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Metals
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Advances in Friction Stir Welding and Processing
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Advances in Friction Stir Welding and Processing

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

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 16330

Special Issue Editor

Prof. Dr. Michael Regev

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Guest Editor
Department of Mechanical Engineering, Braude College of Engineering, Karmiel 2161401, Israel
Interests: metallurgy; magnesium alloys; amorphous alloys; friction stir welding and processing of Al, Cu, Mg and Ti alloys; high temperature mechanical properties; joining processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The friction stir welding process (FSW) was developed in the early 1990s. Over the years, FSW proved itself ideal for creating good-quality butt joints and lap joints in a number of materials, especially the family of nonferrous metallic materials, including even those that are extremely difficult to weld by conventional fusion welding processes. During FSW, the frictional heat that is generated is effectively utilized to facilitate material consolidation and eventual joining with the aid of an axial pressure. The process is, therefore, a non-fusion welding process. As of today, FSW is, due to its advantages, a common industrial welding process. Friction stir processing (FSP) was derived from FSW with the aim of using severe plastic deformation to obtain a stir zone with very fine grain size and hence to improve the mechanical properties of the material. FSP is identical to FSW except that in FSP, the rotating tool does not weld the parts to one another. Thus, its operation may be referred to as a ‘‘bead on plate’’ process. It is my pleasure to invite you to submit a manuscript in the fields of FSW and FSP for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. Michael Regev
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
  • friction stir processing
  • mechanical properties
  • microstructure

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Published Papers (4 papers)

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Research

15 pages, 19508 KiB  
Article
Modeling Friction Stir Welding: On Prediction and Numerical Tool Development
by Max Hossfeld
Metals 2022, 12(9), 1432; https://doi.org/10.3390/met12091432 - 29 Aug 2022
Cited by 7 | Viewed by 4010
Abstract
This paper reports on a simulation framework capable of predicting the outcomes of the friction stir welding process. Numerical tool development becomes directly possible without the need for previous calibration to welding experiments. The predictive power of the framework is demonstrated by a [...] Read more.
This paper reports on a simulation framework capable of predicting the outcomes of the friction stir welding process. Numerical tool development becomes directly possible without the need for previous calibration to welding experiments. The predictive power of the framework is demonstrated by a case study for numerical tool development and validated experimentally. Different tool geometries with high levels of detail and active material flow features are investigated, and their effect on the process outcomes is quantified. The simulation framework is found to be able to predict forces, material flow, temperature fields, weld formation and welding defects a priori, in detail and precisely. This applies to the outer appearance of the weld as well as the location, shape, and size of inner welding defects. Causes for defects can be identified, analyzed and remedied. Compared to the validation experiment, the simulation showed a slight overestimation of the process impact in the case study. Since the framework relies strictly on analytically describable physics, the efforts for modeling the process are moderate considering the precision of the results. Full article
(This article belongs to the Special Issue Advances in Friction Stir Welding and Processing)
►▼ Show Figures

Figure 1

Figure 1
<p>Base geometry: relevant dimensions and manufactured tool made from QRO<sup>®</sup> 90.</p> Full article ">Figure 2
<p>Definition, location and arrangement of the complementary material flow feature (<b>red</b>) as a superposition on the base tool geometry.</p> Full article ">Figure 3
<p>Temperature-dependent thermal and mechanical properties of AA 6061-T6.</p> Full article ">Figure 4
<p>Schematic setup of the numerical model (starting position): isometric, front and side view, shown without tool holder, backing and clamping.</p> Full article ">Figure 5
<p>Setup of numerical model with meshing of Lagrangian tool and Eulerian region, isometric and rear view, Eulerian region partially hidden in each case on the left.</p> Full article ">Figure 6
<p>Areas defined for heat conduction (<b>red</b>) and convection (<b>blue</b>) on tool and workpieces.</p> Full article ">Figure 7
<p>Development stages of the tools manufactured for verification. Base geometry without contouring, third and fifth design iterations with 1.8 mm and 2.6 mm structure width, respectively.</p> Full article ">Figure 8
<p>Outer appearance of weld carried out with the base geometry in simulation (<b>left</b>) and experiment (<b>right</b>).</p> Full article ">Figure 9
<p>Semi-transparent section along the welding direction showing the local velocity distribution. At the top, shortly after the start of the traverse movement, at the bottom after reaching the process’ steady state. Voids shaded, tool not shown.</p> Full article ">Figure 10
<p>Barker-etched cross section of the real welding experimental corresponding to the steady state of <a href="#metals-12-01432-f009" class="html-fig">Figure 9</a> with wormhole defect and burr formation on the right.</p> Full article ">Figure 11
<p>Velocity vectors for base geometry (<b>left</b>) and third design iteration with 1.8 mm structure width (<b>right</b>). Tools not shown. Ellipse left: stagnation point. Ellipses right: induced material flow by and within structure.</p> Full article ">Figure 12
<p>Material flow induced by the 2.6 mm wide structures of the fifth tool design iteration in the area of pin regime and former stagnation point. Tool not shown.</p> Full article ">Figure 13
<p>Etched cross sections of the welding tests carried out for validation with material flow representation at the (former) neuralgic stagnation point. 1.8 mm (<b>top</b>) and 2.6 mm (<b>bottom</b>) structure width.</p> Full article ">Figure 14
<p>Comparison of temperature profiles and gradients in cross-section for base geometry (<b>top</b>) and fifth design iteration (<b>bottom</b>), e.g., with and without active material flow structures.</p> Full article ">
14 pages, 8727 KiB  
Article
Influence of Tool and Welding Parameters on the Risk of Wormhole Defect in Aluminum Magnesium Alloy Welded by Bobbin Tool FSW
by Milan Pecanac, Danka Labus Zlatanovic, Nenad Kulundzic, Miroslav Dramicanin, Zorana Lanc, Miodrag Hadzistević, Slobodan Radisic and Sebastian Balos
Metals 2022, 12(6), 969; https://doi.org/10.3390/met12060969 - 5 Jun 2022
Cited by 4 | Viewed by 2451
Abstract
Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of [...] Read more.
Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of FSW since the bottom shoulder forms the bottom surface of the weld, without the need for a backing plate. Moreover, the tool enters the base metal sideways and travels, forming the joint in a straight line while rotating, without the need for downward and upward motion at the beginning and end of the process. This paper presents a study on the BTFSW tool geometry and parameters on the risk of wormhole defect formation in the AA5005 aluminum–magnesium alloy and the wormhole effect on mechanical properties. It was shown that higher stress imposed by the tool geometry on the joint has a significant influence on heating, an effect similar to the increased rotational speed. Optimal kinematic and geometrical tool properties are required to avoid wormhole defects. Although weld tensile strengths were lower (between ~111 and 115 MPa) compared with a base metal (137 MPa), the ductile fracture was obtained. Furthermore, all welds had a higher impact strength (between ~20.7 and 27.8 J) compared with the base material (~18.5 J); it was found that the wormhole defect only marginally influences the mechanical properties of welds. Full article
(This article belongs to the Special Issue Advances in Friction Stir Welding and Processing)
►▼ Show Figures

Figure 1

Figure 1
<p>Schematic classification of friction stir welding processes, adapted with permission from [<a href="#B18-metals-12-00969" class="html-bibr">18</a>]. 2020, Danka Labus Zlatanovic.</p> Full article ">Figure 2
<p>FSW tools: (<b>a</b>) conventional FSW tool; (<b>b</b>) BTFSW.</p> Full article ">Figure 3
<p>Bobbin friction stir welding process set-up.</p> Full article ">Figure 4
<p>Tools used: in tool A2, <span class="html-italic">β</span><sub>1</sub> = 2°; in tool A4, <span class="html-italic">β</span><sub>2</sub> = 4° (All units in are in milimeters).</p> Full article ">Figure 5
<p>Specimen cutting plan.</p> Full article ">Figure 6
<p>Cross-sectional macrographs of specimens: (<b>a</b>) A2-1; (<b>b</b>) A2-2; (<b>c</b>) A2-3; (<b>d</b>) A4-1; (<b>e</b>) A4-2; and (<b>f</b>) A4-3.</p> Full article ">Figure 7
<p>Microstructure of the base material (<b>a</b>), nugget zone (<b>b</b>), and two transition zones (<b>c</b>,<b>d</b>) in specimen A4-3.</p> Full article ">Figure 8
<p>Thermograms of the BTFSW welding process.</p> Full article ">Figure 9
<p>Results of tensile testing (AS—advancing side; RS—retrieving side; SZ—stir zone; HAZ—heat-affected zone; and TMAZ—thermomechanically affected zone).</p> Full article ">Figure 10
<p>Bend testing specimens over the bottom of the weld.</p> Full article ">Figure 11
<p>Charpy impact test results.</p> Full article ">Figure 12
<p>Force-time charts for (<b>a</b>) base metal; (<b>b</b>) specimen A4-1.</p> Full article ">
17 pages, 11732 KiB  
Article
Basic Tool Design Guidelines for Friction Stir Welding of Aluminum Alloys
by Elizabeth Hoyos and María Camila Serna
Metals 2021, 11(12), 2042; https://doi.org/10.3390/met11122042 - 16 Dec 2021
Cited by 18 | Viewed by 6212
Abstract
Friction Stir Welding (FSW) is a solid-state welding process that has multiple advantages over fusion welding. The design of tools for the FSW process is a factor of interest, considering its fundamental role in obtaining sound welds. There are some commercially available alternatives [...] Read more.
Friction Stir Welding (FSW) is a solid-state welding process that has multiple advantages over fusion welding. The design of tools for the FSW process is a factor of interest, considering its fundamental role in obtaining sound welds. There are some commercially available alternatives for FSW tools, but unlike conventional fusion welding consumables, their use is limited to very specific conditions. In this work, equations to act as guidelines in the design process for FSW tools are proposed for the 2XXX, 5XXX, 6XXX, and 7XXX aluminum series and any given thickness to determine: pin length, pin diameter, and shoulder diameter. Over 80 sources and 200 tests were used and detailed to generate these expressions. As a verification approach, successful welds by authors outside the scope of the original review and the tools used were evaluated under this development and used as case studies or verification for the guidelines. Variations between designs made using the guidelines and those reported by other researchers remain under 21%. Full article
(This article belongs to the Special Issue Advances in Friction Stir Welding and Processing)
►▼ Show Figures

Figure 1

Figure 1
<p>Types of shoulders.</p> Full article ">Figure 2
<p>Types of pins.</p> Full article ">Figure 3
<p>Pin diameter vs. thickness for series: (<b>a</b>) 2XXX; (<b>b</b>) 5XXX; (<b>c</b>) 6XXX, and (<b>d</b>) 7XXX.</p> Full article ">Figure 4
<p>Summary of trend lines for pin diameter vs. thickness.</p> Full article ">Figure 5
<p>Pin length vs. thickness for series: (<b>a</b>) 2XXX; (<b>b</b>) 5XXX; (<b>c</b>) 6XXX; and (<b>d</b>) 7XXX.</p> Full article ">Figure 6
<p>Summary of trend lines for pin length vs. thickness.</p> Full article ">Figure 7
<p>Shoulder diameter vs. thickness for series: (<b>a</b>) 2XXX; (<b>b</b>) 5XXX; (<b>c</b>) 6XXX; and (<b>d</b>) 7XXX.</p> Full article ">Figure 7 Cont.
<p>Shoulder diameter vs. thickness for series: (<b>a</b>) 2XXX; (<b>b</b>) 5XXX; (<b>c</b>) 6XXX; and (<b>d</b>) 7XXX.</p> Full article ">Figure 8
<p>Summary of trend lines for shoulder diameter vs. thickness.</p> Full article ">Figure 9
<p>Tool design: (<b>a</b>) pin; (<b>b</b>) shoulder.</p> Full article ">Figure 10
<p>X-ray of an AA7075-T6 aluminum FSW weld [<a href="#B117-metals-11-02042" class="html-bibr">117</a>].</p> Full article ">Figure 11
<p>Test plate dimensions (all units in mm).</p> Full article ">Figure 12
<p>Tool 1 design: (<b>a</b>) shoulder and (<b>b</b>) pin.</p> Full article ">Figure 13
<p>Tool 1 trial—X-ray of an AA 6061-T6 aluminum FSW weld.</p> Full article ">Figure 14
<p>Tool 2 trial—X-ray of an AA 6061-T6 aluminum FSW weld.</p> Full article ">Figure 15
<p>Ultrasound results with indication for Tool 2 trial (EPOCH 4 ultrasound system).</p> Full article ">Figure 16
<p>Cavity location for Tool 2 trial, according to ultrasound results (EPOCH 4 ultrasound system).</p> Full article ">
11 pages, 1590 KiB  
Article
A Study of the Metallurgical and Mechanical Properties of Friction-Stir-Processed Cu
by Michael Regev and Stefano Spigarelli
Metals 2021, 11(4), 656; https://doi.org/10.3390/met11040656 - 17 Apr 2021
Cited by 12 | Viewed by 2615
Abstract
Friction stir processing (FSP), a severe plastic deformation process, was applied on pure Cu to obtain a stir zone with a very fine grain size. Yet, when FSP is used, the stir zone is as wide as the diameter of the shoulder at [...] Read more.
Friction stir processing (FSP), a severe plastic deformation process, was applied on pure Cu to obtain a stir zone with a very fine grain size. Yet, when FSP is used, the stir zone is as wide as the diameter of the shoulder at the upper surface of the weld and markedly narrower near its opposite surface. This property, as well as the differences between the advancing side and the retreating side, makes it impossible to obtain a uniform cross-section as far as the microstructure and mechanical properties are concerned. For these reasons, a new approach is proposed in which the material was processed on both sides, thus yielding a wider, rectangular and more homogenous stir zone from which all the specimens were machined out. Processing the material from both sides eliminated any microstructural difference between the upper and the lower side, at least within the gauge length’s cross-section of the creep specimens. Although grain refinement was detected, the mechanical properties of the friction-stir-processed (FSP’ed) material are inferior relative to those of the parent material. The TEM study reported in the current paper revealed the existence of nanosized grains in the FSP’ed material due to dynamic recrystallization (DRX) occurring during the processing stage. Because both X-ray inspection and fractography showed that the FSP’ed material was free of defects, the material may not comply with the Hall–Petch relation due to lower dislocation density caused by XRD occurring during FSP. The inverse Hall–Petch effect may also be considered as an assistive mechanism in mechanical property deterioration. Full article
(This article belongs to the Special Issue Advances in Friction Stir Welding and Processing)
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Figure 1

Figure 1
<p>The processing tools: (<b>a</b>) cylindrical (<b>b</b>) square.</p> Full article ">Figure 2
<p>Optical micrographs: (<b>a</b>) parent metal (<b>b</b>) friction-stir-processed material.</p> Full article ">Figure 3
<p>Microhardness profiles across the stir zone.</p> Full article ">Figure 4
<p>SEM micrographs of the fracture surface of broken tensile specimens: (<b>a</b>) parent material; (<b>b</b>) friction-stir-processed (FSP’ed) specimen.</p> Full article ">Figure 5
<p>TEM bright-field (BF) micrographs taken near &lt;<math display="inline"><semantics> <mrow> <mn>011</mn> </mrow> </semantics></math>&gt; Z.A.: (<b>a</b>,<b>b</b>) parent material; (<b>c</b>) FSP’ed material; (<b>d</b>) SADP of &lt;<math display="inline"><semantics> <mrow> <mn>011</mn> </mrow> </semantics></math>&gt; Z.</p> Full article ">
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