Special Issue "Semi-solid Processing of Alloys and Composites"

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

Deadline for manuscript submissions: closed (31 March 2018)

Special Issue Editors

Guest Editor
Dr. Shahrooz Nafisi

Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2M7, Canada
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Interests: metallurgy of aluminum and steel alloys; material characterization; alloy development; testing methodologies; solidification and casting; additive manufacturing
Guest Editor
Assoc. Prof. Reza Ghomashchi

School of Mechanical Engineering, University Adelaide, Adelaide, SA 5005, Australia
Website | E-Mail
Interests: solidification and casting; powder metallurgy; additive manufacturing; energy converting materials; metallurgy of aluminum and steel alloys; advanced composites

Special Issue Information

Dear Colleagues,

Semi-Solid Metal (SSM) processing, as a viable manufacturing route to those of conventional casting and forging, has not yet been fully exploited despite nearly half a century since its introduction to metal industry. The slow pace of adopting SSM routes may be due to various reasons, including capital costs, profit margins, and, most importantly, the lack of detailed analysis of various SSM processes in open literature to confidently establish their advantages over more conventional routes. Therefore, it becomes necessary for SSM community to disseminate their findings more effectively to generate greater confidence in SSM processes in the eyes of our industrial leaders. This why we have embarked on this task to invite the leaders in SSM research to share their findings in a Special Issue dedicated to semi-solid processing of metals and composites.

Semi-Solid Metal (SSM) processing takes advantage of both forming and shaping characteristics usually employed for liquid and solid materials. In the absence of shear forces, the semi-solid metal has similar characteristics to solids, i.e., easily transferred and shaped, while by applying a defined force, the viscosity is reduced and the material flows like a liquid. Such unique characteristics have made SSM routes attractive alternatives to conventional casting on an industrial scale.

With the intention of taking full advantage of SSM characteristics, it is crucial to understand the SSM processing including topics such as solidification and structural evolution, flow behavior through modeling and rheology, new processes and process control, alloy development and properties in general.

This Special Issue is focused on the recent research and findings in the field with the aim of filling the gap between industry and academia, and also to shed light on some of the fundamentals of science and technology of semi-solid processing.

Topics include but not limited to;

  • Processing
  • Materials development and basics of alloy design
  • Solidification and structural evolution
  • Micro/Macro structural characterization
  • Modeling and simulation
  • Rheology
  • Properties of semi-solid alloys
  • Industrial application

Dr. Shahrooz Nafisi
Prof. Reza Ghomashchi
Guest Editors

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. 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

  • Rheo-route
  • Thixo-route
  • Semi-solid
  • Rheology
  • Modeling
  • Characterization
  • Viscosity
  • Solidification
  • Fluidity

Published Papers (11 papers)

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Research

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Open AccessArticle Microstructure, Mechanical Properties and Wear Behavior of the Rheoformed 2024 Aluminum Matrix Composite Component Reinforced by Al2O3 Nanoparticles
Metals 2018, 8(6), 460; https://doi.org/10.3390/met8060460
Received: 3 May 2018 / Revised: 27 May 2018 / Accepted: 14 June 2018 / Published: 15 June 2018
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Abstract
The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that
[...] Read more.
The 2024 nanocomposite reinforced with Al2O3 nanoparticles was fabricated by the ultrasonic assisted semisolid stirring (UASS) method and rheoformed into a cylinder component. Microstructure, mechanical properties, and wear behavior of the rheoformed composite components were investigated. The results showed that the composite components with complete filling status and a good surface were rheoformed successfully. The deformation of semisolid slurries was mainly dominated by flow of liquid incorporating solid grains (FLS), sliding between solid grains (SSG), and plastic deformation of solid grains (PDS). Mechanical properties of the rheoformed composite components were influenced by stirring temperature, stirring time, and volume fraction of Al2O3 nanoparticles. The optimal ultimate tensile strength (UTS) of 358 MPa and YS of 245 MPa were obtained at the bottom of the rheoformed composite components after a 25-min stirring of composite semisolid slurry with 5% Al2O3 nanoparticles at 620 °C. Enhancement of mechanical properties was attributed to high density dislocations and dislocation tangles and uniform dispersed Al2O3 nanoparticles in the aluminum matrix. Natural ageing led to the occurrence of needle-like Al2CuMg phase and short-rod-like Al2Cu phase. UTS of 417 MPa and YS of 328 MPa of the rheoformed composite components were achieved after T6 heat treatment. Improvement of mechanical properties is due to the more precipitated needle-like Al2CuMg phase and short-rod-like Al2Cu phase. Wear resistance of the rheoformed composite components was higher than that of the rheoformed matrix component. Wear resistance of the rheoformed composite component increased with an increase in Al2O3 nanoparticles from 1% to 7%. A slight decrease in wear rate resulted from 10% Al2O3 nanoparticles due to greater agglomeration of Al2O3 nanoparticles. A combination mechanism of adhesion and delamination was determined according to worn surface morphology. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessFeature PaperArticle Thixoforming of an Fe-Rich Al-Si-Cu Alloy—Thermodynamic Characterization, Microstructural Evolution, and Rheological Behavior
Metals 2018, 8(5), 332; https://doi.org/10.3390/met8050332
Received: 28 February 2018 / Revised: 20 April 2018 / Accepted: 20 April 2018 / Published: 9 May 2018
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Abstract
Thixoforming depends on three factors: (a) the thermodynamic stability of the solid-to-liquid transformation in the presence of temperature fluctuations; (b) the size and morphology of the solid particles in the liquid in the semisolid state; and (c) the rheology of the semisolid slurry
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Thixoforming depends on three factors: (a) the thermodynamic stability of the solid-to-liquid transformation in the presence of temperature fluctuations; (b) the size and morphology of the solid particles in the liquid in the semisolid state; and (c) the rheology of the semisolid slurry during formation. In this study, these parameters were characterized for an Al-Si-Cu alloy with a high Fe content (B319+Fe alloy). Fe is usually found in raw metal produced by recycling, and its removal increases processing costs. This study is an attempt to use this lower-cost alloy for the thixoforming route. Thermodynamic analysis was performed by numerical simulation (under Scheil conditions) and the application of the differentiation method (DM) to differential scanning calorimetry (DSC) curves recorded during heating cycles up to 700 °C at 5, 10, 15, 20, and 25 °C/min. The processing window was evaluated by comparing the results of the DM and those of the analysis of open-die thixoforged samples after isothermal heat treatment at 575, 582, 591, and 595 °C for 0, 30, 60, and 90 s. The microstructural and rheological behavior of the semisolid slurry was analyzed at 591 and 595 °C for all four soak times. Isothermal heat treatment caused the refinement and spheroidization of the solid phase. Good agreement between the predicted thermodynamic behavior and the microstructural behavior of the thixoformed B319+Fe alloy samples was observed. Although the alloy exhibited a coarse microstructure, it was microstructurally and rheologically stable at all temperatures and for all the soak times studied, indicating that B319+Fe is a promising raw material for thixoforming. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Microstructure and Mechanical Properties of Thixowelded AISI D2 Tool Steel
Metals 2018, 8(5), 316; https://doi.org/10.3390/met8050316
Received: 9 March 2018 / Revised: 14 April 2018 / Accepted: 19 April 2018 / Published: 4 May 2018
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Abstract
Rigid perpetual joining of materials is one of the main demands in most of the manufacturing and assembling industries. AISI D2 cold work tool steels is commonly known as non-weldable metal that a high quality joint of this kind of material can be
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Rigid perpetual joining of materials is one of the main demands in most of the manufacturing and assembling industries. AISI D2 cold work tool steels is commonly known as non-weldable metal that a high quality joint of this kind of material can be hardly achieved and almost impossible by conventional welding. In this study, a novel thixowelding technology was proposed for joining of AISI D2 tool steel. The effect of joining temperature, holding time and post-weld heat treatment on microstructural features and mechanical properties were also investigated. Acceptable joints without defect were achieved through the welding temperature of 1300 °C, while the welding at lower temperature resulted in a series of cracks across the entire joint that led to spontaneous fracture after joining. Tensile test results showed that maximum joint tensile strength of 271 MPa was achieved at 1300 °C and 10 min holding time, which was 35% of that of D2 base metal. Meanwhile, tensile strength of the joined parts after heat treatment showed a significant improvement over the non-heat treated condition with 560 MPa, i.e., about 70% of that of the strength value of the D2 base metal. This improvement in the tensile strength attributed to the dissolution of some amounts of eutectic chromium carbides and changes in the microstructure of the matrix. The joints are fractured at the diffusion zone, and the fracture exhibits a typical brittle characteristic. The present study successfully confirmed that by avoiding dendritic microstructure, as often resulted from the fusion welding, high joining quality components obtained in the semi-solid state. These results can be obtained without complex or additional apparatuses that are used in traditional joining process. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Microstructure and Properties of Semi-solid ZCuSn10P1 Alloy Processed with an Enclosed Cooling Slope Channel
Metals 2018, 8(4), 275; https://doi.org/10.3390/met8040275
Received: 14 March 2018 / Revised: 11 April 2018 / Accepted: 16 April 2018 / Published: 17 April 2018
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Abstract
Semi-solid ZCuSn10P1 alloy slurry was fabricated by a novel enclosed cooling slope channel (ECSC). The influence of pouring length of ECSC on the microstructures of ZCuSn10P1 alloy semi-solid slurry was studied with an optical microscope an optical microscope (OM), scanning electron microscope (SEM),
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Semi-solid ZCuSn10P1 alloy slurry was fabricated by a novel enclosed cooling slope channel (ECSC). The influence of pouring length of ECSC on the microstructures of ZCuSn10P1 alloy semi-solid slurry was studied with an optical microscope an optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Liquid squeeze casting and semi-solid squeeze casting were performed under the same forming conditions, and the microstructure and properties were compared. The results show that primary α-Cu phase gradually evolved from dendrites to worm-like or equiaxed grains under the chilling action of the inner wall of the ECSC. The mass fraction of tin in the primary α-Cu phase increased from 5.85 to 6.46 after the ECSC process, and intergranular segregation was effectively suppressed. The finest microstructure can be obtained at 300 mm pouring length of ECSC; the equivalent diameter is 46.6 μm and its shape factor is 0.73. The average ultimate tensile strength and average elongation of semi-solid squeeze casting ZCuSn10P1 alloy reached 417 MPa and 12.6%, which were improved by 22% and 93%, respectively, as compared to that of liquid squeeze casting. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Microstructure of Semi-Solid Billets Produced by Electromagnetic Stirring and Behavior of Primary Particles during the Indirect Forming Process
Metals 2018, 8(4), 271; https://doi.org/10.3390/met8040271
Received: 18 February 2018 / Revised: 6 April 2018 / Accepted: 12 April 2018 / Published: 15 April 2018
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Abstract
An A356 alloy semi-solid billet was fabricated using electromagnetic stirring. After inserting the semi-solid billet into an indirect die, a thin plate of 1.2 mm thickness was fabricated by applying compression. The microstructure of the semi-solid billets fabricated in various stirring conditions (solid
[...] Read more.
An A356 alloy semi-solid billet was fabricated using electromagnetic stirring. After inserting the semi-solid billet into an indirect die, a thin plate of 1.2 mm thickness was fabricated by applying compression. The microstructure of the semi-solid billets fabricated in various stirring conditions (solid fraction and stirring force) were analyzed. The deformation and behavior of the primary α-Al particles were analyzed for various parameters (solid fraction, die friction, compression rate, and compression pressure). In the stirred billets, a globular structure was dominant, while a dendrite structure was dominant in the unstirred billets. As the solid fraction decreased and the stirring current increased, the equivalent diameter and roundness of the primary α-Al particles decreased. The primary α-Al particle sizes were reduced as the compressing velocity increased, while a greater number of particles could move as the compressing pressure increased. As the path over which the motion occurred became smoother, the fluidity of the particles improved. Under compression, bonded primary α-Al particles became separated into individual particles again, as the bonds were broken. As wearing caused by friction and collisions between the particles during this motion occurred, the particle sizes were reduced, and the particle shapes become increasingly spheroid. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Study of Semi-Solid Magnesium Alloys (With RE Elements) as a Non-Newtonian Fluid Described by Rheological Models
Metals 2018, 8(4), 222; https://doi.org/10.3390/met8040222
Received: 28 December 2017 / Revised: 15 March 2018 / Accepted: 23 March 2018 / Published: 28 March 2018
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Abstract
This paper includes the results of high-temperature rheological experiments on semi-solid magnesium alloys and the verification of different models describing the rheological behaviour of semi-solid magnesium alloys. Such information is key from the point of view of designing alloy forming processes in their
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This paper includes the results of high-temperature rheological experiments on semi-solid magnesium alloys and the verification of different models describing the rheological behaviour of semi-solid magnesium alloys. Such information is key from the point of view of designing alloy forming processes in their semi-solid states. Magnesium alloys are a very attractive material, due to their light weight and good plastic properties; on the other hand, this material is very reactive in a liquid (semi-solid) state, which is challenging from a testing and forming perspective. Formulating/finding models for an accurate description of the rheological behaviour of semi-solid magnesium alloys seems to be key from the standpoint of developing and optimising forming processes for semi-solid magnesium alloys. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Effect of Segregation and Surface Condition on Corrosion of Rheo-HPDC Al–Si Alloys
Metals 2018, 8(4), 209; https://doi.org/10.3390/met8040209
Received: 22 February 2018 / Revised: 21 March 2018 / Accepted: 23 March 2018 / Published: 24 March 2018
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Abstract
Corrosion properties of two Al–Si alloys processed by Rheo-high pressure die cast (HPDC) method were examined using polarization and electrochemical impedance spectroscopy (EIS) techniques on as-cast and ground surfaces. The effects of the silicon content, transverse and longitudinal macrosegregation on the corrosion resistance
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Corrosion properties of two Al–Si alloys processed by Rheo-high pressure die cast (HPDC) method were examined using polarization and electrochemical impedance spectroscopy (EIS) techniques on as-cast and ground surfaces. The effects of the silicon content, transverse and longitudinal macrosegregation on the corrosion resistance of the alloys were determined. Microstructural studies revealed that samples from different positions contain different fractions of solid and liquid parts of the initial slurry. Electrochemical behavior of as-cast, ground surface, and bulk material was shown to be different due to the presence of a segregated skin layer and surface quality. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Tribological Behavior of Nano-Sized SiCp/7075 Composite Parts Formed by Semisolid Processing
Metals 2018, 8(3), 148; https://doi.org/10.3390/met8030148
Received: 26 December 2017 / Revised: 18 January 2018 / Accepted: 17 February 2018 / Published: 25 February 2018
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Abstract
The tribological behavior of the rheoformed and thixoformed nano-sized SiCp/7075 composite parts is investigated. The semisolid stirring temperature has a little influence on the friction coefficient and wear resistance of the rheoformed composite parts. As for the thixoformed composite parts, the
[...] Read more.
The tribological behavior of the rheoformed and thixoformed nano-sized SiCp/7075 composite parts is investigated. The semisolid stirring temperature has a little influence on the friction coefficient and wear resistance of the rheoformed composite parts. As for the thixoformed composite parts, the average value of the steady-state coefficient of friction increases firstly and then decreases with increasing reheating temperature. Higher wear resistance is achieved at a reheating temperature of 580 °C. The average value of the steady-state friction coefficient of the rheoformed composite parts varies from 0.37 to 0.45 upon applied loads of from 20 to 50 N. Weight loss increases slightly upon an increase of applied load from 20 to 40 N. An applied load of 50 N leads to a significant increase of the weight loss. The wear rate decreases firstly and then increases with increasing applied load. As for the thixoformed composite part, the average value of the steady-state friction coefficient and the weight loss decreased with an increasing applied load. However, the wear rate decreases firstly with increasing applied load and then increases. As for the rheoformed composite part, the average value of the steady-state friction coefficient decreases firstly and then increases a little with increasing sliding velocity. Weight loss and wear rate show a first increase and a followed decrease with increasing sliding velocity. As for the thixoformed composite part, the average value of the steady-state friction coefficient shows a decrease with increasing sliding velocity. Weight loss and wear rate exhibit, at first, an increase, and then a decrease with increasing sliding velocity. The average friction coefficient varies from 0.4 to 0.44 with increasing volume fraction of SiC. Weight loss and wear rate decrease with increasing volume fraction of SiC. An increase in dislocation density around the nano-sized SiC particles and the mismatch of the coefficient of thermal expansion (CTE) between 7075 matrix and nano-sized SiC particles during solidification improve the wear resistance of the composite. The dominant wear mechanisms of the rheoformed and thixoformed composite parts are adhesive wear, abrasive wear and delamination wear. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessFeature PaperArticle An Experimental Evaluation of Electron Beam Welded Thixoformed 7075 Aluminum Alloy Plate Material
Metals 2017, 7(12), 569; https://doi.org/10.3390/met7120569
Received: 8 November 2017 / Revised: 12 December 2017 / Accepted: 13 December 2017 / Published: 15 December 2017
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Abstract
Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 °C, for 3 min. The microstructural evolution and
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Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 °C, for 3 min. The microstructural evolution and mechanical properties of EB welded plates, as well as the heat-treated specimens, were investigated in the Base Metal (BM), Heat Affected Zone (HAZ), and Fusion Zone (FZ), using optical microscopy, Scanning Electron Microscopy (SEM), EDX (Energy Dispersive X-ray Analysis), and Vickers hardness test. Results indicated that after EBW, the grain size substantially decreased from 67 µm in both BM and HAZ to 7 µm in the FZ, and a hardness increment was observed in the FZ as compared to the BM and HAZ. Furthermore, the PWHT led to grain coarsening throughout the material, along with a further increase in hardness in the FZ. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Review

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Open AccessReview Rheological Characterization of Semi-Solid Metals: A Review
Metals 2018, 8(4), 245; https://doi.org/10.3390/met8040245
Received: 18 February 2018 / Revised: 24 March 2018 / Accepted: 4 April 2018 / Published: 7 April 2018
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Abstract
In the present review, the main findings on the rheological characterization of semi-solid metals (SSM) are presented. Experimental results are a fundamental basis for the development of comprehensive and accurate mathematics used to design the process effectively. For this reason, the main experimental
[...] Read more.
In the present review, the main findings on the rheological characterization of semi-solid metals (SSM) are presented. Experimental results are a fundamental basis for the development of comprehensive and accurate mathematics used to design the process effectively. For this reason, the main experimental procedures for the rheological characterization of SSM are given, together with the models most widely used to fit experimental data. Subsequently, the material behavior under steady state condition is summarized. Also, non-viscous properties and transient conditions are discussed since they are especially relevant for the industrial semi-solid processing. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessReview Microstructure and Properties of Semi-Solid Aluminum Alloys: A Literature Review
Metals 2018, 8(3), 181; https://doi.org/10.3390/met8030181
Received: 4 February 2018 / Revised: 6 March 2018 / Accepted: 6 March 2018 / Published: 13 March 2018
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Abstract
Semi-solid processing of aluminum alloys is a well-known manufacturing technique able to combine high production rates with parts quality, resulting in high performance and reasonable component costs. The advantages offered by semi-solid processing are due to the shear thinning behavior of the thixotropic
[...] Read more.
Semi-solid processing of aluminum alloys is a well-known manufacturing technique able to combine high production rates with parts quality, resulting in high performance and reasonable component costs. The advantages offered by semi-solid processing are due to the shear thinning behavior of the thixotropic slurries during the mold filling. This is related to the microstructure of these slurries consisting of solid, nondendritic, near-globular primary particles surrounded by a liquid matrix. This paper presents a review on the formation of this nondendritic microstructure, reports on the different proposed mechanisms that might be responsible, and illustrates the relationship between microstructure and properties, in particular, tensility, fatigue, wear, and corrosion resistance. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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