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Metals
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Friction Stir Welding/Processing Technology
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Friction Stir Welding/Processing Technology

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Welding and Joining".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 11024

Special Issue Editor

Prof. Dr. Hoon-Hwe Cho

E-Mail Website
Guest Editor
Department of Materials Science and Engineering, Hanbat National University, 125 Dongseodae-ro, Yuseong-Gu, Daejeon, Republic of Korea
Interests: advanced structural materials, finite element modeling, welding/joining

Special Issue Information

Dear Colleagues,

Invented by the Welding Institute in the United Kingdom in 1991, friction stir welding (FSW) is an advanced solid-state technique used for joining materials with a wide range of diemensions and also in various joint configurations. Through the years, FSW has undergone various modifications and developments in a bid to extend its applications in areas such as the marine, shipbuilding, aerospace, automotive, and rail industries. Recently, engineers at SpaceX, an aerospace manufacturing company, implemented FSW to join the break-off fuel tanks of their rockets. The reason behind this was the need for exceptional strength in the break-off fuel tanks of the rocket, which cannot be achieved by merely using conventional welding techniques. For this reason and many others, such as the low peak operating temperature to prevent melting, improved mechanical properties due to the refined microstructure in the weld, good quality joints without any defects, and less residual stress and distortion, there has been an elevated interest in FSW as an attractive joining process for many manufacturers.

Notwithstanding these incredible advancements and ever-growing interests in FSW and its variants, such as friction stir processing, friction stir spot welding, and robotic friction stir welding, the FSW technology is not without its challenges. For instance, the resulting microstructure of a joint (especially the stir zone), the size and distribution of precipitates, as well as the mechanical and corrosion behaviors of the weld heavily depend on various pertinent factors. These include the welding parameters, tool dimensions, temperature distribution, as well as the microstructure of the parent materials. Therefore, it is of significant importance to continue the advancement of FSW technology by exploring new approaches that seek to provide innovative solutions to address these challenges. Such approaches could include experimental as well as numerical modeling methods to study the FSW mechanism and its effects on the microstructure and the corresponding mechanical and corrosion behaviors.

This Special Issue will encompass research linking the current progress of the variants of the FSW technology and their applications in the joining and modification of materials. We welcome manuscripts discussing experimental and numerical modeling studies of the interplay between the welding parameters, its resulting microstructures, and subsequent mechanical properties. Furthermore, manuscripts on experimental and numerical modeling studies of the corrosion behaviors (e.g., galvanic, pitting, and stress corrosion) of the weld are also of great interest.

Prof. Dr. Hoon-Hwe Cho
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • friction stir welding/processing
  • microstructure
  • dissimilar joint
  • numerical modeling
  • mechanical properties
  • galvanic corrosion

Published Papers (4 papers)

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Research

20 pages, 8784 KiB  
Article
Tool Downscaling Effects on the Friction Stir Spot Welding Process and Properties of Current-Carrying Welded Aluminum–Copper Joints for E-Mobility Applications
by Aristide Tchouaha Tankoua, Tobias Köhler, Jean Pierre Bergmann, Michael Grätzel, Philip Betz and Dirk Lindenau
Metals 2021, 11(12), 1949; https://0-doi-org.brum.beds.ac.uk/10.3390/met11121949 - 03 Dec 2021
Cited by 4 | Viewed by 2335
Abstract
According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to [...] Read more.
According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process. Full article
(This article belongs to the Special Issue Friction Stir Welding/Processing Technology)
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13 pages, 6969 KiB  
Article
Friction Stir Spot Butt Welding of Dissimilar S45C Steel and 6061-T6 Aluminum Alloy
by Kun Gao, Shengwei Zhang, Mounarik Mondal, Soumyabrata Basak, Sung-Tae Hong and Heechan Shim
Metals 2021, 11(8), 1252; https://0-doi-org.brum.beds.ac.uk/10.3390/met11081252 - 07 Aug 2021
Cited by 15 | Viewed by 2813
Abstract
Friction stir spot welding (FSSW) of dissimilar S45C steel and 6061-T6 aluminum alloy in a butt configuration is experimentally investigated. Butt spot welding is performed using a convex scrolled shoulder tool at different tool rotational speeds. FSSW butt joints are successfully fabricated by [...] Read more.
Friction stir spot welding (FSSW) of dissimilar S45C steel and 6061-T6 aluminum alloy in a butt configuration is experimentally investigated. Butt spot welding is performed using a convex scrolled shoulder tool at different tool rotational speeds. FSSW butt joints are successfully fabricated by offsetting the tool to the steel side. The microstructures of the joints fabricated at three different tool rotational speeds are characterized using scanning electron microscopy and energy dispersive spectrometry. Microstructural analysis shows the presence of intermetallic compounds (IMCs) along the steel/aluminum interface. The thickness of the IMC layer and the tensile strength of the joint increase with increasing the tool rotational speed. The results of tensile tests and microstructural analysis show that the joint performance is closely related to the IMCs at the joint interface. Full article
(This article belongs to the Special Issue Friction Stir Welding/Processing Technology)
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22 pages, 1185 KiB  
Article
A Holistic, Model-Predictive Process Control for Friction Stir Welding Processes Including a 1D FDM Multi-Layer Temperature Distribution Model
by Stefan P. Meyer, Sebastian Fuderer and Michael F. Zaeh
Metals 2021, 11(3), 502; https://0-doi-org.brum.beds.ac.uk/10.3390/met11030502 - 18 Mar 2021
Viewed by 2061
Abstract
Friction press joining is an innovative joining process for bonding plastics and metals without additives in an overlap configuration. This paper presents for the first time a model-based approach for designing a multi-variable model predictive control (MPC) for friction press joining. For system [...] Read more.
Friction press joining is an innovative joining process for bonding plastics and metals without additives in an overlap configuration. This paper presents for the first time a model-based approach for designing a multi-variable model predictive control (MPC) for friction press joining. For system modeling, a differential equation based on the heat flows was proposed and modeled as a torque-dependent function. With this model, it is possible to consider cross-effects between the axial force and the friction zone temperature. With this theoretical approach, adaptive model-predictive process control was implemented and validated for different material combinations (EN AW-6082-T6; EN AW-2024-T3; PE-HD; PA6-GF30; PPS-CF). It could be shown that the MPC has excellent control accuracy even when model uncertainties are introduced. Based on these findings, a 1D Finite Differential Method multi-layer model was developed to calculate the temperature in the plastic component, which is not measurable in situ (r = 0.93). These investigations demonstrate the high potential of the multi-variable MPC for plastic-metal direct joining. Full article
(This article belongs to the Special Issue Friction Stir Welding/Processing Technology)
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20 pages, 8229 KiB  
Article
The Development of WC-Based Composite Tools for Friction Stir Welding of High-Softening-Temperature Materials
by Mohamed M. Z. Ahmed, Waheed S. Barakat, Abdelkarim Y. A. Mohamed, Naser A. Alsaleh and Omayma A. Elkady
Metals 2021, 11(2), 285; https://0-doi-org.brum.beds.ac.uk/10.3390/met11020285 - 06 Feb 2021
Cited by 14 | Viewed by 2959
Abstract
This work presents a detailed investigation for the effect of Y2O3 and Ni additions on the densification behavior, microstructural evolution and mechanical properties of a WC-Co-TaC-NbC composite. With the aim of obtaining WC-based composites with improved fracture toughness, to be [...] Read more.
This work presents a detailed investigation for the effect of Y2O3 and Ni additions on the densification behavior, microstructural evolution and mechanical properties of a WC-Co-TaC-NbC composite. With the aim of obtaining WC-based composites with improved fracture toughness, to be used in severe conditions of high-temperature deformation, different concentrations of Y2O3 were incorporated with and without 5 wt% Ni addition. The consolidated composites were characterized using density measurement, XRD, SEM, hardness, fracture toughness, transverse rupture strength and compression testing. Fully dense composites were obtained through the applied consolidation regime of cold compaction and sintering at 1450 °C for 1.5 h under vacuum with a relative density up to 97%. The addition of 2.5 wt% Y2O3 to the base WC composite increased the relative density and then slightly decreased with the increase of the Y2O3 content. The addition of 5 wt% Ni to the base composites significantly increased the relative density to 97%. The XRD results indicated the existence of the Co3W3C η-phase after sintering, and the intensity of its peaks was reduced with the addition of 5 wt% Ni. The microstructure of the consolidated composites consisted of three phases: WC, Co3W3C and Y2O3. The area fraction of the Y2O3 phase increased as its weight fraction increased. In terms of the fracture toughness, the transverse-rupture strength (TRS) and the compressive strength were significantly improved by the addition of 5 wt% Ni with the 2.5 wt% Y2O3. Accordingly, this composition was used to manufacture the tools for the friction stir welding of the high-softening-temperature materials, which was successfully used for 25 plunges and about 500 cm of butt joints in nickel-based and carbon–steel alloys. Full article
(This article belongs to the Special Issue Friction Stir Welding/Processing Technology)
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