Goss. The pole figures became asymmetric due to the inhomogeneous plastic deformation during FSW. The overall texture intensity was weaker on the advancing side and stronger on the retreating side than that in the starting materials. On the advancing side, {011}〈211〉 and {221}〈012〉 texture components created and the γ-fiber (〈111〉//ND) shear texture developed on the retreating side. Correlation between the microstructure and texture proved that the discontinuous static recrystallization and/or meta-dynamic recrystallization occurred on the advancing side. Microhardness profile on the advancing side was almost identical, while the profile revealed three distinguishable regions on the retreating side.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•The fracture of the dissimilar joints between aluminium and steel can be modelled by ductile damage criterion.•The parameters of the ductile damage can be derived based on the ...fracture surface and microstructure.•The difference of deformation characteristics of aluminium and steel promotes a stress triaxiality in the joint which triggers the fracture initiation.
Striving for lighter and more efficient vehicles, the automotive industry is currently seeking to replace traditional materials like steel with lighter ones such as aluminum alloys. Among the various techniques used to join aluminum to steel, friction stir welding has gained relevance, since it offers important advantages such as lower cost and higher flexibility. However, joint quality is highly dependent on the formation of intermetallic compounds. In the present study, the fracture behavior of an aluminum/steel joint obtained with friction stir welding was investigated experimentally and numerically. After experimental testing, it was found that cracks initiated and propagated through the interface of brittle intermetallic layer and steel. However, ductile fracture characteristics were observed on the fracture surface by a post-failure microscopic scale analysis. Therefore, a ductile damage criterion was utilized to model the fracture behavior of the aluminum/steel joint with an intermetallic layer at the interface. A multi-objective optimization method was utilized to obtain the parameters of the ductile damage criterion, using experimental data and numerical modelling. The obtained parameters were verified by doing experiments on different geometries. Simulation results indicated that the crack initiates from the free edge of the joint layer wherein a high stress triaxiality exists due to non-uniform deformation of aluminum and steel in both sides of the joint. The results of the present study give an understanding of fracture behavior wherein the intermetallic layer is involved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel integrated thermal-fluid-structure coupling model of the friction stir welding process was proposed for simultaneous prediction of the weld formation and tool service life.•A new non-uniform ...distribution model was proposed to describe the interaction at the tool-workpiece contact interface.•The severe reduction of tool-workpiece contact interfacial frictional shear stress is the main reason for the formation of the void defect in friction stir welding.•The difference between the maximum and the minimum tool-workpiece contact pressure could serve as a numerical criterion to predict void defect formation.•The tool is apt to fracture at its root under an improper welding condition since severe stress concentration is located there.
Understanding the void defect formation mechanism and simultaneous predicting the tool service life in friction stir welding are critical for optimizing the welding parameters. However, the void defect formation mechanism in friction stir welding is not yet elucidated. In this study, a novel integrated thermal-fluid-structure coupling model of the friction stir welding process was proposed for simultaneous prediction of the weld formation and tool service life. A new non-uniform distribution model of the tool-workpiece contact pressure was proposed to describe the interaction between the tool and the workpiece. The void defect formation mechanism was quantitatively studied using the proposed integrated thermal-fluid-structure coupling model. The results show that the plastic material flows in the horizontal direction and can completely fill the cavity behind the tool for the welding condition of forming a sound weld. While the tool-workpiece contact interfacial frictional shear stress in the rear of the tool is decreased significantly which leads to a severe decrease in the plastic material flow velocity. Therefore, after bypassing the tool from the retreating side, the plastic material at the bottom of the weld stagnates, and void defect forms in the middle and lower part of the weld at the advancing side. The difference between the maximum and the minimum tool-workpiece contact pressure could serve as a numerical criterion to predict void defects. A sound joint is formed when the difference is lower than the critical value of 15 MPa, while a void defect is formed in the weld if it is higher than this critical value. The maximum equivalent stress acting on the tool is located at the pin root with severe stress concentration at a high welding speed. The front of the tool is subjected to tensile stress while its rear is subjected to compressive stress, therefore the tool is apt to fracture at its root under an inappropriate welding condition. The average normal stress of the tool varies periodically with its period consistent with the rotation period of the tool. The service life of the tool is decreased with the increase in welding speed and the decrease in rotation speed. The model is validated by experimental results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Numerous industrial applications, particularly those in the transport industry, require the joining of dissimilar materials which offers considerable benefits in terms of low cost, design ...flexibility, and weight reduction for overall structures. The problems associated with conventional fusion welding processes have stimulated researchers in recent years to develop new joining methods for dissimilar materials which are particularly difficult to join. Friction stir welding (FSW) originally developed for joining difficult-to-weld Al-alloys and FSSW (a variant of FSW for spot welding) have exhibited great potential for obtaining sound joints in various dissimilar alloy systems in different configurations namely butt-, lap- and spot-welding, particularly in dissimilar Al-alloys systems with different properties, which are very difficult to weld using conventional fusion welding techniques. A major difficulty in joining dissimilar Al-alloys by FSW/FSSW lies in the discontinuity in mechanical and technological properties (such as high-temperature strength, plastic deformation capacity, viscosity, etc.) of the materials to be welded across the abutting surfaces. This discontinuity as well as inherent asymmetry in heat generation and material flow of FWS/FSSW processes causes a higher asymmetry in materials flow behavior in dissimilar welding. However, it is relatively easier to implement the FSW/FSSW process to dissimilar Al-alloys in contrast to FSW of dissimilar materials combinations with very differing properties, such as Al-alloy to Mg-alloy or Al-alloy to steel.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Dissimilar friction stir welding was conducted on the combination of pure Ti and carbon fibre reinforced plastic. The weld interface microstructure and mechanical properties of the obtained joints ...were systematically investigated. Before welding, a surface treatment was performed on the Ti surface using a silane coupling agent. As a result, the silane coupling agent treatment helped to fabricate the sound dissimilar Ti/CFRP joint. The dissimilar Ti/CFRP joints obtained at the interface temperature between the melting point of the CFRP and thermal decomposition point of the CFRP showed superior tensile-shear strength due to the formation of the sufficient reaction between the surface-modified Ti and CFRP and the suppression of welding defect formation in the CFRP near the weld interface.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The paper presents the results of experimental development of the technology of friction stir welding to obtain a nonseparable connection of a special aerospace aluminum, titanium and magnesium ...alloys, high-temperature steels. Regularities and models of heat balance in the welding zone have been determined, which make it possible to predict the technological possibilities of high-speed friction welding. It is established that high-speed friction welding by mixing allows to obtain a high-quality connection at lower loads on the design of the equipment. On the basis of studies of macro-and microstructure, microhardness, level of residual stresses and strength tests, technological recommendations on the choice of welding conditions and conditions were obtained. Presented of experimental and industrial development of special equipment, high-speed friction welding, design and manufacturing of high hardness tools of complex spatial shapes for welding aircraft materials.
The present study focuses on achieving microstructural uniformity in dissimilar Al–Ti joints through static shoulder friction stir welding (SSFSW). This method restricts material mixing at the Al–Ti ...interface due to reduced shoulder action, resulting in peak temperatures of 317 °C (SSFSW) and 491 °C in conventional friction stir welding (CFSW). This reduction in heat input during SSFSW leads to decreased mechanical mixing, resulting in a thinner 2.169 μm intermetallic layer at interface of SSFSW compared to 5.485 μm in CFSW. The resulting weld nugget (WN) microstructure reveals the presence of Ti particles, intermetallic compounds, and fine Al‐associated grains. Rearrangement of dislocations through slip‐and‐climb mechanisms, along with distinct recrystallization processes in SSFSW, significantly reduces grain size within WN. The kernel average misorientation map highlights the presence of nonuniform dislocation concentrations at the interface of CFSW, attributed to the large Ti particles that impede the mobility of dislocations. As a result, the interface of CFSW is found to be the weakest among all the zones, eventually leading to the failure of the CFSW joint near the Ti interface after reaching an ultimate tensile strength of 259 MPa. In contrast, SSFSW welds achieve a higher tensile strength of 289 MPa.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Friction Stir welding (FSW) is a welding method that occurs without fusion and smoothed the granules, used to improve the fine structural properties of metals. In this paper, the enhancement of ...mechanical properties for FSW samples at rotation speeds (1000, 1100 and 1200 rpm) with welding speed (45 mm/min) for 6005 AA is studied by using the method of FSW at the same variable rotating speed and feeding speed. In order to convert a heterogeneous nanoscale structure to a more precise and homogeneous monolithic structure. The best welding results obtained at parameter 45 mm/min are welding speed and rotational speed of 1100 rpm at FSW where efficiency reaches 96% for FSW for maximum tensile strength of mother metals. The FSW was developed as a finite element simulation of (FSW) of 6005 AA. Numerical simulations of thermal conductivity, heat and specific density were developed to find out the relationship between these factors and maximum temperature.
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