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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 61 (2020), No. 2

  • PREFACE

    pp. 221-221

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    DOI:10.2320/matertrans.MPR2019907

  • Drawability of Functional Corrugate Cup Using Roller Die

    pp. 222-227

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    DOI:10.2320/matertrans.MT-ML2019004

    The formability of the corrugated cup was investigated by the deep drawing process. Deep drawing, which is one of press forming, is a plastic processing technology for forming a thin plate into a three-dimensional container or case. For container products, there are many products formed by this technology. Depending on the application, the functionality of the container itself was required. For example, there are embossing, thickening, and tailored blanks processing. In the present study, corrugated cup was formed to enhance the functionality of the cup. A unique die was used to form the cup having a corrugated shape. The shoulders of the die were grooved, and the steel balls were arranged without gaps in the groove. The balls rotated freely during forming. In an experiment, the blanks were commercially extra-low carbon steel SPCC and stainless steel SUS304. The initial diameter and thickness of the blank were 70 to 95 mm and 0.3 to 0.5 mm. The lubricant was the solid powders of molybdenum disulfide. The deep drawing process was performed using an oil hydraulic press at a forming speed of approximately 10 mm/min. The diameter of the punch was 40 mm, and the smallest hole diameter of the die was 41 mm. These tools were tool steel SKD11, and were standard heat treated. The metal sheets were successfully drawn without the cracks. In the side wall of the cup, the distance between the waves was approximately 8.6 mm. The thickness strain at the bottom of the drawn cup SPCC was no more than 0.1.
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  • Experimental and Numerical Investigation of Residual Stresses in Incremental Forming

    pp. 228-233

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    DOI:10.2320/matertrans.MT-ML2019011

    Double Sided Incremental Forming (DSIF) is gaining importance over Single Point Incremental Forming (SPIF) due to its ability to form complex geometries and the capability to obtain better accuracies. In the present work, residual stresses are measured in pyramidal components formed using SPIF, DSIF using X-ray diffraction technique. Residual stress development mechanism during SPIF and DSIF is studied using Finite Element Analysis (FEA). Stress development along circumferential and meridional directions are explained using bending and unbending of sheet material taking place around forming tool. It is observed that the residual stresses are compressive on the outer surface and tensile on the inner surface of sheet in both circumferential and meridional directions. In DSIF, supporting tool restricts the unbending of sheet causing the residual stresses to be less compressive on the outer surface and less tensile on the inner surface compared to SPIF. It is also observed that with an increase in tool diameter, spring back increased, hence, meridional residual stress on the outer surface became more compressive and circumferential residual stress on the inner surface became more tensile. Residual stresses in ISF are compared with FEA predictions of conventional stamping process.
  • Mechanism Study and Optimized Technology of Multi-Pass Drawing Process for Ultrafine-Grained Inconel 718 Micro-Tubes

    pp. 234-238

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    DOI:10.2320/matertrans.MT-ML2019001

    In this paper, Inconel 718 tube blanks are processed into ultrafine-grained Inconel 718 micro-tubes by multi-pass drawing. The mechanism of grain size variation and microstructure evolution has been discussed. Moreover, parameters of tubes have been compared and studied for each pass. Furthermore, optimized sequence on drawing process was determined. Optical microscope (OM) and surface roughness tester (SRT) were used for analyzing the evolution of tube size and surface roughness, separately. To further investigate the mechanical properties and microstructure of Inconel 718 tubes, tensile tests and microstructure analysis were conducted. Ultrafine-grained Inconel 718 micro-tubes with outer diameter of 0.9 mm have been produced successfully. The results show that grains were continuously refined during the drawing process and low angle grain boundaries were finally obtained. On the other hand, plasticity reduced while the strength increased obviously with the drawing process. Compared with the results of two manufacturing plans (5 passes and 11 passes), the manufacturing plan with 7 drawing passes has been accepted as the most topgallant option due to its comprehensive advantages. In general, mechanism study and optimized technology of multi-pass drawing process for ultrafine-grained Inconel 718 micro-tubes were discussed in detail, which provide a theoretical basis for high precision micro-tubes manufacturing process with hardly deformable materials.
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  • Frictional Size Effect of Light-Weight Mg–Li Alloy in Micro Deep Drawing under Nano-Particle Lubrication Condition

    pp. 239-243

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    DOI:10.2320/matertrans.MT-ML2019002

    In microscale due to the increase in the ratio of open to close lubrication pockets and escalation in coefficient of friction, unlike in macroscale, selection of proper lubrication condition has become challenging. In alignment with the aim of microforming, by the meaning of making light-weight energy effective micro-parts, in this study, the behaviour of a novel superlight magnesium–lithium (Mg–Li) alloy LZ91 is investigated during micro deep drawing under some lubrication conditions. Some heat treatments are undertaken to study the deformation behaviour of the Mg–Li alloy. To mitigate the effects of increasing in open to closed lubrication pocket ratio size effect, an innovative TiO2 oil-based nano-additive lubricant is applied, and its performance is determined in regard with the commonly used condition, dry condition. The mass fraction of nano-particles in the lubricant is a critical parameter which in this study 0.5 wt% and 1 wt% are investigated. The results show the drawing force reduces significantly by utilising the 1 wt% TiO2 oil-based nano-additive lubricant in comparison with 0.5 wt% of nano-particle lubricant and dry condition. The unique mechanism of the nano-particles is capable of retaining the lubricant inside surface asperities and hold it during the deformation process.
  • Femtosecond Laser Trimming of CVD-Diamond Coated Punch for Fine Embossing

    pp. 244-250

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    DOI:10.2320/matertrans.MT-ML2019003

    Femtosecond laser machining was employed to trim the surface roughness of diamond coating and to sharpen the edge corner of diamond coated punch toward fine piercing and embossing processes in metal forming. CVD-diamond coated WC (Co) punches with the head diameter of 2 mm were prepared for this laser-trimming process. The initial coated diamond film was 9 µm thick; the curvature of coated punch shoulder was 12 µm. The rotating jig was utilized to attain the homogeneous trimming of punch side surface as well as punch head. SEM (Scanning Electron Microscopy) and Raman spectroscopy were employed to describe the microstructure evolution with trimming as well as the effect of trimming on the nanostructure of diamonds. Fine embossing process into 0.1 mm thick AISI304 sheets with narrow clearance, was utilized to describe their plastic flow around the punch shoulder as well as the geometric distortion by elastic recovery. In addition, EBSD (Electron Back-Scattering Diffraction) was also employed to analyze the difference in plastic flow of AISI304 sheets during micro-embossing between the untrimmed and trimmed punches. The applied load to stroke relation, the plastic strain distribution and the phase mapping as well as the shear droop were compared between two diamond-coated punches to investigate the effect of laser-trimming on the quality of embossed product.
  • Evaluation of the Mechanical and Electromagnetic Shielding Properties of Carbon Fiber Reinforced Thermoplastics Sheet Made of Unidirectional Tape

    pp. 251-255

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    DOI:10.2320/matertrans.MT-ML2019008

    Carbon fiber reinforced thermoplastics (CFRTP) made of carbon fiber-polyamide 6 unidirectional (UD) tape with different layer-configuration and tape-length were fabricated using hot compression-molding, and then their mechanical and electromagnetic shielding properties were evaluated. The mechanical property was evaluated using a three-point bending test method. Whereas, electromagnetic interference shielding effectiveness (EMI-SE) was estimated using Simon formalism based on through-thickness electrical conductivity value. In addition, laminate analysis using a laser microscope was conducted to observe inter and intra-laminar of CFRTP. The results showed that maximum load and flexural modulus of CFRTP has a strong relationship with UD tape arrangement. Unidirectional layer configuration is the highest strength and modulus compared with others due to carbon fiber direction.Furthermore, UD tape length significantly influenced in increasing the modulus for randomly chopped CFRTP. While the total EMI-SE was 29–89 dB in the x-band frequency for all different layer-configuration and tape-length in which quasi-isotropic layer-configuration was the highest electromagnetic shielding performance. Dominant-absorption shielding mechanism was confirmed by higher absorption value rather than reflection, in the range of 21–74 dB from total EMI-SE value. The results revealed an opposite characteristic between mechanical and electromagnetic shielding properties related to UD tape configuration for laminated composite. Also, the intra-laminar analysis showed that electrical volume conductivity strongly influenced by fiber-to-fiber contact in the thickness direction of the composite. It confirmed that quasi-isotropic and bidirectional configuration have higher conductivity resulting in higher electromagnetic shielding performance compared with others.
  • Construction of Material Constitutive Relationship Based on Surface-Layer Model at Micro/Mesoscopic Scale

    pp. 256-260

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    DOI:10.2320/matertrans.MT-ML2019016

    Micro-forming process get extensive attention in the last decades as the rapid development of micro-manufacturing technology. But the traditional metal plastic forming theory becomes no longer applicable in micro-forming process because of the so-called size effect. Many factors such as size effect, grain boundary and grain orientation should be considered to reveal the plastic deformation behaviors of metal material in micro/mesoscopic scale. In this paper, on the basis of classical Hall-Petch relationship, combining the surface layer model and composite model, a constitutive model of material in micro/mesoscopic scale was established with further consideration of grain orientation. The micro-compression experiment of pure copper specimens with different diameters and grain sizes was conducted. Based on the experiment results, the established constitutive relationship was determined and verified, and high consistence and accuracy were found. Finally, the finite element model of micro specimen was built based on the established constitutive model and Voronoi method. Then the numerical simulation of upsetting process of the pure copper was executed, which showed that the simulation results could well reflect the flow stress and deformation of the material at micro/mesoscopic scale, and further proved the availability of the proposed model.
  • Effect of Roll Gap Setup on Shape Defects during a Flexible Roll Forming Process

    pp. 261-265

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    DOI:10.2320/matertrans.MT-ML2019012

    The flexible roll forming process is an advanced sheet metal forming process which manufactures parts with variable cross-section profiles. The metal sheet is incrementally bent into the desired shape by passing it through successive roll stands. In this process, contacts of the flange and web sides are controlled by roll gaps in vertical and horizontal directions. To investigate the effect of the roll gap on shape defects during the flexible roll forming process, experiments were conducted using a lab-scale machine according to different combinations of roll gapsetups: 1) a smaller flange gap than the blank thickness; 2) the same flange and web gaps as the blank thickness; 3) a smaller web gap than the blank thickness. Three kinds of symmetric blanks with trapezoid, concave and convex shapes were used for the experiments. To investigate the effect of the roll gap on shape defects, web-warping and longitudinal strain at the edge for the three different blank shapes were characterized at various combinations of roll gap setups.
  • Microforming of Stainless Steel Miniature Pump by Additive Sheet-Manufacturing

    pp. 266-271

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    DOI:10.2320/matertrans.MT-ML2019007

    Micro-pump had an integrated structure including the valves, the reservoir, the actuating plates and so forth as designed for each application. Various liquid as well as viscous media popped in and out through this unit; each element must have sufficient strength and toughness as well as well-defined accuracy in geometry and dimension. In particular, high leak proof is the highest requirement for this micro-pump in working at the medical operation, at the drug delivery and at the blood transportation. The additive sheet-manufacturing was proposed to make micro-forming of these miniature mechanical elements, devices and systems. This process consisted of three steps. Fist, the original CAD data for a micro-pump were sliced into an assembly of geometric models for each perforated and embossed sheet form. In second, a pair of miniature punch and die was fabricated by the plasma printing process after each geometric model. Then, each bare sheet element was micro-pierced and micro-embossed to transform each CAD-model to each shaped stainless steel sheet element. Finally, the assembly of sheet elements was plasma surface-activated and integrated into the tailored micro-pump by micro-joining. This top-to-down and down-to-top methodology in the above is discussed for further improvement of additive sheet-manufacturing.
  • Combined Effect of Pre-Strain at Elevated Temperature and Pre-Aging on Aging Strength and Microstructures of AA6082

    pp. 272-275

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    DOI:10.2320/matertrans.MT-ML2019010

    With the increasingly serious energy and environmental issues, aluminum alloys are becoming increasingly desirable for transportation facilities due to their high specific strength. Their low formability results in the difficulty of forming complex-shaped panels and bodies. Hot stamping is a new technology developed to address this formability challenge by applying plastic deformation to the heated aluminum alloy sheet at the solution heat treatment temperature. The stamped panels gain high strength via the sequent aging treatment. Different panels, even different regions on the same panel, are subjected to different forming strains. The present paper is focused on the experimentally investigating the effects of the pre-strain at elevated temperature and pre-aging on the mechanical behavior and microstructures of AA6082 after the natural aging, paint-bake treatment, and artificial aging. Sample sheets of AA6082-T6 were pre-strained by uniaxial tension at different levels of strain, and then subjected to the pre-aging, natural aging, paint-bake treatment or artificial aging, respectively. The yield strength, tensile strength and elongation of post-aged samples were gained via the standard uniaxial tensile tests. The results show that both of the pre-strain at elevated temperature and pre-aging suppress the natural aging of AA6082. Pre-strain at elevated temperature induces weak bake softening, and has a detrimental effect on the artificial aging strengthening, while the sequent pre-aging could compensate the strength decrease.
  • Effects of Tool Surface Geometry on Temperature Distribution and Material Properties of an Aluminum Alloy in Friction Stir Welding

    pp. 276-281

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    DOI:10.2320/matertrans.MT-ML2019017

    Friction stir welding is a relatively new welding process that provides advantages over conventional fusion welding processes including the possibility of joining non-fusion-weldable alloys, reducing distortion, and improving their mechanical properties. In the present study, the effects of the tool pin surface geometry on heat transfer and material flow during friction stir welding were investigated. Tapered cylindrical tool pins made of H13 hot work tool steel with and without grooves were used in experiments to join AA6061 aluminum alloy plates at a tool rotation speed of 1800 rpm and transverse speed of 50 mm/min. The changes in workpiece temperature during the process were recorded using K-type thermocouples embedded at four locations. From the experiments, it was found that welds made with the grooved tool pin exhibited better mechanical properties such as tensile strength and microhardness owing to enhanced material flow. It was also observed that the grooved tool pin generated less heat; this could be the reason for the superior properties of the welds it produced during joining processes. From the experiments, it was found that welds s formed by the tool pin with grooves showed better mechanical properties than those formed without grooves, owing to the enhanced material flow. Moreover, the welding strength was improved by using the tool pin with grooves. It was also observed that the tool pin without grooves generated more heat than that with grooves, which could be the reason for the inferior properties of the welds produced using the grooved pin.
  • SiC-Coated SiC Die for Galling-Free Forging of Pure Titanium

    pp. 282-288

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    DOI:10.2320/matertrans.MT-ML2019006

    β-SiC coated SiC die material was employed to investigate the material compatibility between pure titanium in industrial grade I and covalent-bonded β-SiC coating. β-SiC coated SiC die with the coating thickness of 3 mm was first prepared as a staring die material. A micro-groove was machined onto the SiC coating by the picosecond laser machining. A titanium wire specimen with the diameter of 0.98 mm and the length of 20 mm, was upset into this micro-groove by fine CNC-stamping system. This SiC-coated SiC die was fixed into a cassette die. CNC up-setting procedure was employed for experiment to measure the torque power–stroke curve during upsetting at the specified reduction of thickness by 10%, 20% and 30%, respectively. In experiments, SEM, laser- and optical-microscopy were utilized to observe the titanium adhesive film formed onto the die surface. No metallic titanium was detected by SEM-EDX analysis at the contact area to upset titanium on this β-SiC coating even after continuously upsetting in fifteen shots. Titanium oxide debris flakes were splashed and printed as a very thin film onto the β-SiC die.
  • Effect of Production Rate on Lubrication Performance of Environmentally-Friendly Lubricant in Combined Forward-Can and Backward-Can Cold Extrusion Test of Aluminum Alloy

    pp. 289-294

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    DOI:10.2320/matertrans.MT-ML2019013

    The effect of production rate on the lubrication performance of an environmentally-friendly lubricant in the cold forging of aluminum alloy was investigated using the tribological test of combined forward-can and backward-can extrusion proposed by one of the present authors. In this test, the lubrication performance was examined by both finite element analysis and experimentally. A double-layer-type environmentally-friendly solid lubricant was used. The undercoat plays the role of mitigating pick up, whereas the overcoat reduces friction. Using finite element analysis, a calibration diagram of the relationship between the extruded geometry of the workpiece and the punch stroke was prepared at the production rate of 1 and 20 stroke per minutes. The Coulomb friction coefficient between the workpiece and the outer die was identified by plotting the punch stroke and the extruded height of the workpiece on the calibration diagram. Three different surfaces of annealed aluminum alloy A4032 formed by different treatment conditions were used. The first is a surface roughened by a lathe, the second is a surface roughened by a lathe and then alkali-etched, and the third is a surface roughened by a lathe and then shot blasted. The tests were performed by varying the punch stroke between the two production rates. As a result, the dependency of the friction coefficient on the production rate was reasonably clarified, and the friction coefficient value estimated was higher when the production rate was smaller. A significant influence of the surface treatment on the friction coefficient was not observed due to the moderate deformation resistance of workpiece material.
  • Influence of Strain-Induced Martensitic Transformation of Austenitic Stainless Steel Sheet in Precision Blanking on Cut-Surface Quality

    pp. 295-299

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    DOI:10.2320/matertrans.MT-ML2019009

    The main purpose of precision blanking in press stamping is to suppress fracture of the cut surface. The principle is attainable by applying hydrostatic stress on the workpiece by various contrivances, so that the workpiece can maintain its ductility for suppression of fracture. Stainless steel, which is commonly used in medical components, is also known to be a ductile material, but one of problematic characteristics of austenitic stainless steel is martensitic transformation. The phenomenon is that the ductile austenite phase is changed to the brittle martensitic one by processing strain. Therefore, in this study, the effect on the cut surface from martensitic transformation near it in the precision blanking process was investigated. As a result, it was proved that there was a difference in the occurrence or non-occurrence of fracture of the cut surface due to the difference in the strain-induced martensitic transformation.
  • Microstructure Analysis of Graded Interface Layers in a Model Multilayer Al/Al–Zn/Al Sample by Scanning Microbeam Small-Angle X-ray Scattering Measurements

    pp. 300-304

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    DOI:10.2320/matertrans.L-M2019863

    The distribution of precipitation microstructures in the interdiffusion layer of Al/Al–Zn alloy/Al model multilayer was examined using microbeam small-angle X-ray scattering (SAXS) measurements. The change of scattering profiles across the graded interfacial layers reflected the spatial change in the volume fraction, average size, and size distribution in the sample. Microstructural parameters obtained from the SAXS analysis explained the hardness change in the interface area. The present results suggest that small-angle scattering analysis using a scanning microbeam is a useful tool to examine the microstructural distribution and predict the properties of the interface region in multilayer composite sheets, in particular, the microstructure and properties of transient interfacial layers.
  • Change in Mechanical and Electrical Properties of Accumulative Roll Bonding Processed High-Purity Aluminum, Al–0.02 mass%Fe and Al–0.2 mass%Fe Alloys

    pp. 305-310

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    DOI:10.2320/matertrans.L-M2019864

    An accumulative roll bonding process was applied up to 8 cycles on high-purity aluminum, aluminum–0.02 mass%iron and aluminum–0.2 mass%iron in order to measure electrical properties in addition to the mechanical properties. Ultimate tensile strength increases about 3–5 times compared with that of coarse grain metals, whereas, the electrical conductivity at room temperature decreases about a few %IACS. The dislocation density and density of grain boundary were evaluated from XRD and SEM/EBSD measurements. The microstructure change in those parameters explains the change in electrical resistivity measured at 77 K.
  • Solidification Microstructure and Magnetic Properties of Ag-Rich Ag–Cu–La–Fe Immiscible Alloys

    pp. 311-317

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    DOI:10.2320/matertrans.Z-M2019857

    The rapid solidification microstructure and magnetic properties of melt-spun ribbons in Ag52Cu23.2La4.8Fe20 (at%) alloy, which was designed as the combination of Ag-rich Ag65Cu29La6 alloy with high glass-forming ability (GFA) and Fe, were investigated. An amorphous phase formation was observed in a melt-spun ribbon of ternary Ag65Cu29La6 alloy. The composite of Ag–Cu-based crystalline matrix and BCC-Fe globules was obtained in Ag52Cu23.2La4.8Fe20 alloy. The size of BCC-Fe globules embedded in an Ag–Cu-based crystalline matrix was on the order of 50 nm. The Fe addition deteriorated the GFA in Ag-rich Ag–Cu–La alloys. The combination of liquid-phase separation and stabilization of liquid for amorphous phase formation during rapid cooling leads to the formation of the particular solidification microstructure in Ag-rich Ag–Cu–La–Fe immiscible alloy. The melt-spun ribbon shows typical ferromagnetic magnetic properties due to the 50-nm BCC-Fe globules. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 68 (2019) 205–211. Minor corrections in main text were performed with translation from Japanese to English and proofreading by native speakers. Reference 24) was changed from J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 45–51 (written in Japanese) to Mater. Trans. 60 (2019) 554–560 (written in English).
  • Hot Deformation Behavior of 7085 Aluminum Alloy Based on Deformation Heating and Friction

    pp. 318-325

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    DOI:10.2320/matertrans.MT-M2019279

    The hot deformation behavior and constitutive analysis of AA7085 aluminum alloy based on the uncorrected and corrected flow stress for deformation heating and friction were investigated by hot compressive tests. The results show that deformation heating has more significant influence on the flow stress than that of friction. Two constitutive equations with and without deformation heating and friction could properly describe the hot deformation behavior of the material. However, the revised constitutive model to describe the hot deformation of AA7085 aluminum alloy taking account of deformation heating and friction is proposed at high strain rate, which gives the values of correlation coefficient and average absolute relative error are 0.989 and 4.86%, respectively.
  • Microstructure and Damping Capacity of a Mn35Cu60Al3Fe2 Alloy by Semisolid Heat Treatment

    pp. 326-329

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    DOI:10.2320/matertrans.MT-M2019248

    A 35Mn–60Cu–3Al–2Fe (at%) alloy was prepared by vacuum induction melting followed by hot forging at 1073 K, and then heat treated at 1113 K for 5 h. Further, the alloy was semisolid heat treated at 1153, 1163, 1173 and 1183 K for 20 min. The microstructure and damping capacity of the alloys at different temperatures have been investigated comparatively. The results show that the microstructure of the alloy at 1113 K comprises single phase while that at 1153–1183 K consists of Mn-rich and Mn-poor phases. The area fraction of Mn-rich phase raises with increase in semisolid treatment temperature. The damping capacity of the alloy is lowest at 1113 K and raises with increasing the semisolid treatment temperature (1153–1183 K) due to gradually increased amount of Mn-rich phase.
  • Humid Gas Stress Corrosion Cracking in MIG-Welded 5083 Aluminum Alloy Plate

    pp. 330-338

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    DOI:10.2320/matertrans.L-M2019865

    In 5000 series (Al–Mg) alloys, hydrogen embrittlement (HE) becomes a concern when Mg content exceeds 5%. The local Mg content will become higher than 5% due to solidification segregation in the weld joint of 5083 alloy. In this study, resistance to HE of MIG-welded 5083 aluminum alloy at three areas (weld center, weld corner and HAZ) was investigated by newly developed humid gas stress corrosion cracking (HG-SCC) test. Slow strain rate tensile (SSRT) test on base metal and welded joint was also conducted for comparison.It was newly revealed that HG-SCC crack extends only in the sample of weld corner, confirming HE in this area. For the other areas, HG-SCC crack did not propagate, confirming HE resistance of these areas. From the results of SSRT test, neither the base nor welding material showed reduction in strength or ductility. Therefore, it was concluded that HE in 5083 MIG welds is only detectable by HG-SCC test. The reason for this should be in the fact that HG-SCC test can specifically test different local areas, while the softest area (weld center) always deforms preferentially and fractures in SSRT test.
  • Reaction of Molten Aluminum with MgO and Formation of MgAl2O4 Spinel at 1000°C

    pp. 339-345

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    DOI:10.2320/matertrans.MT-M2019220

    The reaction of MgO with molten Al was investigated at 1000°C. When the MgO pellet was heated with Al in an alumina tube, MgAl2O4 spinel formed on both the MgO pellet and the inner surface of the alumina tube. Mg ions were reduced at the interface of the molten Al and MgO pellet, and spinel was formed, although the reaction demonstrated a positive change in the standard Gibbs free energy. The reduced Mg was dissolved in molten Al and reacted at the inner surface of the alumina tube to form the spinel. When Al was melted in the MgO tube, spinel formed at the inner surface of the tube. These reactions can be understood by considering an equilibrium reaction, 4MgO + 2Al ⇄ MgAl2O4 + 3Mg, with activities of Mg and Al in the metal liquid. The formed spinel was black, which was due to the metal aluminum particles inside the formed spinel layer.
  • Experimental and Numerical Analyses of Magnetic Pulse Forming of A1050 Aluminum Sheet

    pp. 346-354

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    DOI:10.2320/matertrans.L-M2019862

    An A1050 aluminum sheet was collided against a steel mold with a small V-shaped through-thickness groove by using magnetic pulse forming (MPF) at various charging energy conditions. Deformation behavior of the sheet was also reproduced by using a series of numerical analyses. The groove was filled at high charging energy condition. Almost no change in grain morphology was observed at the mid-thickness area of the sheet, but extremely large intensive deformation occurred at the metal surface region along the slope of the mold. Deformation of the MPFed Al sheet was numerically analyzed by using ANSYS Emag-Mechanical. Electromagnetic force and deformation of the sheet was reproduced, and the impact velocity of the sheet to the mold was obtained. Deformation behavior of Al under various impact velocity conditions was analyzed by using Smoothed Particle Hydrodynamics (SPH) method of ANSYS AUTODYN. The groove was completely filled with Al at the high impact velocity condition, and an extremely large plastic strain and strain rate were observed only at the sheet surface. These simulation results corresponded very well to the final shape and the local microstructure change observed in the MPFed Al sheet.
  • Refinement of Primary Si Grains of Al–21%Si Alloy Using Vibration Mold

    pp. 355-360

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    DOI:10.2320/matertrans.F-M2019856

    The grain refinement of primary Si in Al–21% Si alloy was investigated using mechanical vibration during solidification. The number of primary Si grains increased and the primary Si grain size decreased with increasing amplitude and frequency of the vibration. Because the frequency and amplitude affect the grain refinement, the primary Si size can be determined from the excitation force including those factors. The primary Si size decreases with increasing excitation force. To determine the grain refinement mechanism after applying vibration, the cooling rate during solidification and vibration start time were changed. Based on this study, the cooling rate did not affect the grain refinement. The primary Si was refined when vibration was applied in the beginning of casting. On the other hand, the primary Si was not refined when the vibration application was continued after pouring. The results of this study suggest that the grain refinement is caused by the crystallization of many primary Si grains on the wall of the mold and at the upper surface of the molten metal and the continuous transport of the grains into the molten metal based on the convection of the molten metal due to the vibration. This Paper was Originally Published in Japanese in J. JFS 91 (2019) 258–263.
  • Fatigue Property and Cytocompatibility of a Biomedical Co–Cr–Mo Alloy Subjected to a High Pressure Torsion and a Subsequent Short Time Annealing

    pp. 361-367

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    DOI:10.2320/matertrans.MT-M2019148

    In the present study, we evaluated the effects of high pressure torsion (HPT) and subsequent short time annealing processing on fatigue properties and cytocompatibility of the biomedical Co–Cr–Mo alloy (CCM). Before processing, CCM was solution treated (CCMST) to achieve a microstructure composed of coarse single γ-phase equiaxed grains with no internal strain. Through HPT processing, an inhomogeneous microstructure containing both micro- and nano-scaled grains is obtained in CCM specimens, which were named as CCMHPT, accompanied by high internal strain and extensive ε martensite. Following a subsequent short time annealing, a uniform single γ-phase ultrafine-grained microstructure with small local strain fields dispersed forms in CCM specimens, which were named as CCMHPTA. This microstructure change improves fatigue strength in CCMHPT, and further in CCMHPTA, because of the enhanced crack initiation and/or propagation resistance. For cytocompatibility evaluation, the cells cultured on CCMST show an immobilization tendency, while those cultured on CCMHPT exhibit a locomotion tendency. The cells cultured on CCMHPTA have an intermediate pattern. Compared with CCMST, much larger numbers of cells are proliferated in both CCMHPT and CCMHPTA. All these results demonstrate that the CCMHPTA offers an improved fatigue property and a good cytocompatibility. Therefore, it is promising for use in biomedical applications.
  • Influence of Brazing Time on Liquid Migration and Cell Structure of Porous Aluminum

    pp. 368-374

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    DOI:10.2320/matertrans.MT-M2019237

    The aim of this study was to clarify the structural evolution of porous aluminum during brazing with an Al–Si-based alloy brazing sheet. High-quality metallurgical bonds between porous aluminum and solid aluminum sheets are required for effective thermal management applications. The authors have proposed a new brazing method using an Al–Si-based alloy brazing sheet that can control the liquid metal for the bonding in smaller amounts. Although the metallurgical bond was realized without filling the pores, the new brazing method influenced the cell structure because of liquid migration. The liquid migration and cell structure evolution in sintered dense aluminum and porous aluminum were experimentally investigated as a function of brazing time. The experimental results indicated that the liquid migration distance in both the dense and porous aluminum obeyed a parabolic law. The velocity of liquid migration in the porous aluminum was higher than that in the sintered dense aluminum, attributed to the high cell wall surface area in the porous aluminum. During liquid migration, the liquid filled former powder boundaries before and after grain coarsening occurred. Therefore, grain coarsening was attributed to liquid film migration, which directly affected evolution of the cell structure. The grain diameter was linearly related to the porosity, where extrapolation of this relationship showed that the grain diameter was equal to the diameter of the raw aluminum powder when the porosity was equal to the initial porosity.
  • C15–Al2Ca Precipitation in a Mg–Al–Ca Alloy

    pp. 375-380

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    DOI:10.2320/matertrans.MT-M2019291

    The coarsening kinetics of a fine C15–Al2Ca Laves phase with a plate-like morphology precipitated within the primary α-Mg grains were investigated for Mg–5Al–1.5Ca alloy aged at 523 K. The Al2Ca precipitate coarsened as its coherence was retained in the aging time below 300 h, and a quantitative relationship was obtained between precipitate length (l) and aging time (t) as lt0.23. However, the α/C15 coherent interface changed into a semi-coherent interface by introduction of misfit dislocations on the planar surface of the precipitates in the aging time above 300 h, which resulted in the promotion of Al2Ca coarsening. The Al2Ca phase was assumed to precipitate through a nucleation and growth mechanism rather than spinodal decomposition, and its coarsening was explained using the terrace-ledge-kink mechanism. The result shows that the aspect ratio of the Al2Ca precipitates was predominantly determined by the aging temperature, and it decreased at higher aging temperatures. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 282–287.
  • Analysis of Bone Regeneration Based on the Relationship between the Orientations of Collagen and Apatite in Mouse Femur

    pp. 381-386

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    DOI:10.2320/matertrans.MT-M2019341

    In this study, we focused on the preferential orientation of the extracellular matrix (ECM) of bone, since ECM orientation has been shown to significantly affect the mechanical functions of bones. Bone analysis is in most cases based on the premise that the apatite crystallizes on the collagen template such that its c-axis is parallel with the running direction of the collagen fibril. Bone regeneration analysis has also been discussed assuming that the apatite c-axis orientation reflects collagen orientation. To understand the regeneration processes of both collagen and apatite individually, the preferential orientations of apatite and collagen in regenerated bone were simultaneously analyzed using a bone regeneration model of mouse femur with an 0.8-mm drill hole defect. The defects in mouse femur were filled with mineralized bone matrix, which shows an intact mineral density. However, the directions of orientation of the collagen and apatite deviate from the femur longitudinal axis in the regenerated bone. Moreover, electron diffraction analysis revealed that the apatite c-axis aligned along the extended axis of a collagen fibril both in regenerated and intact bones, indicating that the direction of the apatite c-axis is regulated by collagen fibril orientation even in the regenerated bone. In conclusion, the less-oriented apatite crystallite observed in the regenerated bone was shown to be formed due to the less-oriented collagen fibrils.
  • The Effect of Heterogeneous Seed Crystals on Arsenite Removal as Biogenic Scorodite

    pp. 387-395

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    DOI:10.2320/matertrans.M-M2019858

    With the aim to effectively oxidize and remove highly toxic As(III) from acidic metal-refinery wastewaters, the seeding effect of different heterogeneous minerals was investigated on the formation of biogenic scorodite (FeAsO4·2H2O), using the Fe2+/As(III)-oxidizing thermo-acidophilic archaeon Acidianus brierleyi. Heterogeneous hematite-seeds exhibited even greater As-removal efficiency relative to homogeneous scorodite-seeds. While the effect of magnetite-seeds was mostly comparable to scorodite-seeds, feeding goethite or ferrihydrite negatively affected the speed of As precipitation, forming jarosite or jarosite/scorodite mixture, respectively, instead of scorodite. Similarly to those formed on scorodite-seeds (TCLP As leachability; 0.49 mg/L), the final scorodite products formed on hematite-seeds or magnetite-seeds were also highly stable (0.51 mg/L or 0.39 mg/L, respectively), well below the US standard of 5 mg/L. The effectiveness of hematite seeding was also demonstrated in the lower-temperature scorodite crystallization reaction (45°C), where Fe2+-oxidizing moderately-thermophilic acidophilic bacterium Acidimicrobium ferrooxidans was employed, after the complete As(III) oxidation by Thiomonas cuprina. The overall results suggested that the effectiveness of hematite was, at least partly, attributed to its highly-positive surface charge. This effect was retained even when cells attached onto the hematite surface. This made the mineral an effective absorbent for anionic As(V) and SO42−, consequently speeding up the reaction by shortening the steady-state induction period between the two As-removal stages, during the biogenic scorodite crystallization process.
  • Microbial Leaching of Iron from Hematite: Direct or Indirect Elution

    pp. 396-401

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    DOI:10.2320/matertrans.M-M2019860

    Exiguobacterium oxidotolerans was found to be effective for dissolving Fe2+ from hematite via reduction under alkaline conditions. However, the possible mechanism for bacterial reduction of hematite in seawater is still unclear. The present work has investigated the reductive dissolution of iron by the bacteria in two elution systems, namely direct and indirect elution systems. Greater than 30 mg L−1 of Fe was dissolved and measured in a direct elution system. Fourier transform infrared (FTIR) and field-emission scanning electron microscopy (FE-SEM) revealed the surface oxidation and particle aggregation in our direct elution system. The obtained results suggest that direct interaction of bacterial cells with hematite facilitates iron elution, probably due to electron transfer to hematite via the cell membrane, resulting in reductive elution of hematite.
  • Scorodite Crystal Formation on Hematite (Fe2O3) Surface in Fe(II) Solution Containing As(V)

    pp. 402-411

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    DOI:10.2320/matertrans.M-M2019859

    Scorodite crystal formation on a hematite (Fe2O3) surface in excess Fe(II) solution containing As(V) was observed under various conditions using the direct hematite addition method. Gel-like precursors initially formed and covered the entire hematite surface. Scorodite crystal nuclei then appeared preferentially on the grain boundaries of each hematite crystal, rather than on the flat hematite crystal surface. These grew into faceted crystalline scorodite particles through stepwise structure formation. The effects of solution temperature (50, 70, and 95°C), initial solution pH (0.6, 0.9, and 1.6), initial Fe(II) concentration (0, 25, and 55.9 g/L), and initial As concentration (25 and 50 g/L) on gel-like precursor and scorodite crystal formation were comprehensively investigated. The reaction temperature only affected the scorodite crystal formation rate and not the crystal shape in the studied range of 50–95°C. Octahedral faceted scorodite was obtained at all temperatures studied. The solution pH strongly affected scorodite crystal formation, with a higher pH favoring scorodite formation in the studied range of pH 0.6–1.6. Scorodite crystals were not obtained at pH 0.6 because of the lower AsO43− concentration in solution. Octahedral faceted scorodite crystals were also obtained at a lower Fe(II) concentration (25 g/L), but the gel-like precursor and scorodite crystals were not obtained in the absence of Fe(II). The As(V) concentration in solution affected the overall scorodite formation rate. Imperfect octahedral-shaped scorodite crystals with larger diameters were observed at lower As(V) concentration (25 g/L), which was attributed to the lower AsO43− concentration. This study provides important information for As treatment through scorodite crystal formation using the hematite addition method.
  • Tailored Mechanical and Conductive Properties of Continuous Rheo-Extruded Al–Sc–Zr Alloy Conductors by Thermomechanical Treatment

    pp. 412-415

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    DOI:10.2320/matertrans.MT-M2019297

    Al–0.12Sc–0.04Zr (mass%) alloy conductive wires were designed and produced by continuous rheo-extrusion process. The effects of cold drawing process on microstructure, mechanical and conductive properties of the wires after aging treatment at different temperature were studied. Results showed that after cold drawing process, secondary Al3(Sc–Zr) phase homogeneously precipitated and became smaller in size. The tensile strength increased from 115 MPa to 217 MPa due to the homogeneous distribution of secondary Al3(Sc–Zr) phase in smaller size. Cold drawing process did not result in severe loss of conductive property.
  • Static Recrystallization Behavior and Mechanical Properties of Heterogeneous Nanostructured Duplex Phase Stainless Steel

    pp. 416-419

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    DOI:10.2320/matertrans.MT-M2019302

    Static recrystallization (SRX) behavior and tensile property of a 92% cold-rolled duplex phase stainless steel were investigated. Lamellae structure, in which austenite (γ) and ferrite (α) phases were complicatedly stacked, was developed by heavy cold rolling. The lamellae gradually changed to equi-axed fine grains during annealing at 1023 K and fully SRXed after 1.44 × 104 s (4 h). Because of precipitation and its impediment of grain-boundary migration, grain coarsening was strongly suppressed even by prolonged annealing to 2.59 × 105 s (72 h). While volume fraction of γ phase was about 30% before annealing, it drastically increased up to 90%. The transformed phase from γ to α by heavy cold rolling re-transformed to stable equilibrium γ at 1023 K and occurrence of SRX. No softening took place even with the occurrence of SRX and exhibited quite high HV hardness of 5.9 GPa due to precipitation, which effectively suppressed grain growth. Tensile strength was barely changed before and after annealing and stayed about 1.5 GPa on average, while ductility rapidly decreased.
  • Editor's Announcement

    pp. 420-420

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    DOI:10.2320/matertrans.EAM2019704

  • Editor's Announcement

    pp. 421-421

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    DOI:10.2320/matertrans.EAM2019705

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