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Metals, Volume 9, Issue 7 (July 2019)

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Open AccessFeature PaperArticle
Micro-Macro Relationship between Microstructure, Porosity, Mechanical Properties, and Build Mode Parameters of a Selective-Electron-Beam-Melted Ti-6Al-4V Alloy
Metals 2019, 9(7), 786; https://doi.org/10.3390/met9070786
Received: 12 June 2019 / Revised: 3 July 2019 / Accepted: 10 July 2019 / Published: 15 July 2019
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Abstract
The performance of two selective electron beam melting operation modes, namely the manual mode and the automatic ‘build theme mode’, have been investigated for the case of a Ti-6Al-4V alloy (45–105 μm average particle size of the powder) in terms of porosity, microstructure, [...] Read more.
The performance of two selective electron beam melting operation modes, namely the manual mode and the automatic ‘build theme mode’, have been investigated for the case of a Ti-6Al-4V alloy (45–105 μm average particle size of the powder) in terms of porosity, microstructure, and mechanical properties. The two operation modes produced notable differences in terms of build quality (porosity), microstructure, and properties over the sample thickness. The number and the average size of the pores were measured using a light microscope over the entire build height. A density measurement provided a quantitative index of the global porosity throughout the builds. The selective-electron-beam-melted microstructure was mainly composed of a columnar prior β-grain structure, delineated by α-phase boundaries, oriented along the build direction. A nearly equilibrium α + β mixture structure, formed from the original β-phase, arranged inside the prior β-grains as an α-colony or α-basket weave pattern, whereas the β-phase enveloped α-lamellae. The microstructure was finer with increasing distance from the build plate regardless of the selected build mode. Optical measurements of the α-plate width showed that it varied as the distance from the build plate varied. This microstructure parameter was correlated at the sample core with the mechanical properties measured by means of a macro-instrumented indentation test, thereby confirming Hall-Petch law behavior for strength at a local scale for the various process conditions. The tensile properties, while attesting to the mechanical performance of the builds over a macro scale, also validated the indentation property measurement at the core of the samples. Thus, a direct correlation between the process parameters, microstructure, porosity, and mechanical properties was established at the micro and macro scales. The macro-instrumented indentation test has emerged as a reliable, easy, quick, and yet non-destructive alternate means to the tensile test to measure tensile-like properties of selective-electron-beam-melted specimens. Furthermore, the macro-instrumented indentation test can be used effectively in additive manufacturing for a rapid setting up of the process, that is, by controlling the microscopic scale properties of the samples, or to quantitatively determine a product quality index of the final builds, by taking advantage of its intrinsic relationship with the tensile properties. Full article
(This article belongs to the Special Issue Processing-Structure-Property Relationships in Metals)
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Open AccessCommunication
Low-Temperature Induced Martensitic Transformation Enhancing Mechanical Properties of Metastable Fe-Ni-P Alloy
Metals 2019, 9(7), 785; https://doi.org/10.3390/met9070785
Received: 15 June 2019 / Revised: 9 July 2019 / Accepted: 13 July 2019 / Published: 14 July 2019
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Abstract
The metastable Fe-Ni-P alloy with phosphorus (P) solid-solution structure has been fabricated by spark plasma sintering. Its face-centered cubic (FCC) matrix without the precipitation of phosphide attains a high plasticity and an excellent strain hardening ability at room temperature. This Fe-Ni-P alloy is [...] Read more.
The metastable Fe-Ni-P alloy with phosphorus (P) solid-solution structure has been fabricated by spark plasma sintering. Its face-centered cubic (FCC) matrix without the precipitation of phosphide attains a high plasticity and an excellent strain hardening ability at room temperature. This Fe-Ni-P alloy is subjected to cryogenic treatment at various temperatures (−20 °C and −50 °C), to investigate the role of phosphorus on the microstructural evolution and mechanical properties of γ-(Fe-Ni) alloy at low temperatures. The results indicate that the addition of phosphorus can destabilize the Fe-Ni-P alloy and facilitate its martensitic transformation during cryogenic treatment. P-doping does not lead to obvious embrittlement of Fe-Ni-P alloy at low temperatures, but strengthens the alloy by promoting microstructure evolution. The Fe-Ni-P alloy has high plasticity and good strain hardening ability after treated at −20 °C, and is converted to acicular martensite structure after being treated at −50 °C, resulting in a significant increase in its hardness (433 HV) and compressive yield strength (1271 MPa). Developing this Fe-Ni-P alloy as a load-bearing component for low-temperature conditions shows great promise. Full article
(This article belongs to the Special Issue Phase Transformations in Metallic Materials)
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Open AccessArticle
Comparison of the Dislocation Structure of a CrMnN and a CrNi Austenite after Cyclic Deformation
Metals 2019, 9(7), 784; https://doi.org/10.3390/met9070784
Received: 14 May 2019 / Revised: 19 June 2019 / Accepted: 19 June 2019 / Published: 13 July 2019
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Abstract
In the literature, the effects of nitrogen on the strength of austenitic stainless steels as well as on cold deformation are well documented. However, the effect of N on fatigue behaviour is still an open issue, especially when comparing the two alloying concepts [...] Read more.
In the literature, the effects of nitrogen on the strength of austenitic stainless steels as well as on cold deformation are well documented. However, the effect of N on fatigue behaviour is still an open issue, especially when comparing the two alloying concepts for austenitic stainless steels—CrNi and CrMnN—where the microstructures show a different evolution during cyclic deformation. In the present investigation, a representative sample of each alloying concept has been tested in a resonant testing machine at ambient temperature and under stress control single step tests with a stress ratio of 0.05. The following comparative analysis of the microstructures showed a preferred formation of cellular dislocation substructures in the case of the CrNi alloy and distinct planar dislocation glide in the CrMnN steel, also called high nitrogen steel (HNS). The discussion of these findings deals with potential explanations for the dislocation glide mechanism, the role of N on this phenomenon, and the consequences on fatigue behaviour. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Open AccessArticle
Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools
Metals 2019, 9(7), 783; https://doi.org/10.3390/met9070783
Received: 22 June 2019 / Revised: 10 July 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
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Abstract
Cold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality [...] Read more.
Cold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59–61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions. Full article
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Open AccessArticle
Effect of Substrate Roughness on Oxidation Resistance of an Aluminized Ni-Base Superalloy
Metals 2019, 9(7), 782; https://doi.org/10.3390/met9070782
Received: 12 June 2019 / Revised: 30 June 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
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Abstract
In the present work, it is shown that the surface preparation method used on two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD) is one of the most important factors determining the oxidation resistance of aluminized Ni-based superalloys. It was found that [...] Read more.
In the present work, it is shown that the surface preparation method used on two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD) is one of the most important factors determining the oxidation resistance of aluminized Ni-based superalloys. It was found that grit-blasting the substrate surface negatively affects the oxidation resistance of the aluminized coatings. For grit-blasted and aluminized IN 625, a thicker outer NiAl coating was formed compared to that of IN 738. In contrast, no effect on NiAl coating thickness was found for grit-blasted and aluminized IN 738. However, a thicker interdiffusion zone (IDZ) was observed. It was shown that the systems with grit-blasted surfaces reveal worse oxidation resistance during thermal shock tests—namely, a higher mass loss was observed for both grit-blasted and aluminized alloys, as compared to ground and aluminized alloys. A possible reason for this effect of remaining alumina particles originating from surface grit-blasting on the diffusion processes and stress distribution at the coating/substrate is proposed. Full article
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Open AccessArticle
Ultrasonic Vibration as a Primary Mixing Tool in Accelerating Aluminum–Copper Alloys Preparation from Their Pure Elements
Metals 2019, 9(7), 781; https://doi.org/10.3390/met9070781
Received: 12 June 2019 / Revised: 4 July 2019 / Accepted: 4 July 2019 / Published: 12 July 2019
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Abstract
In this study, ultrasonic vibration (USV) was evaluated in preparation of Al–8wt.%Cu alloys at a lab-scale. Moreover, the role of Ti–6Al–4V sonotrode erosion and its contribution in grain refining were analyzed. Based on the experimental conditions/parameters, it was found that the amount of [...] Read more.
In this study, ultrasonic vibration (USV) was evaluated in preparation of Al–8wt.%Cu alloys at a lab-scale. Moreover, the role of Ti–6Al–4V sonotrode erosion and its contribution in grain refining were analyzed. Based on the experimental conditions/parameters, it was found that the amount of impurities and the associated porosity were significantly reduced in USV treated alloys. Furthermore, USV reduced the time needed for dissolving the alloying element Cu, nevertheless, the best dissolving of Cu in this study was not possible without introducing further holding time. As a result of using a titanium-based sonotrode, a noticeable content of Ti was found in the ultrasonically treated alloys due to sonotrode erosion under USV. The dispersion of TiAl3 promoted, as a main factor, a grain refining effect at relatively constant and high melt temperature, other possible mechanisms of grain refining have been discussed. Full article
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Open AccessArticle
Leaching of Pure Chalcocite in a Chloride Media Using Sea Water and Waste Water
Metals 2019, 9(7), 780; https://doi.org/10.3390/met9070780
Received: 25 June 2019 / Revised: 11 July 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
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Abstract
Chalcocite is the most important and abundant secondary copper ore in the world with a rapid dissolution of copper in an acid-chloride environment. In this investigation, the methodology of surface optimization will be applied to evaluate the effect of three independent variables (time, [...] Read more.
Chalcocite is the most important and abundant secondary copper ore in the world with a rapid dissolution of copper in an acid-chloride environment. In this investigation, the methodology of surface optimization will be applied to evaluate the effect of three independent variables (time, concentration of sulfuric acid and chloride concentration) in the leaching of pure chalcocite to extract the copper with the objective of obtaining a quadratic model that allows us to predict the extraction of copper. The kinetics of copper dissolution in regard to the function of temperature is also analyzed. An ANOVA indicates that the linear variables with the greatest influence are time and the chloride concentration. Also, the concentration of chloride-time exerts a significant synergic effect in the quadratic model. The ANOVA indicates that the quadratic model is representative and the R2 value of 0.92 is valid. The highest copper extraction (67.75%) was obtained at 48 h leaching under conditions of 2 mol/L H2SO4 and 100 g/L chloride. The XRD analysis shows the formation of a stable and non-polluting residue; such as elemental sulfur (S0). This residue was obtained in a leaching time of 4 h at room temperature under conditions of 0.5 mol/L H2SO4 and 50 g/L Cl. Full article
(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy)
Open AccessArticle
The Analytical Model of Stress Zone Formation of Ti4Al4V/AA1050/AA2519 Laminate Produced by Explosive Bonding
Metals 2019, 9(7), 779; https://doi.org/10.3390/met9070779
Received: 27 June 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
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Abstract
This paper contains an analytical description of the deformation of the upper layer AA2519/AA1050/Ti6Al4V laminate produced by an explosive bonding method. The basic parameters of the explosive welding process that influence the quality of the bonding are the detonation velocity of the explosive, [...] Read more.
This paper contains an analytical description of the deformation of the upper layer AA2519/AA1050/Ti6Al4V laminate produced by an explosive bonding method. The basic parameters of the explosive welding process that influence the quality of the bonding are the detonation velocity of the explosive, the explosion energy, and the impact angle of the combined materials. The developed description uses the theory of elastodynamic character of materials deformation at the connection point due to local traction load. The presence of high pressure during joining was limited to the region where the plane surface moving with a constant subsonic velocity. An analytical description of the residual stresses distribution was also a performer. Results of analytical investigations were verified by structure examination of the bond zone. The work was supplemented by the chemical composition analysis of the base materials and a monotonic stretching test characterizing the basic mechanical properties of the produced laminate. Full article
(This article belongs to the Special Issue Explosive Welding)
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Open AccessArticle
Influence of Microstructure on Mechanical Properties of Bainitic Steels in Railway Applications
Metals 2019, 9(7), 778; https://doi.org/10.3390/met9070778
Received: 3 June 2019 / Revised: 24 June 2019 / Accepted: 29 June 2019 / Published: 11 July 2019
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Abstract
Wheel–rail contact creates high stresses in both rails and wheels, which can lead to different damage, such as plastic deformation, wear and rolling contact fatigue (RCF). It is important to use high-quality steels that are resistant to these damages. Mechanical properties and failure [...] Read more.
Wheel–rail contact creates high stresses in both rails and wheels, which can lead to different damage, such as plastic deformation, wear and rolling contact fatigue (RCF). It is important to use high-quality steels that are resistant to these damages. Mechanical properties and failure of steels are determined by various microstructural features, such as grain size, phase fraction, as well as spatial distribution and morphology of these phases in the microstructure. To quantify the mechanical behavior of bainitic rail steels, uniaxial tensile experiments and hardness measurements were performed. In order to characterize the influence of microstructure on the mechanical behavior, various microscopy techniques, such as light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), were used. Three bainitic grades industrially known as B360, B1400 plus and Cr-Bainitic together with commonly used R350HT pearlitic grade were studied. Influence of isothermal bainitic heat treatment on the microstructure and mechanical properties of the bainitic grades was investigated and compared with B360, B1400 plus, Cr-Bainitic and R350HT in as-received (AR) condition from the industry. The results show that the carbide-free bainitic steel (B360) after an isothermal heat treatment offers the best mechanical performance among these steels due to a very fine, carbide-free bainitic microstructure consisting of bainitic ferrite and retained austenite laths. Full article
(This article belongs to the Special Issue Microstructure, Texture and Properties Control in Alloys)
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Open AccessFeature PaperArticle
Precipitation Kinetics and Evaluation of the Interfacial Mobility of Precipitates in an AlSi7Cu3.5Mg0.15 Cast Alloy with Zr and V Additions
Metals 2019, 9(7), 777; https://doi.org/10.3390/met9070777
Received: 10 June 2019 / Revised: 9 July 2019 / Accepted: 9 July 2019 / Published: 11 July 2019
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Abstract
Recent environmental restrictions constrained car manufacturers to promote cast aluminum alloys working at high temperatures (180 °C–300 °C). The development of new alloys permits the fabrication of higher-strength components in engine downsizing. Those technologies increase internal loadings and specific power and stretch current [...] Read more.
Recent environmental restrictions constrained car manufacturers to promote cast aluminum alloys working at high temperatures (180 °C–300 °C). The development of new alloys permits the fabrication of higher-strength components in engine downsizing. Those technologies increase internal loadings and specific power and stretch current materials to their limits. Transition metals in aluminum alloys are good candidates to improve physical, mechanical, and thermodynamic properties with the aim of increasing service life of parts. This study is focused on the modified AlSi7Cu3.5Mg0.15 alloy where Mn, Zr, and V have been added as alloying elements for high-temperature applications. The characterization of the cast alloy in this study helps to evaluate and understand its performance according to their physical state: As-cast, as-quenched, or artificially aged. The precipitation kinetics of the AlSi7Cu3.5Mg0.15 (Mn, Zr, V) alloy has been characterized by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) observations, and micro-hardness testing. The Kissinger analysis was applied to extract activation energies from non-isothermal DSC runs conducted at different stationary heating rates. Finally, first-order evaluations of the interfacial mobility of precipitates were obtained. Full article
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Open AccessArticle
Improving Mechanical Properties of 18%Mn TWIP Steels by Cold Rolling and Annealing
Metals 2019, 9(7), 776; https://doi.org/10.3390/met9070776
Received: 15 June 2019 / Revised: 5 July 2019 / Accepted: 10 July 2019 / Published: 11 July 2019
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Abstract
The microstructures and mechanical properties of Fe-0.4C-18Mn and Fe-0.6C-18Mn steels subjected to large strain cold rolling followed by annealing were studied. Cold rolling with a total reduction of 86% resulted in substantial strengthening at expense of plasticity. The yield strength and the ultimate [...] Read more.
The microstructures and mechanical properties of Fe-0.4C-18Mn and Fe-0.6C-18Mn steels subjected to large strain cold rolling followed by annealing were studied. Cold rolling with a total reduction of 86% resulted in substantial strengthening at expense of plasticity. The yield strength and the ultimate tensile strength of above 1400 MPa and 1600 MPa, respectively, were achieved in both steels, whereas total elongation decreased below 30%. Subsequent annealing at temperatures above 600 °C was accompanied with the development of recrystallization leading to fine-grained microstructures with an average grain size of about 1 μm in both steels. The fine-grained steels exhibited remarkable improved mechanical properties with a product of ultimate tensile strength by total elongation in the range of 50 to 70 GPa %. The fine-grained steel with relatively high carbon content of 0.6%C was characterized by ultimate tensile strength well above 1400 MPa that was remarkably higher than that of about 1200 MPa in the steel with 0.4%C. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Open AccessArticle
Optimization of Process Parameters to Improve the Effective Area of Deposition in GMAW-Based Additive Manufacturing and its Mechanical and Microstructural Analysis
Metals 2019, 9(7), 775; https://doi.org/10.3390/met9070775
Received: 29 May 2019 / Revised: 28 June 2019 / Accepted: 5 July 2019 / Published: 10 July 2019
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Abstract
Additive manufacturing of metals using gas metal arc welding has an associated problem of variations of height in the onset and extinguishing parts of the weld bead. In this research, robot-assisted welding has been performed to investigate the problem, using AWS ER70S-6 low [...] Read more.
Additive manufacturing of metals using gas metal arc welding has an associated problem of variations of height in the onset and extinguishing parts of the weld bead. In this research, robot-assisted welding has been performed to investigate the problem, using AWS ER70S-6 low alloy steel welding electrode wire. After adjustment of welding parameters for a single-layer, single-pass, an optimal profile of welding energy was used to construct a thin wall which exhibited good forming characteristics with an effective area of approximately 97%. The resulting structure was ductile in nature with better tensile strength and microhardness as compared to the rolled steel available in industry with similar carbon content. The microstructure analysis revealed equiaxed grains in most parts of the structure having a fine grain size. Full article
(This article belongs to the Special Issue Arc-based Additive Manufacturing)
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Open AccessArticle
Study on the Corrosion Fatigue Properties of 12Cr1MoV Steel at High Temperature in Different Salt Environments
Metals 2019, 9(7), 774; https://doi.org/10.3390/met9070774
Received: 6 June 2019 / Revised: 25 June 2019 / Accepted: 7 July 2019 / Published: 10 July 2019
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Abstract
Biomass energy, as a reliable renewable energy source, has gained more and more attention. However, microstructure degradation and corrosion fatigue damage of heat pipes hinder its further application. In this paper, high temperature corrosion fatigue characteristics of 12Cr1MoV steel under a mixed alkali [...] Read more.
Biomass energy, as a reliable renewable energy source, has gained more and more attention. However, microstructure degradation and corrosion fatigue damage of heat pipes hinder its further application. In this paper, high temperature corrosion fatigue characteristics of 12Cr1MoV steel under a mixed alkali metal chloride salt environment and mixed sulfate salt environment were investigated. Fatigue tests with different total strain amplitudes were performed. Results show that the effect of total strain amplitude on the cyclic stress response of the alloy is approximately the same under three different deformation conditions. With the increase of the cyclic numbers, the alloyed steel mainly exhibited cyclic hardening during loading. The fatigue properties in air environment were the best, which is most obvious when the total strain amplitude is ±0.3%. The fatigue life of samples in mixed alkali metal salts is the shortest. Furthermore, the fatigue fracture morphology of the alloyed steel in different environments were also deeply analyzed. This experimental study attempts to provide a theoretical reference for solving the problem of rapid failure of heat pipes in biomass boilers, and to establish a scientific basis for the material selection and safety operation. Full article
(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)
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Open AccessArticle
Effect of Thermal Fatigue on Microstructure and Mechanical Properties of H13 Tool Steel Processed by Selective Laser Surface Melting
Metals 2019, 9(7), 773; https://doi.org/10.3390/met9070773
Received: 11 June 2019 / Revised: 5 July 2019 / Accepted: 8 July 2019 / Published: 10 July 2019
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Abstract
Selective laser surface melting, which brings together the bionic theory and the laser process, is an effective way to enhance the thermal fatigue behavior of materials. In this study, in order to examine the relationship between the mechanical properties and thermal fatigue behavior [...] Read more.
Selective laser surface melting, which brings together the bionic theory and the laser process, is an effective way to enhance the thermal fatigue behavior of materials. In this study, in order to examine the relationship between the mechanical properties and thermal fatigue behavior of materials processed by selective laser surface melting, the tensile properties at room temperature and elevated temperature of treated specimens and untreated specimens after different numbers of thermal fatigue cycles were investigated and compared. Moreover, the microstructure evolution and the microhardness of the laser-affected zone were investigated after different numbers of thermal fatigue cycles. The results show that microhardness of the laser-melted zone gradually decreases with an increasing number of thermal fatigue cycles; the number of thermal fatigue cycles has little effect on the grain size in the laser-melted zone, and the percentage of low-angle grain boundaries decreases with an increasing number of thermal fatigue cycles. The strength of specimens gradually decreases, whereas the fracture elongation gradually increases with an increasing number of thermal fatigue cycles at room temperature and elevated temperature. In addition, the stress distribution on the specimen surface during tensile test was investigated using the finite element method, and the results indicate that the stress transfer exists between the laser-affected zone and the untreated zone. Full article
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Open AccessArticle
Computer-Aided Material Design for Crash Boxes Made of High Manganese Steels
Metals 2019, 9(7), 772; https://doi.org/10.3390/met9070772
Received: 14 June 2019 / Revised: 2 July 2019 / Accepted: 4 July 2019 / Published: 10 July 2019
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Abstract
During the last decades, high manganese steels (HMnS) were considered as promising materials for crash-relevant automobile components due to their extraordinary energy absorption capability in tensile tests. However, in the case of a crash, the specific energy, absorbed by folding of a crash [...] Read more.
During the last decades, high manganese steels (HMnS) were considered as promising materials for crash-relevant automobile components due to their extraordinary energy absorption capability in tensile tests. However, in the case of a crash, the specific energy, absorbed by folding of a crash box, is lower for HMnS as compared to the dual phase steel DP800. This behavior is related to the fact that the crash box hardly takes advantage of the high plastic formability of a recrystallized HMnS during deformation. It was revealed that with the help of an alternative heat treatment after cold rolling, the strength of HMnS could be increased for low strains to achieve a crash behavior comparable to DP800. In this work, a multi-scale finite element simulation approach was used to analyze the crash behavior of different material conditions of an HMnS. The crash behavior was evaluated under consideration of material efficiency and passenger safety criteria to identify the ideal material condition and sheet thickness for crash absorption by folding. The proposed simulation methodology reduces the experimental time and effort for crash box design. As a result of increasing material strength, the simulation exhibits a possible weight reduction of the crash box, due to thickness reduction, up to 35%. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Open AccessArticle
Processing Variants in Medium-Mn Steels
Metals 2019, 9(7), 771; https://doi.org/10.3390/met9070771
Received: 10 June 2019 / Revised: 1 July 2019 / Accepted: 4 July 2019 / Published: 10 July 2019
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Abstract
This paper highlights some recent efforts to extend the use of medium-Mn steels for applications other than intercritically batch-annealed steels with exceptional ductility (and strengths in the range of about 1000 MPa). These steels are shown to enable a range of promising properties. [...] Read more.
This paper highlights some recent efforts to extend the use of medium-Mn steels for applications other than intercritically batch-annealed steels with exceptional ductility (and strengths in the range of about 1000 MPa). These steels are shown to enable a range of promising properties. In hot-stamping application concepts, elevated Mn concentration helps to stabilize austenite and to provide a range of attractive property combinations, and also reduces the processing temperatures and likely eliminates the need for press quenching. The “double soaking” concept also provides a wide range of attractive mechanical property combinations that may be applicable in cold-forming applications, and could be implemented in continuous annealing and/or continuous galvanizing processes where Zn-coating would typically represent an additional austempering step. Quenching and partitioning of steels with elevated Mn concentrations have exhibited very high strengths, with attractive tensile ductility; and medium-Mn steels have been successfully designed for quenching and partitioning using room temperature as the quench temperature, thereby effectively decoupling the quenching and partitioning steps. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Open AccessArticle
Isothermal Sections of the Ni-Cr-Ta Ternary System at 1200 °C and 1300 °C
Metals 2019, 9(7), 770; https://doi.org/10.3390/met9070770
Received: 14 June 2019 / Revised: 4 July 2019 / Accepted: 5 July 2019 / Published: 10 July 2019
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Abstract
Two isothermal sections of the Ni-Cr-Ta ternary system at 1200 °C and 1300 °C have been determined by using electron probe microanalysis, energy dispersive spectroscopy and differential scanning calorimeter. A Laves phase (Ni, Cr)2Ta(HT)(C14 structure) with large solid solubility stabilized by [...] Read more.
Two isothermal sections of the Ni-Cr-Ta ternary system at 1200 °C and 1300 °C have been determined by using electron probe microanalysis, energy dispersive spectroscopy and differential scanning calorimeter. A Laves phase (Ni, Cr)2Ta(HT)(C14 structure) with large solid solubility stabilized by the Ni addition was determined in both two isothermal sections. The composition range of this phase was about 25.8–66.0 at.% Cr, 2.5-44.3 at.% Ni, and 24.0-40.0 at.% Ta at 1200 °C, which increased with raising temperature. The melting point of the Ni-Cr alloys decreased with the addition of Ta. No ternary compound was found in both these two isothermal sections. The present work could be significant for practical application of nickel-based alloys and future thermodynamics assessment of the Ni-Cr-Ta ternary system. Full article
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Open AccessEditorial
Sustainable Utilization of Metals-Processing, Recovery and Recycling
Metals 2019, 9(7), 769; https://doi.org/10.3390/met9070769
Received: 1 July 2019 / Accepted: 2 July 2019 / Published: 10 July 2019
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Abstract
Our modern everyday life and thus our technical progress is based on a variety of metals [...] Full article
Open AccessReview
Using Ball Milling for Modification of the Hydrogenation/Dehydrogenation Process in Magnesium-Based Hydrogen Storage Materials: An Overview
Metals 2019, 9(7), 768; https://doi.org/10.3390/met9070768
Received: 23 May 2019 / Revised: 27 June 2019 / Accepted: 29 June 2019 / Published: 9 July 2019
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Abstract
Magnesium-based hydrogen storage materials are considered to be one of the most promising solid-state hydrogen storage materials due to their large hydrogen storage capacity and low cost. However, slow hydrogen absorption/desorption rate and excessive hydrogen absorption/desorption temperature limit the application of magnesium-based hydrogen [...] Read more.
Magnesium-based hydrogen storage materials are considered to be one of the most promising solid-state hydrogen storage materials due to their large hydrogen storage capacity and low cost. However, slow hydrogen absorption/desorption rate and excessive hydrogen absorption/desorption temperature limit the application of magnesium-based hydrogen storage materials. The present paper reviews recent progress in improving the hydrogen storage properties by element substitution and additives. Ball milling is the promising technology for preparing magnesium-based hydrogen storage materials. The research and development of approaches for modifying magnesium-based hydrogen storage materials prepared by ball milling is systematically expounded. It is concluded that ball milling can significantly improve the kinetic and electrochemical properties of magnesium-based hydrogen storage materials and increase the hydrogen storage capacity. In the future, the research of magnesium-based hydrogen storage materials should be developed in terms of hydrogen storage mechanism, computer design of materials and development of a more optimized catalytic system. Full article
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Open AccessArticle
Improving Strength and Ductility of a Mg-3.7Al-1.8Ca-0.4Mn Alloy with Refined and Dispersed Al2Ca Particles by Industrial-Scale ECAP Processing
Metals 2019, 9(7), 767; https://doi.org/10.3390/met9070767
Received: 24 June 2019 / Revised: 5 July 2019 / Accepted: 8 July 2019 / Published: 9 July 2019
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Abstract
Tailoring the morphology and distribution of the Al2Ca second phase is important for improving mechanical properties of Al2Ca-containing Mg-Al-Ca based alloys. This work employed the industrial-scale multi-pass rotary-die equal channel angular pressing (RD-ECAP) on an as-cast Mg-3.7Al-1.8Ca-0.4Mn (wt %) [...] Read more.
Tailoring the morphology and distribution of the Al2Ca second phase is important for improving mechanical properties of Al2Ca-containing Mg-Al-Ca based alloys. This work employed the industrial-scale multi-pass rotary-die equal channel angular pressing (RD-ECAP) on an as-cast Mg-3.7Al-1.8Ca-0.4Mn (wt %) alloy and investigated its microstructure evolution and mechanical properties under three different processing parameters. The obtained results showed that RD-ECAP was effective for refining the microstructure and breaking the network-shaped Al2Ca phase. With the increase of the ECAP number and decrease of the processing temperature, the average sizes of Al2Ca particles decreased obviously, and the dispersion of the Al2Ca phase became more uniform. In addition, more ECAP passes and lower processing temperature resulted in finer α-Mg grains. Tensile test results indicated that the 573 K-12p alloy with the finest and most dispersed Al2Ca particles exhibited superior mechanical properties with tensile yield strength of 304 MPa, ultimate tensile strength of 354 MPa and elongation of 10.3%. The improved comprehensive mechanical performance could be attributed to refined DRX grains, nano-sized Mg17Al12 precipitates and dispersed Al2Ca particles, where the refined and dispersed Al2Ca particles played a more dominant role in strengthening the alloys. Full article
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Open AccessArticle
Role of Vanadium Addition on Hot Deformation Behavior of Aluminum Alloy 5083
Metals 2019, 9(7), 766; https://doi.org/10.3390/met9070766
Received: 10 June 2019 / Revised: 3 July 2019 / Accepted: 5 July 2019 / Published: 8 July 2019
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Abstract
The effect of V addition on the hot deformation behavior of AA5083 was investigated. Single axial compression tests were conducted on the cast and homogenized samples with strain rates ranging from 0.01 to 10 s−1 and deformation temperatures ranging from 300 to [...] Read more.
The effect of V addition on the hot deformation behavior of AA5083 was investigated. Single axial compression tests were conducted on the cast and homogenized samples with strain rates ranging from 0.01 to 10 s−1 and deformation temperatures ranging from 300 to 450 °C. The results showed that the contents of V (0–0.10, in wt.%) do not change the grain size of alloy 5083 significantly in the as cast and homogenized conditions, but the formation of fine Al3V particles in the alloy with an addition of 0.05 wt.% V can increase the flow stress, and its activation energy is 10.0% higher than that of V-free alloy 5083. The processing maps show that the appropriate process domain for alloy 5083 with 0.05 wt.% V changes at different true strains. The mechanism for deformation softening is discussed as well. Full article
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Open AccessArticle
Study on Microstructure and Properties of a New Warm-Stamped Niobium-Alloyed Steel
Metals 2019, 9(7), 765; https://doi.org/10.3390/met9070765
Received: 21 May 2019 / Revised: 26 June 2019 / Accepted: 3 July 2019 / Published: 8 July 2019
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Abstract
The warm stamping technology is a promising technology to meet the needs of car weight reduction and energy conservation. In order to compare with the mechanical properties of the traditional hot-stamped boron-alloyed steel 22MnB5, a new warm-stamped niobium-alloyed steel 22Mn3SiNb was designed and [...] Read more.
The warm stamping technology is a promising technology to meet the needs of car weight reduction and energy conservation. In order to compare with the mechanical properties of the traditional hot-stamped boron-alloyed steel 22MnB5, a new warm-stamped niobium-alloyed steel 22Mn3SiNb was designed and tested. The optimal heating parameters for warm forming process were explored through mechanical tests, and the process of their microstructure evolution was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD), etc. The experimental results indicate that the optimal heating parameters for the niobium-alloyed steel 22Mn3SiNb are a heating temperature of 800 °C and a soaking time of 5 min. Compared to the hot-stamped boron-alloyed steel 22MnB5 under their respective optimal heating parameters, the properties and microstructure characteristics of 22Mn3SiNb are greatly improved, and nearly no decarburized layer is found on the surface of the niobium-alloyed steel 22Mn3SiNb. In addition, the addition of Nb produces the effects of grain refinement and precipitation strengthening due to the introduction of plenty of nano-precipitated particles and dislocations. In the end, it can be predicted that the new warm-stamped niobium-alloyed steel will replace the conventional hot-stamped boron-alloyed steel. Full article
(This article belongs to the Special Issue Advances in Structural Steel Research)
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Open AccessArticle
Deposits in Gas-fired Rotary Kiln for Limonite Magnetization-Reduction Roasting: Characteristics and Formation Mechanism
Metals 2019, 9(7), 764; https://doi.org/10.3390/met9070764
Received: 4 June 2019 / Revised: 28 June 2019 / Accepted: 5 July 2019 / Published: 8 July 2019
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Abstract
The formation mechanism of deposits in commercial gas-fired magnetization-reduction roasting rotary kiln was studied. The deposits ring adhered on the kiln wall based on the bonding of low melting point eutectic liquid phase, and the deposit adhered on the air duct head by [...] Read more.
The formation mechanism of deposits in commercial gas-fired magnetization-reduction roasting rotary kiln was studied. The deposits ring adhered on the kiln wall based on the bonding of low melting point eutectic liquid phase, and the deposit adhered on the air duct head by impact deposition. The chemical composition and microstructure of the deposits sampled at different locations varied slightly. Besides a small amount of quartz and limonite, main phases in the deposits are fayalite, glass phase and magnetite. The formation of the deposits can be attributed to the derivation of low melting point eutectic of fine limonite and coal ash, and the solid state reaction between them. Coal ash, originated from the reduction coal, combining together with fine limonite particles, results in the accumulation of deposits on the kiln wall and air duct. Fayalite, the binder phase, was a key factor for deposit formation. The residual carbon in limonite may cause an over-reduction of limonite and produce FeO. Amid the roasting process, SiO2, originated from limonite and coal ash, may combine with FeO and reduce the liquefaction temperature, therewith liquid phase generates at high temperature zone, which can significantly promote the growth of deposits. Full article
(This article belongs to the Special Issue Advances in Pyrometallurgy)
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Open AccessArticle
Interface Structure and Mechanical Properties of 7075Al Hybrid Composite Reinforced with Micron Ti Metal Particles Using Pressure Infiltration
Metals 2019, 9(7), 763; https://doi.org/10.3390/met9070763
Received: 30 May 2019 / Revised: 4 July 2019 / Accepted: 4 July 2019 / Published: 8 July 2019
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Abstract
Micron Ti metal particles were incorporated into SiCp/7075Al composites using pressure infiltration. The interface structure between the Ti metal particles and the matrix during the casting processes were investigated. Results show that the dispersed unreacted Ti particles form mutual diffusion layer at the [...] Read more.
Micron Ti metal particles were incorporated into SiCp/7075Al composites using pressure infiltration. The interface structure between the Ti metal particles and the matrix during the casting processes were investigated. Results show that the dispersed unreacted Ti particles form mutual diffusion layer at the interface without the formation of low-temperature intermetallic phases during the solidification processes. The interaction between the micron Ti and the molten aluminum alloy is subject to the mutual diffusion coefficient of Ti–Al rather than the reaction activation energy. The tensile strength and plasticity of the composite were improved simultaneously due to the high interfacial bonding strength and released thermal misfit stress cause by the incorporated Ti metal particles. Full article
(This article belongs to the Special Issue Advances in Metal Composites and Processing Technologies)
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Open AccessArticle
Physical and Theoretical Modeling of the Nitrogen Content of Duplex Stainless Steel Weld Metal: Shielding Gas Composition and Heat Input Effects
Metals 2019, 9(7), 762; https://doi.org/10.3390/met9070762
Received: 13 June 2019 / Revised: 3 July 2019 / Accepted: 4 July 2019 / Published: 7 July 2019
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Abstract
Duplex stainless steels (DSSs) are gaining more and more attention in corrosion-resistant applications and also in the transport and automotive industry. The outstanding mechanical and corrosion properties of DSSs highly depends on the austenite-to-ferrite phase balance (A/F). This phase ratio can shift in [...] Read more.
Duplex stainless steels (DSSs) are gaining more and more attention in corrosion-resistant applications and also in the transport and automotive industry. The outstanding mechanical and corrosion properties of DSSs highly depends on the austenite-to-ferrite phase balance (A/F). This phase ratio can shift in a large scale during welding. Thus, the heat input and the shielding gas composition should be optimized. Nitrogen addition to argon shielding is frequently used in DSS welding, because it is a potent austenite former. The dissolved nitrogen content in the heat-affected zone and the weld metal (WM) predetermines the A/F. To determine the effect of heat input and nitrogen content in shielding gas, two different heat inputs and six different gas compositions were used in autogenous tungsten inert gas welding. An improved theoretical model was established in order to simulate the WM dissolved nitrogen content, which calculates it with less error than the initial models. The correlation between nitrogen content and arc voltage was also determined. This improved model delivers the basics for shielding gas selection and the subsequent weld design for optimal A/F for industrial applications. Full article
(This article belongs to the Special Issue Joining of Advanced High Strength Steels for the Automotive Industry)
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Open AccessArticle
Deformation Behavior of a Double Soaked Medium Manganese Steel with Varied Martensite Strength
Metals 2019, 9(7), 761; https://doi.org/10.3390/met9070761
Received: 15 June 2019 / Revised: 29 June 2019 / Accepted: 4 July 2019 / Published: 7 July 2019
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Abstract
The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite [...] Read more.
The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite strength and microstructural characteristics, which composed the bulk of the matrix phase, were characterized. It was found that the addition of either as-quenched or tempered athermal martensite led to an improvement in mechanical properties as compared to a ferrite plus austenite medium manganese steel, although the yielding and work hardening behavior were highly dependent upon the martensite characteristics. Specifically, athermal martensite was found to promote continuous yielding and improve the work hardening rate during deformation. The results of this study are particularly relevant when considering the effect of post-processing thermal heat treatments, such as tempering or elevated temperature service environments, on the mechanical properties of medium manganese steels containing athermal martensite. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
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Open AccessArticle
Assessment of Self-Piercing Riveted Joints Using the Analytic Hierarchy Process
Metals 2019, 9(7), 760; https://doi.org/10.3390/met9070760
Received: 6 June 2019 / Revised: 20 June 2019 / Accepted: 2 July 2019 / Published: 6 July 2019
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Abstract
Self-piercing riveting (SPR) as a solid-state joining technology has recently found extensive applications in the automotive industry, mostly in the joining of car body aluminium sheets. To achieve an acceptable joint, key operation and tooling parameters, including set force, die profile, and rivet [...] Read more.
Self-piercing riveting (SPR) as a solid-state joining technology has recently found extensive applications in the automotive industry, mostly in the joining of car body aluminium sheets. To achieve an acceptable joint, key operation and tooling parameters, including set force, die profile, and rivet shape and hardness, should be selected appropriately. To evaluate joint performance, the interlocking parameters and joint strength have to be determined. In the current laboratory and industrial practices, joint quality is assessed according to requirements of individual applications, lacking a systematic assessment method. The goal of the present study is to develop a method to determine the SPR conditions that produce a joint of the best quality, based on an analytic hierarchy process (AHP), which is a methodology for relative measurement. A general AHP model was proposed for analysing SPR and joint performance in different conditions and with an unlimited number of criteria and alternatives. Joints of two layers of 2.5 mm thick AA6082 aluminium sheets in T6 condition were produced using various dies, rivets, and SPR processing conditions. A selection of seven joints, which achieved minimum requirements in terms of interlocking parameters and strength, was nominated for AHP assessment. With the application of six criteria, including head height, bottom thickness, minimum bottom thickness, deformed rivet diameter, shear strength, and peel strength, the AHP assessment was able to define the best conditions for the SPR joining of the aluminium alloy sheets. Full article
(This article belongs to the Special Issue Advances in Joining of Automotive Alloys)
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Open AccessArticle
Annealing Response of a Cold-Rolled Binary Al–10Mg Alloy
Metals 2019, 9(7), 759; https://doi.org/10.3390/met9070759
Received: 7 May 2019 / Revised: 30 June 2019 / Accepted: 3 July 2019 / Published: 5 July 2019
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Abstract
The effect of annealing temperature on microstructure and mechanical properties of a cold-rolled Al–10Mg alloy has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and tensile testing. The results showed that supersaturated Mg precipitated along grain boundaries [...] Read more.
The effect of annealing temperature on microstructure and mechanical properties of a cold-rolled Al–10Mg alloy has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and tensile testing. The results showed that supersaturated Mg precipitated along grain boundaries and deformation bands during annealing treatment and precipitation size and the concentration of solid solution Mg atoms increased with the rising of annealing temperature. When annealed at low temperature, accumulation and annihilation of dislocations were the primary way of recovery; as temperature increased to 300 °C, recrystallized grains were formed around the large size β phase through particle-stimulated nucleation. A high ultimate strength (550 MPa) and a middle ductility (14%) were obtained when the Al–10Mg alloy was annealed at 200 °C for 1 h. The abnormal decrease of elongation when the Al–10Mg alloy was annealed at 250–300 °C was due to the formation of a continuous network distribution of large size β phase particles along grain boundaries. Full article
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Open AccessArticle
Kinetics and Energy Consumption for a Three-Stage Electrocoagulation Process for the Recovery of Au and Ag from Cyanide Leachates
Metals 2019, 9(7), 758; https://doi.org/10.3390/met9070758
Received: 6 June 2019 / Revised: 2 July 2019 / Accepted: 3 July 2019 / Published: 5 July 2019
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Abstract
The most common processes used for the recovery of gold and silver from cyanide leachates are Merril-Crowe, activated carbon in pulp, and ion exchange resins; the process of electrocoagulation (EC) also is a promising new technique. EC is an electrochemical process whose mechanisms [...] Read more.
The most common processes used for the recovery of gold and silver from cyanide leachates are Merril-Crowe, activated carbon in pulp, and ion exchange resins; the process of electrocoagulation (EC) also is a promising new technique. EC is an electrochemical process whose mechanisms include oxidation, reduction, decomposition, deposition, coagulation, absorption, flotation, and precipitation. It has been used for the treatment of water and wastewater with different degrees of success. This study aimed to determine the kinetics of the reaction and the energy consumption at constant voltage, and at constant current using aluminum electrodes with two different distances between electrodes. EC was run in three stages for the removal of gold and silver from aqueous cyanide solutions from samples supplied by a Mexican mining company. Characterization of the sample showed initial concentrations of 49.48 and 383 mg/L of gold and silver, respectively. Results showed the effectiveness of the process by achieving removals up to 98.59% of gold and 99.43% of silver. Additionally, it was determined that the kinetics of the reaction is of zero order and that the lowest energy consumption can be achieved when working at constant voltage and with a separation of 0.8 cm between electrodes. Full article
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Open AccessArticle
Analysis of Laser Tracker-Based Volumetric Error Mapping Strategies for Large Machine Tools
Metals 2019, 9(7), 757; https://doi.org/10.3390/met9070757
Received: 28 May 2019 / Revised: 1 July 2019 / Accepted: 3 July 2019 / Published: 5 July 2019
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Abstract
The measurement and compensation of volumetric error in milling machines of medium and large size is a key aspect to meeting the precision requirements of the most demanding applications. There are several solutions for volumetric error measurement—usually based on laser or in calibrated [...] Read more.
The measurement and compensation of volumetric error in milling machines of medium and large size is a key aspect to meeting the precision requirements of the most demanding applications. There are several solutions for volumetric error measurement—usually based on laser or in calibrated artifacts—that offer different specifications and lead to a variety of levels of precision, complexity of implementation and automation, cost of equipment, and measurement time, amongst others. Therefore, it is essential to have tools that allow, in each case, analysis as to which is the optimal calibration strategy, providing the criteria for evaluating different measurement equipment and strategies. To respond to this need, several tools have been developed which are able to simulate the entire calibration and compensation process (machine, measurement, model adjustment, etc.) and apply optimization methods to find the best measurement strategy for each application. For a given machine architecture and expected error ranges, the compensation error for each strategy is obtained by propagating measurement uncertainties and expected machine errors through the measurement and compensation model fitting process by Monte Carlo simulations. The use of this tool will be demonstrated through the analysis of the influence of the main design parameters of a measurement strategy for the calibration of a 3-axis machine tool, based on the measurement of tool position with a laser tracker. Full article
(This article belongs to the Special Issue New Processes and Machine Tools for Advanced Metal Alloys)
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