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Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding

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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 39571

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Dr. Alessandro Morri

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Department of Industrial Engineering (DIN), Alma Mater Studiorum, University of Bologna, Viale del Risorgimento 4, 40136 Bologna, Italy
Interests: friction stir welding; linear friction welding and friction stir processing of aluminum alloys and metal matrix composites; heat treatment of light alloys (aluminum, magnesium and titanium); high-temperature behavior of aluminum alloys, steels and cast irons
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Prof. Lorella Ceschini

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Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, Viale Risorgimento 4, 40136 - Bologna, Italy
Interests: microstructure–property–process relationships for light alloys (aluminum, magnesium and their composites), steels and cast irons; metallurgical aspects of addictive manufacturing by selective laser melting

Dr. Stefania Toschi

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Department of Industrial Engineering, University of Bologna, Viale Risorgimento 4, 40136 - Bologna, Italy
Interests: light alloys; metal matrix composites; heat treatment of aluminum alloys; microstructure–property–process relationship in metallic materials; selective laser melting

Special Issue Information

Dear Colleagues,

In recent years, the increasing need to reduce fuel consumption and enhance performance has fostered research on structural alloys with increased specific properties and their related processing technologies. In this context, many advanced techniques have been developed on the basis of solid state welding processes, namely friction stir welding (FSW) and linear friction welding. These new technologies emerged as high-potential techniques meant for the solid state manufacturing of metallic products, and which may be applied to the processing of metals or their corresponding metal matrix composites (MMC). Among such new techniques, it is worth mentioning friction stir processing (FSP), surface cladding (FSSC), additive manufacturing (FSAM) and riveting (FSR).

The aim of this Special Issue is to disseminate the latest research on the abovementioned applications of techniques based on advanced friction stir welding and linear friction welding, applied both to metals and metals matrix composites. Progress in the comprehension of the microstructure–process–mechanical relationship will be addressed; particular attention will be given to advanced characterization techniques, and a critical discussion of the benefits and drawbacks of these advanced techniques in comparison to traditional techniques is also encouraged.

Prof. Alessandro Morri
Prof. Lorella Ceschini
Dr. Stefania Toschi
Guest Editors

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Keywords

Friction Stir Welding
Linear Friction Welding
Friction Stir Processing Techniques
Friction Stir Surface Processing
Friction Stir Additive Manufacturing
Friction Stir Surface Cladding
Microstructure
Mechanical properties
Metal Alloys
Metal Matrix Composites

Published Papers (14 papers)

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Research

18 pages, 9384 KiB

Open AccessArticle

Novel Technique for Enhancing the Strength of Friction Stir Spot Welds through Dynamic Welding Parameters

by Ahmed Badwelan, Ali M. Al-Samhan, Saqib Anwar and Lotfi Hidri

Metals 2021, 11(2), 280; https://doi.org/10.3390/met11020280 - 5 Feb 2021

Cited by 3 | Viewed by 1997

Abstract

Presently, friction stir spot welding (FSSW) has become a common alternative for spot welding technologies. Over the years, researchers have implemented various methods for enhancing weld strength. However, the literature shows that the previously reported approaches have used static (constant) welding parameters set at the beginning of the welding stroke (i.e., the FSSW parameters were kept constant during the welding stroke). In contrast, in this study, an innovative technique is proposed for enhancing the weld strength for Al 1050 material by adjusting the FSSW process parameters during the welding stroke. Two FSSW parameters, namely, feed rate and spindle speed (dynamic parameters), are used in this study with a stepwise variation function and are changed during the welding stroke. The results of this study show that the weld tensile strength is enhanced by 12–21% when using the proposed novel dynamic welding parameter technique. This is a significant increase in the weld strength compared to when static welding parameters are employed during the welding stroke. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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11 pages, 5331 KiB

Open AccessFeature PaperArticle

Microstructure and Mechanical Properties of Friction Stir Welded AA6061/AA6061 + 40 vol% SiC Plates

by Sara Señorís-Puentes, Ricardo Fernández Serrano, Gaspar González-Doncel, Jesper Henri Hattel and Oleg V. Mishin

Metals 2021, 11(2), 206; https://doi.org/10.3390/met11020206 - 23 Jan 2021

Cited by 6 | Viewed by 2485

Abstract

The feasibility of butt friction stir welding (FSW) of a metal matrix composite (MMC) with a very high SiC particle content to a monolithic aluminum alloy is tested in this work. It is demonstrated for the first time that sound FSW joints can be obtained between an AA6061 aluminum plate and a thick MMC plate consisting of AA6061 reinforced with 40 vol% SiC particles. The joints withstand tensile testing, with ductile failure taking place in a soft region of the heat-affected zone on the alloy side. Metallographic examination of the MMC side after FSW reveals curved bands, where both the frequency of SiC particles and hardness are significantly lower than those in any other region on the MMC side. It is suggested that these bands are produced by transporting the alloy material to the MMC side, where the alloy is mechanically mixed with the MMC. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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14 pages, 8305 KiB

Open AccessArticle

Process Optimization and Formation Analysis of Friction Plug Welding of 6082 Aluminum Alloy

by Zhongke Zhang, Xuanbai Li, Zaolong Zhao, Changming Jiang and Huaxia Zhao

Metals 2020, 10(11), 1454; https://doi.org/10.3390/met10111454 - 30 Oct 2020

Cited by 4 | Viewed by 2016

Abstract

The response surface analysis method was used to systematically study the effect of various parameters on the tensile strength of 6082 aluminum alloy friction plug welding (FPW) joints in this work. The fluidity of the joint and microstructure were observed with a metallurgical microscope. Combined with the temperature field and force analysis, the reason why the root of the joint appears as a weak zone was explained. The results showed that the degree of influence on the tensile strength of FPW joints was rotational speed > upsetting speed > welding time. The optimal FPW joint was obtained when the rotational speed was 2254 rpm, the upsetting speed was 2 mm/s, and the welding time was 25 s, so the tensile strength could reach 262.34 MPa. The microstructure of the FPW joint appeared heterogeneous. According to the different plastic metal fluidities of the joint, it could be divided into four areas. The interaction force at the friction interface was not strong at the root of the FPW joint, so the root often becomes the weak area of the FPW joint. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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14 pages, 6056 KiB

Open AccessArticle

The Influence of Multiple Pass Submerged Friction Stir Processing on the Microstructure and Mechanical Properties of the FSWed AA6082-AA8011 Joints

by Sipokazi Mabuwa and Velaphi Msomi

Metals 2020, 10(11), 1429; https://doi.org/10.3390/met10111429 - 28 Oct 2020

Cited by 3 | Viewed by 1498

Abstract

The AA6082–AA8011 friction stir-welded joints were subjected to submerged multiple pass friction stir processing to evaluate the microstructure and mechanical properties of the joints. A maximum of four submerged friction stir processed passes were used in this study. All the specimens were extracted from three different joint positions (start, middle and end). The tests conducted included microstructural analysis, tensile tests, hardness and fracture surface morphology of the post-tensile specimens, were performed using a scanning electron microscope (SEM). There was no particular trend in the microstructure and mechanical properties when looking at the specimen positioning in all the passes. The minimum mean grain sizes were refined from 3.54 to 1.49 µm and the standard deviation from 5.43 to 1.87 µm. The ultimate tensile strength was improved from 84.96 to 94.77 MPa. The four-pass SFSPed specimens were found to have more ductile properties compared to the one-pass SFSPed one. The hardness of the stir zones in all the passes was found to be higher compared to the AA8011 base material but lower than the AA6082 one. The maximum stir zone hardness of 75 HV was observed on the one-pass SFSP joints. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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12 pages, 4747 KiB

Open AccessArticle

Analysis of the Oscillation Behavior of Hybrid Aluminum/Steel Joints Realized by Ultrasound Enhanced Friction Stir Welding

by Marco Thomä, Andreas Gester, Guntram Wagner and Marco Fritzsche

Metals 2020, 10(8), 1079; https://doi.org/10.3390/met10081079 - 10 Aug 2020

Cited by 10 | Viewed by 2795

Abstract

Friction stir welding (FSW) is an innovative solid-state joining process, which is suitable for joining dissimilar materials with strongly differing physical and chemical properties such as aluminum and steel. Where other joining methods such as fusion welding struggle to achieve appropriate joint strengths due to the excessive formation of brittle aluminum-rich intermetallic phases (IMP), FSW joints of aluminum and steel only show small layers of IMP, thus, sufficient tensile strengths in proximity to the maximum tensile strength of the weaker aluminum base material can be reached. With the aim to optimize the mechanical and microstructural properties of such dissimilar joints for widening the field for possible industrial applications, several hybrid friction stir welding methods have been developed which include an additional energy input, whereas the ultrasound enhancement (USE-FSW) is one of the most promising. The current work was carried out on AA6061/DC04 joints which were successfully friction stir welded with and without ultrasound support, in respect to the influence of varying the ultrasound transmission side. The functionality of the USE-FSW setup could be verified by multi point laser vibrometer measurements. Additionally, a higher proportion of transversal oscillation for the transmission of power ultrasound into aluminum could be detected using a scanning vibrometer. In comparison to the conventionally friction stir welded joints the ultrasound enhancement led to an avoidance of weld defects and an increase of the steel particle volume in the stir zone. The joint produced with power ultrasound transmission via aluminum resulted in a more uniform interface. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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19 pages, 24569 KiB

Open AccessArticle

Tensile-Shear Mechanical Behaviors of Friction Stir Spot Weld and Adhesive Hybrid Joint: Experimental and Numerical Study

by Guishen Yu, Xin Chen, Biao Zhang, Kaixuan Pan and Lifei Yang

Metals 2020, 10(8), 1028; https://doi.org/10.3390/met10081028 - 31 Jul 2020

Cited by 9 | Viewed by 3650

Abstract

In this work, the tensile-shear mechanical behaviors of friction stir spot weld and adhesive hybrid joint were performed from both numerical and experimental viewpoints. Weld through (WT) and flow in (FI) processes were studied in this research. The focus was to evaluate joint defects, tensile-shear failure load (TSFL), failure energy, failure mode and stress distribution of the joint. In FI joints, keyhole and hook defects appeared in the weld zone and the areas of material removed from the base metal were filled with adhesive. In the WT joints, the adhesive layer close to the weld zone was carbonized due to the welding heat. Meanwhile, under the rotating movement of welding tool, the adhesive impurities entered the stirring zone (SZ) and heat affected zone (HAZ) of the weld, which decreased mechanical performances of WT joints. Compared to the friction stir spot welding (FSSW) joint, the TSFL value, stiffness and failure energy of FI joint were increased by 2.7, 1.1 and 8.14 times, respectively. In order to study the stress distribution of the joints, a finite element (FE) model, which considered the weld structure and mechanical properties of weld regions, was implemented. Moreover, the adhesive layer was simplified by the cohesive zone model (CZM). FE results show that the FI process effectively decreases the stress concentration of the weld edge from 243.09 to 15.5 MPa, under the 2 kN tensile load. The weld can block the adhesive crack propagation, and the adhesive optimized the stress distribution of FI joints through a synergistic effect. So, the use of FI process for aluminum alloy connection is strongly recommended, especially in crucial structure areas. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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9 pages, 7813 KiB

Open AccessArticle

Effect of Backing Plate Materials in Micro-Friction Stir Butt Welding of Dissimilar AA6061-T6 and AA5052-H32 Aluminum Alloys

by SeongHwan Park, YoungHwan Joo and Myungchang Kang

Metals 2020, 10(7), 933; https://doi.org/10.3390/met10070933 - 10 Jul 2020

Cited by 13 | Viewed by 3641

Abstract

Thin sheets of lightweight aluminum alloys, which are increasingly used in automotive, aerospace, and electronics industries to reduce the weight of parts, are difficult to weld. When applying micro-friction stir welding (μ-FSW) to thin plates, the heat input to the base materials is considerably important to counter the heat loss to the jig and/or backing plate. In this study, three different backing-plate materials—cordierite ceramic, titanium alloy, and copper alloy—were used to evaluate the effect of heat loss on weldability in the μ-FSW process. One millimeter thick AA6061-T6 and AA5052-H32 dissimilar aluminum alloy plates were micro-friction stir welded by a butt joint. The tensile test, hardness, and microstructure of the welded joints using a tool rotational speed of 9000 rpm, a welding speed of 300 mm/min, and a tool tilting angle of 0° were evaluated. The heat loss was highly dependent on the thermal conductivity of the backing plate material, resulting in variations in the tensile strength and hardness distribution of the joints prepared using different backing plates. Consequently, the cordierite backing plate exhibited the highest tensile strength of 222.63 MPa and an elongation of 10.37%, corresponding to 86.7% and 58.4%, respectively, of those of the AA5052-H32 base metal. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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18 pages, 3436 KiB

Open AccessArticle

Torque-Based Temperature Control in Friction Stir Welding by Using a Digital Twin

by Martina E. Sigl, Andreas Bachmann, Thomas Mair and Michael F. Zaeh

Metals 2020, 10(7), 914; https://doi.org/10.3390/met10070914 - 8 Jul 2020

Cited by 10 | Viewed by 3249

Abstract

Friction stir welding (FSW) is an innovative solid-state welding technology that produces high quality joints and is widely used in the aerospace industry. Previous studies have revealed welding temperature to be a decisive factor for joint quality. Consequently, several temperature control systems for FSW have been developed. These output feedback control systems usually require delicate and expensive temperature measuring equipment, which reduces their suitability for industrial practice. This paper presents a novel state feedback system of the welding temperature to remedy this shortcoming. The system uses a physical model of the FSW process (digital twin) for the determination of the welding temperature signal from the process torque signal. The digital twin is based on a multi-input nonlinear time invariant model, which is fed with the torque signal from the spindle motor. A model-based ℒ₁ adaptive controller was employed for its robustness with respect to model inaccuracies and fast adaption to fluctuations in the controlled system. The experimental validation of the feedback control system showed improved weld quality compared to welded joints produced without temperature control. The achieved control accuracies depended on the results of the temperature calculation. Control deviations of less than 10 K could be achieved for certain welding parameters, and even for a work piece geometry, which deliberately caused heat accumulation. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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11 pages, 4848 KiB

Open AccessArticle

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

by Archimede Forcellese and Michela Simoncini

Metals 2020, 10(1), 15; https://doi.org/10.3390/met10010015 - 20 Dec 2019

Cited by 4 | Viewed by 1983

Abstract

The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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13 pages, 1973 KiB

Open AccessArticle

Thermal Cycles and Deformation Characters During High-Speed Micro Friction Stir Welding Process of AA7075-T6 Sheets

by Yu Ni, Yue Mao, Dingqiang Qin, Xuan Xiao and Li Fu

Metals 2019, 9(11), 1236; https://doi.org/10.3390/met9111236 - 18 Nov 2019

Cited by 2 | Viewed by 3033

Abstract

Thermal cycles and deformations during high-speed micro friction stir welding (μFSW) under different welding conditions were studied by experimental methods. The results show that the peak temperature and elevated-temperature exposure time (t₁₅₀) increased with the increasing of rotational speed and decreased with the increasing of welding speed. Increasing rotational speed or welding speed led to an increase in both heating and cooling rates. The joint fabricated by the pinless tool experienced a lower peak temperature, a shorter elevated-temperature exposure time, and a larger temperature gradient than that by the pin tool. The welded sheet presented an anti-saddle deformation character, with convex bending in a longitudinal direction and concave angular bending in a transverse direction. In comparison to the pin tool, the longitudinal maximum bending deformation, Z_max, of the joint fabricated by the pinless tool was reduced by 12.35%, and the transverse angular deformation, α, was reduced by 6.67%. In comparison to the steel backing plate, the Z_max of the joint produced using a copper backing plate was reduced by 40.66%, but the α was increased by 53.27%. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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11 pages, 1752 KiB

Open AccessArticle

Friction Stir Spot Welding with Additional Bonding of Thick Sheet Aluminum Joints

by Marcel Hatzky, Antonia Frank and Stefan Böhm

Metals 2019, 9(7), 732; https://doi.org/10.3390/met9070732 - 28 Jun 2019

Cited by 7 | Viewed by 2639

Abstract

The high-strength aluminum alloys offer great potential for realizing lightweight constructions in car body construction. However, the use of aluminum alloys increases the overall thickness of the material, which poses new challenges for potential joining processes. This paper examines a process combination of friction stir spot welding (FSSW) and bonding for 4 mm EN AW 6082-T6 sheets. For the investigations, adhesive or glass beads were applied between the joining components and then the sheets were welded using FSSW. The analysis shows that the adhesive and the glass beads have a very small influence on the joint formation. The use of glass beads in FSSW with bonding is recommended because less adhesive is displaced from the joint area, which increases the joint strength. The target of obtaining high weld spot strengths without strength-reducing adhesive burn-off could not be achieved because a certain residence time is necessary to form a weld spot with high strength at this sheet thickness in order to sufficiently plasticize the material. Adhesive burn-up cannot be completely avoided. For this reason, it is necessary to weigh up which characteristics are required for the specific application and adjust the welding parameters accordingly. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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13 pages, 10547 KiB

Open AccessArticle

A Study on Microstructure and Mechanical Properties of Micro Friction Stir Welded Ultra-Thin Al-1060 Sheets by the Shoulderless Tool

by Changqing Zhang, Weijie Wang, Xin Jin, Chen Rong and Zhuo Qin

Metals 2019, 9(5), 507; https://doi.org/10.3390/met9050507 - 30 Apr 2019

Cited by 15 | Viewed by 3662

Abstract

The welding tool is the key of micro friction stir welding (μFSW), which affects the heat input and the plastic forming of weld metal. In this paper, 0.8-mm-thick ultra-thin 1060-H24 aluminum sheets μFSW butt joints were used to compare and analyze the influence of the conventional tool and shoulderless tool on weld shaping, microstructure and mechanical properties. Besides, by measuring the axial force, transverse force and weld temperature in μFSW process, the influence of these two different tools on the heat input and metal flow mechanism of the weld were analyzed. The results show that the weld generated by the shoulderless tool has narrower width, less heat input and metal involved in plastic forming resulting in smaller HAZ (heat affected zone). The hardness of NZ (nugget zone) is obviously increased compared with that of the base metal. The highest tensile strength can reach 108.6 MPa, accounting for 78.6% of the base metal and 117.3% of the joint by the conventional tool. But the welding defects have to be overcome for industrial application of the shoulderless tool. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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14 pages, 5649 KiB

Open AccessArticle

Study on Friction Stir Lap Welding of Aluminium to Steel Sheets

by Lingfei Meng, Shujin Chen, Jiaqi Zhang, Di Wang, Hao Zhang and Xiaopeng Wei

Metals 2019, 9(5), 498; https://doi.org/10.3390/met9050498 - 28 Apr 2019

Cited by 3 | Viewed by 2824

Abstract

Friction stir lap welding (FSLW) of 6061-T6 aluminium sheet and DX51D galvanized steel sheet was carried out by adding zinc foil to the lap interface and studying the influence of the zinc foil on the formation mechanisms and mechanical properties. The influence of the thickness of zinc foil, the plunge depth of the shoulder and the shape of the tools on the mechanical properties of the weld are discussed. Zinc foil reduced the generation of brittle intermetallic compounds, such as Fe₄Al₁₃. During the welding process, the axial force was small due to the high rotating speed. Liquid zinc was retained at the interface, where eutectic Al–Zn with low melting point and an Fe–Zn compound were generated to achieve the metallurgical combination of aluminium and steel. The fracture was located in the heat affected zone (HAZ) of the 6061-T6 base aluminium. The results showed that when the zinc foil was too thin, there was less zinc content at the interface; the resulting Al–Zn eutectic had low melting point, was not fully spread and had poor continuity, resulting in poor mechanical properties. When the zinc foil was too thick, a large amount of zinc-based solid solution was generated at the interface, and most of the fracture occurred in the zinc-rich layer. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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12 pages, 4312 KiB

Open AccessArticle

Study of the Microstructure and Fracture Toughness of TC17 Titanium Alloy Linear Friction Welding Joint

by Xiaohong Li, Jianchao He, Yajuan Ji, Tiancang Zhang and Yanhua Zhang

Metals 2019, 9(4), 430; https://doi.org/10.3390/met9040430 - 11 Apr 2019

Cited by 8 | Viewed by 3220

Abstract

In this paper, the fracture toughness of the thermo-mechanically affected zone (TMAZ) and the weld zone (WZ) of the TC17 titanium alloy linear friction welding joint was studied. The relationship between microstructure and fracture toughness of the joint, as well as the morphologies of the joint microstructure and fracture were investigated. The results indicate that after heat treatment, there was no significant difference in hardness between the WZ and the TMAZ of the joint, which was about 420 HV. However, the microstructures of the different zones of the joint were significantly different. The TMAZ was composed of coarse grains having an internal basket-shaped α phase with an uneven grain size, while the WZ was composed of relatively uniform fine grains and contained a sheet-like α phase. The fracture toughness of the TMAZ was found to be higher than that of the WZ, indicating that the microstructure of the joint had a significant impact on the fracture toughness. In addition, the fracture resistance of the TMAZ with coarser grains and uneven microstructure was better than that of the WZ with fine grains and uniform microstructure. Full article

(This article belongs to the Special Issue Advanced Process Technologies Based on Friction Stir Welding and Linear Friction Welding)

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