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Metals, Volume 11, Issue 7 (July 2021) – 152 articles

Cover Story (view full-size image): We studied how voids in LPBF AISI 316L can be closed by the laser exposure of subsequent layers. We used standard process parameters for the laser exposure to build a cylindrical specimen in which certain quarters were not exposed by the laser. Increasing the layer thickness to four times the standard layer thickness does not create additional porosity. The combined results of ex situ computed tomography and in situ optical tomography reveal that the melt pools of superjacent layers can melt powder particles up to 500 µm below the current surface. Void formation in regions below the current surface is not only caused by an insufficient overlap of the melt pool width, but also the surface roughness of the solid material below the non-exposed sections creates seeding points for void formation. View this paper.
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Article
Leaching Behavior of Lithium-Bearing Bauxite with High-Temperature Bayer Digestion Process in K2O-Al2O3-H2O System
Metals 2021, 11(7), 1148; https://doi.org/10.3390/met11071148 - 20 Jul 2021
Viewed by 820
Abstract
Lithium is one of the secondary mineral elements occurring in bauxite. The behavior of lithium-bearing bauxite in the digestion process was investigated, and the effect of digestion conditions on the extraction rates of lithium was studied. The results demonstrate that the mass ratio [...] Read more.
Lithium is one of the secondary mineral elements occurring in bauxite. The behavior of lithium-bearing bauxite in the digestion process was investigated, and the effect of digestion conditions on the extraction rates of lithium was studied. The results demonstrate that the mass ratio of the added CaO to bauxite, the KOH concentration, and the digestion temperature had a significant effect on the lithium extraction efficiency. An L9(34) orthogonal experiment demonstrated that the order of each factor for lithium extraction from primary to secondary is lime dosage, caustic concentration, and reaction temperature. Under the optimal conditions (t = 60 min, T = 260 °C, ρ(K2O) = 280 g/L, and 16% lime dosage), the leaching efficiencies of lithium and alumina are 85.6% and 80.09%, respectively, with about 15% of lithium entering into red mud. The findings of this study maybe useful for controlling lithium content in alumina products and lithium recovery from the Bayer process. Full article
(This article belongs to the Section Extractive Metallurgy)
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Article
Comparative Study of the Metallurgical Quality of Primary and Secondary AlSi10MnMg Aluminium Alloys
Metals 2021, 11(7), 1147; https://doi.org/10.3390/met11071147 - 20 Jul 2021
Cited by 2 | Viewed by 800
Abstract
The use of secondary aluminium is increasingly being promoted in the automotive industry for environmental reasons. The purpose of this study was to demonstrate that it is possible to obtain a recycled AlSi10MnMg(Fe) aluminium alloy with equal metallurgical quality to that of a [...] Read more.
The use of secondary aluminium is increasingly being promoted in the automotive industry for environmental reasons. The purpose of this study was to demonstrate that it is possible to obtain a recycled AlSi10MnMg(Fe) aluminium alloy with equal metallurgical quality to that of a primary AlSi10MnMg alloy when an adequate melt treatment is applied. The melt treatment consisted of deoxidation, degassing and skimming in accordance with the detailed procedure described in this article. The metallurgical qualities of one primary and two secondary alloys were assessed using thermal analysis, the density index test, the macroinclusion test and the microinclusion level test before and after melt treatment. The thermal analysis allowed us to compare the variables of the solidification cooling curve (Al primary temperature and its undercooling; Al-Si eutectic temperature and its predictive modification rate). The density index test was used to evaluate the hydrogen gas content in the melt. The macroinclusion test was used to evaluate the melt cleanliness, while the microinclusion level test was used to perform the inclusion identification and quantification analyses. This study showed the feasibility of manufacturing structural components using 100% recycled secondary aluminium alloy through V-HPDC technology. Full article
(This article belongs to the Section Metal Casting, Forming and Heat Treatment)
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Article
Reduction of Warping in Kinematic L-Profile Bending Using Local Heating
Metals 2021, 11(7), 1146; https://doi.org/10.3390/met11071146 - 20 Jul 2021
Cited by 2 | Viewed by 709
Abstract
Kinematic bending of profiles allows to manufacture parts with high flexibility concerning the geometry. Still, the production of profiles with asymmetric cross-sections regarding the force application axis using kinematic bending processes offers challenges regarding springback and warping. These geometric deviations can be reduced [...] Read more.
Kinematic bending of profiles allows to manufacture parts with high flexibility concerning the geometry. Still, the production of profiles with asymmetric cross-sections regarding the force application axis using kinematic bending processes offers challenges regarding springback and warping. These geometric deviations can be reduced by partial, cross-sectional heating during the process as it lowers the flow stress locally. In this work, the influence of partial, cross-sectional heating during a three-roll push-bending process on the warping and springback of L-profiles is investigated. Numerical and experimental methods reveal the influence of temperature on warping and springback. A newly developed analytical model predicts the warping and bending moment in the design phase and assists to understand the effect of warping reduction through partial heating during plastic bending. With increasing temperature of the heated profile area, the warping is reduced up to 76% and the springback of the bend profiles is decreased up to 44%. The warping reduction is attributed to a shift in stress free fiber due to the temperature gradient between heated and room temperature areas. The shift of stress-free fiber leads to an adapted shear center position, resulting in an approximated “quasi-symmetric” bending case. Full article
(This article belongs to the Special Issue Tube and Sheet Metal Forming Processes and Applications)
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Article
Effect of abc Pressing at 573 K on the Microstructure and Martensite Transformation Temperatures in Ti49.8Ni50.2 (at%)
Metals 2021, 11(7), 1145; https://doi.org/10.3390/met11071145 - 20 Jul 2021
Cited by 3 | Viewed by 623
Abstract
This paper presents experimental data on the microstructure and martensite transformation temperatures of Ti49.8Ni50.2 (at%) after abc pressing (multi-axial forging) to different true strains e from 1.84 to 9.55 at 573 K. The data show that increasing the true strain [...] Read more.
This paper presents experimental data on the microstructure and martensite transformation temperatures of Ti49.8Ni50.2 (at%) after abc pressing (multi-axial forging) to different true strains e from 1.84 to 9.55 at 573 K. The data show that increasing the true strain results in grain–subgrain refinement on different scales at a time. With e = 9.55 at 573 K, the average grain–subgrain size measured approximately 130 nm. Decreasing the abc pressing temperature from 723 to 573 K caused a decrease in all martensite transformation temperatures, a change in the lattice parameters, R phase formation, and angular shifts of diffraction peaks and their broadening. The largest change in the microstructure of Ti49.8Ni50.2 was provided by abc pressing to e = 1.84. Increasing the true strain to e = 9.55 resulted in a much smaller effect, suggesting that the alloy obtained a high density of structural defects even at e = 1.84. Two possible mechanisms of grain–subgrain refinement are discussed. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)
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Article
Towards Greener Industry: Modelling of Slag Heat Recovery
Metals 2021, 11(7), 1144; https://doi.org/10.3390/met11071144 - 20 Jul 2021
Viewed by 1194
Abstract
The steel industry, in accordance with the momentum of greener industry, has welcomed the changes and is actively pursuing that objective. One such activity is the commitment to energy recovery from by-products such as slag since the average energy content of ferrous slags [...] Read more.
The steel industry, in accordance with the momentum of greener industry, has welcomed the changes and is actively pursuing that objective. One such activity is the commitment to energy recovery from by-products such as slag since the average energy content of ferrous slags is around 1 to 2 GJ/tslag. The recovered energy could, then, be used in heating or drying process among others. The RecHeat was designed and modelled iteratively to achieve an optimised heat recovery apparatus. The model shows that the temperature of different sections of the heat exchanger part varies from 170 to 380 °C after slag pouring while the average air temperature at the entrance of the heat exchanger is less than 150 °C. Furthermore, the temperature of the fluid medium changes from 125–140 °C to 260–340 °C from one end of the heat exchanger part to the other at the end of the simulation. The outlet temperature at the end of the simulation is calculated to be around 340 °C, which shows an increase by at least 200 °C in the temperature of the air entering the apparatus. Full article
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Article
Influence of Cooling Process Routes after Intercritical Annealing on Impact Toughness of Duplex Type Medium Mn Steel
Metals 2021, 11(7), 1143; https://doi.org/10.3390/met11071143 - 20 Jul 2021
Cited by 1 | Viewed by 691
Abstract
To apply the duplex type low-carbon medium-manganese steel to the hot/warm-forging and -stamping products, the influence of cooling process routes immediately after intercritical annealing such as air-cooling (AC) and isothermal transformation (IT) processes on the impact toughness of 0.2%C-1.5%Si-5%Mn (in mass %) duplex [...] Read more.
To apply the duplex type low-carbon medium-manganese steel to the hot/warm-forging and -stamping products, the influence of cooling process routes immediately after intercritical annealing such as air-cooling (AC) and isothermal transformation (IT) processes on the impact toughness of 0.2%C-1.5%Si-5%Mn (in mass %) duplex type medium-Mn (D-MMn) steel was investigated. Moreover the microstructural and tensile properties were also investigated. The AC process increased the volume fraction of reverted austenite but decreased the thermal and mechanical stability in the D-MMn steel, compared to the IT process. The AC process increased the tensile strength but decreased the total elongation. The Charpy V-notch impact value and ductile-brittle transition temperature were deteriorated by the AC process, compared to the IT process. This deterioration of the impact toughness was mainly related to the reverted austenite characteristics and fracture mode. Full article
(This article belongs to the Special Issue Recent Advances in High-Strength Forging Steels)
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Article
Effects of Aging under Stress on Mechanical Properties and Microstructure of EN AW 7075 Alloy
Metals 2021, 11(7), 1142; https://doi.org/10.3390/met11071142 - 20 Jul 2021
Viewed by 856
Abstract
In the present study, microstructural and mechanical properties of EN AW 7075 following stress-aging were assessed. For this purpose, properties of stress-aged samples were compared with values obtained for conventionally aged counterparts. It is revealed that the strength and hardness of EN AW [...] Read more.
In the present study, microstructural and mechanical properties of EN AW 7075 following stress-aging were assessed. For this purpose, properties of stress-aged samples were compared with values obtained for conventionally aged counterparts. It is revealed that the strength and hardness of EN AW 7075 can be increased by the presence of external stresses during aging. Precipitation kinetics were found to be accelerated. The effects of conventional and stress-aging on the microstructure were analyzed using synergetic techniques: the differently aged samples were probed by differential scanning calorimetry (DSC) in order to characterize the precipitation processes. DSC was found to be an excellent screening tool for the analysis of precipitation processes during aging of this alloy with and without the presence of external stresses. Furthermore, using electron microscopy it was revealed that an improvement in mechanical properties can be correlated to changes in the morphologies and sizes of precipitates formed. Full article
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Article
Effect of Al Addition on Martensitic Transformation Stability and Microstructural and Mechanical Properties of CuZr Based Shape Memory Alloys
Metals 2021, 11(7), 1141; https://doi.org/10.3390/met11071141 - 20 Jul 2021
Cited by 1 | Viewed by 544
Abstract
In this work, the effect of the Al content (x = 5, 10, and 15 at. %) on the martensitic transformation (MT) and microstructure and mechanical properties of Cu(50−x)Zr50Alx alloys was studied. The microstructure of the alloys was [...] Read more.
In this work, the effect of the Al content (x = 5, 10, and 15 at. %) on the martensitic transformation (MT) and microstructure and mechanical properties of Cu(50−x)Zr50Alx alloys was studied. The microstructure of the alloys was characterized at room temperature by means of scanning electron microscopy and X-ray diffraction. An increase in Al content reduces the amount of transforming CuZr phase, and consequently the secondary phase formation is favored. The evolution of the MT upon thermal cycling was investigated as a function of the Al content by differential scanning calorimetry. MT temperatures and enthalpies were found to be decreased when increasing the Al content. Al addition can induce a sudden, stable MT below 0 °C, while the binary alloy requires ten complete thermal cycles to stabilize. Finally, the mechanical properties were investigated through microhardness and compression testing. No linear dependence was found with composition. Hardness lowering effect was observed for 5–10 at. % of Al content, while the hardness was increased only for 15 at. % Al addition with respect to the binary alloy. Similarly, compressive response of the alloys showed behavior dependent on the Al content. Up to 10 at. % Al addition, the alloys indicate a superelastic response at room temperature, while higher Al content induced untimely failure. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2020)
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Article
RANS versus Scale Resolved Approach for Modeling Turbulent Flow in Continuous Casting of Steel
Metals 2021, 11(7), 1140; https://doi.org/10.3390/met11071140 - 19 Jul 2021
Cited by 1 | Viewed by 794
Abstract
Numerical modeling is the approach used most often for studying and optimizing the molten steel flow in a continuous casting mold. The selection of the physical model might very much influence such studies. Hence, it is paramount to choose a proper model. In [...] Read more.
Numerical modeling is the approach used most often for studying and optimizing the molten steel flow in a continuous casting mold. The selection of the physical model might very much influence such studies. Hence, it is paramount to choose a proper model. In this work, the numerical results of four turbulence models are compared to the experimental results of the water model of continuous casting of steel billets using a single SEN port in a downward vertical orientation. Experimental results were obtained with a 2D PIV (Particle Image Velocimetry) system with measurements taken at various cut planes. Only hydrodynamic effects without solidification are considered. The turbulence is modeled using the RANS (Realizable k-ε, SST k-ω), hybrid RANS/Scale Resolved (SAS), and Scale Resolved approach (LES). The models are numerically solved by the finite volume method, with volume of fluid treatment at the free interface. The geometry, boundary conditions, and material properties were entirely consistent with those of the water model experimental study. Thus, the study allowed a detailed comparison and validation of the turbulence models used. The numerical predictions are compared to experimental data using contours of velocity and velocity plots. The agreement is assessed by comparing the lateral dispersion of the liquid jet in a streamwise direction for the core flow and the secondary flow behavior where recirculation zones form. The comparison of the simulations shows that while all four models capture general flow features (e.g., mean velocities in the temporal and spatial domain), only the LES model predicts finer turbulent structures and captures temporal flow fluctuations to the extent observed in the experiment, while SAS bridges the gap between RANS and LES. Full article
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Article
Structure and Properties of Ti-Al-Ta and Ti-Al-Cr Cladding Layers Fabricated on Titanium
Metals 2021, 11(7), 1139; https://doi.org/10.3390/met11071139 - 19 Jul 2021
Viewed by 731
Abstract
Being one of the most high-demand structural materials, titanium has several disadvantages, including low resistance to high-temperature oxidation and wear. The properties of titanium and its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thick Ti-Al-Ta and [...] Read more.
Being one of the most high-demand structural materials, titanium has several disadvantages, including low resistance to high-temperature oxidation and wear. The properties of titanium and its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thick Ti-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beam cladding. The microstructure and phase compositions of the samples were different for various alloying elements. The Cr-containing layer consisted of α2, γ, and B2 phases, while the Ta-containing layer additionally consisted of ω′ phase (P3¯m1). At the same atomic concentrations of aluminum and an alloying element in both layers, the volume fraction of the B2/ω phase in the Ti-41Al-7Ta alloy was significantly lower than in the Ti-41Al-7Cr alloy, and the amount of γ phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximum oxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Ti-Based Alloys)
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Article
Edge Microstructure and Strength Gradient in Thermally Cut Ti-Alloyed Martensitic Steels
Metals 2021, 11(7), 1138; https://doi.org/10.3390/met11071138 - 19 Jul 2021
Viewed by 577
Abstract
Recently developed Ti-alloyed martensitic steels are believed to exhibit higher wear resistance than traditionally quenched and tempered medium carbon steels. However, their properties may deteriorate during thermal cutting and welding as a result of microstructure tempering. This would present significant challenges for the [...] Read more.
Recently developed Ti-alloyed martensitic steels are believed to exhibit higher wear resistance than traditionally quenched and tempered medium carbon steels. However, their properties may deteriorate during thermal cutting and welding as a result of microstructure tempering. This would present significant challenges for the metal fabrication industries. A decrease in strength and wear resistance associated with tempering should vary with steel composition, initial steel microstructure and properties, and cutting method. In this work, we investigated the effect of thermal cutting on the edge microstructure and properties in two alloyed plate steels containing 0.27C-0.40Ti and 0.39C-0.60Ti (wt.%) commercially rolled to 12 mm thickness. Three cutting methods were applied to each of the two plates: oxy-fuel, plasma and water-jet. Microstructure characterisation was carried out using optical and scanning electron microscopy. With an increase in thermal effect, from water-jet to plasma to oxy-fuel, the heat affected zone width increased and hardness decreased in both steels. However, the hardness profile from the cut edge to the base metal significantly varied with steel composition, particularly C and Ti contents. The dependence of grain structure and precipitation kinetics on steel composition, and cutting method, were thoroughly investigated and linked to the hardness profile variation. The obtained results will be used to optimise the technological parameters for cutting and welding of Ti-alloyed martensitic steels. Full article
(This article belongs to the Special Issue Novel Steel Compositions and Processing Technologies)
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Article
Non-Isothermal Reduction Kinetics of Iron Ore Fines with Carbon-Bearing Materials
Metals 2021, 11(7), 1137; https://doi.org/10.3390/met11071137 - 19 Jul 2021
Viewed by 824
Abstract
This study investigates the non-isothermal reduction of iron ore fines with two different carbon-bearing materials using the thermogravimetric technique. The iron ore fines/carbon composites were heated from room temperature up to 1100 °C with different heating rates (5, 10, 15, and 20 °C/min) [...] Read more.
This study investigates the non-isothermal reduction of iron ore fines with two different carbon-bearing materials using the thermogravimetric technique. The iron ore fines/carbon composites were heated from room temperature up to 1100 °C with different heating rates (5, 10, 15, and 20 °C/min) under an argon atmosphere. The effect of heating rates and carbon sources on the reduction rate was intensively investigated. Reflected light and scanning electron microscopes were used to examine the morphological structure of the reduced composite. The results showed that the heating rates affected the reduction extent and the reduction rate. Under the same heating rate, the rates of reduction were relatively higher by using charcoal than coal. The reduction behavior of iron ore-coal was proceeded step wisely as follows: Fe2O3 → Fe3O4 → FeO → Fe. The reduction of iron ore/charcoal was proceeded from Fe2O3 to FeO and finally from FeO to metallic iron. The reduction kinetics was deduced by applying two different methods (model-free and model-fitting). The calculated activation energies of Fe2O3/charcoal and of Fe2O3/coal are 40.50–190.12 kJ/mol and 55.02–220.12 kJ/mol, respectively. These indicated that the reduction is controlled by gas diffusion at the initial stages and by nucleation reaction at the final stages. Full article
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Article
Heat Treatment Design for a QP Steel: Effect of Partitioning Temperature
Metals 2021, 11(7), 1136; https://doi.org/10.3390/met11071136 - 19 Jul 2021
Cited by 1 | Viewed by 1520
Abstract
Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels [...] Read more.
Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels display an excellent relationship between strength and formability, making them able to fulfill the requirements of safety, while reducing automobile weight to enhance the performance during service. The main attribute of QP steels is the TRIP effect that retained austenite possesses, which allows a significant energy absorption during deformation. The present study is focused on evaluating some process parameters, especially the partitioning temperature, in the microstructures and mechanical properties attained during a QP process. An experimental steel (0.2C-3.5Mn-1.5Si (wt%)) was selected and heated according to the theoretical optimum quenching temperature. For this purpose, heat treatments in a quenching dilatometry and further microstructural and mechanical characterization were carried out by SEM, XRD, EBSD, and hardness and tensile tests, respectively. The samples showed a significant increment in the retained austenite at an increasing partitioning temperature, but with strong penalization on the final ductility due to the large amount of fresh martensite obtained as well. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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Article
Real-Time Weld Gap Monitoring and Quality Control Algorithm during Weaving Flux-Cored Arc Welding Using Deep Learning
Metals 2021, 11(7), 1135; https://doi.org/10.3390/met11071135 - 18 Jul 2021
Viewed by 1443
Abstract
In the flux-cored arc welding process, which is most widely used in shipbuilding, a constant
external weld bead shape is an important factor in determining proper weld quality; however, the
size of the weld gap is generally not constant, owing to errors generated [...] Read more.
In the flux-cored arc welding process, which is most widely used in shipbuilding, a constant
external weld bead shape is an important factor in determining proper weld quality; however, the
size of the weld gap is generally not constant, owing to errors generated during the shell forming
process; moreover, a constant external bead shape for the welding joint is difficult to obtain when
the weld gap changes. Therefore, this paper presents a method for monitoring the weld gap and
controlling the weld deposition rate based on a deep neural network (DNN) for the automation
of the hull block welding process. Welding experiments were performed with a welding robot
synchronized with the welding machine, and the welding quality was classified according to the
experimental results. Welding current and voltage signals, as the robot passed through the weld
seam, were measured using a trigger device and analyzed in the time domain and frequency domain,
respectively. From the analyzed data, 24 feature variables were extracted and used as input for the
proposed DNN model. Consequently, the offline and online performance verification results for new
experimental data using the proposed DNN model were 93% and 85%, respectively Full article
(This article belongs to the Special Issue Quality Assessment and Process Management of Welded Joints)
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Editorial
Strengthening Mechanisms in Metallic Materials
Metals 2021, 11(7), 1134; https://doi.org/10.3390/met11071134 - 18 Jul 2021
Cited by 1 | Viewed by 1022
Abstract
The mechanical properties of contemporary engineering alloys are approaching their natural limits [...] Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
Review
Promising Methods for Corrosion Protection of Magnesium Alloys in the Case of Mg-Al, Mg-Mn-Ce and Mg-Zn-Zr: A Recent Progress Review
Metals 2021, 11(7), 1133; https://doi.org/10.3390/met11071133 - 18 Jul 2021
Cited by 6 | Viewed by 1479
Abstract
High specific strength characteristics make magnesium alloys widely demanded in many industrial applications such as aviation, astronautics, military, automotive, bio-medicine, energy, etc. However, the high chemical reactivity of magnesium alloys significantly limits their applicability in aggressive environments. Therefore, the development of effective technologies [...] Read more.
High specific strength characteristics make magnesium alloys widely demanded in many industrial applications such as aviation, astronautics, military, automotive, bio-medicine, energy, etc. However, the high chemical reactivity of magnesium alloys significantly limits their applicability in aggressive environments. Therefore, the development of effective technologies for corrosion protection is an urgent task to ensure the use of magnesium-containing structures in various fields of application. The present paper is aimed to provide a short review of recent achievements in corrosion protection of magnesium alloys, both surface treatments and coatings, with particular focus on Mg-Al-Mn-Ce, Mg-Al-Zn-Mn and Mg-Zn-Zr alloys, because of their wide application in the transport industry. Recent progress was made during the last decade in the development of protective coatings (metals, ceramics, organic/polymer, both single layers and multilayer systems) fabricated by different deposition techniques such as anodization, physical vapour deposition, laser processes and plasma electrolytic oxidation. Full article
(This article belongs to the Special Issue Surface Chemistry and Corrosion of Light Alloys)
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Article
Experimental and Analytical Study of Horizontally Curved I-Girders Subjected to Equal End Moments
Metals 2021, 11(7), 1132; https://doi.org/10.3390/met11071132 - 17 Jul 2021
Viewed by 657
Abstract
If bending and torsional moments are applied to an I-shaped beam member, the coupling of those two forces could reduce the bending moment capacity of that member. Therefore, the interaction between bending and torsional moments is an important issue for horizontally curved members [...] Read more.
If bending and torsional moments are applied to an I-shaped beam member, the coupling of those two forces could reduce the bending moment capacity of that member. Therefore, the interaction between bending and torsional moments is an important issue for horizontally curved members that are always simultaneously subjected to bending and torsion. In this study, the behavior of the horizontally curved steel I-beam was investigated through numerical analysis. The ultimate state of sharply curved members that showed large displacement was defined in accordance with the stiffness reduction ratio to consist of strength curves. Based on the analysis results, interaction curves were established, and a strength equation was derived. The uniform torsional moment capacity, curvature, and slenderness parameters were considered in the equation, which were the main factors that affected the ultimate strength of curved members. The curvature effect was considered individually, so that the strength of the straight or curved girder could be estimated with a unified equation. To verify the accuracy of the suggested equation, experimental studies were also conducted. Consequently, the suggested equation shows very good agreement with the test results, and is expected to provide useful information for the design of curved members. Full article
(This article belongs to the Special Issue Advances in Structural Application of Metals)
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Article
Influence of Cutting Speed in Turning and Force in Subsequent Diamond Smoothing on Magnetic Properties of Steel 100Cr6
Metals 2021, 11(7), 1131; https://doi.org/10.3390/met11071131 - 16 Jul 2021
Viewed by 613
Abstract
Magnetic properties are known to be crucial in the application of electrical steel and they are therefore covered by manifold studies. Other ferromagnetic materials are out of scope in this respect, even if the importance of magnetism of conventional steel is evident. Additionally, [...] Read more.
Magnetic properties are known to be crucial in the application of electrical steel and they are therefore covered by manifold studies. Other ferromagnetic materials are out of scope in this respect, even if the importance of magnetism of conventional steel is evident. Additionally, there is a contradiction regarding the major influence on magnetic properties. Machining, transport, and storage are possible influencing variables. In the experimental investigations, specimens consisting of the bearing steel 100Cr6 are machined by turning and partly by subsequent diamond smoothing. While machining using several cutting speeds and smoothing forces, the thermoelectrical voltage, current, and the components of the resultant force are recorded. The results show how the near-surface plastic deformations evolve throughout the machining process. Additionally, it was found that the magnetic properties and other properties of the surface layer are influenced in different ways depending on turning and diamond smoothing parameters. Correlations between in situ and ex situ measured values are shown. This study aims to solve the aforementioned question by quantification of machining impacts of cutting speed in turning and force in diamond smoothing and its dependence on transport and storage. Full article
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Article
Quantification of Solid Solution Strengthening and Internal Stresses through Creep Testing of Ni-Containing Single Crystals at 980 °C
Metals 2021, 11(7), 1130; https://doi.org/10.3390/met11071130 - 16 Jul 2021
Cited by 2 | Viewed by 1042
Abstract
Various alloy compositions were cast as single crystals in a Bridgman vacuum induction furnace and creep tested at 980 °C: pure Ni, the equiatomic alloys CoCrNi and CrMnFeCoNi (Cantor alloy), single-phase fcc (Ni) solid solution alloys (with the composition of the matrix-phase of [...] Read more.
Various alloy compositions were cast as single crystals in a Bridgman vacuum induction furnace and creep tested at 980 °C: pure Ni, the equiatomic alloys CoCrNi and CrMnFeCoNi (Cantor alloy), single-phase fcc (Ni) solid solution alloys (with the composition of the matrix-phase of CMSX-3 and CMSX-4), and two-phase Ni-based superalloys CMSX-3 and CMSX-4. Due to the single-crystal state, grain size effects, grain boundary sliding, and grain boundary diffusion can be excluded. The results identify two major strengthening mechanisms: solid solution strengthening and other mechanisms summarized as precipitation hardening. Configurational entropy does not increase creep strength: The Cantor alloy, with the highest configurational entropy of all alloys tested, shows a weak and similar creep strength at 980 °C in comparison to pure Ni with zero configurational entropy. The element Re is a very effective strengthener, both in single-phase fcc (Ni) solid solution alloys as well as in two-phase superalloys. Quantitative estimations of different strengthening mechanisms: internal back stress, misfit stresses, Orowan bowing, and γ′-phase cutting (in the case of two-phase superalloys) are presented. Finite element simulations allow estimating the influence of solid solution strengthening of the matrix on the creep behavior of the two-phase superalloys. Full article
(This article belongs to the Special Issue Advances in Superalloys and High Temperature Intermetallics)
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Article
Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel
Metals 2021, 11(7), 1129; https://doi.org/10.3390/met11071129 - 16 Jul 2021
Viewed by 552
Abstract
15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, [...] Read more.
15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, and vacuum casting were studied. The results show that the DS-type inclusions with sizes larger than 20 μm were CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions in vacuum degassing, typical inclusions were spinel or Al2O3. After Ca–Si additions during ladle treatment, typical inclusions were liquid or dual-phase Al2O3–CaO–SiO2–MgO. During the solidification process, due to the segregation of S and the decrease in solubility, the typical inclusions in the final casting became Al2O3–CaO–SiO2–MgO–CaS. For optimal fatigue performance of stainless steel castings, slag and refractory composition control were also necessary because the [Mg] contents mainly come from the slag and lining. Full article
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Editorial
High-Temperature Behavior of Metals
Metals 2021, 11(7), 1128; https://doi.org/10.3390/met11071128 - 16 Jul 2021
Viewed by 513
Abstract
The design of new alloys as well as the optimization of processes involving whichever form of high-temperature deformation cannot disregard the characterization and/or modelling of the high-temperature structural response of the material [...] Full article
(This article belongs to the Special Issue High-Temperature Behavior of Metals)
Article
Mechanisms of Cracking in Laser Welding of Magnesium Alloy AZ91D
Metals 2021, 11(7), 1127; https://doi.org/10.3390/met11071127 - 15 Jul 2021
Cited by 1 | Viewed by 901
Abstract
Considerable research has been carried out to study the laser welding of magnesium alloys. However, the studies are mainly devoted to butt welding, and there has been limited information in the published literature concerning the bead-on-plate laser welding of AZ91D, even though bead-on-plate [...] Read more.
Considerable research has been carried out to study the laser welding of magnesium alloys. However, the studies are mainly devoted to butt welding, and there has been limited information in the published literature concerning the bead-on-plate laser welding of AZ91D, even though bead-on-plate welding is required for the repair of cast AZ91D parts with surface defects. In the present investigation, surface cracking of the weld metal was observed when an AZ91D magnesium alloy was bead-on-plate welded using the laser welding method. This paper presents the experimental results and analyses to show that the cracking is “solidification cracking” initiated from the weld surface under high thermal stresses. This is in contrast to the “liquation cracking” observed in heat affected zones in tungsten inert gas welding of the same magnesium alloy. Laser power was found to be one of the main factors affecting the distance of the crack propagation. The higher laser power resulted in longer crack propagation distance into the weld metal. It is demonstrated that hot cracking could be avoided by lowering the laser power and welding speed. Full article
(This article belongs to the Special Issue Application of Correlative Microscopy in Metallurgical Research)
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Article
Thermal Fatigue Life Prediction under Temperature Uncertainty for Shot Sleeve of Squeeze Casting Machine
Metals 2021, 11(7), 1126; https://doi.org/10.3390/met11071126 - 15 Jul 2021
Cited by 1 | Viewed by 604
Abstract
To quantify the influence of temperature uncertainty on thermal fatigue life prediction of a shot sleeve in an injection mechanism, an uncertainty analysis method based on a Kriging surrogate model and Monte Carlo simulation (MCS) was proposed. The training samples of the surrogate [...] Read more.
To quantify the influence of temperature uncertainty on thermal fatigue life prediction of a shot sleeve in an injection mechanism, an uncertainty analysis method based on a Kriging surrogate model and Monte Carlo simulation (MCS) was proposed. The training samples of the surrogate model were obtained by a finite element simulation, and the response relationships between input variables, such as pouring and preheating temperature, and target variables, such as strain and stress, were constructed by the Kriging surrogate model. The input variables were sampled by the MCS, and the predicted stress and strain parameters were combined with the modified universal slope equation to predict the thermal fatigue life of the shot sleeve. The statistical characteristics of the predicted life were obtained. The comparative analysis results indicate that the predicted life considering temperature uncertainty is more accurate than the deterministically predicted value. Full article
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Article
Influence of Pulsed Exposure Strategies on Overhang Structures in Powder Bed Fusion of Ti6Al4V Using Laser Beam
Metals 2021, 11(7), 1125; https://doi.org/10.3390/met11071125 - 15 Jul 2021
Viewed by 802
Abstract
Manufacturing structures with low overhang angles without support structures is a major challenge in powder bed fusion of metals using laser beam (PBF-LB/M). In the present work, various test specimens and parameter sets with continuous wave (cw) and pulsed exposure are used to [...] Read more.
Manufacturing structures with low overhang angles without support structures is a major challenge in powder bed fusion of metals using laser beam (PBF-LB/M). In the present work, various test specimens and parameter sets with continuous wave (cw) and pulsed exposure are used to investigate whether a reduction of downskin roughness and overhang angle can be achieved in PBF-LB/M of Ti6Al4V. Starting from cw exposure, the limits of overhang angle and surface roughness at the downskin surface are investigated as a reference. Subsequently, the influence of laser power, scanning speed, and hatch distance with fixed pulse duration (τpulse = 25 µs) and repetition rate (υrep = 20 kHz) on surface roughness Ra is investigated. Pulsed exposure strategies enable the manufacturing of flatter overhang angles (≤20° instead of ≥25°). Furthermore, a correlation between the introduced volume energy density and the downskin roughness can be observed for pulsed exposure. As the reduction in volume energy density causes an increase in porosity, the combination of pulsed downskin exposure and commercial cw infill exposure is investigated. The larger the gap in volume energy density between the infill area and downskin area, the more challenging it is combining the two parameter sets. By combining cw infill and pulsed downskin exposure, flatter overhang structures cannot be manufactured, and a reduction in roughness can be achieved. Full article
(This article belongs to the Special Issue Advances in Additive Manufacturing of Metals)
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Article
Enhancement of Corrosion Properties of Fe-18Cr-9Mn-5.5Ni-0.3(C + N) Austenitic Stainless Steels by Carbon Alloying
Metals 2021, 11(7), 1124; https://doi.org/10.3390/met11071124 - 15 Jul 2021
Cited by 1 | Viewed by 657
Abstract
In this study, the resistance to pitting corrosion of Fe-18Cr-9Mn-5.5Ni-0.3(C + N) austenitic stainless steel γ-SSs (in wt%) with different C/(C + N) ratios (0.02, 0.29, and 0.60) was evaluated. It was found to be difficult to form a γ-matrix without precipitation, because [...] Read more.
In this study, the resistance to pitting corrosion of Fe-18Cr-9Mn-5.5Ni-0.3(C + N) austenitic stainless steel γ-SSs (in wt%) with different C/(C + N) ratios (0.02, 0.29, and 0.60) was evaluated. It was found to be difficult to form a γ-matrix without precipitation, because the Cr23C6 precipitation rate in the γ-SSs with the C/(C + N) value of 0.60 was too fast. Thus, it was recommended to maintain the C/(C + N) ratio below 0.6 in Fe-18Cr-9Mn-5.5Ni-0.3(C + N) γ-SSs. As a result of the potentiodynamic polarization tests, the γ-SS with a C/(C + N) ratio of 0.29 showed the highest resistance to pitting corrosion, and the resistance level of this alloy was superior to that of the AISI 304 γ-SS. Analysis of the passive film and matrix dissolution rates revealed that a higher C/(C + N) ratio of γ-SS increased the protective ability of the passive film and decreased the growth rate of the pits. Therefore, it could be concluded that partial substitution of C for N was advantageous for improving the pitting corrosion resistance of Fe-18Cr-9Mn-5.5Ni-0.3(C + N) γ-SSs, as long as C and N existed in a solid solution state. Full article
(This article belongs to the Special Issue Corrosion and Protection of Stainless Steels)
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Article
Experimental Investigation of the Effects of Irradiating Schemes in Laser Tube Bending Process
Metals 2021, 11(7), 1123; https://doi.org/10.3390/met11071123 - 15 Jul 2021
Viewed by 878
Abstract
The laser tube bending process (LTBP) process is a thermal non-contact process for bending tubes with less springback and less thinning of the tube. In this paper, the laser tube bending process will be studied experimentally. The length of irradiation and irradiation scheme [...] Read more.
The laser tube bending process (LTBP) process is a thermal non-contact process for bending tubes with less springback and less thinning of the tube. In this paper, the laser tube bending process will be studied experimentally. The length of irradiation and irradiation scheme are two main affecting process parameters in the LTBP process. For this purpose, different samples according to two main irradiation schemes (Circular irradiating scheme (CIS) and axial irradiating scheme (AIS)) and different lengths of laser beam irradiation (from 4.7 to 28.2 mm) are fabricated. The main bending angle of laser-bent tube, lateral bending angle, ovality, and thickness variations is measured experimentally, and the effects of the irradiating scheme and the length of irradiation are investigated. An 18 mm diameter, 1 mm thick mild steel tube was bent with 1100 Watts laser beam. The results show that for both irradiating schemes, by increasing the irradiating length of the main and lateral bending angle, the ovality and thickness variation ratio of the bent tube are increased. In addition, for a similar irradiating length, the main bending angle with AIS is considerably higher than CIS. The lateral bending angle by AIS is much less than the lateral bending angle with CIS. The results demonstrate that the ovality percentage and the thickness variation ratio for the laser-bent tube obtained by CIS are much more than the values associated with by AIS laser-bent tube. Full article
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Article
Ce-Bearing FeSi Alloy Inoculation of Electrically Melted, Low Sulphur Grey Cast Irons for Thin Wall Castings
Metals 2021, 11(7), 1122; https://doi.org/10.3390/met11071122 - 15 Jul 2021
Viewed by 592
Abstract
Electrically melted and over-heated (>1500 °C) grey cast iron at less than 0.04%S, as commonly used, solidifies large amounts of carbides and/or undercooled graphite, especially in thin wall castings; this is necessary to achieve a stronger inoculation. The efficiency of Ce-bearing FeSi alloy [...] Read more.
Electrically melted and over-heated (>1500 °C) grey cast iron at less than 0.04%S, as commonly used, solidifies large amounts of carbides and/or undercooled graphite, especially in thin wall castings; this is necessary to achieve a stronger inoculation. The efficiency of Ce-bearing FeSi alloy is tested for lower ladle addition rates (0.15 and 0.25 wt.%), compared to the base and conventional inoculated iron (Ba,Ca-bearing FeSi alloy). The present work explores chill and associated structures in hypoeutectic grey iron (3.6–3.8%CE, 0.02%S, (%Mn) × (%S) = 0.013–0.016, Alres < 0.002%), in wedge castings W1, W2 and W3 (ASTM A 367, furan resin sand mould), at a lower cooling modulus (1.1–3.5 mm) that is typically used to control the quality of thin wall iron castings. Relatively clear and total chill well correlated with the standard thermal (cooling curve) analysis parameters and structural characteristics in wedge castings, at different wall thickness, displayed as the carbides/graphite ratio and presence of undercooled graphite morphologies. The difference in effects of the two inoculants addition is seen as the ability to decrease the amount of carbides and undercooled graphite, with Ce-bearing FeSi alloy outperforming the conventional inoculant, especially as the wall thickness decreased. It appears that Ce-bearing FeSi alloy could be a solution for low sulphur, electric melt, thin wall iron castings production. Full article
(This article belongs to the Special Issue Optimizing Techniques and Understanding in Casting Processes)
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Article
Microstructures and Properties of Auto-Tempering Ultra-High Strength Automotive Steel under Different Thermal-Processing Conditions
Metals 2021, 11(7), 1121; https://doi.org/10.3390/met11071121 - 14 Jul 2021
Cited by 1 | Viewed by 668
Abstract
Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the [...] Read more.
Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the steels under water quenching, there was approximately a 70% increase in the strength and elongation of steels under air cooling, in which the martensite was well-tempered. Although the elongation of the steel with a microstructure composed of ferrite, well-tempered martensite and less-tempered martensite could exceed 15%, the hole expansion ratio was still lower because of the undesirable hardness distribution between the hard phases and the soft phases. It followed from the calculation results based on SEM, TEM and XRD analyses, that for the steel under air cooling, the strengthening mechanism was dominated by the solid solution strengthening and the elongation was determined by the auto-tempering of martensite. Experiments and analyses aimed to explore the strengthening and plasticity mechanisms of auto-tempering steels under the special process of flash heating. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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Article
Influence of Sc Microalloying on the Microstructure of Al5083 Alloy and Its Strengthening Effect
Metals 2021, 11(7), 1120; https://doi.org/10.3390/met11071120 - 14 Jul 2021
Viewed by 620
Abstract
In this study, we investigate the influence of Sc microalloying on the microstructure of the Al5083 alloy. Trace amounts of Sc addition drastically improve the mechanical properties of the Al5083 alloy from 216 MPa to 233 MPa. Macroscopically, the addition of Sc significantly [...] Read more.
In this study, we investigate the influence of Sc microalloying on the microstructure of the Al5083 alloy. Trace amounts of Sc addition drastically improve the mechanical properties of the Al5083 alloy from 216 MPa to 233 MPa. Macroscopically, the addition of Sc significantly reduces the grain size of Al by approximately 50%. Additionally, a microstructural investigation reveals that the Sc microalloying element induces fine Al3Sc nanoprecipitates in the Al matrix. The formation of Al3Sc nanoprecipitates results in a pinning effect on the dislocations, leading to accumulated dislocations. Compared to a Sc-free Al5083 alloy specimen, the number density of dislocations in the Sc-added Al5083 alloy significantly increases after hot rolling, enhancing the tensile properties. We reveal that the improved mechanical properties of Al5083 with Sc microalloying originate from the grain refinement and the formation of fine Al3Sc nanoprecipitates. Full article
(This article belongs to the Special Issue High-Strength Alloys)
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Article
Behavior of Nitrogen in GH4169 Superalloy Melt during Vacuum Induction Melting Using Returned Materials
Metals 2021, 11(7), 1119; https://doi.org/10.3390/met11071119 - 13 Jul 2021
Cited by 1 | Viewed by 664
Abstract
The nitrogen behavior of superalloy melt GH4169 during the vacuum induction melting (VIM) process was clarified by using different proportions of returned materials including block-shaped returned material, chip-shaped returned material, and pure materials to produce a high–purity superalloy melt and provide guidance for [...] Read more.
The nitrogen behavior of superalloy melt GH4169 during the vacuum induction melting (VIM) process was clarified by using different proportions of returned materials including block-shaped returned material, chip-shaped returned material, and pure materials to produce a high–purity superalloy melt and provide guidance for the purification of the superalloy melt. For the nitrogen removal during the VIM process, the denitrification rate in the refining period reached 10 ppm per hour on average, which is significantly higher than 1 ppm per hour on average in the melting period. The denitrification reaction of superalloy melt GH4169 under extremely low vacuum pressure is controlled by both the mass transfer of nitrogen in the melt and the chemical reaction of the liquid–gas interface. The nitrogen removal of superalloy melts during VIM occurs through the two methods of gasification denitrification and nitride floatation because the nitrides begin to precipitate in the liquid phase at 1550 °C. A higher nitrogen removal rate can be obtained by increasing the proportion of chip-shaped material or decreasing the proportion of block-shaped material. Full article
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