Friction Stir Research Articles

Wear performance enhancement of interface layer in CMT-WAAM fabricated ER4043/ER5356 Bimetallic wall through Friction Stir Surface Treatment

Abstract The cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) technique has limited wear applications compared to other manufacturing methods due to its lower wear resistance. However, integrating friction stir processing (FSP) with WAAM can enhance mechanical or wear performance, making it a promising and reliable manufacturing process for aerospace, automotive, and marine applications. In this work, CMT-WAAM technique has been used to fabricate a bimetallic wall of aluminium alloys (ER4043/ER5356), employing a bidirectional depositional strategy. The impact of FSP on the interface layer of the WAAM wall, serving as a post-processing treatment on the wall's surface, is studied in terms of microstructure and microhardness. Additionally, a pin-on-disk wear test is performed on the interface layer of both WAAM and FSP-treated WAAM walls under loads of 20N, 30N, and 40N. Results from optical and Field emission scanning electron microscopy (FESEM) microstructures revealed the grain refinement in the stirred zone, with a higher wt. % of Mg through Energy Dispersive Spectrometer (EDS) analysis. X-ray diffraction (XRD) identifies various intermetallic compounds, including Al12Mg17, Al3.21Si0.47, and Mg2Si, with higher peak intensities in the FSP-treated wall. Electron Backscatter Diffraction (EBSD) analysis indicates a decrease in the average grain size of stirred area, which is ~72.40 µm in unstirred area and ~5.57 µm in stirred area due to the local strain concentration effect during FSP. Grain refinement during FSP leads to an increase in average hardness by 35.9%. The wear rate and coefficient of friction (COF) get reduced, credited to high-temperature dynamic recrystallization and continuous grain recovery in FSP. Scanning electron microscope (SEM) analysis of worn surfaces highlights abrasion, delamination, and adhesion as significant wear mechanisms.

Modified CEL method for determination of defect formation mechanism in underwater stationary shoulder FSW based on softened pressure-overclosure contact relationship

The Coupled Eulerian-Lagrangian (CEL) method was employed to simulate underwater friction stir welding with a stationary shoulder tool (USSFSW). The governing equations in the CEL method were formulated for FSW based on the immersed boundary method. A new softened pressure-overclosure model was introduced to define contact pressure within the overclosure zone, and an initial nodal clearance control method was implemented to prevent the penetration of Eulerian elements into the Lagrangian domain. For modeling the mechanical and thermal interactions between surfaces, the VUINTERACTION subroutine was utilized. The study focused on the defect formation mechanisms during USSFSW, highlighting the roles of material flow velocity and nodal forces. Simulation results demonstrated close alignment with experimental data, revealing three flow paths that developed during the process, merging in the empty area behind the pin and generating upward material flow. Notably, the maximum flow velocity at the boundary of the third and fourth quadrants ranged from 0.189 to 0.495 m/s, while the overall maximum material flow velocity varied from 0.193 to 0.502 m/s. The nodal force was found to vary between 180 and 600 N; notably, when this force dropped below 200 N, the driving force for material flow decreased, resulting in the inability to fill the cavity behind the tool. Conversely, increasing the nodal force enhanced both backward flow (BF) and horizontal flow (HF), promoting higher material extrusion into the cavity. ​Ultimately, when the flow velocity fell below approximately 0.25 mm/s and the nodal force dropped below about 200 N, cavity defects in USSFSW became inevitable.

Multiresponse optimization applied to friction-stir processing to enhance wear and corrosion performance in Al–Si alloys

In this study, friction stir processing (FSP) parameters were optimized using the response surface method (RSM) to enhance hardness, reduce the friction coefficient and minimize the corrosion rate in cast Al12Si and Al14Si alloys. The FSP tool, made of AISI H13 tool steel, features a concave shoulder and conical pin designed to induce severe plastic deformation. Microstructural analysis was performed via optical microscopy and SEM–EDS, and the particle size and distribution were assessed via ImageJ software. Microhardness profiles were measured across the Nugget, TMAZ, HAZ, and substrate zones. The corrosion resistance was evaluated using an AutoLab potentiostat/galvanostat following ASTM G59-97 standards, whereas the wear performance was assessed using a reciprocating linear tribometer (ASTM G133). FSP led to the fragmentation and uniform distribution of silicon and Fe-rich intermetallic phases within the aluminum matrix. The multiresponse optimization identified the optimal FSP parameters for Al12Si alloys at a tool rotation speed of 1100 rpm and a travel speed of 16 mm/min. Under these conditions, the Al12Si samples presented the highest microhardness (93 Hv), significant fragmentation of silicon particles (2.82 μm) and Fe-rich intermetallic phases (2.07 μm), reduced friction coefficient (0.60) and low corrosion rate (1.28 × 10⁻4 mm/y). The proposed model offers a reliable method to optimize FSP, leading to aluminum surfaces with superior microstructure, hardness, wear resistance and corrosion resistance.

Impact of tool geometry and friction stir welding parameters on AZ31 magnesium alloy weldment wear behaviour and process optimization

This study investigates the impact of friction-stir welding (FSW) tool pin shape (TPS) and processing variables, viz., rotation speed (RS), axial load (AL), and traverse speed (TS), on weld beads’ wear characteristics as per ASTM G99 standard. Wear rate (WR), friction force (FF), and coefficient of friction (CoF) are analyzed based on Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). FSW performed with a hexagonal TPS provides a better material flow between the plates, influencing the joint’s strength and improving the wear resistance of weldments. Higher RS leads to high material flashing, providing lower strength and wear properties. Changes in TPS from triangle to pentagon and from pentagon to hexagon produced higher tensile strength, at 11.16% and 12.15%, respectively. The Chimp Optimization Algorithm (ChOA) shows an optimal condition of hexagon TPS, AL of 2 kN, RS of 1800 rpm, and TS of 25 mm/min, whereas TOPSIS optimal condition are hexagon TPS, AL of 4 kN, RS of 1400 rpm, and TS of 50 mm/min. Confirmation experiments with optimal conditions shows, ChOA producing lower WR, CoF, and FF by 12.5, 2.56, and 1.54% than TOPSIS. Compared with TOPSIS, ChOA produced lower WR, CoF, and FF by 12.5%, 2.56%, and 1.54%.

Investigating impact of in-process cooling mediums on microstructural and mechanical properties of FSWed AA2219 T6 joints

This study investigates the influence of various in-process cooling techniques on the microstructural characteristics and mechanical properties of the friction stir-welded AA-2219-T6 alloy. The in-process cooling methods used include normal air, dry fan, an oil-water mixture (20:80), and water. The primary objective is to determine the optimal cooling strategy for enhancing the quality of the weldment. The characterization included light microscopy, tensile testing, X-ray diffraction (XRD), microhardness testing, and scanning electron microscopy (SEM) analysis of fractured surfaces to evaluate the microstructure and mechanical properties. It was seen that in-process cooling methods significantly affect the microstructural features and mechanical properties of AA 2219-T6 alloy weldments. Findings indicated that the water-cooled method at 55 °C resulted in the highest density of Al2Cu particles, leading to superior hardness and mechanical properties compared to other in-process cooling methods. Specifically, the water-cooled samples exhibited a ~ 17% increase in hardness compared to air-cooled samples and achieved an ultimate tensile strength equivalent to 65.4% of the base metal. Furthermore, a notable volume of second-phase particles was observed on the fractured surfaces in the water-cooled condition, attributed to the lower in-process temperatures, thus underscoring the effectiveness of water cooling in friction stir welding.

Implications of incorporating CrFeNiTiZn high-entropy alloy on the tribomechanical and microstructure morphology behaviour of A356 composites processed by friction stir processing

Abstract This study investigated the impact of incorporating a CrFeNiTiZn High Entropy Alloy (HEA) into the A356 aluminum matrix through the friction stir processing (FSP) technique. The CrFeNiTiZn HEA, renowned for its compositional complexity and high-performance potential, was incorporated into the A356 alloy with different weight percent combinations to enhance its mechanical and tribological characteristics. The results revealed a refined microstructure characterized by solid solution phases and potential intermetallic compound formation due to the HEA addition for A356/2 %Cr2 %Fe2 %Ni2 %Ti2 %Zn composition. Strong interfacial bond strength was also observed among the matrix and reinforcement particles for the A356/2 %Cr2 %Fe2 %Ni2 %Ti2 %Zn composition. The number of grains was found to be about 1820.34 (average grain size is 686 µm) for A356/2 %Cr2 %Fe2 %Ni2 %Ti2 %Zn processed composite with FSP per square inch at 500 magnifications. The A356/2 %Cr2 %Fe2 %Ni2 %Ti2 %Zn composite exhibited improved tensile strength (35.70 %) and hardness (63.33 %) after the addition of 2 %Cr2 %Fe2 %Ni2 %Ti2 %Zn into A356 alloy, attributed to the strengthening effect of HEA particles. Furthermore, wear resistance is notably enhanced, likely due to the synergistic effects of the HEA’s inherent hardness and the modified microstructure.

The Effect of Rotational Speed on Microstructure and Mechanical Properties of Al/Ti Dissimilar Joint Produced by Refill Friction Stir Spot Welding

The Effect of Rotational Speed on Microstructure and Mechanical Properties of Al/Ti Dissimilar Joint Produced by Refill Friction Stir Spot Welding

Influence of AlCoCrFeNiCuSn HEA reinforcement particles on the plastic flow behaviour of the friction stir processed composite material under constrained confined deformation conditions

In the present investigation, an AlCoCrFeNiCuSn high entropy alloy (HEA) reinforced (with 2.5, 5, 7.5 weight percentage (wt.%)) AA7050-based metal matrix composite has been developed by utilising the friction-stir processing (FSP) technique. Further, the representative volume element (RVE) based finite element analysis (FEA) model and macro-mechanical static indentation FEA model have been developed to analyze the plastic deformation of developed composite material under constrained confined deformation conditions at a load range of 4.90 to 49.03 kN. The microstructural investigation confirms the fair distribution of AlCoCrFeNiCuSn HEA particles in the AA7050 matrix. The micro-mechanical RVE-based FEA model and macro-mechanical static indentation FEA model were successfully validated with experimental and analytical models (ECM and FPM) with less than 5% percentage difference. The yield strength of matrix material was increased with 6.51%, 10.47%, and 15.19% by increasing the AlCoCrFeNiCuSn HEA reinforcement particle with 2.5wt.%, 5wt.%, and 7.5wt.% respectively. Further, the tensile strength of matrix material was increased with 1.88%, 3.93%, and 10.49% by increasing the AlCoCrFeNiCuSn HEA reinforcement particle with 2.5wt.%, 5wt.%, and 7.5wt.% respectively. Additionally, Composition 1 (AA7050/2.5wt.% AlCoCrFeNiCuSn HEA), composition 2 (AA7050/5wt.% AlCoCrFeNiCuSn HEA) and composition 3 (AA7050/7.5wt.% AlCoCrFeNiCuSn HEA) show 7.39%, 11.91% and 22.16% more Meyer’s hardness than matrix material.

Finite element simulation of hybrid manufacturing of Ti–6Al–4 V by arc-directed energy deposition and friction stir processing

ABSTRACT FSP is a novel technology that can improve the microstructure and mechanical properties of ADED. In this study, an FSP-ADED hybrid manufacturing finite element model was constructed for stress and strain simulating the Ti–6Al–4 V alloy. The results show that continuous shrinkage of the deposition wall was broken after inter-layer FSP. The minimum tensile RS was obtained near the wall top. The tensile RS was increased after the deposition of the second layer; however, the overall stress level was lower than that of ADED alone. After two layers of FSP, the average value of longitudinal stress in the stirred zone was reduced by 54%. The warping deformation of hybrid manufactured components was reduced by 30.9%. It was proved that FSP-ADED hybrid manufacturing is an effective method to reduce RS and deformation of titanium alloy large-scale structural parts in the aerospace field.

The effect of the Zn layer on the microstructural evolution of Al/Cu composite material joints during friction stir spot welding

This study introduced Zn interlayer at the Al/Cu interface to form an Al-Zn-Cu tri-layer composite joint. The growth of the interfacial layer was enhanced by the generation of the liquid phase with increasing rotational speed and heat input during the welding process. Among the phases formed in the Al-Zn-Cu joint, the Cu5Zn8 phase exhibited the highest growth constant, making it the primary phase at the interface. The growth sequence of the Al2Cu phase was found to be between that of the Cu5Zn8 and AlCu phases. As welding progressed, Al2Cu acted as an ‘anchor point’ for the subsequent formation of the AlCu phase and was gradually consumed in the process. No Al4Cu9 phase was observed in the joint.

Enhanced material flow and joint formation of FSWed AA2024 by using protruding cylinder tool

The optimization mechanism of the protruding cylinder on the modified tool for the performance of friction stir welding (FSW) joints in 2024 aluminum alloy was investigated. The results indicate that the presence of a protruding cylinder on the modified tool significantly improves the surface quality of the weld, increases the width and area of the weld nugget zone(WNZ), and refines the grain size. Additionally, the size of the precipitated phases is reduced, and their distribution becomes more uniform, which in turn enhances the tensile strength and hardness of the joint. Furthermore, the presence of a protruding cylinder facilitated material flow, stabilized the welding process, and contributed to the formation of uniform welds.

Investigation of three-dimensional forces during additive friction stir deposition — How could force signals reveal the deposition quality?

Additive friction stir deposition (AFSD) is a solid-phase forming technology based on microzone forging, which is essentially a force-driven additive manufacturing process. This work focuses on the effects of the AFSD parameters on the force signals and forming quality, which is highly important for optimizing the process parameters and controlling the forming quality. By analyzing the force features in the time‒frequency domain, the evolution mechanism of three-dimensional forces during AFSD was explored. A 3D scanner, scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) were used to clarify the surface morphology and microstructures of the deposition layers. It was found that deposition defects were accompanied by a lack of plasticization or nonuniform deformation between the advancing side (AS) and the retreating side (RS). Moreover, the relationships among the process parameters, three-dimensional forces and deposition quality were investigated. It is proved that force signal can effectively reflect the deposition quality. A comprehensive prediction model based on three-dimensional force features was developed, achieving an accurate prediction of deposition quality. Furthermore, this work demonstrated the feasibility of AFSD quality control on the basis of force signals. The currently employed control strategies can be further extended to address the AFSD of large components in the future.

The influence of laser-induced tempering on the microstructure and mechanical properties of 1500 MPa martensitic steel friction stir welded joints

A comprehensive comparison illustrates the role of laser technology in altering the macro morphology and microstructure of martensitic steel joints produced by friction stir welding (FSW). In this study, laser-induced tempering (LIT) was introduced to the FSW of 1500 MPa martensitic steel. The mechanism by which LIT enhanced the mechanical properties of the FSW joints was elucidated by comparing joints produced with and without LIT. Experimental findings revealed that LIT effectively eradicated tunnel defects under the same FSW parameters. Even with an increase in travelling speed from 60 mm/min to 120 mm/min, flawless welds were achieved under LIT conditions. At 500 rpm and 60 mm/min, the bottom of the stir zone (SZ) in conventional FSW (C-FSW) joint exhibited a ferrite and martensite dual-phase microstructure. In contrast, the SZ of the LIT-FSW joint had a fully martensitic structure. Moreover, LIT resulted in significant variations in the martensitic hierarchical structure within the SZ. LIT reduced ferrite distribution in the dual-phase zone, caused recrystallized ferrite to appear further from the SZ. The stress concentration in the dual-phase zone attributed to joint fracture. The improvement in the mechanical properties of martensitic steel FSW joints was explained by analyzing the correlation between the stress concentration factor and phase fraction. Additionally, the increase in traveling speed narrowed the dual-phase zone, triggered a constraint effect that led to a maximum ultimate tensile strength (UTS) increase from 986 MPa at 60 mm/min joint to 1142 MPa at 120 mm/min joint.

Effects of plunge depth on the intermetallic compounds and mechanical properties of Al/Cu joints fabricated by micro friction stir welding

0.5 mm thick 6061-T4 Al and T2 Cu were butt-joined by micro friction stir welding (μFSW) at different plunge depths (D1=0.04 mm, D2=0.08 mm, D3=0.12 mm), the temperature distribution was studied by numerical simulation. The results showed that the control of thickness reduction and intermetallic compounds (IMCs) are the keys to obtain a joint with excellent performance. When the plunge depth is 0.04 mm, the peak temperature and residence time are both minimum, the reduction rate of the weld thickness and the proportion of agglomerated IMCs are minimum, which are 4 % and 9 % respectively, the average thickness of IMCs layer is only 112 nm. The tensile strength is the largest (94.1 % of Al base material), the joint fails in the heat-affected zone (HAZ) of Al side due to lowest hardness. Agglomerated IMCs (including Al2Cu and Al4Cu9) are formed in the upper nugget zone (NZ), and IMCs layer (including Al2Cu, AlCu and Al4Cu9) are formed in the lower NZ. As the plunge depth increases, the proportion of agglomerated IMCs and the thickness of IMCs layer increases. So, preferential sites of crack nucleation appear at the agglomerated IMCs. Subsequently, crack growth is exacerbated by the inherent brittleness of AlCu, resulting in ductile fracture in the upper NZ and cleavage fracture in the lower NZ.

Microstructure Evolution and Corrosion Resistance of As-Extruded AZ91–Ca Alloy During Friction Stir Back Extrusion

Microstructure Evolution and Corrosion Resistance of As-Extruded AZ91–Ca Alloy During Friction Stir Back Extrusion

Material Flow and Microstructural Evolution in Friction Stir Welding of LAZ931 Duplex Mg-Li Alloys

The material flow behavior during friction stir welding (FSW) plays a critical role in the quality of final joints. In this study, the FSW of LAZ931 duplex Mg alloy was carried out at a rotation speed of 800 rpm and welding speeds of 50, 100, and 200 mm/min, respectively. A thin pure Mg strip inserted at the interface between the two Mg-Li alloy plates was used as a marker to study the flow behavior of the materials in the FSW process. Sound welds with no defects were obtained for all three welding speeds. The microstructural evaluations along the marker on the horizontal cross-section around the keyhole of the welds were characterized. As the welding speed increased, the marker came closer to the keyhole, indicating the decreased extent of the plastic deformation of the material. In the shoulder-affected zone (SAZ), the thickness of the marker reduced gradually in the accelerating stage and finally accumulated together in the decelerating stage. However, in the pin-affected zone (PAZ), the thickness of the marker reduced sharply in the accelerating stage and then became dispersed in the decelerating stage, and the degree of dispersion decreased as the weld speed increased. As a result, an elongated grain structure was formed in the SAZ, while two equiaxial grain structures were formed in the PAZ. The material on the advancing side was refined by the pin and deposited in the weld to form a fine equiaxial grain structure due to the high strain rate. In contrast, the material on the retreating side was pushed by the pin and thus directly deposited in the weld to form a coarse equiaxial grain structure. In addition, the area of the fine equiaxial grain structure was reduced obviously with the increase in welding speed.

Notch fatigue behaviour of friction stir welded AA6061-T651 aluminium alloy joints: Role of microstructure, and residual stresses

The main objective of this study was to investigate the combined effect of microstructure and residual stresses on notch fatigue behaviour of friction stir-welded (FSW) AA 6061-T651 aluminium alloy joints. Two different microstructures of FSW joints were produced at different welding speeds. A completely reverse-rotating fatigue testing machine was utilized to investigate the fatigue properties of notched specimens. The test results showed that the notch fatigue strength of a welded joint made at a speed of 25 mm/min was 33 % of the welded joint’s yield strength and 23 % of its tensile strength. To understand the overall fatigue behaviour of the welded joints, fatigue data were further analyzed using the Basquin equation variables. Microstructure investigation using optical and orientation imaging microscopy, transmission electron microscopy, and X-ray diffraction analysis of the joints was analyzed and discussed. The microstructure complexity and the weld zone tensile residual stress significantly affect the welded joints fatigue behaviour. It was found that the notch fatigue properties of the joints were extremely sensitive to their microstructural characteristics and residual stresses. An increase in tensile residual stresses decreases the notch fatigue life of the welded joints. The results of electron backscattered diffraction analysis indicated that joints with a fine grain microstructure exhibit higher microstructural stability and less initial damage. A fractography investigation showed that joints with fine grain microstructure have increased crack resistance in stage I and lower crack propagation in stage II.

Investigation on the welded joint properties of pinless friction stir spot welding of copper under different tool grooves

Three types of pinless friction stir spot welding (PFSSW) tools were designed employing Fibonacci spiral curve, involute curve, and Archimedean spiral curve to create corresponding grooves. Subsequently, PFSSW experiments were conducted on copper sheets using these three distinct tools. The surface morphology, cross-sectional macrostructure and microstructure, microhardness, joint strength, fracture type, and fracture surface morphology of the joints were analyzed under the influence of different tools. The research findings indicate that the Fibonacci spiral curve groove (FSCG) tool exhibits the highest disparity in three-dimensional morphology within the central zone of the joint, followed by the involute curve groove (ICG) tool and the Archimedean spiral curve groove (ASCG) tool. The ICG tool generates the widest stirring zone (SZ) in the joint, while the FSCG tool produces the deepest SZ. The grains of SZ under all three tools is coarser compared to the base material. The microhardness values under the ASCG tool are relatively higher, whereas those under the FSCG tool are lower. Among the welded specimens, those created using the FSCG tool exhibit the highest average tensile-shear failure load of 8.21 kN, followed by the ICG tool of 7.80 kN, and the ASCG tool yielding the lowest average tensile-shear failure load of 7.77 kN. The fracture type of the specimens welded by FSCG tool is semi-nugget pull-out fracture, while the joint specimens of ICG tool and ASCG tool are both nugget pull-out fracture. The fracture mode of the joints under all three tools is characterized as ductile fracture. The conducted research can not only enrich the variety of PFSSW tool grooves, but also enhance the comprehension of joint properties under distinct tool groove configurations.

Additive friction stir deposition of an Al-Cu-Mg alloy: Microstructure evolution and mechanical properties

Additive Friction Stir Deposition (AFSD), an emerging solid-based additive manufacturing technology, has demonstrated significant potential in the fabrication of high-strength aluminum alloys. In this study, a 22 mm thick 2024 aluminum alloy deposit having ten layers was for the first time successfully fabricated using the AFSD technique. The correlation between the microstructure evolution and mechanical properties within the deposit was revealed. The results indicated that the deposit exhibited very fine recrystallized microstructure and excellent mechanical properties. Dynamic recrystallization occurred with the average grain sizes at the top, center, and bottom of the deposit being 3.0 μm, 4.7 μm, and 4.8 μm, respectively. The Al2CuMg (S phase) at grain boundaries of the deposit was observed to fracture due to the plastic deformation of the feedstock during the deposition process. The Vickers hardness of the deposit cross-section along the build direction (BD) changed from 125 HV of the top to 85 HV of the bottom. Better tensile properties in the TD compared to the BD were observed with the excellent tensile strength of 532 MPa and 473 MPa, and the elongation of 31.2 % and 15.2 %, respectively. The synergistically improvement of the tensile strength and elongation in the TD was attributed to the uniform microstructure and mechanical properties exhibited by each deposit layer.

Elevating alloy performance: the role of bioactive glass in Mg-9Al-Zn matrix composites through friction stir back extrusion

ABSTRACT This study investigates the impact of friction stir back extrusion (FSBE) parameters on the microstructure and mechanical properties of magnesium matrix composites reinforced with bioactive glass particles. Higher rotational speeds (1600 rpm) generate more heat and stirring, promoting finer grains and better particle dispersion, while lower speeds lead to larger grains. Conversely, slower extrusion speeds allow more time for heat dissipation and better mixing, contributing to smaller grains and a more uniform particle distribution. Key findings show that increasing the bioactive glass content enhances both hardness and ultimate tensile strength (UTS), with optimal mechanical properties achieved at 1600 rpm rotational speed, 48.97 mm/min extrusion speed, and 5 vol.% bioactive glass. The introduction of bioactive glass particles restricts grain growth and improves load transfer, thereby reinforcing the composite. Additionally, the study identifies a gradient microstructure in the composite wire, with smaller grains near the surface due to higher plastic strain and temperature, in contrast to the core, which exhibits larger grains.