Special Issue "Recent Achievements in Rotary, Linear and Friction Stir Welding of Metals Alloys"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 28 February 2018

Special Issue Editor

Guest Editor
Prof. Dr. Giuseppe Casalino

Dip. di Meccanica, Matematica e Management, Politecnico di Bari, Viale Japigia 182, 70126 Bari, Italy
Website1 | Website2 | E-Mail
Interests: welding; laser materials processing; numerical and analytical modeling of manufacturing processes

Special Issue Information

Dear Colleagues,

Rotary, linear, and friction stir welding of metals alloys are solid-state joining processes in which a joint between two metals can be formed by a combination of frictional heating and applied force.

While linear and rotary friction processes have been established as niche technologies in aero-engines and dissimilar metals circular parts, respectively, friction stir welding is fast becoming the process of choice for manufacturing lightweight transport structures.

As the interest of scientists and researchers have been growing exponentially, this Special Issue aims to collect recent meaningful researches that can help to significantly improve our understanding and the diffusion of those welding processes in the manufacturing practice of joining dissimilar and recent developed metal alloys.

The desired papers would report on the effect of frictional heating and applied force on metals microstructure and mechanical properties. Numerical and analytical models would explore the complexity of the thermal and mechanical phenomena interactions during the welding process. Quality solutions would warrant the reliability and reproducibility of the weld.

Therefore, contributions on weld characterization, quality solutions and process modeling of “Rotary, Linear and Friction Stir Welding” are encouraged and welcomed from academic and industrial experts and researchers.

Prof. Dr. Giuseppe Casalino
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 papers will be 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 1000 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

  • linear
  • rotary
  • stir friction welding
  • weld characterization
  • modeling
  • quality solutions

Published Papers (7 papers)

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Research

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Open AccessArticle 3D Modelling of Flash Formation in Linear Friction Welded 30CrNiMo8 Steel Chain
Metals 2017, 7(10), 449; doi:10.3390/met7100449 (registering DOI)
Received: 20 September 2017 / Revised: 17 October 2017 / Accepted: 18 October 2017 / Published: 21 October 2017
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Abstract
Linear friction welding (LFW) is a solid-state welding process that has been thoroughly investigated for chain welding in recent years in order to replace the currently in use Flash Butt Welding (FBW) process. Modelling has proven to be an indispensable tool in LFW,
[...] Read more.
Linear friction welding (LFW) is a solid-state welding process that has been thoroughly investigated for chain welding in recent years in order to replace the currently in use Flash Butt Welding (FBW) process. Modelling has proven to be an indispensable tool in LFW, thus providing necessary insight to the process, regardless of its final application. This article describes a 3D model developed in the commercial software DEFORM to study the LFW process of 30CrNiMo8 high strength steel in the Hero chain. Hence, a weakly coupled thermal and mechanical model were used, by means of the process experimental input such as displacement histories. The flash morphology and intervening mechanisms were analyzed. A thermal evaluation of different regions in the studied geometry was considered, and a correlation of the modeled and experimental width of the extrusion zone was established. Full article
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Open AccessArticle Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds
Metals 2017, 7(10), 423; doi:10.3390/met7100423
Received: 4 September 2017 / Revised: 3 October 2017 / Accepted: 6 October 2017 / Published: 11 October 2017
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Abstract
BACKGROUND—The solid-phase joining of A6082-T6 plates by bobbin friction stir welding (BFSW) is problematic. Better methods are needed to evaluate the microstructural evolution of the weld. However, conventional Al reagents (e.g., Keller’s and Kroll’s) do not elucidate the microstructure satisfactorily, specifically regarding grain
[...] Read more.
BACKGROUND—The solid-phase joining of A6082-T6 plates by bobbin friction stir welding (BFSW) is problematic. Better methods are needed to evaluate the microstructural evolution of the weld. However, conventional Al reagents (e.g., Keller’s and Kroll’s) do not elucidate the microstructure satisfactorily, specifically regarding grain size and morphology within the weld region. APPROACH—We developed innovative etchants for metallographic observations for optical microscopy. RESULTS—The macrostructure and microstructure of A6082-T6 BFSW welds were clearly demonstrated by optical microscopy analysis. The microetching results demonstrated different microstructures of the Stir Zone (S.Z) distinct from the Base Metal (B.M) and Heat Affected Zone (HAZ) & Thermo-mechanical Affected Zone (TMAZ). The micrographs showed a significant decrease in grain size from 100 μm in B.M to ultrafine 4–10 μm grains for the S.Z. Also, the grain morphology changed from directional columnar in the B.M to equiaxed in the S.Z. Furthermore, thermomechanical recrystallization was observed by the morphological flow of the grain distortion in HAZ and TMAZ. The etchants also clearly show the polycrystalline structure, microflow patterns, and the incoherent interface around inclusion defects. ORIGINALITY—Chemical compositions are identified for a suite of etchant reagents for metallographic examination of the friction-stir welded A6082-T6 alloy. The reagents have made it possible to reveal microstructures not previously evident with optical microscopy. Full article
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Open AccessArticle Study of the Microstructure Evolution and Properties Response of a Friction-Stir-Welded Copper-Chromium-Zirconium Alloy
Metals 2017, 7(9), 381; doi:10.3390/met7090381
Received: 17 August 2017 / Revised: 9 September 2017 / Accepted: 11 September 2017 / Published: 19 September 2017
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Abstract
In this article, the copper-chromium-zirconium (CuCrZr) alloys plates with 21 mm in thickness were butt joined together by means of FSW (friction stir welding). The properties of the FSW joints are studied. The microstructure variations during the process of FSW were investigated by
[...] Read more.
In this article, the copper-chromium-zirconium (CuCrZr) alloys plates with 21 mm in thickness were butt joined together by means of FSW (friction stir welding). The properties of the FSW joints are studied. The microstructure variations during the process of FSW were investigated by optical microscopy (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the grains size in the nugget zone (NZ) are significantly refined, which can be attributed to the dynamic recrystallization (DRX). The microstructure distribution in the NZ is inhomogeneous and the size of equiaxed grains are decreased gradually along the thickness direction from the top to bottom area of the welds. Meanwhile, it is found that the micro-hardness and tensile strength of the welds are slightly increased along the thickness direction from the top to the bottom area of the welds. All the nano-strengthening precipitates in the BM are dissolved into the Cu matrix in the NZ. Therefore, the decreases in hardness, tensile strength, and electrical conductivity can be attributed to the comprehensive effect of dissolution of nano-strengthening precipitates into the supersaturation matrix and severe DRX in the welded NZ. Full article
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Open AccessFeature PaperArticle Influence of Process Parameters on the Vertical Forces Generated during Friction Stir Welding of AA6082-T6 and on the Mechanical Properties of the Joints
Metals 2017, 7(9), 350; doi:10.3390/met7090350
Received: 31 July 2017 / Revised: 28 August 2017 / Accepted: 31 August 2017 / Published: 5 September 2017
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Abstract
The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging
[...] Read more.
The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging between 30 and 100 mm/min. The effect of the tool dwelling was also analysed. The force vs. processing time curve has shown a very complex behaviour during the lowering motion of the pin tool related to the occurrence of both primary and secondary plunging. The tool dwelling produces a quick decrease in the vertical force with growing processing time until reaching a constant value. It was also seen that the tool dwelling does not influence the vertical force in the subsequent stage. As the tool began its welding motion, the vertical force immediately gets to a constant value until tool pulling out takes place. Furthermore, it was shown that the growth in the welding speed and the decrease in the rotational speed lead to an increase in the vertical force. The mechanical properties of the joints were evaluated versus the process parameters and the relationships among the ultimate tensile strength and ultimate elongation and the vertical force were defined. Finally, the microstructure developed during the friction stir welding was investigated and related to the mechanical properties of the joints. Full article
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Open AccessArticle A Finite Element Model to Simulate Defect Formation during Friction Stir Welding
Metals 2017, 7(7), 256; doi:10.3390/met7070256
Received: 16 June 2017 / Revised: 27 June 2017 / Accepted: 28 June 2017 / Published: 7 July 2017
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Abstract
In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and
[...] Read more.
In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and void size with those obtained experimentally. The results compared indicate that the simulated temperature and the data measured are in good agreement with each other. In addition, the model can predict the plasticized zone shape and the presence of a void in the weld quite accurately. However, the void size is overestimated. The effects of welding parameters and tool pin profile are also analyzed. The results reveal that welding at low welding speed or high tool rotational speed could produce a smaller void. Moreover, compared to a smooth tool pin, a featured tool pin can enhance plastic flow in the weld and achieve defect-free weldment. The results are helpful for the optimization of the welding process and the design of welding tools. Full article
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Open AccessArticle The Role of Mechanical Connection during Friction Stir Keyholeless Spot Welding Joints of Dissimilar Materials
Metals 2017, 7(6), 217; doi:10.3390/met7060217
Received: 9 May 2017 / Revised: 5 June 2017 / Accepted: 5 June 2017 / Published: 13 June 2017
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Abstract
Contrast experiments of lap joints among dissimilar AZ31B Mg alloy, Mg99.50, zinc-coated DP600 sheet, and non-zinc-coated DP600 sheet were made by friction stir keyholeless spot welding (FSKSW) and vacuum diffusion welding (VDW), respectively. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were
[...] Read more.
Contrast experiments of lap joints among dissimilar AZ31B Mg alloy, Mg99.50, zinc-coated DP600 sheet, and non-zinc-coated DP600 sheet were made by friction stir keyholeless spot welding (FSKSW) and vacuum diffusion welding (VDW), respectively. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to investigate the microstructures and components of the joints welded. The experimental results show that the FSKSW bonding method is a kind of compound mode that contains a mechanical connection and element diffusion fusion connection, in which mechanical connection has the main decisive function on joints of Mg/steel. Elements diffusion exists in the interfacial region of the joints and the elements diffusion extent is basically the same to that of VDW. The elements’ diffusion in Mg/steel using FSKSW is defined in the reaction between small amounts elements of the base metal and zinc-coated metals. The intermetallic compounds and composite oxide perform some reinforcement on the mechanical connection strength. Full article
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Review

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Open AccessReview A Comparison of Different Finite Element Methods in the Thermal Analysis of Friction Stir Welding (FSW)
Metals 2017, 7(10), 450; doi:10.3390/met7100450 (registering DOI)
Received: 28 August 2017 / Revised: 21 September 2017 / Accepted: 22 September 2017 / Published: 21 October 2017
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Abstract
Friction Stir Welding (FSW) is a novel kind of welding for joining metals that are impossible or difficult to weld by conventional methods. Three-dimensional nature of FSW makes the experimental investigation more complex. Moreover, experimental observations are often costly and time consuming, and
[...] Read more.
Friction Stir Welding (FSW) is a novel kind of welding for joining metals that are impossible or difficult to weld by conventional methods. Three-dimensional nature of FSW makes the experimental investigation more complex. Moreover, experimental observations are often costly and time consuming, and usually there is an inaccuracy in measuring the data during experimental tests. Thus, Finite Element Methods (FEMs) has been employed to overcome the complexity, to increase the accuracy and also to reduce costs. It should be noted that, due to the presence of large deformations of the material during FSW, strong distortions of mesh might be happened in the numerical simulation. Therefore, one of the most significant considerations during the process simulation is the selection of the best numerical approach. It must be mentioned that; the numerical approach selection determines the relationship between the finite grid (mesh) and deforming continuum of computing zones. Also, numerical approach determines the ability of the model to overcome large distortions of mesh and provides an accurate resolution of boundaries and interfaces. There are different descriptions for the algorithms of continuum mechanics include Lagrangian and Eulerian. Moreover, by combining the above-mentioned methods, an Arbitrary Lagrangian–Eulerian (ALE) approach is proposed. In this paper, a comparison between different numerical approaches for thermal analysis of FSW at both local and global scales is reviewed and the applications of each method in the FSW process is discussed in detail. Observations showed that, Lagrangian method is usually used for modelling thermal behavior in the whole structure area, while Eulerian approach is seldom employed for modelling of the thermal behavior, and it is usually employed for modelling the material flow. Additionally, for modelling of the heat affected zone, ALE approach is found to be as an appropriate approach. Finally, several significant challenges and subjects remain to be addressed about FSW thermal analysis and opportunities for the future work are proposed. Full article
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