Metals

11 pages, 2561 KiB

Open AccessArticle

Sustainable Steel Carburization by Using Snack Packaging Plastic Waste as Carbon Resources

by Songyan Yin, Ravindra Rajarao, Farshid Pahlevani and Veena Sahajwalla

Metals 2018, 8(1), 78; https://doi.org/10.3390/met8010078 - 22 Jan 2018

Cited by 4 | Viewed by 6950

In recent years, the research regarding waste conversion to resources technology has attracted growing attention with the continued increase of waste accumulation issues and rapid depletion of natural resources. However, the study, with respect to utilizing plastics waste as carbon resources in the [...] Read more.

In recent years, the research regarding waste conversion to resources technology has attracted growing attention with the continued increase of waste accumulation issues and rapid depletion of natural resources. However, the study, with respect to utilizing plastics waste as carbon resources in the metals industry, is still limited. In this work, an environmentally friendly approach to utilize snack packaging plastic waste as a valuable carbon resources for steel carburization is investigated. At high temperature, plastic waste could be subject to pyrolytic gasification and decompose into small molecular hydrocarbon gaseous products which have the potential to be used as carburization agents for steel. When heating some snack packaging plastic waste and a steel sample together at the carburization temperature, a considerable amount of carbon-rich reducing gases, like methane, could be liberated from the plastic waste and absorbed by the steel sample as a carbon precursor for carburization. The resulting carburization effect on steel was investigated by optical microscopy, scanning electron microscopy, electron probe microanalyzer, and X-ray photoelectron spectrometer techniques. These investigation results all showed that snack packaging plastic waste could work effectively as a valuable carbon resource for steel carburization leading to a significant increase of surface carbon content and the corresponding microstructure evolution in steel. Full article

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13 pages, 4310 KiB

Open AccessArticle

Intensification Behavior of Mercury Ions on Gold Cyanide Leaching

by Qiang Zhong, Yongbin Yang, Lijuan Chen, Qian Li, Bin Xu and Tao Jiang

Metals 2018, 8(1), 80; https://doi.org/10.3390/met8010080 - 21 Jan 2018

Cited by 10 | Viewed by 5666

Abstract

Cyanidation is the main method used to extract gold from gold raw materials; however, a serious problem with this method is the low leaching rate. In order to improve gold leaching, the intensification behavior of mercury ions on gold cyanide leaching, for two [...] Read more.

Cyanidation is the main method used to extract gold from gold raw materials; however, a serious problem with this method is the low leaching rate. In order to improve gold leaching, the intensification behavior of mercury ions on gold cyanide leaching, for two types of materials, sulphide gold concentrate and oxide gold ore, was investigated. The results showed that mercury ions, with only a 10⁻⁵ M dosage, could significantly intensify leaching and gold recovery. The dissolution behavior of gold plate was also intensified by 10⁻⁵ M mercury ions. Microstructure analysis showed that mercury ions intensified the cyanidation corrosion of the gold surface, resulting in a loose structure, where a large number of deep ravines and raised particles were evident across the whole gold surface. The loose structure added contact surface between the gold and cyanide, and accelerated gold dissolution. Moreover, mercury ions obstructed the formation of insoluble products, such as AuCN, Au(OHCN), and Au(OH)_x, that lead to a passivation membrane on the gold surface, reducing contact between the gold and cyanide. These effects, brought about by mercury ions, change the structure and product of the gold surface during gold cyanidation and promote gold leaching. Full article

(This article belongs to the Special Issue Advances in Hydrometallurgy)

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6 pages, 1345 KiB

Open AccessArticle

Fabrication of Nickel Nanosized Powder from LiNiO₂ from Spent Lithium-Ion Battery

by Shun-Myung Shin, Dong-Won Lee and Jei-Pil Wang

Metals 2018, 8(1), 79; https://doi.org/10.3390/met8010079 - 21 Jan 2018

Cited by 11 | Viewed by 4774

Abstract

In this study, a fabrication of nickel nanoparticles from LNO(LiNiO₂), which is a cathode active material, was synthesized by the liquid reduction process of NiSO₄, obtained through a leaching and purification process. Hydrazine monohydrate (N₂H₄·H [...] Read more.

In this study, a fabrication of nickel nanoparticles from LNO(LiNiO₂), which is a cathode active material, was synthesized by the liquid reduction process of NiSO₄, obtained through a leaching and purification process. Hydrazine monohydrate (N₂H₄·H₂O) was used as a liquid reducing agent and it was added to NiSO₄ at a volume ratio of NiSO₄:N₂H₄·H₂O = 10:3 and reacted for 10 min to synthesize the nickel hydrazine complex. Sodium hydroxide was added to the nickel hydrazine complex at the weight ratio of NiSO₄:NaOH = 10:1.25–1.5 and the reduction reaction was performed at 80 °C for 15 min to synthesize nickel particles. Synthesized nickel particles were agglomerated and had a mean size of 200 nm to 300 nm. Ultrasonic dispersion, which is a physical dispersion method, was conducted. The nickel had particles of 100 nm or less when dispersed for 2 h at an ultrasonic intensity of 40 kHz. In order to prevent the agglomeration of the dispersed particles again, polyvinylpyrrolidone (PVP), an interfacial stabilizer, was added to stabilize the dispersed particles. It was confirmed that the nanoparticles were stably retained when PVP was added in an amount of 1 to 2 wt % based on the weight of the nickel. The purity of nickel recovered was found to be 99.62 wt %. Full article

(This article belongs to the Special Issue Valuable Metal Recycling)

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13 pages, 4663 KiB

Open AccessArticle

Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification

by Xiaojian Cao, Luopeng Xu, Xiaoli Xu and Qingyuan Wang

Metals 2018, 8(1), 77; https://doi.org/10.3390/met8010077 - 20 Jan 2018

Cited by 16 | Viewed by 5014

Abstract

The influence of ultrasonic nanocrystal surface modification (UNSM) on the fatigue fracture characteristics of Ti6Al4V was investigated. Two groups of specimens were separated due to different heat treatment conditions. Group one was stress-relief annealed at 650 °C, and group two was then treated [...] Read more.

The influence of ultrasonic nanocrystal surface modification (UNSM) on the fatigue fracture characteristics of Ti6Al4V was investigated. Two groups of specimens were separated due to different heat treatment conditions. Group one was stress-relief annealed at 650 °C, and group two was then treated with solid solution-aging. UNSM with the conditions of a static load of 25 N, vibration amplitude of 30 μm, and 36,000 strikes per unit produced about 40 μm surface severe plastic deformation (SPD) layers on both groups of specimens. UNSM improved the microhardness and the compressive residual stress. UNSM also helped achieve a neat surface, almost without changing the surface roughness. The fatigue strengths of these two groups were improved by 7% and 11.7%, respectively. After UNSM, fatigue cracks mainly initiated from the surface of the specimen before the fatigue life of 10⁶ cycles, while they appeared at the internal compress deformed α-phase at the zone between the SPD layer and the core after the fatigue life of 106 cycles. The cracks usually extended along the deformation overflow bands and the process traces on the surface. Through the change of micro-dimples in the fatigue final rupture region, nanocrystals were achieved in the SPD layer. The crystal slip and the surface remodeling together influenced the energy field of crack evolution. Full article

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19 pages, 24576 KiB

Open AccessArticle

Numerical Study on Flow, Temperature, and Concentration Distribution Features of Combined Gas and Bottom-Electromagnetic Stirring in a Ladle

by Yang Li, Anyuan Deng, Huan Li, Bin Yang and Engang Wang

Metals 2018, 8(1), 76; https://doi.org/10.3390/met8010076 - 19 Jan 2018

Cited by 17 | Viewed by 4798

Abstract

A novel method of combined argon gas stirring and bottom-rotating electromagnetic stirring in a ladle refining process is presented in this report. A three-dimensional numerical model was adopted to investigate its effect on improving flow field, eliminating temperature stratification, and homogenizing concentration distribution. [...] Read more.

A novel method of combined argon gas stirring and bottom-rotating electromagnetic stirring in a ladle refining process is presented in this report. A three-dimensional numerical model was adopted to investigate its effect on improving flow field, eliminating temperature stratification, and homogenizing concentration distribution. The results show that the electromagnetic force has a tendency to spiral by spinning clockwise on the horizontal section and straight up along the vertical section, respectively. When the electromagnetic force is applied to the gas-liquid two phase flow, the gas-liquid plume is shifted and the gas-liquid two phase region is extended. The rotated flow driven by the electromagnetic force promotes the scatter of bubbles. The temperature stratification tends to be alleviated due to the effect of heat compensation and the improved flow. The temperature stratification tends to disappear when the current reaches 1200 A. The improved flow field has a positive influence on decreasing concentration stratification and shortening the mixing time when the combined method is imposed. However, the alloy depositing site needs to be optimized according to the whole circulatory flow and the region of bubbles to escape. Full article

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25 pages, 3968 KiB

Open AccessReview

A Review of the As-Built SLM Ti-6Al-4V Mechanical Properties towards Achieving Fatigue Resistant Designs

by Dylan Agius, Kyriakos I. Kourousis and Chris Wallbrink

Metals 2018, 8(1), 75; https://doi.org/10.3390/met8010075 - 19 Jan 2018

Cited by 163 | Viewed by 15210

Abstract

Ti-6Al-4V has been widely used in both the biomedical and aerospace industry, due to its high strength, corrosion resistance, high fracture toughness and light weight. Additive manufacturing (AM) is an attractive method of Ti-6Al-4V parts’ fabrication, as it provides a low waste alternative [...] Read more.

Ti-6Al-4V has been widely used in both the biomedical and aerospace industry, due to its high strength, corrosion resistance, high fracture toughness and light weight. Additive manufacturing (AM) is an attractive method of Ti-6Al-4V parts’ fabrication, as it provides a low waste alternative for complex geometries. With continued progress being made in SLM technology, the influence of build layers, grain boundaries and defects can be combined to improve further the design process and allow the fabrication of components with improved static and fatigue strength in critical loading directions. To initiate this possibility, the mechanical properties, including monotonic, low and high cycle fatigue and fracture mechanical behaviour, of machined as-built SLM Ti-6Al-4V, have been critically reviewed in order to inform the research community. The corresponding crystallographic phases, defects and layer orientations have been analysed to determine the influence of these features on the mechanical behaviour. This review paper intends to enhance our understanding of how these features can be manipulated and utilised to improve the fatigue resistance of components fabricated from Ti-6Al-4V using the SLM technology. Full article

(This article belongs to the Special Issue Fatigue Damage of Additively-Manufactured Metallic Materials)

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15 pages, 15727 KiB

Open AccessArticle

Investigation on the Effect of Tool Pin Profiles on Mechanical and Microstructural Properties of Friction Stir Butt and Scarf Welded Aluminium Alloy 6063

by Pankul Goel, Arshad Noor Siddiquee, Noor Zaman Khan, Mohd Azmal Hussain, Zahid A. Khan, Mustufa Haider Abidi and Abdulrahman Al-Ahmari

Metals 2018, 8(1), 74; https://doi.org/10.3390/met8010074 - 19 Jan 2018

Cited by 41 | Viewed by 7487

Abstract

In the present study, friction stir welding (FSW) of butt and scarf joints of Al 6063-T6 were investigated. Five different tool pin profiles (cylindrical, tapered cylindrical, square, triangular, and hexagonal) were applied for performing welding. Scarf joint, being a new joint configuration, was [...] Read more.

In the present study, friction stir welding (FSW) of butt and scarf joints of Al 6063-T6 were investigated. Five different tool pin profiles (cylindrical, tapered cylindrical, square, triangular, and hexagonal) were applied for performing welding. Scarf joint, being a new joint configuration, was used and effect of pin profiles was investigated on this type of joint configuration. The effect of pin profiles on microstructure, micro-hardness, impact and tensile properties of friction stir welded Al 6063-T6 was investigated. Scanning electron and optical microscopy were employed to characterize the different zones of welded joints. A thorough discussion on correlation between mechanical properties and microstructure has been made. In addition, the formation of various defects during the FSW was discussed with the help of fractography of the fractured surfaces. Full article

(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)

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15 pages, 4969 KiB

Open AccessArticle

Comprehensive Characterisation of a Newly Developed Mg–Dy–Al–Zn–Zr Alloy Structure

by Lenka Kunčická and Radim Kocich

Metals 2018, 8(1), 73; https://doi.org/10.3390/met8010073 - 19 Jan 2018

Cited by 20 | Viewed by 3618

Abstract

This is a report on the structure phases and precipitates in a newly developed Mg–10Dy–3Al–1Zn–0.2Zr alloy. Specimens from the cast alloy were heat treated at temperatures of 480 °C, 520 °C and 560 °C, all for 8 and 16 h, and subsequently quenched. [...] Read more.

This is a report on the structure phases and precipitates in a newly developed Mg–10Dy–3Al–1Zn–0.2Zr alloy. Specimens from the cast alloy were heat treated at temperatures of 480 °C, 520 °C and 560 °C, all for 8 and 16 h, and subsequently quenched. The structures were then analysed using scanning and transmission electron microscopy, while the mechanical properties were investigated using microhardness measurements. The results showed the different temperatures, as well as times, influence both the chemical composition and morphology of the precipitated phases. The occurrence of the β-phase changed with increasing temperature and time from grain boundary segregations through fine elongated particles to coarse plate-like precipitates. Polygon-shaped Dy-rich precipitates were observed in all the samples; however, their size decreased and their distribution homogenised with increasing annealing temperature and time. The samples annealed at 520 °C and 560 °C exhibited the presence of lamellar 18R-type long period stacking ordered (LPSO) phases. Microhardness measurements were in accordance with results of the microscopic analyses; although the values varied between 60 and 65 HV for all the material states, the most uniform distribution was observed for the 560 °C/8-h sample, which featured the finest precipitates and LPSO phases. Full article

(This article belongs to the Special Issue Latest Developments in Magnesium Technology—Alloying, Processing, Microstructure, Deformation Mechanism and Mechanical Properties)

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16 pages, 8357 KiB

Open AccessArticle

Comparing the Structure and Mechanical Properties of Welds on Ductile Cast Iron (700 MPa) under Different Heat Treatment Conditions

by Ronny M. Gouveia, Francisco J. G. Silva, Olga C. Paiva, Maria De Fátima Andrade, Lucas Augusto Pereira, Paulo Cezar Moselli and Konrad J. M. Papis

Metals 2018, 8(1), 72; https://doi.org/10.3390/met8010072 - 19 Jan 2018

Cited by 15 | Viewed by 5886

Abstract

The weldability of ductile iron, as widely known, is relatively poor, essentially due to its typical carbon equivalent value. The present study was developed surrounding the heat treatability of welded joints made with a high strength ductile cast iron detaining an ultimate tensile [...] Read more.

The weldability of ductile iron, as widely known, is relatively poor, essentially due to its typical carbon equivalent value. The present study was developed surrounding the heat treatability of welded joints made with a high strength ductile cast iron detaining an ultimate tensile strength of 700 MPa, and aims to determine which heat treatment procedures promote the best results, in terms of microstructure and mechanical properties. These types of alloys are suitable for the automotive industry, as they allow engineers to reduce the thickness of parts while maintaining mechanical strength, decreasing the global weight of vehicles and providing a path for more sustainable development. The results allow us to conclude that heat treatment methodology has a large impact on the mechanical properties of welded joints created from the study material. However, the thermal cycles suffered during welding promote the formation of ledeburite areas near the weld joint. This situation could possibly be dealt through the implementation of post-welding heat treatments (PWHT) with specific parameters. In contrast to a ductile cast iron tested in a previous work, the bull-eye ductile cast iron with 700 MPa ultimate tensile strength presented better results during the post-welding heat treatment than during preheating. Full article

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9 pages, 5196 KiB

Open AccessArticle

Generation of a Layer of Severe Plastic Deformation near Friction Surfaces in Upsetting of Steel Specimens

by Sergei Alexandrov, Leposava Šidjanin, Dragiša Vilotić, Dejan Movrin and Lihui Lang

Metals 2018, 8(1), 71; https://doi.org/10.3390/met8010071 - 19 Jan 2018

Cited by 10 | Viewed by 4017

Abstract

Narrow layers of severe plastic deformation are often generated near frictional interfaces in deformation processes as a result of shear deformation caused by friction. This results in material behavior that is very different from that encountered in conventional tests. To develop models capable [...] Read more.

Narrow layers of severe plastic deformation are often generated near frictional interfaces in deformation processes as a result of shear deformation caused by friction. This results in material behavior that is very different from that encountered in conventional tests. To develop models capable of predicting the behavior of material near frictional surfaces, it is necessary to design and carry out tests that account for typical features of deformation processes in a narrow sub-surface layer. In the present paper, upsetting of steel specimens between conical and flat dies is used as such a test. The objective of the paper is to correlate the thickness of the layer of severe plastic deformation generated near the friction surface and the die angle using a new criterion for determining the boundary between the layer of severe plastic deformation and the bulk. Full article

(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

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13 pages, 10433 KiB

Open AccessArticle

Thermodynamic Alloy Design of High Strength and Toughness in 300 mm Thick Pressure Vessel Wall of 1.25Cr-0.5Mo Steel

by Hye-sung Na, Byung-hoon Kim, Sang-hoon Lee and Chung-yun Kang

Metals 2018, 8(1), 70; https://doi.org/10.3390/met8010070 - 19 Jan 2018

Cited by 8 | Viewed by 5232

Abstract

In the 21st century, there is an increasing need for high-capacity, high-efficiency, and environmentally friendly power generation systems. The environmentally friendly integrated gasification combined-cycle (IGCC) technology has received particular attention. IGCC pressure vessels require a high-temperature strength and creep strength exceeding those of [...] Read more.

In the 21st century, there is an increasing need for high-capacity, high-efficiency, and environmentally friendly power generation systems. The environmentally friendly integrated gasification combined-cycle (IGCC) technology has received particular attention. IGCC pressure vessels require a high-temperature strength and creep strength exceeding those of existing pressure vessels because the operating temperature of the reactor is increased for improved capacity and efficiency. Therefore, high-pressure vessels with thicker walls than those in existing pressure vessels (≤200 mm) must be designed. The primary focus of this research is the development of an IGCC pressure vessel with a fully bainitic structure in the middle portion of the 300 mm thick Cr-Mo steel walls. For this purpose, the effects of the alloy content and cooling rates on the ferrite precipitation and phase transformation behaviors were investigated using JMatPro modeling and thermodynamic calculation; the results were then optimized. Candidate alloys from the simulated results were tested experimentally. Full article

(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)

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17 pages, 10051 KiB

Open AccessArticle

Direct Production of Ferrochrome by Segregation Reduction of Chromite in the Presence of Calcium Chloride

by Dawei Yu and Dogan Paktunc

Metals 2018, 8(1), 69; https://doi.org/10.3390/met8010069 - 19 Jan 2018

Cited by 10 | Viewed by 6434

Abstract

A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation [...] Read more.

A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation catalyst. Experiments were performed in the temperature range of 1200–1400 °C to evaluate the influences of various design parameters using both a thermogravimetric analyzer and an electric tube furnace with continuous off-gas analysis. The reduced products were characterized by scanning electron microscopy, X-ray powder diffraction, synchrotron X-ray absorption spectroscopy, and were subjected to wet chemical analysis. It was concluded that the addition of calcium chloride not only accelerated the carbothermic reduction of chromite but also promoted the formation and growth of individual ferrochrome alloy particles. The alloy formation within chromite particles was minimized, enabling the effective separation of ferrochrome alloy particles from the unwanted gangue without the need for fine grinding. Majority of the calcium chloride remained in a recoverable form, with a small percentage (<10 wt %) consumed by reacting with the siliceous gangue forming wadalite. Pure ferrochrome alloy powders were successfully produced with high metal recovery using elutriating separation. Full article

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8 pages, 3709 KiB

Open AccessCommunication

Determination of Three-Dimensional Morphology and Inner Structure of Second-Phase Inclusions in Metals by Non-Aqueous Solution Electrolytic and Room Temperature Organic Methods

by Jing Guo, Keming Fang, Hanjie Guo, Yiwa Luo, Shengchao Duan, Xiao Shi and Wensheng Yang

Metals 2018, 8(1), 68; https://doi.org/10.3390/met8010068 - 18 Jan 2018

Cited by 8 | Viewed by 3593

Abstract

The secondary-phase particles in metals, particularly those composed of non-metallic materials, are often detrimental to the mechanical properties of metals; thus, it is crucial to control inclusion formation and growth. One of the challenges is determining the three-dimensional morphology and inner structures of [...] Read more.

The secondary-phase particles in metals, particularly those composed of non-metallic materials, are often detrimental to the mechanical properties of metals; thus, it is crucial to control inclusion formation and growth. One of the challenges is determining the three-dimensional morphology and inner structures of such inclusions. In this study, a non-aqueous solution electrolytic method and a room-temperature organic technique were developed based on the principle of electrochemistry to determine the three-dimensional morphologies and inner structures of non-metallic inclusions in Al-killed steel, Si-killed steel, and ductile cast iron. The inclusions were first extracted without any damage to the inclusions, and then the collected inclusions were wrapped and cut through Cu ion deposition. The results revealed that the inclusions in Al-killed steel had an irregular morphology, that those in the Si-killed steel were mainly spherical, and that almost all the spheroidal graphite in the ductile cast iron featured a uniform globular morphology. In addition, nucleation was not observed in the inner structures of the inclusions in the Al-killed steel, while some dendritic or rod-like MnS phase precipitates appeared on the silicate inclusion surfaces, and some silicate-rich phases were detected in their inner matrix. For spheroidal graphite, rare-earth oxides (one particle or more) were observed as nuclei in the center of almost every graphite particle. The formation and evolution of inclusions in these types of metals can be better understood by means of the two developed methods. Full article

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14 pages, 4858 KiB

Open AccessArticle

Simple Fabrication and Characterization of an Aluminum Nanoparticle Monolayer with Well-Defined Plasmonic Resonances in the Far Ultraviolet

by María Del Pilar Aguilar-Del-Valle, Héctor De Jesús Cruz-Manjarrez and Arturo Rodríguez-Gómez

Metals 2018, 8(1), 67; https://doi.org/10.3390/met8010067 - 18 Jan 2018

Cited by 8 | Viewed by 4242

Abstract

Currently, aluminum plasmonics face technical challenges for the manufacture of reproducible structures by simple and low-cost techniques. In this work, we used a direct current (DC) sputtering system to grow a set of quasi-spherical aluminum nanoparticles with diameters below 10 nm. Our particles [...] Read more.

Currently, aluminum plasmonics face technical challenges for the manufacture of reproducible structures by simple and low-cost techniques. In this work, we used a direct current (DC) sputtering system to grow a set of quasi-spherical aluminum nanoparticles with diameters below 10 nm. Our particles are uniformly distributed over the surface of quartz and nitrocellulose substrates. We review in detail the methodology for the determination of adequate deposition parameters to allow great reproducibility in different production runs. Likewise, we carry out an exhaustive nanostructural characterization by means of scanning and transmission electron microscopy. The latter allowed us to identify that our depositions are nanoparticle monolayers with thicknesses equal to the average particle diameter. Finally, by means of absorbance spectra we identify the presence of a very well-defined plasmonic resonance at 186 nm that is associated with the dipolar mode in particles smaller than 10 nm. Due to the sharpness of their plasmonic resonances as well as their great manufacturing simplicity and high reproducibility, our aluminum nanoparticles could be used as optical sensors. Full article

(This article belongs to the Special Issue Metallization of Non-Conductive Substrates)

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15 pages, 4963 KiB

Open AccessArticle

Quadratic Midpoint Integration Method for J₂ Metal Plasticity

by Inkyu Rhee and Woo Kim

Metals 2018, 8(1), 66; https://doi.org/10.3390/met8010066 - 18 Jan 2018

Cited by 1 | Viewed by 5104

Abstract

The quadratic variants of the generalized midpoint rule and return map algorithm for the J₂ von Mises metal plasticity model are examined for the accuracy of deviatoric stress integration of the constitutive equation. The accuracy of stress integration using a strain rate [...] Read more.

The quadratic variants of the generalized midpoint rule and return map algorithm for the J₂ von Mises metal plasticity model are examined for the accuracy of deviatoric stress integration of the constitutive equation. The accuracy of stress integration using a strain rate vector for arbitrary direction is presented in terms of an iso-error map for comparison with the exact solution. Accuracy and stability issues of the quadratic integration method are discussed using a two-dimensional metal panel problem with a single slit-like defect in the center. The scale factor and shape factor were introduced to a quadratic integration rule for assuming a returning directional tensor from a trial stress onto the final yield surface. Luckily enough, the perfectly plastic model is the only case where the analytical solution is possible. Thus, solution accuracies were compared with those of the exact solutions. Since the standard scale factor ranges from 0 to 1, which is similar to the linear

α

-method, the penalty scale factors that are greater than 1 were mainly explored to examine the solution accuracies and computational efficiency. A higher value of scale factor above five shows a better computational efficiency but a decreased solution accuracy, especially in the higher plastification zone. A well-balanced scale factor for both computational efficiency and solution accuracy was found to be between one and five. The trade-off scale factor was proposed to be five. The proper shape factor was also proposed to be {1,1,4}/6 among the different combinations of weight distribution over a time interval. This proposed scale factor and shape factor is also valid for relatively long time periods. Full article

(This article belongs to the Special Issue Constitutive Modelling for Metals)

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14 pages, 2146 KiB

Open AccessArticle

Thermophysical and Mechanical Analyses of UO₂-36.4vol % BeO Fuel Pellets with Zircaloy, SiC, and FeCrAl Claddings

by Wei Zhou and Wenzhong Zhou

Metals 2018, 8(1), 65; https://doi.org/10.3390/met8010065 - 18 Jan 2018

Cited by 7 | Viewed by 4783

Abstract

The thermophysical performance and solid mechanics behavior of UO₂-36.4vol % BeO fuel pellets cladded with Zircaloy, SiC, and FeCrAl, and Zircaloy cladding materials coated with SiC and FeCrAl, are investigated based on simulation results obtained by the CAMPUS code. In addition, [...] Read more.

The thermophysical performance and solid mechanics behavior of UO₂-36.4vol % BeO fuel pellets cladded with Zircaloy, SiC, and FeCrAl, and Zircaloy cladding materials coated with SiC and FeCrAl, are investigated based on simulation results obtained by the CAMPUS code. In addition, the effect of coating thickness (0.5, 1 and 1.5 mm) on fuel performance and mechanical interaction is discussed. The modeling results show that Zircaloy claddings are more effective in decreasing fuel centerline temperature and fission gas release than other kinds of cladding material because of the smaller gap between cladding and fuel at the same burnup. SiC claddings and SiC-coated Zircaloy claddings possess smaller plenum pressure than other kinds of cladding. SiC claddings contribute more to fuel radial displacement but less to fuel axial displacement. FeCrAl claddings exhibit very different radial and axial displacements in different axial positions. FeCrAl-coated Zircaloy claddings have a lower fuel centerline temperature than Zircaloy claddings at burnup below 850 MWh/kg U, but a higher fuel centerline temperature at higher burnup. The gap between FeCrAl-coated Zircaloy claddings and fuel pellets closes earlier than that of Zircaloy claddings. SiC-coated claddings increase fuel radial and axial displacements, and cladding axial displacements of inner and outer cladding surfaces. Full article

(This article belongs to the Special Issue Zirconium Alloys)

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13 pages, 5101 KiB

Open AccessArticle

Resistivity and Passivity Characterization of Ni-Base Glassy Alloys in NaOH Media

by Khadijah M. Emran and Hanaa Al-Refai

Metals 2018, 8(1), 64; https://doi.org/10.3390/met8010064 - 18 Jan 2018

Cited by 6 | Viewed by 3753

Abstract

Resistivity and passivation behavior of two Ni-base bulk metallic glasses, with the nominal composition of Ni₇₀Cr₂₁Si_0.5B_0.5P₈C ≤ 0.1Co ≤ 1Fe ≤ 1 (VZ1) and Ni_72.65Cr_7.3-Si_6.7B_2.15C [...] Read more.

Resistivity and passivation behavior of two Ni-base bulk metallic glasses, with the nominal composition of Ni₇₀Cr₂₁Si_0.5B_0.5P₈C ≤ 0.1Co ≤ 1Fe ≤ 1 (VZ1) and Ni_72.65Cr_7.3-Si_6.7B_2.15C ≤ 0.06Fe_8.2Mo₃ (VZ2), in various concentrations of NaOH solutions were studied. The investigations involved cyclic polarization (CP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) methods. Cyclic polarization measurements showed spontaneous passivation for both Ni-base glassy alloys at all alkaline concentrations, due to the presence of chromium as an alloying element that formed an oxide film on the alloy surface. The EIS analysis showed that the passive layers grown on the two Ni-base glassy alloy surfaces are formed by a double oxide layer structure. Scanning electron microscope (SEM) examinations of the electrode surface showed Cr, Ni, Fe, and O rich corrosion products that reduced the extent of corrosion damage. Atomic force microscopy (AFM) imaging technique was used to evaluate the topographic and morphologic features of surface layers formed on the surface of the alloys. Full article

(This article belongs to the Special Issue Metallic Glasses: Pathways to Viable Applications)

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10 pages, 22299 KiB

Open AccessFeature PaperArticle

On the Effect of Natural Aging Prior to Low Temperature ECAP of a High-Strength Aluminum Alloy

by Sebastian Fritsch and Martin Franz-Xaver Wagner

Metals 2018, 8(1), 63; https://doi.org/10.3390/met8010063 - 18 Jan 2018

Cited by 13 | Viewed by 7195

Abstract

Severe plastic deformation (SPD) can be used to generate ultra-fine grained microstructures and thus to increase the strength of many materials. Unfortunately, high strength aluminum alloys are generally hard to deform, which puts severe limits on the feasibility of conventional SPD methods. In [...] Read more.

Severe plastic deformation (SPD) can be used to generate ultra-fine grained microstructures and thus to increase the strength of many materials. Unfortunately, high strength aluminum alloys are generally hard to deform, which puts severe limits on the feasibility of conventional SPD methods. In this study, we use low temperature equal-channel angular pressing (ECAP) to deform an AA7075 alloy. We perform ECAP in a custom-built, cooled ECAP-tool with an internal angle of 90° at −60 °C and with an applied backpressure. In previous studies, high-strength age hardening aluminum alloys were deformed in a solid solution heat treated condition to improve the mechanical properties in combination with subsequent (post-ECAP) aging. In the present study, we systematically vary the initial microstructure—i.e., the material condition prior to low temperature ECAP—by (pre-ECAP) natural aging. The key result of the present study is that precipitates introduced prior to ECAP speed up grain refinement during ECAP. Longer aging times lead to accelerated microstructural evolution, to increasing strength, and to a transition in fracture behavior after a single pass of low temperature ECAP. These results demonstrate the potential of these thermo-mechanical treatments to produce improved properties of high-strength aluminum alloys. Full article

(This article belongs to the Special Issue Scientific and Engineering Progress on Aluminum-Based Light-Weight Materials: Research Reports from the German Collaborative Research Center 692)

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14 pages, 12855 KiB

Open AccessFeature PaperArticle

FeS Corrosion Products Formation and Hydrogen Uptake in a Sour Environment for Quenched & Tempered Steel

by Elien Wallaert, Tom Depover, Iris De Graeve and Kim Verbeken

Metals 2018, 8(1), 62; https://doi.org/10.3390/met8010062 - 17 Jan 2018

Cited by 15 | Viewed by 5849

Abstract

Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H₂S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently [...] Read more.

Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H₂S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently their impact on the corrosion rate. In this paper, corrosion product formation and the impact of the Mo content of the base material on the composition of the corrosion products and hydrogen absorption in a sour environment was investigated. The corrosion layer was composed of a double layered mackinawite (FeS_1−x) structure, which was enriched with molybdenum and chromium. The layers were formed via two different mechanisms, i.e., the inner layer was created via a general oxide film formation corrosion mechanism, whereas the upper layer was formed by a precipitation mechanism. The presence of this double corrosion layer had a large influence on the amount of diffusible hydrogen in the materials. This amount decreased as a function of contact time with the H₂S saturated solution, while the corrosion rate of the materials shows no significant reduction. Therefore, the corrosion products are assumed to act as a physical barrier against hydrogen uptake. Mo addition caused a decrease in the maximal amount of diffusible hydrogen. Full article

(This article belongs to the Special Issue Environmentally Assisted Cracking in Advanced High Strength Alloys)

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7 pages, 4475 KiB

Open AccessArticle

Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds

by Degang Zhao, Lin Wang, Lin Bo and Di Wu

Metals 2018, 8(1), 61; https://doi.org/10.3390/met8010061 - 17 Jan 2018

Cited by 31 | Viewed by 5920

Abstract

The Ni-doped ZrCo_1−xNi_xSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo_1−xNi_xSb compounds [...] Read more.

The Ni-doped ZrCo_1−xNi_xSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo_1−xNi_xSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo_1−xNi_xSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo_1−xNi_xSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo_0.92Ni_0.08Sb sample at 850 K. Full article

(This article belongs to the Special Issue Heusler Compounds)

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10 pages, 10367 KiB

Open AccessArticle

Preparation and Characterization of TiB₂-(Supra-Nano-Dual-Phase) High-Entropy Alloy Cermet by Spark Plasma Sintering

by Shulei Zhang, Yuchen Sun, Boren Ke, Yulin Li, Wei Ji, Weimin Wang and Zhengyi Fu

Metals 2018, 8(1), 58; https://doi.org/10.3390/met8010058 - 17 Jan 2018

Cited by 17 | Viewed by 5521

Abstract

This paper introduces the preparation method and characterization results of TiB₂ ceramics with CoCrFeNiAl high-entropy alloy (HEA) as a sintering aid by Spark Plasma Sintering (SPS). Good wettability between HEA and TiB₂ was proved by the sessile drop method, indicating promising [...] Read more.

This paper introduces the preparation method and characterization results of TiB₂ ceramics with CoCrFeNiAl high-entropy alloy (HEA) as a sintering aid by Spark Plasma Sintering (SPS). Good wettability between HEA and TiB₂ was proved by the sessile drop method, indicating promising prospects for this composite. The sintering results showed that the addition of HEA could dramatically promote the sinterability of TiB₂. TiB₂-5 wt. % HEA dense ceramics prepared at the optimal temperature of 1650 °C showed fine morphology without formation of brittle phases. The liquid phase in the ceramics was highly consistent with the so-called “supra-nano-dual-phase materials (SNDPM)”, with near-ideal strength. This study represents the first time that a ceramic-SNDPM composite has been fabricated since the invention of such structures. Full article

(This article belongs to the Special Issue Spark Plasma Sintering-A Key Technology towards the Development of New Materials)

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12 pages, 5077 KiB

Open AccessArticle

The Corrosion Behavior of Ti-Based Metallic Glass Matrix Composites in the H₂SO₄ Solution

by Junwei Qiao, Jing Fan, Fan Yang, Xiaohui Shi, Huijun Yang and Aidong Lan

Metals 2018, 8(1), 52; https://doi.org/10.3390/met8010052 - 17 Jan 2018

Cited by 13 | Viewed by 4059

Abstract

In-situ metallic glass matrix composites (MGMCs) are a new kind of promising structural engineering material. In this study, a comprehensive study about the corrosion behavior of in-situ Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ MGMCs versus their size was conducted. [...] Read more.

In-situ metallic glass matrix composites (MGMCs) are a new kind of promising structural engineering material. In this study, a comprehensive study about the corrosion behavior of in-situ Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ MGMCs versus their size was conducted. It is interesting to find that the large sample exhibits a more excellent corrosion resistance than the small sample in the 10% H₂SO₄ solution both in chemical and electrochemical tests at room temperature. Furthermore, the results obtained from X-ray photoelectron spectra (XPS) demonstrate that the quality of the passive film formed on the large-sized sample is indeed superior to the small-sized sample. Based on (scanning electron microscope) SEM observation, the possible mechanisms of the observed phenomenon have been discussed in the present study. Full article

(This article belongs to the Special Issue Metallic Glasses: Pathways to Viable Applications)

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10 pages, 14132 KiB

Open AccessArticle

Transient Liquid Phase Bonding of Magnesium Alloy AZ31 Using Cu Coatings and Cu Coatings with Sn Interlayers

by Abdulaziz Nasser AlHazaa, Muhammad Ali Shar, Anas Mahmoud Atieh and Hiroshi Nishikawa

Metals 2018, 8(1), 60; https://doi.org/10.3390/met8010060 - 16 Jan 2018

Cited by 12 | Viewed by 5082

Abstract

Transient liquid phase bonding (TLP) of AZ31 samples has been investigated using Cu coatings and Cu coatings with Sn interlayer. Copper coatings were used for one set of the bonds, and a combination of Cu coatings and Sn interlayer was used for the [...] Read more.

Transient liquid phase bonding (TLP) of AZ31 samples has been investigated using Cu coatings and Cu coatings with Sn interlayer. Copper coatings were used for one set of the bonds, and a combination of Cu coatings and Sn interlayer was used for the other set of bonds. The bonding temperature was fixed at 520 °C, and various bonding times were applied. This study shows that the bonds produced using only Cu coatings have shown weaker bonds compared to the bonds made using Cu coatings and Sn interlayer. The Cu₂Mg particles were detected at the joint region of both bonds made by Cu coatings and Cu coatings with Sn interlayer by X-ray diffraction (XRD). However, it has been observed that the joint region was dominated by solid solution which is rich in Mg. Sn interlayer was not contributed to the intermetallic compound (IMC) at the joint region, and therefore it was diffused away through the Mg matrix. Within the joint interface, a slight increase of micro-hardness was observed compared to Mg base metal alloy. This was attributed to the formation and presence of IMC’s within the joint region. It was noticed that the presence of the Sn interlayer improved the joint strength by reducing the pores at the joint region. Pores were clearly observed for those bonds made using Cu coatings—especially for region where the fracture occurs; this was accomplished by scanning electron microscope (SEM). Full article

(This article belongs to the Special Issue Diffusion Bonding and Brazing of Advanced Materials)

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19 pages, 4542 KiB

Open AccessArticle

Experimental Study for Improving the Repair of Magnesium–Aluminium Hybrid Parts by Turning Processes

by Eva María Rubio, María Villeta, José Luis Valencia and José Manuel Sáenz de Pipaón

Metals 2018, 8(1), 59; https://doi.org/10.3390/met8010059 - 16 Jan 2018

Cited by 12 | Viewed by 3856

Abstract

One of the lightest metallic materials used in the aeronautics, aerospace, and automotive industries, among others, is magnesium, due to its excellent weight/strength ratio. Most parts used in these industries need to be made of materials that are rigid, strong, and lightweight, but [...] Read more.

One of the lightest metallic materials used in the aeronautics, aerospace, and automotive industries, among others, is magnesium, due to its excellent weight/strength ratio. Most parts used in these industries need to be made of materials that are rigid, strong, and lightweight, but sometimes the materials do not simultaneously satisfy all of the properties required. An alternative is to combine two or more materials, giving rise to a hybrid component that can satisfy a wider range of properties. The pieces machined in these industrial fields must satisfy stringent surface roughness requirements that conform to the design specifications. This work shows an experimental study to analyse the surface roughness reached in hybrid components made up of a base of magnesium alloy (UNS M11917) and two inserts of aluminium alloy (UNS A92024) obtained by turning. Its purpose is to determine the influence of the factors and their possible interactions on the response variable, the surface roughness Ra. The study is carried out using a design of experiments (DOE). A product of a full factorial 2³ and a block of two factors 3 × 2 was selected. The factors identified as possible sources of variation of the surface roughness are: depth of cut, feed rate, spindle speed, type of tool, location with respect to the specimen (LRS), and location with respect to the insert (LRI). Data were analysed by means of the analysis of variance (ANOVA) method. The main conclusion is the possibility to carry out the repair and maintenance of parts of magnesium–aluminum hybrid components by dry turning; that is, without cutting fluids and, therefore, in the most sustainable way that the process can be carried out. In addition, different combinations of cutting parameters have been identified that allow these operations to be carried out in an efficient manner, reducing mechanization times and, therefore, also the direct and indirect costs associated with them. Full article

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10 pages, 1620 KiB

Open AccessArticle

Chemical Degradation of a Mixture of tri-n-Octylamine and 1-Tridecanol in the Presence of Chromium(VI) in Acidic Sulfate Media

by Alexandre Chagnes and Gérard Cote

Metals 2018, 8(1), 57; https://doi.org/10.3390/met8010057 - 15 Jan 2018

Cited by 9 | Viewed by 4588

Abstract

The chemical degradation of an extraction solvent composed of a mixture of tri-n-octylamine (extractant) and 1-tridecanol (phase modifier) in n-dodecane in contact with an acidic aqueous sulfate solution containing chromium(VI) has been investigated. The kinetics of degradation and the degradation [...] Read more.

The chemical degradation of an extraction solvent composed of a mixture of tri-n-octylamine (extractant) and 1-tridecanol (phase modifier) in n-dodecane in contact with an acidic aqueous sulfate solution containing chromium(VI) has been investigated. The kinetics of degradation and the degradation products have been determined. GC-MS analyses evidenced the formation of 1-tridecanal, di-n-octylamine, N,N,N-octen-1-yl-dioctylamine, and an unidentified degradation compound, which may have contained a double bond and a carboxylic acid function. The mechanisms of degradation have been discussed on the basis of these identified degradation compounds. The study of the degradation kinetics showed that an increase of tri-n-octylamine concentration in the organic phase is responsible for a decrease of the degradation rate, while an increase in sulfuric acid concentration in the aqueous phase leads to a strong increase in the degradation rate. Full article

(This article belongs to the Special Issue Advances in Hydrometallurgy)

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17 pages, 3563 KiB

Open AccessArticle

Numerical Simulation of Tensile Behavior of Corroded Aluminum Alloy 2024 T3 Considering the Hydrogen Embrittlement

by Marina C. Vasco, Konstantinos Tserpes and Spiros G. Pantelakis

Metals 2018, 8(1), 56; https://doi.org/10.3390/met8010056 - 15 Jan 2018

Cited by 8 | Viewed by 4704

Abstract

A multi-scale modeling approach for simulating the tensile behavior of the corroded aluminum alloy 2024 T3 was developed, accounting for both the geometrical features of corrosion damage and the effect of corrosion-induced hydrogen embrittlement (HE). The approach combines two Finite Element (FE) models: [...] Read more.

A multi-scale modeling approach for simulating the tensile behavior of the corroded aluminum alloy 2024 T3 was developed, accounting for both the geometrical features of corrosion damage and the effect of corrosion-induced hydrogen embrittlement (HE). The approach combines two Finite Element (FE) models: a model of a three-dimensional Representative Unit Cell (RUC), representing an exfoliated area and its correspondent hydrogen embrittled zone (HEZ), and a model of the tensile specimen. The models lie at the micro- and macro-scales, respectively. The characteristics of the HEZ are determined from measurements of nanoindentation hardness, conducted on pre-corroded specimens. Using the model of the RUC, the local homogenized mechanical behavior of the corroded material is simulated. Then, the behavior of the exfoliated areas is assigned into different areas (elements) of the tensile specimen and final analyses are performed to simulate the tensile behavior of the corroded material. The approach was applied to model specimens after 8, 16 and 24 h exposure periods of the Exfoliation Corrosion (EXCO) test. For validation of the approach, tensile tests were used. The numerical results show that this approach is suitable for accurately simulating the tensile behavior of pre-corroded experimental specimens, accounting for both geometrical features of corrosion damage and corrosion-induced HE. Full article

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18 pages, 8793 KiB

Open AccessFeature PaperArticle

Strain Localization during Equal-Channel Angular Pressing Analyzed by Finite Element Simulations

by Tobias Daniel Horn, Christian Bert Silbermann, Philipp Frint, Martin Franz-Xaver Wagner and Jörn Ihlemann

Metals 2018, 8(1), 55; https://doi.org/10.3390/met8010055 - 15 Jan 2018

Cited by 14 | Viewed by 5970

Abstract

Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) [...] Read more.

Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) can emerge. This paper studies this phenomenon numerically adopting two-dimensional finite element simulations of one ECAP pass. The mechanical behavior of aluminum is modeled using phenomenological plasticity theory with isotropic or kinematic hardening. The effects of the two different strain hardening types are investigated numerically by systematic parameter studies: while isotropic hardening only causes minor fluctuations in the plastic strain fields, a material with high initial hardening rate and sufficient strain hardening capacity can exhibit pronounced localized deformation after ECAP. The corresponding finite element simulation results show a regular pattern of shear and matrix bands. This result is confirmed experimentally by ECAP-processing of AA6060 material in a severely cold worked condition, where microstructural analysis also reveals the formation of shear and matrix bands. Excellent agreement is found between the experimental and numerical results in terms of shear and matrix band width and length scale. The simulations provide additional insights regarding the evolution of the strain and stress states in shear and matrix bands. Full article

(This article belongs to the Special Issue Scientific and Engineering Progress on Aluminum-Based Light-Weight Materials: Research Reports from the German Collaborative Research Center 692)

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8 pages, 3179 KiB

Open AccessArticle

Compositional Approach to Designing Fcc High-Entropy Alloys that Have an Enlarged Equiaxed Zone

by Minju Kang, Jong Woo Won, Ka Ram Lim, Heoun-Jun Kwon, Seong Moon Seo and Young Sang Na

Metals 2018, 8(1), 54; https://doi.org/10.3390/met8010054 - 13 Jan 2018

Cited by 10 | Viewed by 5275

Abstract

A compositional approach to designing alloys that have an enlarged equiaxed zone is suggested in this study. The partitioning of elements during the solidification of CoCrFeMnNi high-entropy alloy (HEA) was confirmed through a directional solidification quenching experiment. Several HEAs were designed to maximize [...] Read more.

A compositional approach to designing alloys that have an enlarged equiaxed zone is suggested in this study. The partitioning of elements during the solidification of CoCrFeMnNi high-entropy alloy (HEA) was confirmed through a directional solidification quenching experiment. Several HEAs were designed to maximize the effects of constitutional and thermal undercooling by considering factors including solute enrichment at the columnar front and the melting temperatures and thermal conductivities of the individual elements. The newly designed HEAs were shown to have successfully enlarged equiaxed zones, and improved anisotropic properties. Full article

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12 pages, 5406 KiB

Open AccessArticle

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

by Prabhukumar Sellamuthu, D. G. Harris Samuel, D. Dinakaran, V. P. Premkumar, Zushu Li and Sridhar Seetharaman

Metals 2018, 8(1), 53; https://doi.org/10.3390/met8010053 - 12 Jan 2018

Cited by 71 | Viewed by 11093

Abstract

Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength, [...] Read more.

Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength, percentage elongation and impact energy were evaluated for the as-cast and austempered samples. Microstructures were investigated using microscopy, coupled with analyzing software and a scanning electron microscopy. The specific wear of samples was tested using pin-on-disc wear testing machine. X-ray diffraction was performed to calculate the amount of retained austenite present in the ausferrite matrix. As-cast microstructure consists of ferrite and pearlite, whereas austempered ductile iron (ADI) contains a mixture of acicular ferrite and carbon enriched austenite, called “ausferrite”. Hardness and strength decreased, whereas ductility and impact strength improved with an increase in the austempering temperature. XRD analysis revealed that the increase in austempering temperature increased the retained austenite content. A decrease in wear resistance with austempering temperature was observed. Modified Quality Index (MQI) values were envisaged, incorporating tensile strength, elongation and wear resistance. MQI for samples austempered at 340 °C and 360 °C showed a better combination of properties. About an 8% reduction in energy consumption was gained when the heat treatment parameters were optimized. Full article

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9 pages, 6123 KiB

Open AccessArticle

Influence of Extrusion Temperature on the Aging Behavior and Mechanical Properties of an AA6060 Aluminum Alloy

by Nadja Berndt, Philipp Frint and Martin F.-X. Wagner

Metals 2018, 8(1), 51; https://doi.org/10.3390/met8010051 - 12 Jan 2018

Cited by 20 | Viewed by 6970

Abstract

Processing of AA6060 aluminum alloys for semi-products usually includes hot extrusion with subsequent artificial aging for several hours. Processing below the recrystallization temperature allows for an increased strength at a significantly reduced annealing time by combining strain hardening and precipitation hardening. In this [...] Read more.

Processing of AA6060 aluminum alloys for semi-products usually includes hot extrusion with subsequent artificial aging for several hours. Processing below the recrystallization temperature allows for an increased strength at a significantly reduced annealing time by combining strain hardening and precipitation hardening. In this study, we investigate the potential of cold and warm extrusion as alternative processing routes for high strength aluminum semi-products. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature, 120 or 170 °C, followed by an aging treatment. Electron microscopy and mechanical testing were performed on the as-extruded as well as the annealed materials to characterize the resulting microstructural features and mechanical properties. All of the extruded profiles exhibit similar, strongly graded microstructures. The strain gradients and the varying extrusion temperatures lead to different stages of dynamic precipitation in the as-extruded materials, which significantly alter the subsequent aging behavior and mechanical properties. The experimental results demonstrate that extrusion below recrystallization temperature allows for high strength at a massively reduced aging time due to dynamic precipitation and/or accelerated precipitation kinetics. The highest strength and ductility were achieved by extrusion at 120 °C and subsequent short-time aging. Full article

(This article belongs to the Special Issue Scientific and Engineering Progress on Aluminum-Based Light-Weight Materials: Research Reports from the German Collaborative Research Center 692)

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