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Metals, Volume 8, Issue 11 (November 2018)

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Cover Story (view full-size image) The possibility of joining titanium alloys to advanced ceramics and producing components with [...] Read more.
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Open AccessArticle Annealing Behavior of Surface-Locally Cold-Deformed Low-Carbon Steel with a Large Strain Gradient
Metals 2018, 8(11), 976; https://doi.org/10.3390/met8110976
Received: 23 October 2018 / Revised: 11 November 2018 / Accepted: 16 November 2018 / Published: 21 November 2018
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Abstract
The annealing behavior of surface-locally cold-deformed 0.2 mass% carbon steel with a large strain gradient was investigated, with special attention paid to the change in grain size. The surface local deformation was introduced by a ball-dropping (BD) model experiment. The local plastic strain
[...] Read more.
The annealing behavior of surface-locally cold-deformed 0.2 mass% carbon steel with a large strain gradient was investigated, with special attention paid to the change in grain size. The surface local deformation was introduced by a ball-dropping (BD) model experiment. The local plastic strain profile evaluated from pure iron was used to confirm the occurrence of surface local deformation. It was found that the BD test led to severe local deformation near the surface, with a large strain gradient. Both the ferrite and as-transformed austenite exhibited a gradual change in grain size along the depth direction after annealing. The increased nucleation density of austenite in the deformed surface layer is not attributed to the increase in the density of the recrystallized ferrite–ferrite grain boundaries, but rather to the broken and dispersed cementite particles introduced by the deformation. The gradual change in ferrite and austenite grain size should be attributed to be the gradual change in the deformation degree of ferrite and perlite. Full article
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Open AccessArticle The Wear Properties of TiC/Al-Based Composite Coating Applied by Laser Cladding
Metals 2018, 8(11), 975; https://doi.org/10.3390/met8110975
Received: 23 October 2018 / Revised: 5 November 2018 / Accepted: 19 November 2018 / Published: 21 November 2018
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Abstract
Aluminum powders with different concentrations of TiC ceramic particles were applied to an AZ31B magnesium alloy by laser cladding. Due to differences in coefficients of thermal expansion, the distribution of TiC ceramic particles in the cladding layer was not uniform. The results show
[...] Read more.
Aluminum powders with different concentrations of TiC ceramic particles were applied to an AZ31B magnesium alloy by laser cladding. Due to differences in coefficients of thermal expansion, the distribution of TiC ceramic particles in the cladding layer was not uniform. The results show that the degree of TiC ceramic particle agglomeration in the cladding layer increases with increasing TiC content. The phases of cladding metal mainly consisted of Al, γ-Al12Mg17, β-Al3Mg2, and TiC. The γ-Al12Mg17 phase mainly distributed to the bottom of the cladding layer, and the β-Al3Mg2 phase distributed to the middle and surface areas. The existence of the γ-Al12Mg17 phase enhanced the hardness of the fusion zone. The microhardness of the cladding layer increased with increasing TiC ceramic particle content. An appropriate TiC content improved the wear resistance of the cladding layer. When the TiC content was excessive, the agglomeration behavior of TiC ceramic particles strongly affected the wear resistance of the coatings. Full article
(This article belongs to the Special Issue Graphene-Metal Composite)
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Open AccessArticle Effect of Heat Treatment on the Phase Composition, Microstructure and Mechanical Properties of Al0.6CrFeCoNi and Al0.6CrFeCoNiSi0.3 High-Entropy Alloys
Metals 2018, 8(11), 974; https://doi.org/10.3390/met8110974
Received: 28 October 2018 / Revised: 14 November 2018 / Accepted: 16 November 2018 / Published: 21 November 2018
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Abstract
High-entropy alloys exhibit some interesting mechanical properties including an excellent resistance against softening at elevated temperatures. This gives high-entropy alloys (HEAs) great potential as new structural materials for high-temperature applications. In a previous study of the authors, oxidation behavior of Al0.6CrFeCoNi
[...] Read more.
High-entropy alloys exhibit some interesting mechanical properties including an excellent resistance against softening at elevated temperatures. This gives high-entropy alloys (HEAs) great potential as new structural materials for high-temperature applications. In a previous study of the authors, oxidation behavior of Al0.6CrFeCoNi and Al0.6CrFeCoNiSi0.3 high-entropy alloys at T = 800 °C, 900 °C and 1000 °C was investigated. Si-alloying was found to increase the oxidation resistance by promoting the formation of a continuous Al2O3 layer, avoiding the formation of AlN at T = 800 °C. Obvious phase changes were identified in the surface areas of both alloys after the oxidation experiments. However, the effects of heat treatment and Si-alloying on the phase transition in the bulk were not investigated yet. In this study, Al0.6CrFeCoNi and Al0.6CrFeCoNiSi0.3 high-entropy alloys were heat-treated at T = 800 °C and T = 1000 °C to investigate the effect of heat treatment on microstructure, phase composition and mechanical properties of both alloys. The results show that alloying Al0.6CrFeCoNi with Si caused a phase transition from dual phases consisting of BCC and FCC to a single BCC phase in an as-cast condition. Furthermore, increased hardness for as-cast and heat-treated samples compared with the Al0.6CrFeCoNi alloy was observed. In addition, the heat treatment facilitated the phase transition and the precipitation of the intermetallic phase, which resulted in the change of the mechanical properties of the alloys. Full article
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Open AccessArticle The Effect of Concentrate/Iron Ore Ratio Change on Agglomerate Phase Composition
Metals 2018, 8(11), 973; https://doi.org/10.3390/met8110973
Received: 17 October 2018 / Revised: 16 November 2018 / Accepted: 19 November 2018 / Published: 21 November 2018
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Abstract
The work is focused on studying the influence of the ratio of concentrate to iron ore on the phase composition of the iron ore agglomerate. The concentrate has significantly higher iron content than used iron ore, and is a determining factor, which influences
[...] Read more.
The work is focused on studying the influence of the ratio of concentrate to iron ore on the phase composition of the iron ore agglomerate. The concentrate has significantly higher iron content than used iron ore, and is a determining factor, which influences the richness of the batch and consequently, the richness of the agglomerate. The increased iron content in the agglomerate can be achieved by adjusting the raw material ratio in which iron ore materials are added to the agglomeration mixture. If the ratio is in favor of iron ore this reflects in lower iron content in the resulting agglomeration mixture. If the ratio is in favor of a concentrate, which is finer, the fraction share of less than 0.5 mm will be increased, the permeability of the batch will be reduced, the performance of the sintering belt will decrease and the presence of solid pollutants will increase. The possibility of concentrate replacement by iron-rich iron ore with granulometry similar to that of concentrate was experimentally verified. The effect of the concentrate replacement by the finer iron-rich ore was tested in a laboratory sintering pan. There were performed six sinterings, with gradually changing ratio concentrate/iron ore (C/O). The change in the ratio of concentrate to iron ore, does not cause the occurrence of new phases, only the change in their prevalence, which does not bring a significant change of the qualitative indicators of the compared agglomerates. Concentrate replacement by iron ore up to 50% was optimal from technological, quality, and environmental aspects. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessArticle The Effects of TIG Welding Rod Compositions on Microstructural and Mechanical Properties of Dissimilar AISI 304L and 420 Stainless Steel Welds
Metals 2018, 8(11), 972; https://doi.org/10.3390/met8110972
Received: 17 October 2018 / Revised: 15 November 2018 / Accepted: 19 November 2018 / Published: 21 November 2018
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Abstract
The usage of AISI/SAE 304L austenitic and 420 martensitic stainless steels is receiving greater interest especially in the defence and navy industries. 304L stainless steels exhibit excellent resistance to oxidizing media, while martensitic 420 alloy provides high strength values besides satisfactory corrosion properties
[...] Read more.
The usage of AISI/SAE 304L austenitic and 420 martensitic stainless steels is receiving greater interest especially in the defence and navy industries. 304L stainless steels exhibit excellent resistance to oxidizing media, while martensitic 420 alloy provides high strength values besides satisfactory corrosion properties at ambient atmospheres. In this work; 420 quality martensitic stainless steel is TIG (Tungsten Inert Gas) welded with 304L quality low carbon austenitic stainless steel plates. As filler metal dominantly determines the weld metals chemical compositions and final microstructures, 3 different TIG welding rods of ER312, ER316L ve ER2209 are used in welding operations in order to obtain 3 discrete weld metal contents under high purity argon shielding gas. Microstructural inspection, microhardness survey and Charpy V-notch impact tests are applied to all joints after welding operations. The specimen welded by ER2209 TIG welding rod executed the highest impact test results besides exhibiting the lowest micro-hardness profiles at heat affected zones and weld metals. All of the welded specimens weld region hardness profiles were determined to be lower than unwelded 420 martensitic stainless steel base metal. Full article
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Open AccessArticle Effect of Heat Treatment on Microstructure and Mechanical Properties of the AZ31/WE43 Bimetal Composites
Metals 2018, 8(11), 971; https://doi.org/10.3390/met8110971
Received: 30 October 2018 / Revised: 12 November 2018 / Accepted: 15 November 2018 / Published: 20 November 2018
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Abstract
Effect of heat treatment on the microstructure and mechanical properties of the AZ31/WE43 bimetal composites was investigated, and the optimized solution treatment and ageing treatment parameters were achieved. After heat treatment, it was found that that the high melting-point Y-rich phases and Mg-RE
[...] Read more.
Effect of heat treatment on the microstructure and mechanical properties of the AZ31/WE43 bimetal composites was investigated, and the optimized solution treatment and ageing treatment parameters were achieved. After heat treatment, it was found that that the high melting-point Y-rich phases and Mg-RE (rare earth) phases at the interface were distributed more uniformly, so the interfacial strength and plasticity were improved. Meanwhile, the shear strength and plasticity of AZ31 were increased, and the shear strength of WE43 was also improved by heat treatment. The evolution of interface morphologies and enhancement of the mechanical properties at the interface will be discussed in detail. Full article
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Open AccessReview Analysis of Weak Zones in Friction Stir Welded Magnesium Alloys from the Viewpoint of Local Texture: A Short Review
Metals 2018, 8(11), 970; https://doi.org/10.3390/met8110970
Received: 19 October 2018 / Revised: 8 November 2018 / Accepted: 9 November 2018 / Published: 20 November 2018
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Abstract
Friction stir welding (FSW) is a promising approach for the joining of magnesium alloys. Although many Mg alloys have been successfully joined by FSW, it is far from industrial applications due to the texture variation and low mechanical properties. This short review deals
[...] Read more.
Friction stir welding (FSW) is a promising approach for the joining of magnesium alloys. Although many Mg alloys have been successfully joined by FSW, it is far from industrial applications due to the texture variation and low mechanical properties. This short review deals with the fundamental understanding of weak zones from the viewpoint of texture analysis in FSW Mg alloys, especially for butt welding. Firstly, a brief review of the microstructure and mechanical properties of FSW Mg alloys is presented. Secondly, microstructure and texture evolutions in weak zones are analyzed and discussed based on electron backscatter diffraction data and Schmid factors. Then, how to change the texture and strengthen the weak zones is also presented. Finally, the review concludes with some future challenges and research directions related to the texture in FSW Mg alloys. The purpose of the paper is to provide a basic understanding on the location of weak zones as well as the weak factors related to texture to improve the mechanical properties and promote the industrial applications of FSW Mg alloys. Full article
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Open AccessArticle Microstructure, Mechanical Properties and Strengthening Mechanism Analysis in an AlMg5 Aluminium Alloy Processed by ECAP and Subsequent Ageing
Metals 2018, 8(11), 969; https://doi.org/10.3390/met8110969
Received: 23 October 2018 / Revised: 15 November 2018 / Accepted: 16 November 2018 / Published: 20 November 2018
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Abstract
A coarse-grained microstructure of solution treated AlMg5 aluminium alloy was prepared by equal channel angular pressing through route BC. Microstructure evolution of the alloy was analysed by using an optical microscope, X-ray diffraction, and EBSD (electron backscatter diffraction). The results reported
[...] Read more.
A coarse-grained microstructure of solution treated AlMg5 aluminium alloy was prepared by equal channel angular pressing through route BC. Microstructure evolution of the alloy was analysed by using an optical microscope, X-ray diffraction, and EBSD (electron backscatter diffraction). The results reported that grains were refined due to the interactions of shear bands with low-to-moderate grain boundaries, and this structure was transformed into a bimodal after ageing at 180 °C for 4 h. Moreover, the results of the tensile testing showed that the yield strength was increased from 110 to 326 MPa, and the corresponding tensile strength increased from 269 to 395 MPa, maintaining an appropriate elongation of ~18%. After ageing at 180 °C elongation increased to 23% and the sample still kept high yield strength of 255 MPa, which may be associated with the mutual influence of the dislocation density decrease and recrystallization processes. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle A Study on the Machining Characteristics of Curved Workpiece Using Laser-Assisted Milling with Different Tool Paths in Inconel 718
Metals 2018, 8(11), 968; https://doi.org/10.3390/met8110968
Received: 29 October 2018 / Revised: 14 November 2018 / Accepted: 17 November 2018 / Published: 20 November 2018
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Abstract
Difficult-to-cut materials are being increasingly used in many industries because of their superior properties, including high corrosion resistance, heat resistance and specific strength. However, these same properties make the materials difficult to machine using conventional machining techniques. Laser-assisted milling (LAM) is one of
[...] Read more.
Difficult-to-cut materials are being increasingly used in many industries because of their superior properties, including high corrosion resistance, heat resistance and specific strength. However, these same properties make the materials difficult to machine using conventional machining techniques. Laser-assisted milling (LAM) is one of the effective method for machining difficult-to-cut materials. In laser-assisted milling, the machining occur after the workpiece is locally preheated using a laser heat source. Laser-assisted milling has been studied by many researchers on flat workpiece or micro end-milling. However, there is no research on the curved shape using laser assisted milling. This study investigated the use of laser-assisted milling to machine a three-dimensional curved shape workpiece based on NURBS (Non-uniform rational b-spline). A machining experiment was performed on Inconel 718 using different tool paths (ramping, contouring) under various machining conditions. Finite elements analysis was conducted to determine the depth of cut. Cutting force, specific cutting energy and surface roughness characteristics were measured, analyzed and compared for conventional and LAM machining. LAM significantly improved these machining characteristics, compared to conventional machining. There results can be applied to the laser-assisted milling of various three-dimensional shapes. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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Open AccessArticle New Insight on the Hydrogen Absorption Evolution of the Mg–Fe–H System under Equilibrium Conditions
Metals 2018, 8(11), 967; https://doi.org/10.3390/met8110967
Received: 11 October 2018 / Revised: 31 October 2018 / Accepted: 12 November 2018 / Published: 19 November 2018
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Abstract
Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions
[...] Read more.
Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6. Full article
(This article belongs to the Special Issue Metals in Hydrogen Technology)
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Open AccessEditorial Bainite and Martensite: Developments and Challenges
Metals 2018, 8(11), 966; https://doi.org/10.3390/met8110966
Received: 14 November 2018 / Accepted: 17 November 2018 / Published: 19 November 2018
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Abstract
Both microstructures, martensite and bainite, although share some common features, when studied in further detail depict a plethora of subtle differences that make them unique. [...] Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
Open AccessArticle Probability-Statistical Estimation Method of Feed Influence on As-Turned Finish of Steels and Non-Ferrous Metals
Metals 2018, 8(11), 965; https://doi.org/10.3390/met8110965
Received: 11 October 2018 / Revised: 13 November 2018 / Accepted: 15 November 2018 / Published: 19 November 2018
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Abstract
Based on the experimental data on the roughness parameter Ra, which stands for the mean arithmetic deviation of the profile, as obtained in the process of turning test specimens from different materials with constant elements of the cutting mode (depth a
[...] Read more.
Based on the experimental data on the roughness parameter Ra, which stands for the mean arithmetic deviation of the profile, as obtained in the process of turning test specimens from different materials with constant elements of the cutting mode (depth a and velocity v) and structural-geometric parameters of the cutting tool, but with different feed rates f, the probability-statistical method for estimating the influence of feed rate f on the resulting surface roughness by the parameter Ra is proposed using the theory of a small sample. Full article
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Open AccessReview Major Impediment to Highly Efficient, Stable and Low-Cost Perovskite Solar Cells
Metals 2018, 8(11), 964; https://doi.org/10.3390/met8110964
Received: 21 October 2018 / Revised: 13 November 2018 / Accepted: 13 November 2018 / Published: 19 November 2018
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Abstract
Organic–inorganic hybrid perovskite solar cells (PSCs) have made immense progress in recent years, owing to outstanding optoelectronic properties of perovskite materials, such as high extinction coefficient, carrier mobility, and low exciton binding energy. Since the first appearance in 2009, the efficiency of PSCs
[...] Read more.
Organic–inorganic hybrid perovskite solar cells (PSCs) have made immense progress in recent years, owing to outstanding optoelectronic properties of perovskite materials, such as high extinction coefficient, carrier mobility, and low exciton binding energy. Since the first appearance in 2009, the efficiency of PSCs has reached 23.3%. This has made them the most promising rival to silicon-based solar cells. However, there are still several issues to resolve to promote PSCs’ outdoor applications. In this review, three crucial aspects of PSCs, including high efficiency, environmental stability, and low-cost of PSCs, are described in detail. Recent in-depth studies on different aspects are also discussed for better understanding of these issues and possible solutions. Full article
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Open AccessEditorial Cermets and Hardmetals
Metals 2018, 8(11), 963; https://doi.org/10.3390/met8110963
Received: 14 November 2018 / Accepted: 17 November 2018 / Published: 19 November 2018
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Abstract
Cermets and hardmetals combine the most favorable characteristics of ceramics and metals, namely the high hardness and elastic moduli of the former, and the ductility and toughness of the latter. [...] Full article
(This article belongs to the Special Issue Cermets and Hardmetals)
Open AccessArticle Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach
Metals 2018, 8(11), 962; https://doi.org/10.3390/met8110962
Received: 10 October 2018 / Revised: 26 October 2018 / Accepted: 16 November 2018 / Published: 18 November 2018
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Abstract
Nanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced
[...] Read more.
Nanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced to a sometimes-extraordinary grain size reduction via different severe plastic deformation (SPD) methods. In the present study, a dual strategy was followed to obtain a sound and stable nanostructured commercially pure cobalt. Powdered cobalt of 2 μm was compacted by ball-milling (BM) followed by spark-plasma sintering (SPS) to obtain a bulk metallic material whose relative mass density reached a value of 95.8%. This process constituted a bottom-up strategy to obtain ultrafine submicrometer-grained bulk cobalt, and a top-down strategy of subjecting the BM + SPS submicrometer-grained cobalt to a specific SPD technique, namely equal-channel angular pressing (ECAP). The latter was carried out in one to four passes following so-called route BC, reaching 98.4% density and a nanometric-grained microstructure. The material was microstructurally and mechanically characterized by TEM (transmission electron microscope) and nanoindentation. The obtained results are a representative solid example for obtaining nanostructured metallic materials using both grain-refining strategies, bottom-up and top-down. Full article
(This article belongs to the Special Issue Non-Ferrous Metallic Materials)
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Open AccessArticle Optimization of A354 Al-Si-Cu-Mg Alloy Heat Treatment: Effect on Microstructure, Hardness, and Tensile Properties of Peak Aged and Overaged Alloy
Metals 2018, 8(11), 961; https://doi.org/10.3390/met8110961
Received: 31 October 2018 / Revised: 13 November 2018 / Accepted: 14 November 2018 / Published: 17 November 2018
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Abstract
The aim of the present work is the study of T6 heat treatment of A354 (Al-Si-Cu-Mg) casting alloy. The heat treatment was optimized by maximizing mechanical strength of the alloy while keeping the treatment cost effective, reducing treatment time and temperature. Due to
[...] Read more.
The aim of the present work is the study of T6 heat treatment of A354 (Al-Si-Cu-Mg) casting alloy. The heat treatment was optimized by maximizing mechanical strength of the alloy while keeping the treatment cost effective, reducing treatment time and temperature. Due to the presence of low melting compounds, a double stage solution treatment was proposed. The first stage was aimed at the homogenization and dissolution of the low melting phase while a second stage at a higher temperature was evaluated to foster dissolution of Cu/Mg rich intermetallics and keep the solution time and temperature as low as possible. Microstructural investigations were performed through optical and electronic microscopy, which allowed the assessment of the evolution of intermetallic phases during the solution treatment. Artificial aging was studied at different temperatures from 160 °C to 210 °C where the peak aging condition was identified. Over aging of the heat treated alloy was evaluated by soaking T6 samples at 200, 245, and 290 °C for up to 168 h. Tensile behavior of the T6 and over-aged alloy (i.e., after soaking at 210 °C for 50 h) was evaluated at room temperature. Results showed that the proposed treatment allowed the enhancement of mechanical properties of the alloy in comparison to industrial practice treatment, maintaining a good level of ductility and conferring a superior resistance to long-term high temperature exposure. Full article
(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)
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Open AccessArticle One-Step Preparation of Super-Hydrophobic Micro-Nano Dendrites on Al Alloy for Enhanced Corrosion Resistance
Metals 2018, 8(11), 960; https://doi.org/10.3390/met8110960
Received: 1 October 2018 / Revised: 7 November 2018 / Accepted: 14 November 2018 / Published: 17 November 2018
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Abstract
Corrosion failure is a thorny issue that restricts the applications of Al alloys. As a research hotspot in functional realization, hydrophobic fabrication exactly offers an efficient method to settle metallic corrosions. This work has developed a facile and low-cost method to enhance corrosion
[...] Read more.
Corrosion failure is a thorny issue that restricts the applications of Al alloys. As a research hotspot in functional realization, hydrophobic fabrication exactly offers an efficient method to settle metallic corrosions. This work has developed a facile and low-cost method to enhance corrosion resistance of Al alloys. The micro-nano dendrites have been firstly prepared on metallic substrate using one-step potentiostatic deposition. Then, wetting and electrochemical behaviors have been systematically investigated after stearic acid modification. Results show that the as-prepared surface possesses amplified and durable water repellence with an apparent contact angle (CA) of 154.2° and a sliding angle (SA) of 4.7°. Meanwhile, owing to the trapped air in dendrites, the newly-generated solid-air-liquid interfaces help to resist seawater penetration by reducing interfacial interactions on the super-hydrophobic surface as well as significantly enhance its corrosion resistance. This work sheds positive insights into extending the applications of Al alloys in many areas, especially for ocean engineering fields. Full article
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Open AccessEditorial Diffusion Bonding and Brazing of Advanced Materials
Metals 2018, 8(11), 959; https://doi.org/10.3390/met8110959
Received: 8 November 2018 / Accepted: 14 November 2018 / Published: 16 November 2018
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Abstract
Advanced materials generally require the development of novel joining techniques, as this is crucial to integrate them into functional structures and to widen their application field. [...] Full article
(This article belongs to the Special Issue Diffusion Bonding and Brazing of Advanced Materials)
Open AccessArticle Phase Equilibria of the Co-Ti-Ta Ternary System
Metals 2018, 8(11), 958; https://doi.org/10.3390/met8110958
Received: 29 October 2018 / Revised: 13 November 2018 / Accepted: 14 November 2018 / Published: 16 November 2018
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Abstract
The phase equilibria of the Co-Ti-Ta ternary system at 1000 °C, 1100 °C, and 1200 °C were experimentally investigated using an electron probe microanalyzer and X-ray diffraction. Experimental results show that: (1) No ternary compound exists in the studied isothermal sections; (2) the
[...] Read more.
The phase equilibria of the Co-Ti-Ta ternary system at 1000 °C, 1100 °C, and 1200 °C were experimentally investigated using an electron probe microanalyzer and X-ray diffraction. Experimental results show that: (1) No ternary compound exists in the studied isothermal sections; (2) the β(Ti) and β(Ta) phases form the continuous solid solution β(Ti,Ta) in the Ti-Ta side; (3) the solubility of Ta in the (αCo) is less than 5%; (4) the phases of Co2Ti(h) and γ-Co2Ta, Co2Ti(c) and β-Co2Ta form the continuous solid solutions Co2(Ta,Ti)(h) and Co2(Ta,Ti)(c), respectively. Full article
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Open AccessArticle Effective Gold Recovery from Near-Surface Oxide Zone Using Reductive Microwave Roasting and Magnetic Separation
Metals 2018, 8(11), 957; https://doi.org/10.3390/met8110957
Received: 23 October 2018 / Revised: 8 November 2018 / Accepted: 15 November 2018 / Published: 16 November 2018
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Abstract
High content of gold in near-surface oxide zones above the gold ore deposit could be recovered using cyanidation. However, restricting the use of cyanide in mines has made it difficult to recover gold within the oxide zone. In this study, we investigated an
[...] Read more.
High content of gold in near-surface oxide zones above the gold ore deposit could be recovered using cyanidation. However, restricting the use of cyanide in mines has made it difficult to recover gold within the oxide zone. In this study, we investigated an application of the reductive microwave roasting and magnetic separation (RMR-MS) process for the effective gold recovery from ores in a near-surface oxide zone. Ore samples obtained from the near-surface oxide zone in Moisan Gold Mine (Haenam, South Korea) were used in RMR-MS tests for the recovery of iron and gold. The effect of the RMR process on the recovery of iron and gold was evaluated by given various conditions of the microwave irradiation as well as the dosages of reductant and additive. The microwave roasting resulted in a chemical reduction of non-magnetic iron oxide minerals (hematite) to magnetite minerals, such as magnetite and maghemite. This mineral phase change could induce the effective separation of iron minerals from the gangue minerals by magnetic separation process. The increased iron recovery was directly proportional to the gold recovery due to the coexistence of gold with iron minerals. The RMR-MS process could be a promising method for gold recovery from the ores in near-surface oxide zones. Full article
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Open AccessArticle Effects of CaO Addition on the Iron Recycling from Nickel Slags by Oxidation-Magnetic Separation
Metals 2018, 8(11), 956; https://doi.org/10.3390/met8110956
Received: 31 October 2018 / Revised: 12 November 2018 / Accepted: 14 November 2018 / Published: 16 November 2018
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Abstract
To recover iron from water-quenched nickel slags, CaO was added. Thermodynamic analysis showed that CaO promotes the reaction between fayalite (Fe2SiO4) and O2. Phase diagrams of the FeO-SiO2-MgO-CaO slag with various CaO contents in an
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To recover iron from water-quenched nickel slags, CaO was added. Thermodynamic analysis showed that CaO promotes the reaction between fayalite (Fe2SiO4) and O2. Phase diagrams of the FeO-SiO2-MgO-CaO slag with various CaO contents in an air atmosphere drawn by FactSage 7.1 showed that the phase components can be significantly affected by the CaO contents. With increasing CaO content, the fusion characteristic temperatures decreased rapidly to a minimum and subsequently increased slightly. The oxidization of Fe2SiO4 in nickel slags was accelerated significantly by the addition of CaO, which led to an increase of FeO activity and decrease of Fe2O3 activity to promote the formation of MgFe2O4. Excess addition of CaO led to the formation of more silicates. In addition, the crystallization temperature was also reduced with increasing CaO content, causing less spinel to crystalize. With increasing CaO content, the iron recovery and yield of concentrate first increased and subsequently decreased, while the total iron (TFe) content was almost not influenced and maintained a relatively stable value. Full article
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Open AccessArticle Finite Element Implementation of a Temperature-Dependent Cyclic Plastic Model for SA508-3 Steel
Metals 2018, 8(11), 955; https://doi.org/10.3390/met8110955
Received: 22 October 2018 / Revised: 6 November 2018 / Accepted: 14 November 2018 / Published: 16 November 2018
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Abstract
A new temperature-dependent cyclic plastic model, combining the nonlinear cyclic softening and kinematic hardening rules is established for a nuclear material of SA508-3 steel. A modified isotropic hardening rule is proposed to capture the temperature-dependent cyclic softening, and a modified kinematic hardening rule
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A new temperature-dependent cyclic plastic model, combining the nonlinear cyclic softening and kinematic hardening rules is established for a nuclear material of SA508-3 steel. A modified isotropic hardening rule is proposed to capture the temperature-dependent cyclic softening, and a modified kinematic hardening rule is established to improve the prediction of the ratcheting behavior by introducing an exponential function related to the accumulated plastic strain. The stress is updated by the radial return mapping algorithm based on the backward Euler integration. A new expression of consistent tangent modulus for the equilibrium iteration is derived, and then the proposed model is implemented into the finite element software ABAQUS by using the user material subroutine (UMAT) to simulate the temperature-dependent ratcheting behaviors of SA508-3 steel. Finally, the ratcheting evolutions of notched bars at elevated temperature are obtained by uniaxial stress-controlled cyclic tests, and the nonuniform strain fields on the surface of plates with a center hole is measured by using the digital image correlation (DIC) technology. Comparisons between experimental and simulated results of a material point and structural examples show that the implemented model can provide reasonable predictions for ratcheting behaviors and nonuniform strain fields of structures at different temperatures for SA508-3 steel. Full article
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Open AccessArticle Effects of Platform Pre-Heating and Thermal-Treatment Strategies on Properties of AlSi10Mg Alloy Processed by Selective Laser Melting
Metals 2018, 8(11), 954; https://doi.org/10.3390/met8110954
Received: 12 October 2018 / Revised: 9 November 2018 / Accepted: 13 November 2018 / Published: 15 November 2018
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Abstract
The AlSi10Mg alloy was processed by selective laser melting using both hot- and cold-build platforms. The investigation was aimed at defining suitable platform pre-heating and post-process thermal treatment strategies, taking into consideration the peculiar microstructures generated. Microstructural analyses, differential scanning calorimetry, and high-resolution
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The AlSi10Mg alloy was processed by selective laser melting using both hot- and cold-build platforms. The investigation was aimed at defining suitable platform pre-heating and post-process thermal treatment strategies, taking into consideration the peculiar microstructures generated. Microstructural analyses, differential scanning calorimetry, and high-resolution diffraction from synchrotron radiation, showed that in the cold platform as-built condition, the amount of supersaturated Si was higher than in hot platform samples. The best hardness and tensile performance were achieved upon direct aging from cold platform-printed alloys. The hot platform strategy led to a loss in the aging response, since the long processing times spent at high temperature induced a substantial overaging effect, already in the as-built samples. Finally, the standard T6 temper consisting of post-process solution annealing followed by artificial aging, resulted in higher ductility but lower mechanical strength. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle A Study on Two-Stage Cold Forging for a Drive Shaft with Internal Spline and Spur Gear Geometries
Metals 2018, 8(11), 953; https://doi.org/10.3390/met8110953
Received: 2 November 2018 / Revised: 12 November 2018 / Accepted: 13 November 2018 / Published: 15 November 2018
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Abstract
A two-stage cold forging process was proposed to manufacture a drive shaft with an internal spline and spur gear geometries, and this process was mainly composed of a forward extrusion for preform and a forward-backward extrusion for the drive shaft. In the process
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A two-stage cold forging process was proposed to manufacture a drive shaft with an internal spline and spur gear geometries, and this process was mainly composed of a forward extrusion for preform and a forward-backward extrusion for the drive shaft. In the process design, the preform was designed using a volume apportioning scheme from the required target shape, thereafter, the initial round billet was outlined. AISI 1035 carbon steel was selected as the raw material, and a spheroidizing heat treatment was adopted. Using the raw and spheroidizing annealed workpieces, uni-axial tensile and compression tests were carried out to evaluate the effect of the heat treatment and to measure the mechanical properties. Finite element simulations were sequentially performed to assure the suitability of the proposed process design. Considering the results from the process design and the numerical simulations, the related tool components were prepared and applied to a series of experimental investigations. The preform and the drive shaft fabricated by the two-stage cold forging experiments were compared with the required target and the numerically predicted configurations. The results indicated that the two-stage cold forging process proposed in this study could be well applied to the production of the drive shaft with an internal spline and spur gear structures. Full article
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Open AccessArticle Residual Stress Differences between Uniform and Non-Uniform Heating Treatment of Bimetallic Roll: Effect of Creep Behavior on Residual Stress
Metals 2018, 8(11), 952; https://doi.org/10.3390/met8110952
Received: 2 October 2018 / Revised: 24 October 2018 / Accepted: 1 November 2018 / Published: 15 November 2018
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Abstract
The work roll is one of the most important tools in the steel rolling industry. Work rolls are used under extremely severe conditions such as high temperature, high loading, and an aggressive atmosphere. To meet those demands, bimetallic rolls have recently been used
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The work roll is one of the most important tools in the steel rolling industry. Work rolls are used under extremely severe conditions such as high temperature, high loading, and an aggressive atmosphere. To meet those demands, bimetallic rolls have recently been used to replace conventional single material rolls. Usually, a compressive residual stress is introduced to prevent surface cracking. However, a tensile residual stress at the center appears to balance the compressive residual stress. This center residual stress sometimes causes roll failure. In this paper, therefore, a simulation is performed using the finite element method (FEM) for the quenching process of the bimetallic roll by considering the creep behavior. Then the effect of pre-heating conditions is discussed. The results show that the maximum stress point for the tensile stress at the roll center for non-uniform heating is 24% less than that achieved with uniform heating, although the same compressive stresses appear at the surface. Then, using different work roll diameters, the center tensile residual stress for non-uniform heating is found to be smaller than the uniform heating. Also, it is found that the area ratios of the shell-core only have a small influence on the residual stress of the bimetallic roll for both heating treatments. Full article
(This article belongs to the Special Issue Wear and Fracture of Steel Manufacturing Apparatus and Tools)
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Open AccessArticle A New Approach to Simulate HSLA Steel Multipass Welding through Distributed Point Heat Sources Model
Metals 2018, 8(11), 951; https://doi.org/10.3390/met8110951
Received: 28 August 2018 / Revised: 17 September 2018 / Accepted: 18 September 2018 / Published: 15 November 2018
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Abstract
Mechanical properties of welded joints depend on the way heat flows through the welding passes. In multipass welding the reheating of the heat affected zone (HAZ) can form local brittle zones that need to be delimited for evaluation. The difficulty lies in the
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Mechanical properties of welded joints depend on the way heat flows through the welding passes. In multipass welding the reheating of the heat affected zone (HAZ) can form local brittle zones that need to be delimited for evaluation. The difficulty lies in the choice of a model that can simulate multipass welding. This study evaluated Rosenthal’s Medium Thick Plate (MTP) and the Distributed heat Sources (DHS) of Mhyr and Gröng models. Two assumptions were considered for both models: constant and temperature-dependent physical properties. It was carried out on a multipass welding of an API 5L X80 tube, with 1016 mm (42″) external diameter, 16 mm thick and half V-groove bevel, in the 3G up position. The root pass was welded with Gas Metal Arc Welding (GMAW) process with controlled short-circuit transfer. The Flux Cored Arc Welding (FCAW) process was used in the filling and finishing passes, using filler metal E111T1-K3M-JH4. The evaluation criteria used were overlapping the simulated isotherms on the marks revealed in the macrographs and the comparison between the experimental thermal cycle and those simulated by the proposed models. The DHS model with the temperature-dependent properties presented the best results and simulated with accuracy the HAZ of root and second welding passes. In this way, it was possible to delimit the HAZ heated sub-regions. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
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Open AccessArticle Springback Prediction of Aluminum Alloy Sheet under Changing Loading Paths with Consideration of the Influence of Kinematic Hardening and Ductile Damage
Metals 2018, 8(11), 950; https://doi.org/10.3390/met8110950
Received: 20 October 2018 / Revised: 7 November 2018 / Accepted: 13 November 2018 / Published: 14 November 2018
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Abstract
Springback prediction of sheet metal forming is always an important issue in the industry, because it greatly affects the final shape of the product. The accuracy of simulation prediction depends on not only the forming condition but also the chosen material model, which
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Springback prediction of sheet metal forming is always an important issue in the industry, because it greatly affects the final shape of the product. The accuracy of simulation prediction depends on not only the forming condition but also the chosen material model, which determines the stress and strain redistributions in the formed parts. In this paper, a newly proposed elastoplastic constitutive model is used, in which the initial and induced anisotropies, combined nonlinear isotropic and kinematic hardenings, as well as isotropic ductile damage, are taken into account. The aluminum alloy sheet metal AA7055 was chosen as the studied material. In order to investigate springback under non-proportional strain paths, three-point bending tests were conducted with pre-strained specimens, and five different pre-straining states were considered. The comparisons between numerical and experimental results highlighted the hard effect of both kinematic hardening and ductile damage on the springback prediction, especially for a changed loading path case. Full article
(This article belongs to the Special Issue Modelling and Simulation of Sheet Metal Forming Processes)
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Open AccessArticle Electrochemical Investigation of Corrosion of X80 Steel under Elastic and Plastic Tensile Stress in CO2 Environment
Metals 2018, 8(11), 949; https://doi.org/10.3390/met8110949
Received: 23 October 2018 / Revised: 8 November 2018 / Accepted: 10 November 2018 / Published: 14 November 2018
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Abstract
An investigation into the electrochemical corrosion behavior of X80 pipeline steel under different elastic and plastic tensile stress in a CO2-saturated NaCl solution has been carried out by using open-circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analysis techniques. The
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An investigation into the electrochemical corrosion behavior of X80 pipeline steel under different elastic and plastic tensile stress in a CO2-saturated NaCl solution has been carried out by using open-circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analysis techniques. The results show that the corrosion rate of X80 steel first increases and then slightly decreases with the increase of elastic tensile stress, whereas the corrosion rate sharply increases with the increase of plastic tensile stress. Both elastic and plastic tensile stress can enhance steel corrosion by improving the electrochemical activity of both anodic and cathodic reactions. Moreover, compared with elastic tensile stress, plastic tensile stress has a more significant effect. Furthermore, electrochemical reactions for CO2 corrosion and mechanoelectrochemical effect are used to reasonably explain the corrosion behavior of stressed X80 steel in CO2 environment. Full article
(This article belongs to the Special Issue Failure Mechanisms in Alloys)
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Open AccessArticle A Potential Biodegradable Mg-Y-Ag Implant with Strengthened Antimicrobial Properties in Orthopedic Applications
Metals 2018, 8(11), 948; https://doi.org/10.3390/met8110948
Received: 16 October 2018 / Revised: 5 November 2018 / Accepted: 12 November 2018 / Published: 14 November 2018
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Abstract
In order to design a potential biodegradable implant, which combines with fine mechanical and antimicrobial properties, Mg-4Y-1Ag (mass fraction, %) alloys were produced by permanent mold casting and then hot extrusion. The microstructure, mechanical behavior, anti-corrosion behavior, and antimicrobial properties of the experimental
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In order to design a potential biodegradable implant, which combines with fine mechanical and antimicrobial properties, Mg-4Y-1Ag (mass fraction, %) alloys were produced by permanent mold casting and then hot extrusion. The microstructure, mechanical behavior, anti-corrosion behavior, and antimicrobial properties of the experimental alloys were comprehensively investigated. The results showed that α-Mg, Mg24Y5 (ε), and AgMg4 phases existed in the Mg-4Y-1Ag. The grain size of Mg-4Y-1Ag was greatly refined through hot-extrusion. The as-extruded Mg-4Y-1Ag alloy exhibit an ultimate tensile strength of 202.7 MPa with a good elongation of 33.6%. The compressive strength of as-extruded Mg-4Y-1Ag was 385 MPa, and the strength remained 183 MPa after immersing in PBS solution for four weeks. The as-extruded alloy had better corrosion resistance than as-cast alloy and as-extruded pure magnesium in PBS solution, for the reason of refined grain and the formation of Y2O3 film on the surface of Mg-4Y-1Ag alloy. Furthermore, the as-extruded Mg-4Y-1Ag alloys were superior to Ti6Al4V (TC4) and as-extruded pure magnesium in antimicrobial property for released Ag+ ion. Obvious inhibition halo was observed in the LB agar plate adding with as-extruded Mg-4Y-1Ag alloys. Also as-extruded Mg-4Y-1Ag alloys showed no cytotoxicity by co-culturing with L929 using the MTT method. Full article
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Open AccessArticle A Study on the Cooling Performance of Newly Developed Slice Die in the Hot Press Forming Process
Metals 2018, 8(11), 947; https://doi.org/10.3390/met8110947
Received: 21 September 2018 / Revised: 30 October 2018 / Accepted: 11 November 2018 / Published: 14 November 2018
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Abstract
The cooling performance of a slice die is studied numerically and experimentally. The slice die is designed to improve the cooling performance compared to that of a conventional die that is generally used in the Hot Press Forming (HPF) process by modifying the
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The cooling performance of a slice die is studied numerically and experimentally. The slice die is designed to improve the cooling performance compared to that of a conventional die that is generally used in the Hot Press Forming (HPF) process by modifying the cooling channel layout and arrangement. In order to understand the physical phenomenon of the slice die cooling performance, the cooling performance of the conventional die is also simulated and their results are compared with the slice die results. From the results of the maximum temperature of the blank and die and the temperature distribution of the blank, the slice die has considerably improved cooling performance. To validate the simulation results, the slice die is prototyped and a blank is produced by the HPF process. Blank temperatures are measured by a thermal imaging camera at several holding times. The simulation and experimental results of the blank temperatures are compared and agree with the error rate of 3%. In order to verify the quality of the produced blank, ultimate tensile stress, yield stress, and elongation tests are conducted for specimens that are extracted from the blank and are compared with existing literature results. Full article
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