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

MATERIALS TRANSACTIONS Vol. 64 (2023), No. 2

  • Characterization of the Incorporation and Adsorption of Arsenate and Phosphate Ions into Iron Oxides in Aqueous Solutions

    pp. 307-317

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    DOI:10.2320/matertrans.MT-M2022104

    This article provides an overview of the incorporation and adsorption of arsenate and phosphate into iron oxides formed in aqueous solutions. Although arsenic (As) and phosphorus (P) and belong to the same group in the periodic table, As is usually toxic, whereas P is a biological element. Arsenate and phosphate ions can be incorporated into iron oxides through different routes, depending on the solution conditions. In aqueous solutions, the chemical state of Fe in iron oxides is FeII (ferrous) or FeIII (ferric), that of As is AsIII (arsenite) and AsV (arsenate), and that of phosphorus is PV (phosphate). The composition and structure of iron oxides, including ferric oxyhydroxides and hydroxides formed in aqueous solutions, are affected by solution conditions such as the electrochemical potential, pH, temperature, and the chemical state and composition of the relevant elements. Moreover, arsenate and phosphate ions are usually adsorbed on the surface of iron oxides in aqueous solutions, but the incorporation and adsorption of arsenate and phosphate ions in iron oxides cannot be easily explained using simple thermodynamic models. This is because these characteristics are accompanied by different stages of coprecipitation, incongruent dissolution of multicomponent iron oxides, and so on. Since hydrated iron-oxide particles are often very fine and poorly crystallized, they are difficult to filter. However, it has been shown that coarse polyhedral particles of hydrated iron oxide can be synthesized by oxidizing FeII ions. In addition, the coarse particles of hydrated iron oxide are transformed into agglomerates of fine FeIII oxides with a coarse outer shell by alkaline treatment, and these coarse porous iron-oxide particles exhibit good anion-adsorption capacity in aqueous solutions. The formation mechanisms of these different iron-oxide particles are discussed based on the results of the incorporation and adsorption of arsenate and phosphate ions in iron oxides in aqueous solutions.
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  • PREFACE

    pp. 318-318

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    DOI:10.2320/matertrans.MPR2023902

  • Role and Potential of Aluminium and Its Alloys for a Zero-Carbon Society

    pp. 319-333

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    DOI:10.2320/matertrans.MT-LA2022009

    The environmental impact of aluminium can be greatly reduced through recycling. However, recycled aluminium ingots are currently used for the fabrication of lower-grade materials (i.e., cascade recycling) and cannot be used for the production of high-purity and high-grade wrought materials, for which demand is expected to increase in the future. Researching and developing upgrade recycling methods for aluminium is therefore urgently needed, where recycled ingots with a lower environmental impact are used for the fabrication of wrought materials. This approach will substantially reduce greenhouse gas (GHG) emissions and ultimately promote a sophisticated resource-recycling society in which aluminium resources can be almost completely recycled.
  • Design and Applications of Additively Manufactured Porous Aluminum Alloys

    pp. 334-340

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    DOI:10.2320/matertrans.MT-LA2022051

    Additive manufacturing (AM) technology enables to manufacture many types of porous aluminum alloys. Present study focusses on AM porous Al–4.8Mg–0.7Sc alloys manufactured through laser powder bed fusion process. Eight types of ordered cell structures are designed by 3D-Voronoi division. AM porous Al–4.8Mg–0.7Sc alloys consisting of ordered cells show anisotropic compression behavior. Oscillated stress-strain curves are due to the heterogeneous deformation of cell struts. Post-annealed AM porous Al–4.8Mg–0.7Sc alloy shows excellent mechanical properties compared to post-annealed AM porous Al–10Si–0.3Mg alloy. This is because of solid solution hardening in Al–4.8Mg–0.7Sc alloy.
  • History of the Development of Extra Super Duralumin and Future Research Issues of Al–Zn–Mg Alloys

    pp. 341-351

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    DOI:10.2320/matertrans.MT-LA2022019

    Almost 85 years have passed since the development of Al–Zn–Mg–Cu Extra Super Duralumin in Japan in 1936. This alloy was developed by Dr. Igarashi in response to the Japanese Navy’s order to Sumitomo to develop an alloy with tensile strength of 588 MPa (60 kg/mm2) or higher, exceeding Alcoa’s super duralumin 24S. This alloy was then adopted for use in the Zero fighter. Based on this alloy, Alcoa’s 75S was developed in 1943. This paper describes the history of the development of Extra Super Duralumin, starting with Duralumin. The paper also discusses the issues that are considered important for the future development of the aluminum alloys based on the historical review and our study. One is the relationship between quench sensitivity and age-hardening properties of Al–Zn–Mg alloys and the second is the occurrence of shear fracture in the Al–Zn–Mg–(Cu)–Zr alloys. This is the points to be noted in the development of high strength and high toughness Al–Zn–Mg–Cu alloys.
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  • Intermetallic Phase Layers in Cold Metal Transfer Aluminium-Steel Welds with an Al–Si–Mn Filler Alloy

    pp. 352-359

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    DOI:10.2320/matertrans.MT-LA2022046

    In welding of aluminium (Al) alloys to steels, a major challenge is excessive growth of brittle intermetallic phases along the bonded Al-steel interfaces. The formation and growth of these phases are influenced by the heat input and the alloying elements present. This work focuses on the phases formed between a low alloyed steel and an Al–Si–Mn alloy that was used as the filler wire in a cold metal transfer joint. During lap shear testing of the joint, fracture ran through the melted Al, and the joint reached a strength of 174 ± 21 MPa. Scanning and transmission electron microscopy showed that the formed ∼2.5 µm thick intermetallic phase layer consisted of polyhedral αc-Al–(Fe,Mn)–Si, elongated or rounded θ-Fe4Al13 and near equiaxed η-Fe2Al5 grains. Electron backscatter diffraction was used to study the crystal orientations of the formed phases. Altogether this work aims to contribute to better understanding of the formation and growth of intermetallic phases in Al-steel welds where the Al alloy contains Si and Mn.
  • The Integration of Neural Network and High Throughput Multi-Scale Simulation for Establishing a Digital Twin for Aluminium Billet DC-Casting

    pp. 360-365

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    DOI:10.2320/matertrans.MT-LA2022038

    A digital twin for Aluminium billet DC-casting, a digital replica of the physical casting process, creates a living simulation platform that can analyse, update, and change the process to achieve the multi-objectives process optimization. In this work, we assess the possibility of integrating high throughput micro-macro scale computation, SQL database and an artificial neural network (ANN) to establish an analytical twin for the prediction of a typical Direct Chill casting defect of Al alloys, i.e., hot tearing. The high throughput computation consists of solidification path computation at the microscopic scale (dendrite arm scale with software Alstruc) and heat transfer, fluid flow and stress/strain computation at the macroscopic scale (the scale of billet/ingot dimensions with software Alsim). The two-scale computations are coupled via sharing with Alsim the compositional dependent solidification path (Solid fraction-Temperature curve), thermo-physical properties such as densities, thermal conductivities calculated by Alstruc. Then Alsim calculates all the field variables including thermal stress, volumetric strain, and predicts the locations of the most vulnerable position and its hot tearing susceptibility. We demonstrate that the proposed framework can efficiently predict sump depth and hot-tearing tendency in the center of billets for a range of industrial AA6xxx alloy composition, casting parameters including casting speed and casting temperature. The data generated by the multi-scale computation are used to build a SQL database for training and testing the neural network. The utilities of the trained neural network and established SQL database are discussed for their application to optimize DC casting recipes of 6xxx extrusion billets. Our conclusion is that the proposed high throughput multi-scale simulation, SQLite database and ANN parameterization are three essential pillars supporting the establishment of a digital casting twin, and such a twin can provide a quick screening and selection/adjustment of process parameters before casting or during casting to avoid hot-tears.
  • Effect of Casting Conditions on Surface Defect and Segregation of Strips Cast by a High-Speed Twin-Roll Caster

    pp. 366-372

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    DOI:10.2320/matertrans.MT-LA2022012

    In this study, the effects of the roll load and superheating on the appearance of surface defects in Al–Mg and Al–Si alloy strips cast using a high-speed twin-roll caster were investigated. The band zone that existed in the center of the thickness direction was investigated. The alloy compositions were Al–4.8%Mg and Al–Si with Si contents of 1, 2, 3 and 11%. The diameter and width of the copper roll in the twin-roll caster were 300 and 50 mm, respectively. The superheating temperature of the molten metal was 5 and 50°C, and the roll load was varied from 2 to 88 N/mm. A roll speed of 30 m/min was utilized. The existence of surface cracks was investigated by penetrant inspection and bending test. The amount of surface cracking in the Al–Mg alloy was affected by the roll load, and the number of surface cracks decreased with decreasing roll load. Surface cracks occurred more easily in the Al–4.8%Mg alloy than in the Al–Si alloys. The degree of cracking could not be reduced by cold-rolling. In the Al–Si alloys, the ripple marks were affected by the Si content, degree of superheating of the molten metal and the roll load. In the Al–3%Si alloy, ripple marks were produced, and worsened as the roll load and the superheating of the molten metal were increased. A specimen for observation of the microstructure near the roll bite was obtained by performing a roll-stop during casting, and observed using Weck’s reagent. A band zone was found to exist. The band zone in Al–Si consisted of globular crystals, and that in Al–Mg consisted of equiaxed dendrites and Mg-rich areas.
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    3. Monitoring of Laser Quenching of the Carbon Steel by Acoustic Emission MATERIALS TRANSACTIONS Vol.64(2023), No.2
  • Effect of Nozzle Shape on Periodic Surface Patterns of Al–3 mass% Si Alloy Strips Fabricated by Vertical-Type High-Speed Twin-Roll Casting

    pp. 373-378

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    DOI:10.2320/matertrans.MT-LA2022014

    Shiny and un-shiny periodic patterns are formed on the cast strip surface of aluminum alloys fabricated by using vertical-type high-speed twin-roll casting. The periodic surface patterns reduce the ductility of the rolled sheets produced from the cast strip, and thus should be suppressed. The surface patterns are caused by the vibration of the molten metal in the gap at the contact point between the nozzle tip and roll surface. In the present study, three types of nozzles (normal, release agent, and bent tip nozzle) were prepared. The effect of the nozzle shape on the surface patterns of Al–3 mass% Si alloy containing 1 mass% Fe, 0.5 mass% Mg, and 0.8 mass% Cu cast strips was investigated. The normal nozzle produced a periodic surface pattern and Si segregation in the un-shiny region was observed. Cross-sectional observation showed a difference in cooling rate between the shiny and un-shiny regions caused by the vibration of the molten metal near the nozzle tip. The release agent nozzle suppressed the periodic surface pattern slightly and Si segregation remained. The bent tip nozzle produced a strip surface where the shiny and un-shiny regions were mixed instead of a periodic surface pattern, and Si segregation was not observed. Because the gap near the nozzle tip was small, the vibration of the molten metal was strongly suppressed.
  • Effect of Homogenization Heat Treatment on Elongation Anisotropy in Cold-Rolled and Annealed Al–Si Alloy Sheets Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strips

    pp. 379-384

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    DOI:10.2320/matertrans.MT-LA2022017

    Vertical-type high-speed twin-roll casting (VT-HSTRC), which is characterized by a high production rate and cooling rate, is a promising method for upgrade recycling of aluminum cast alloy scrap to wrought alloys in the near future. To produce wrought alloy sheets from cast alloy scrap, the strips must be isotropic to achieve good formability. However, in cold-rolled and annealed Al–7% Si alloy and A356 alloy sheets fabricated from the HSTRC strips, average elongation is much greater in the rolling direction than in the transverse direction. This elongation anisotropy results from both the morphology and the alignment of eutectic Si particles. In the present study, the effect of homogenization heat treatment on the microstructure and elongation was investigated. Al–7% Si and Al–11% Si alloy strips were fabricated by HSTRC and were homogenized by heat treatment at 540°C for 10 h and 500°C for 10 h, respectively. The strips were cold rolled at a reduction rate of 50% and annealed. The eutectic Si particles were spheroidized and coarsened by the homogenization heat treatment, and they were uniformly dispersed after cold rolling. There was no significant difference in elongation between the rolling and transverse directions in the Al–7% Si and Al–11% Si alloys. These results show that the homogenization heat treatment of the strips reduced the elongation anisotropy.
  • Thermodynamics of Formation of Al3Fe Inter-Metallic Compound for Fe Removal from Molten Al–Mg Alloy

    pp. 385-391

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    DOI:10.2320/matertrans.MT-LA2022025

    Recycling Al scraps is extremely important to achieve carbon neutrality. However, almost all impurity elements cannot be easily removed by oxidation and evaporation once dissolved in molten Al alloy. Therefore, it is necessary to develop an impurity removal process in molten Al. Iron is one of the impurity elements in Al, which easily forms intermetallic compounds with Al. On the contrary, Fe is immiscible with Mg in the liquid state. These facts suggest that the repulsive interaction between Fe and Mg in molten Al alloy enhances the precipitation of such intermetallic compounds as Al3Fe. This study proposed the Fe removal method from molten Al alloy by the precipitation of the Al3Fe inter-metallic compound by adding Mg. Molten Al–Mg alloy was equilibrated with Al3Fe, and the Fe content of molten Al–Mg alloy was investigated. Fe content decreased with increasing Mg content, and this method was proved to be adequate for removing Fe from molten Al–Mg alloy. The standard Gibbs energy change for the precipitation of Al3Fe at 873 K and the activity coefficient of Fe in molten Al–Mg alloy as a function of Mg content and temperature have been derived from the experimental results.[ This part of text is omitted ]Using the derived values, the removal limit of Fe in molten Al–Mg alloy in the present method was discussed. Fe content can be decreased at higher Mg content and lower temperature, and the lowering limit of Fe is 0.0029 mass percent at the eutectic point of Al–Mg alloy.
  • Thermodynamics of Formation of Al6Mn Inter-Metallic Compound for Mn Removal from Molten Al–Mg Alloy

    pp. 392-397

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    DOI:10.2320/matertrans.MT-LA2022027

    To reduce CO2 emission, recycling Al scrap into wrought alloy is desired. However, impurity elements are inevitably contained in the Al scrap recovered from the society, and most of them are difficult to be removed by the current pyro-metallurgical processes. Mn is one of the major alloying elements of Al alloys and steels and is contained in Al scraps. Therefore, a removal method of Mn from Al is necessary. Mn easily forms an inter-metallic compound with Al; on the other hand, it is immiscible with Mg in the liquid state, which suggests that the repulsive interaction between Mg and Mn in molten Al enhances the precipitation of intermetallic compounds such as Al6Mn. This study proposed Mn removal from molten Al–Mg alloy through precipitation of Al6Mn inter-metallic compound. Molten Al–Mg alloy was equilibrated with Al6Mn, and the reducing limit of Mn concentration was thermodynamically discussed. Mn concentration becomes lower at higher Mg content of molten Al and lower temperature. The activity coefficient of Mn in molten Al–Mg alloy was increased with the addition of Mg, and the following equation was obtained as a function of temperature and molar fraction of Mg:[ This part of text is omitted ]It was found that Al6Mn will precipitate due to the repulsive interaction of Mn and Mg when the Mg content of Al is increased. The thermodynamic analysis showed the possibility of reducing the Mn content of Al to 0.0030 mass% at 733 K and 34 mass%Mg by the present removal process.
  • Phase Composition and Microstructure of High Strength AA6xxx Aluminium Alloys with Nickel Additions

    pp. 398-405

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    DOI:10.2320/matertrans.MT-LA2022047

    High strength AA6XXX series aluminium alloys have become the material of choice for body structures of lightweight automotive vehicles. The properties can be tailored through thermomechanical processing and strict adherence to impurity level. Although some nickel-containing AA6XXX Al alloys were introduced previously, the effect of Ni addition is still out of significant attention. Presently, an AlMgSiCu alloys with 0.1, 0.2 and 0.3 wt.% Ni addition was studied along with thermodynamic analysis. The predicted intermetallic phases in the as-cast base alloy were Al15(Fe, Mn)3Si2, Al5FeSi, Mg2Si and Q phases and also Al3Ni and Al3(CuNi)2 in the as-cast Ni-added alloys. The Al3(CuNi)2 phase with irregular shape was found in all as-cast Ni-added alloys and Al9FeNi phase was also found around dendritic cells in the as-cast alloy containing 0.3 wt.% Ni. After homogenization the Al3(CuNi)2 phase became much leaner in Cu content showing a possible phase transformation occurred. It was found that even at the low Ni content the excess Ni atoms could interact with neighbouring Fe atoms upon heat treatment to form Al9FeNi phase and the Cu atoms were released into the matrix. Thus, the Ni addition could not only lead to the loss of Cu atoms available for subsequent age hardening but also reduce Si entrapment associated with Fe-rich intermetallics. Moreover, improved circularity of intermetallics was found due to appearance of the Al9FeNi phase that could potentially mitigate the detrimental effects of Fe.
  • Evolution of Microstructure and Elevated-Temperature Properties during Thermal Exposure with Transition Elements (V, Zr and Mo) in Al–Si 356 Type Cast Alloys

    pp. 406-413

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    DOI:10.2320/matertrans.MT-LA2022003

    Precipitation-hardened Al–Si 356 cast alloys are widely used in fabricating the automotive engine parts due to their excellent castability and strength/weight ratio. However, with the increasing demand of the engine service temperature at 250–350°C, the mechanical properties of Al–Si 356 alloys greatly deteriorate owing to the rapid coarsening of precipitates at elevated temperatures. In this study, individual and combined transition elements (V, Zr and Mo) were introduced into Al–Si 356 type cast alloys to form thermally stable dispersoids, and their influences on the strength and creep resistance at 300°C was investigated. During thermal exposure (300°C/100 h) after T7 treatment, the nano-scale β′ and Q′ precipitated during aging were transformed to the equilibrium coarse β and Q phases, loosing their contribution to mechanical strength. However, different types of dispersoids formed during the solution treatment were stable during the thermal exposure, resulting in the different but promising contribution to the elevated-temperature properties. The combined additions of V, Zr and Mo showed the highest mechanical and second highest creep properties at 300°C, which possess 22% and 100% improvement on the strength and creep resistance compared to the base alloy.
  • Punchless Piecing Process of Aluminum Tube Wall by Impulsive Water Pressure

    pp. 414-420

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    DOI:10.2320/matertrans.MT-LA2022007

    Piecing of the aluminum alloy A6063-T6 tube was attempted with the help of impulsive water pressure in the tube caused by the impact of drop-hammer. The availability of this approach was investigated. Shapes of the die hole were circular, square and long rectangle. The outer diameter was 40 mm, and the wall thickness was 1 mm. The maximum impact velocity was 10 m·s−1. The pressure at the occurrence of crack was almost same for different impact velocity of the drop-hammer. However, if the number of holes was increased from 2 to 4, all the holes could not be pierced. The circular hole with a diameter of 10 mm and the square hole with an edge length of 10 mm were successfully created. When the size was doubled, the material did not partially separate. The water pressure rapidly increased and crack occurs at around 1 ms depending on the impact velocity. The effect of positive strain-rate sensitivity of the material was observed in comparison with the quasistatic experimental result. Profile of the hole edge was tapered. Burr formation was not observed, which is a significant advantage of this process.
  • Influence of Initial Extruded Microstructures of Al–4.4Zn–1.4Mg Alloy Flat Bar on VDA Bendability

    pp. 421-428

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    DOI:10.2320/matertrans.MT-LA2022015

    The bendability of extruded Al–4.4Zn–1.4Mg (mass%) alloy flat bars with 1.4 mm thickness having two types of microstructures which are fibrous and recrystallized is evaluated by a Verband der Automobilindustrie (VDA) bending test without pre-strain. The recrystallized specimen has better bendability than the fibrous one. The texture condition nearby the surfaces affects the VDA bendability the most. However, the microvoid formations also contribute in faster cracking phenomena during the load drop of the VDA bending test.
  • Effect of Short-Time Heating after ECAP Processing on Mechanical Properties of 6061 Aluminum Alloy

    pp. 429-435

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    DOI:10.2320/matertrans.MT-LA2022028

    This study aimed to improve the strength and ductility of Al–Mg–Si alloys by combining severe plastic deformation and heat treatment. A 6061 aluminum alloy subjected to equal-channel angular pressing (ECAP) after solution treatment was heated from 100°C to 400°C for 10 s. Results of electron backscatter diffraction analysis indicated that the fine grains obtained via ECAP processing in the present experiment remained after a short heating duration of 10 s at 400°C. Results from the hardness test suggest that the alloy starts to recover after a short-time heating at approximately 200°C, and that its strengthening phase precipitates at approximately 250°C. In the case of artificial aging without short-time heating after ECAP processing decreased the strength of the alloy, possibly owing to the effect of recovery (reduction in dislocation density) during the artificial aging. The 0.2% proof stress and ultimate tensile strength of specimens short-time heated at 200°C after ECAP processing increased by 18 and 15 MPa, respectively, owing to the subsequent artificial aging. We assumed that hardening due to precipitation strengthening was caused by the artificial aging, whereas the reduction in dislocation density was due to the short-time heating. Specimens short-time heated at 300°C after ECAP showed a significant decrease in strength after artificial aging. Although recovery occurred after ECAP processing followed by short-time heating, the precipitation state that occurred simultaneously contributed to the strength and ductility of the alloy in the subsequent artificial aging.
  • Production of Ultrafine-Grained Aluminum Alloys in Upsized Sheets Using Process of Incremental Feeding High-Pressure Sliding (IF-HPS)

    pp. 436-442

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    DOI:10.2320/matertrans.MT-LA2022032

    This study introduces a process of severe plastic deformation (SPD) called incremental feeding high-pressure sliding (IF-HPS) where significant grain refinement is possible in an enlarged sheet area. The IF-HPS process is applied to Al alloys such as A1050, A3105, A5052 and A5182. The grain sizes were refined to the submicrometer ranges and the tensile strength increased to almost twice as much as the annealed states. The conditions for the IF-HPS process are optimized so that the tensile strength remains high without initiation of cracks. The process conditions are also investigated to achieve homogeneous development of the tensile properties throughout the processed sheets. It is demonstrated that the IF-HPS process is useful to extend the SPD-processed area without increasing the machine capacity while maintaining enhanced mechanical properties.
  • Effects of Sc and Zr Addition on the Mechanical Properties of 7000 Series Aluminum Alloys

    pp. 443-447

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    DOI:10.2320/matertrans.MT-LA2022041

    Scandium addition to aluminum alloys has been evaluated at various research institutions, and it is known that the Al3Sc precipitates effectively increase their strengths. In this study, the effect of Sc addition on the strengths of two types of 7000 series aluminum alloys was investigated. As a result, the strength increased by the Sc addition to both types of alloys, but the increased amounts were limited to 10–40 MPa. It was considered that because the strengthening effect by the η′ phase was sufficiently high, the precipitation strengthening by the dispersion of Al3(Sc1−xZrx) particles was relatively low in these alloys.
  • Mechanical Properties and Microstructures of Highly Fe-Containing Al–Mg–Si Alloys Processed by Severe Plastic Deformation under High Pressure

    pp. 448-457

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    DOI:10.2320/matertrans.MT-LA2022054

    In this study, A6022-based Al–Mg–Si alloys with three additional Fe contents are processed by high-pressure torsion (HPT) and high-pressure sliding (HPS). Both processes yield a similar tensile strength exceeding 400 MPa. Fe intermetallics were finely and homogeneously fragmented to an average size of ∼2 µm by the HPT process. The high tensile strength is attributed to such a fine and homogeneous fragmentation of Fe intermetallics. It is also demonstrated that the finely fragmented Fe intermetallics play an important role to maintain finer grain size even after solution treatment.
  • Soft X-ray XAFS Analysis of Cluster Formation Process during 353 K Aging in Al–Mg–Si Alloys

    pp. 458-466

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    DOI:10.2320/matertrans.MT-LA2022004

    This study investigated the cluster formation process in the early stages of 353 K aging in Al–1.04 mass%Si–0.55 mass%Mg alloys by means of soft X-ray absorption fine structure (XAFS) measurements and first-principles calculations. XAFS at the Si-K and Mg-K edges was carried out at the BL27SU beamline at SPring-8. To observe the structural changes in detail, an XAFS apparatus able to hold the sample at 353 K in a vacuum chamber and cool it rapidly to suppress the progress of clustering was developed. Density functional theory (DFT) calculations were used to simulate the Si-K and Mg-K edge spectra for various cluster models. Based on the results, the cluster formation process in the early stages of aging at 353 K was qualitatively clarified. Initially, Mg–Va (Va: vacancy) pairs and Si–Va pairs were formed, then 2-MgVa clusters formed by bonding between Mg–Va pairs along (100); subsequently, L10 clusters were formed by Mg atoms ordered along (100), and then SiVa-py clusters with Va adjacent to the first-nearest-neighbor atom of Si atoms and Si-py without adjacent Va were formed, in which Mg–Va pairs and Si–Va pairs were individually united, respectively. Monolayer and multilayer structures then developed as aging proceeded, involving Mg and Si atoms ordered along (100), in which Mg and Si atoms were bonded.
  • Modelling Age Hardening of Aluminium Alloys with Consideration of GP Zones or Clusters

    pp. 467-472

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    DOI:10.2320/matertrans.MT-LA2022037

    The work reported here follows the theme of our previous research presented at the ICAA16 and ICAA17 conferences, where material models have been developed to predict the microstructure evolution and precipitation hardening of aluminium alloys during cooling and ageing. The models have two important features: one is the consideration of quenched-in vacancies and their effect on precipitation kinetics, which was discussed in past conferences; the other is the formation of GP zones or clusters and their transition to other hardening phases during ageing, which is the focus of this paper. GP zones or clusters are known to serve as precursor phases for various hardening phases. Depending on the ageing temperature being above or below the solvus temperature of the precursor phase, precipitates can either form on their own from the matrix (heterogeneous or HET type) or form on existing GP zones or clusters (homogeneous or HOM type). In the latter case, GP zones or clusters are allowed to form first from the matrix, which will later transform to their metastable counterparts. Both HET and HOM types of precipitates are considered in the current strengthening model for predicting age hardening curves for aluminium alloys. The age hardening model has been validated over a wide range of commercial aluminium alloys and demonstrated good agreement with experimental data in the form of age hardening curve and T5/T6 peak position and strength.
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  • Self-Healing Coatings with Double-Layered Structure for Corrosion Protection of Aluminum Alloys

    pp. 473-478

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    DOI:10.2320/matertrans.MT-LA2022050

    Surface treatments of Al alloys are generally performed to protect them from corrosion before they are used as many kinds of industrial product. However, corrosion protection abilities of the surface layers formed by the surface treatment are lost by unexpected physical damages because the metal substrate is exposed to corrosive environments at the damaged area. From the viewpoint described above, surface films with self-healing properties should be developed to keep corrosion protection abilities high for long periods without any maintenance. In this study, double-layered films with self-healing abilities were formed on Al alloys by the combination of anodizing and organic coating. Corrosion tests in Cl/Cu2+ solutions after physical damaging were carried out to compare corrosion protection abilities of the double-layered films formed by three processes: formation of film including 1) no healing agent in the outer and inner layers, 2) healing agents only in the inner layer, and 3) healing agents both in the outer and inner layers. The double-layered film including healing agents in both layers showed much higher self-healing ability than other coatings.
  • Interfacial Microstructure and Strength of Magnetic Pulse Welded A5052 Aluminum Alloy/SPCC Steel Lap Joint

    pp. 479-484

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    DOI:10.2320/matertrans.MT-LA2022018

    A5052 aluminum alloy and SPCC steel plates were welded using magnetic pulse welding, and interfacial microstructure and strength of the lap joint were examined. The A5052 aluminum alloy and the SPCC steel plates were used for a flyer plate and a parent plate, respectively. Charging energy stored in capacitor and gap between the A5052 aluminum alloy and the SPCC steel plates were changed. Microstructure was examined by using an optical microscope, a scanning electron microscope and a scanning transmission electron microscope. Tensile-shear test was used for evaluating the strength of the joint. The magnetic pulse welding of A5052 aluminum alloy and SPCC steel was achieved at the charging energy above 6.0 kJ and at the gap between the plates above 1.0 mm. The range of charging energy in which the strong welding is accomplished was different at each gap and the range increased with decreasing the gap. The lap joint was not fractured at the welding interface by the tensile-shear test whereas the fracture occurred at a part of the aluminum base metal. The welding interface exhibited characteristic wavy morphology. An intermediate layer was produced along the wavy interface. Scanning transmission electron microscope observation revealed that the intermediate layer is composed of fine Al–Mg grains and dispersed dendritic Al–Fe intermetallic compound particles.
  • Appraising Tool Wear during Secondary Heating Assisted Dissimilar Friction Stir Welding between 6061 and 7075 Aluminium Alloys

    pp. 485-491

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    DOI:10.2320/matertrans.MT-LA2022034

    The tool pin profile damage during successive passes in friction stir welding (FSW) of dissimilar aluminium alloys AA6061-T6 and AA7075-T651 is recorded during the present investigation. A right-hand threaded with three intermittent flat faces tool pin at 900 rpm tool rotation and 98 mm/min of weld speed without and with the application of secondary heating (using butane gas torch) is used for joint fabrication. Two separate tools are used to obtain weld length of total 1 metre each without and with secondary heating. Tool profile damage is progressively monitored using scanning electron microscopy along with measuring tensile strength of the joints obtained. The leading edge of the threaded profile (at the end of flat face) distorts with mechanical damage and chipping while the incident material is being plasticized and pressurized by flat region. Secondary heating helps in eased material flow by material softening leading to load reduction and thereby tool wear. The tools experienced slight bending, tearing near shoulder. For both the tools certain amount of wear is being noticed however joint strength is retained without significant adverse effect even after completion of welding for a meter of total weld length.
  • Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast Al–Fe Binary Alloy

    pp. 492-499

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    DOI:10.2320/matertrans.MT-LA2022010

    In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast Al–Fe alloys, we have fabricated various Al–Fe-based alloys with compositions of Al–1%Fe, Al–1%Fe–1%Mn, Al–1%Fe–1%Cu, and Al–1%Fe–1%Cu–1%Mn (mol%) solidified at different cooling rates (0.3 K·s−1 and 145 K·s−1). In the Al–1%Fe binary alloy, the coarsened θ-Al13Fe4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s−1), whereas the cast sample (145 K·s−1) exhibited several elongated α phases surrounded by fine α/Al6Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al–1%Fe–1%Cu alloy, whereas the Al23CuFe4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al–1%Fe–1%Mn alloy, the Al6(Fe, Mn) phase was formed regardless of the cooling rate. Finer α/Al6(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al–1%Fe–1%Cu–1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al–1%Fe–1%Cu–1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast Al–Fe alloys.
  • In-Line Hot Rolling of Al–Mg Strip Casts Using Unequal-Diameter Twin-Roll Caster

    pp. 500-505

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    DOI:10.2320/matertrans.MT-LA2022016

    A model experiment for in-line hot rolling was proposed, and its effectiveness in reducing surface cracking and improving the mechanical properties of cast strips of AC7A Al–Mg alloy was investigated. The strips were cast using an unequal-diameter twin-roll caster at 60 m/min. The strips had a width of 100 mm, and were immediately cut to a length of 200 mm and hot rolled at temperatures of 300, 350, 400, 450 and 500°C. The temperature of the strip surface was measured using a K-type thermocouple. The center area in the width direction of the strips was hot rolled. The thickness of the as-cast strips was 2 mm, and the width of the rolled region was 20 mm. The roll diameter was 70 mm, and the rolling speed was 15 m/min. The thickness reduction caused by hot rolling ranged from 19 to 42%. Surface cracking was reduced by the in-line hot rolling process. The hot-rolled strips were cold rolled down to a thickness of 0.5 mm and then annealed, and tensile tests were conducted. The in-line hot rolling process induced shear deformation of the microstructure. The most appropriate conditions for in-line hot rolling of AC7A were a thickness reduction of 27% and a temperature of 350°C, judging from the tensile strength and elongation results.
  • Effects of Strain Rate on Stress-Strain Curves in 2024 Aluminum Alloy After Solution Heat Treatment

    pp. 506-513

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    DOI:10.2320/matertrans.MT-LA2022020

    Strain rate sensitivity of effective stress and fracture strain of aluminum alloy 2024 were examined considering the period from solution heat treatment. Notched round bar tensile test specimens were employed for obtaining stress-strain curves. Because the necking area of tensile tests is under multiaxial stress, effective stresses of aluminum alloy 2024 were corrected by an optimization method using experimental and simulation results. In the optimization, the experimental and finite element method simulation results of tensile force–true strain of the notched area in the tensile direction were compared. After stress correction, the effective stresses at a true strain of 0.002 were almost the same or showed a small strain rate sensitivity. The effective stresses at a true strain of 0.15 and 0.20 clearly decreased with increasing strain rate and clearly increased at a high strain rate. Fracture strain also decreased clearly with increasing strain rate and clearly increased at a high strain rate.
  • Development of High-Strength Al–Cu–Mg Alloy by Combined Application of High-Pressure Torsion and Aging Treatment

    pp. 514-521

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    DOI:10.2320/matertrans.MT-LA2022049

    Solution treated Al–Cu–Mg alloys with three different compositions were subjected to high-pressure torsion (HPT) for 1 to 50 turns, and then aged at 423 K. By conducting HPT process, the hardness of the three alloys significantly increased after 50 turns, and the average grain sizes were refined to 130–140 nm. After aging treatment, the hardness was further increased to 271 HV, 288 HV and 273 HV in the peak aging condition for the Al–4Cu–1.5Mg, Al–4Cu–3Mg and Al–5Cu–3Mg (in mass%) alloys, respectively. The contribution of several strengthening mechanisms was quantitatively evaluated in terms of grain boundary hardening, dislocation hardening, solid solution hardening and cluster/precipitation hardening. It is shown from the quantitative evaluation that simultaneous strengthening due to grain refinement and nanoscale precipitates is successfully achieved by combined application of HPT process and subsequent aging treatment.
  • Band Effective Masses of Cubic (GeTe)10Sb2Te3 and Its Anisotropy

    pp. 522-526

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    DOI:10.2320/matertrans.MT-E2022002

    Recent progress observed in the band engineering of thermoelectric GeTe-based materials is significantly dependent on the enhancement of its electronic band degeneracy and anisotropic effective mass. Here, we evaluated the anisotropic effective mass of cubic (GeTe)10Sb2Te3 according to first-principles calculation, based on the Korringa-Kohn-Rostoker coherent-potential-approximation method, by comparing it with cubic GeTe. We found alloying with Sb2Te3 decreased the band gap energy and shifted the valence band maxima closer to the Fermi level, indicating straightforward convergence of the multiple Σ, L, and Δ valence bands. The obtained band structure suggested that the Δ band is expected to contribute electronic transport properties at the experimental carrier concentration which was reported previously. The Δ band had unique characteristics with a heavier density-of-states effective mass and higher band anisotropy than the conventional Σ and L bands, possibly leading to enhancement in Seebeck coefficient of (GeTe)10Sb2Te3. The alloying with Sb2Te3 did not significantly change band anisotropies while it increased overall band effective masses of Σ, L, Δ valence bands. Therefore, it is suggested that alloying GeTe with Sb2Te3 enhances its band degeneracy and band effective masses while keeping its anisotropy. This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 18 (2021) 73–78.
  • In Situ Quantitative Measurement of Stress Distribution in Tensile Specimen Using a Detachable Mechanoluminescence Film

    pp. 527-534

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    DOI:10.2320/matertrans.MT-L2022022

    Mechanoluminescence (ML) materials, e.g., SrAl2O4:Eu2+, emit visible light when mechanical stress is applied. It was reported that the intensity of the light is in proportion to the applied von Mises stress. Therefore, acting von Mises stress can be measured from the intensity using a calibration curve. To make the ML measurements easier and more flexible, a detachable ML film has been newly developed. One surface of the base sheet was coated with detachable adhesive, while the other was coated with ∼5 µm thick ML layer. Two ML films were taken from one ML sheet so that the two pieces have identical ML properties. One piece was pasted on an A6061 aluminum alloy test piece (JIS13B, t = 1.0 mm) to obtain a calibration curve by the tensile test. The other piece was pasted on another A6061 test piece with a circular opening at the center to reveal the nonuniform stress distribution. The von Miese stress converted from the ML intensity showed a good agreement with the prediction by finite element analysis (FEA). It is concluded that the detachable ML film is sufficiently accurate and practical means to measure stress distribution in the target material.
  • Disorientation Angles among Grains around Triple Junctions in Deformed and Annealed Aluminum

    pp. 535-539

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    DOI:10.2320/matertrans.MT-M2022133

    Characterization of triple junctions has been performed by considering the disorientation angles among grains around triple junctions. The disorientation angles for each triple junction are called θmin, θmid and θmax, which satisfy θmin ≤ θmid ≤ θmax. Disorientation-angle diagrams that relates θmin and Σθi = θmin + θmid + θmax were constructed for the triple junctions in deformed and annealed aluminum. By comparing the disorientation-angle diagrams before and after grain growth, we found self-similarity of the distribution of the disorientation angles around the triple junctions during the grain growth.
  • Influence of Metal Cations on Corrosion Behavior of Aluminum Alloy 2024-T3 in Model Freshwater

    pp. 540-547

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    DOI:10.2320/matertrans.MT-C2022006

    The influence of metal cations on corrosion behavior of aluminum alloy (AA2024-T3) in model freshwater was examined by immersion experiments, surface analysis, and electrochemical measurements. After long-time immersion, the corrosion rate of AA2024-T3 decreased as the corrosion indicator Y increased, and the corrosion rate of the alloy was reduced by Zn2+. The specimen immersed in Zn2+ containing solution showed less corrosion products which were observed by scanning electron microscopy (SEM). The results of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed that Zn2+ attaches to aluminum alloys and forms protective layers. Electrochemical impedance spectroscopy (EIS) results suggested that Zn2+ reduced the area of defects in the passive film.
  • Study on Extremely-Low-Cycle Fatigue of Fe–15Mn–10Cr–8Ni–4Si Alloy

    pp. 548-554

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    DOI:10.2320/matertrans.MT-Z2022018

    The extremely-low-cycle fatigue behavior and post-fatigue microstructure of an Fe–15Mn–10Cr–8Ni–4Si austenitic alloy were investigated under a strain rate and maximum strain amplitude of 0.5%/s and 10%, respectively, in the axial direction. The results can be summarized as follows. (1) A steel damper made of Fe–15Mn–10Cr–8Ni–4Si alloy can withstand approximately 15 swings back even if the structure is distorted by approximately 10% due to a large earthquake. (2) The εpaNf relationship of the Fe–15Mn–10Cr–8Ni–4Si alloy demonstrated a linear relationship, and it was confirmed that Manson-Coffin rule holds. (3) Even in an extremely-low-cycle fatigue test with a strain rate of 0.5%/s, the test specimen temperature did not exceed 40°C under all test conditions. Therefore, the ε phase was formed in the fatigue test under all test conditions. (4) Various facets and secondary cracks were observed in the fatigue propagation region of the fracture surface. Accordingly, it was inferred that most of the main cracks propagated at the γ/ε interface and the secondary cracks merged. Consequently, the fatigue crack could not propagate linearly, and the generation of the secondary cracks caused a decrease in the displacement at the tip of the crack when the stress was redistributed, thus extending the fatigue life. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 70 (2021) 751–757.
  • Investigating the Phase Diagram of SiO2–CaO–CrOx System to Evaluate Distribution of Platinum between Slag and Molten Copper

    pp. 555-563

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    DOI:10.2320/matertrans.MT-M2022144

    In the hydrometallurgical process used for recycling platinum group metals (PGMs), a residue containing mainly Cr2O3 and a small amount of PGMs is generated. In the present work, a pyrometallurgical process was applied in which PGMs from the residue generated in the hydrometallurgical process are concentrated in a molten copper phase as a collector-metal, and Cr2O3 is separated into a slag phase with SiO2 and CaO as a flux. To reduce the loss of PGMs to the slag, it is necessary to have a homogenous liquid and a lower dissolution of PGMs into the slag. Therefore, the phase diagram of the SiO2–CaO–CrOx system was investigated at 1773 and 1873 K in an oxygen partial pressure pO2 = 10-10 to obtain knowledge of the homogeneous melts. Based on the determined phase diagram, the distribution ratios of Pt as representative PGMs between the liquid SiO2–CaO–Al2O3–CrOx or the liquid SiO2–CaO–CrOx slag and molten copper were measured at 1773 K in pO2 = 10-10. The experimental results showed that CrOx solubility in the slag increased with decreasing slag basicity, B defined as B = (mass%CaO)/(mass%SiO2). Furthermore, the results showed that the distribution of Pt in the slag increased with increasing CrOx concentration in the slag.
  • Study on the Increase of Co Concentration and the Purification of La–Co Cosubstituted M-Type Sr Ferrite by Oxygen Partial Pressure Control

    pp. 564-567

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    DOI:10.2320/matertrans.MT-Y2022008

    The La–Co cosubstituted M-type strontium ferrite attracts attention as a base material for high-performance ferrite magnets. It is known that the uniaxial magnetic anisotropy of the material is enhanced by increasing the amount of Co by heat treatment under high oxygen pressure, but there is a problem in obtaining a pure sample. The present study investigated the conditions to obtain a single phase with increased La–Co substitution by heat treatments under several oxygen pressures. A single phase of M-type ferrite was obtained up to x = 0.35 at pO2 = 1 atm, and up to x = 0.65 at pO2 = 10 atm with the composition formula of Sr1−xLaxFe12−xCoxO19. The magnetic anisotropy is enhanced according to the Co concentration in these samples. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 69 (2022) 288–292.
  • Chemical Conversion Treatment of AA5083 Aluminum Alloy and AISI 1045 Carbon Steel under Galvanically Coupled Condition in Na2MoO4: Effect of pH on Corrosion Resistance

    pp. 568-577

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    DOI:10.2320/matertrans.MT-M2022163

    To ascertain the effect of solution pH of Na2MoO4 chemical conversion treatment for aluminum/steel joints on corrosion resistance, AA5083 aluminum alloy and AISI 1045 carbon steel were immersed in 50 mM Na2MoO4 at pH ranges of 8–12 under galvanically coupled condition. Subsequently, in diluted synthetic seawater, the galvanic corrosion resistance of the AA5083 alloy connected to the AISI 1045 carbon steel was assessed. The number of localized corrosion damages was counted, and AA5083 treated at pH 11 was found to be the better corrosion resistance. The oxygen reduction current on bulk Al6(Fe, Mn) decreased with increasing solution pH of the conversion treatment. The Al6(Fe, Mn) particles on AA5083 were not preferential cathodes, and alkalization through oxygen reduction would not occur when the treatment was performed above pH 9. Auger electron spectroscopy analysis showed that Mo-accumulation, Fe-removal, and film thickening occurred on the particles of AA5083 treated at pH 11. These factors contributed to the suppression of the cathodic activity of the Al6(Fe, Mn) particles, resulting in the improved galvanic corrosion resistance of AA5083.
  • The Roles of the CuO Buffer Layer on the Photocatalytic Activity of the p-Si/p-CuO/n-ZnO Composite Films

    pp. 578-585

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    DOI:10.2320/matertrans.MT-M2022145

    The photocatalytic activity of p-Si/p-CuO buffer layer/n-ZnO nanorod (NR) composite films was studied using experimental and simulation methods. The simulation results indicated that in the p-Si/p-CuO/n-ZnO composite film, the 250 nm CuO buffer layer contributes the highest value of 11% to the total current density compared to the p-Si/n-ZnO composite film. Besides that, the experimental results also indicated that by introducing the p-CuO buffer layer, the pseudo-order rate constant (k) could be enhanced up to 12% compared to the composite film without the p-CuO buffer layer - the p-Si/n-ZnO composite film. Furthermore, the recycle result indicated that the pseudo-order rate constant - k value decreased sharply after the first three reaction cycle times and gradually stabilized at a value of 0.88 s−1 after the fourth reaction cycle. Therefore, it can be concluded that by introducing the 250 nm thick of p-CuO buffer layer in the p-Si/p-CuO/n-ZnO NRs composite film, the photocatalytic activity could be improved up to 12% compared to that without the p-CuO buffer layer. In addition, the composite film, p-Si/p-CuO buffer layer/n-Zno, is a reusable photocatalyst with high photostability.
  • Effective Thermal Conductivity and Thermal Resistance of Electroless Copper Plated Carbon Fiber and Fe Composite

    pp. 586-595

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    DOI:10.2320/matertrans.MT-M2022123

    The effective thermal conductivity (TC) of copper plated carbon fiber (Cf-Cu)/Fe composites is significantly influenced by the anisotropic TC of Cf-Cu and the interfacial thermal resistance. TC of the composite under the layer-in-parallel (ROM) and the effective medium approximation (EMA) models was calculated, and the finite element volume method is used to simulate the thermal distribution of the elements on the 2D section to obtain the simulated TC. By comparing the calculated TC, the simulated TC, and the measured TC, the degree of influence of the porosity of volume fraction, orientation, and aspect ratio of the Cf-Cu on the TC of the composite was investigated. The orientation and aspect ratio of Cf-Cu are the main factors affecting the TC of the composites. The thermal resistances under the ROM model and the EMA model are 2.08–3.6 × 10−8 m2 K W−1 and 2.56–4.26 × 10−8 m2 K W−1, respectively. When the volume fraction of Cf-Cu is 20%, the contact thermal resistance and the negatively oriented Cf-Cu decrease the TC and the positively oriented Cf-Cu increases the TC cancel each other out. Both measured TC and simulated TC reach the maximum value, 68.89 W m−1 K−1 and 71.02 W m−1 K−1, respectively. When the volume fraction of Cf-Cu exceeds 20%, the reduction effect of contact thermal resistance and negatively oriented Cf-Cu on TC dominates.
  • Detection Method for Shrinkage Cavities Inside Spheroidal Graphite Cast Iron Using Vibration Measurement by Electromagnetic Force Excitation

    pp. 596-603

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    DOI:10.2320/matertrans.F-M2022814

    The inspection of shrinkage cavities formed inside spheroidal graphite cast iron during the manufacturing process of spheroidal graphite cast products, including large cast structures and machine parts, is considered to be important for quality assurance of cast products. X-ray and ultrasonic methods are generally used for this inspection. However, the former inspection method takes a long time and considerable equipment costs, the latter method requires the use of water as a contact couplant and to polish the surface of the inspection site of the cast iron. In an actual manufacturing factory, there is a demand for a simple and quick method for inspecting shrinkage cavities inside cast iron. In this research, as a simple and high-speed inspection method to evaluate shrinkage cavities inside cast iron by measuring of the vibration of the electromagnetic force is proposed. Three-dimensional electromagnetic field analysis using the finite element method and displacement analysis was performed to analyze the phenomenon, and the usefulness of this method was confirmed by verification experiments. This Paper was Originally Published in Japanese in J. JFS 94 (2022) 3–10.
  • Monitoring of Laser Quenching of the Carbon Steel by Acoustic Emission

    pp. 604-612

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    DOI:10.2320/matertrans.MT-M2022148

    This study aims to establish fundamental knowledge for online non-destructive inspection in the laser quenching process utilizing acoustic emission. Acoustic emission is the transient elastic wave phenomenon due to release of strain energy in a solid material. And it is well known that the martensitic transformation can induce the acoustic emission. In this study, the acoustic emission monitoring of martensitic transformation during laser quenching experiment was conducted with the chromium molybdenum carbon steel (SCM440 in Japanese Industrial Standards) as the specimen. The experiment was carried out with seven kinds of laser irradiation power for different volume generation of heat-affected zone. After experiment, the martensite structure was confirmed at the heat-affected zone and the volume of the martensite structure within the zone was estimated. Only the specimen irradiated by the lowest laser power had no martensite structure. The acoustic emission waves were analyzed using parameters that showed the generation time duration and scale of source phenomenon. As a result, the relationship between the volume of martensite structure and information of acoustic emission was positive. It was suggested that the acoustic emission monitoring have application for the online non-destructive inspection for the laser quenching process. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 335–343.
  • HRTEM Characterization of an Age-Hardened Mg–Ca Binary Alloy

    pp. 613-616

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    DOI:10.2320/matertrans.MT-M2022039

    A Mg–2.8 mass% Ca binary alloy was subjected to a homogenization treatment. The three-dimensional morphology and coherency of the Mg2Ca phase (with C14 structure), which precipitated in the primary α-Mg dendrite, were investigated for the specimens aged at 423 K. The Mg2Ca precipitate exhibited a hexagonal plate-like morphology, with a planar surface that is parallel to the (0001)α basal plane and sides that are parallel to the {-1010}α columnar plane of the α-Mg matrix. The coarsening Mg2Ca precipitate retained coherency with the α-Mg matrix for aging time of 3 h, which corresponded to the peak-aged condition. Furthermore, during the coarsening process, misfit dislocations were introduced on the planar surface of the precipitates, and the coherent interface became a semi-coherent interface for aging time of 100 h, which corresponded to the over-aged condition. The Mg2Ca precipitates evolved from a hexagonal plate-like morphology to a rectangular morphology and then to a polygonal morphology during aging treatment at 423 K.
  • Development of AIH-FPP Carburizing Process Using Carbon Powder

    pp. 617-625

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    DOI:10.2320/matertrans.MT-Z2022020

    In this study, the surface of industrial pure iron was treated with atmospheric-controlled induction heating fine particle peening (AIH-FPP) using mechanical coating (MC) particles of carbon/steel obtained by mixing carbon powder and fine steel particles using mechanical milling. The surface modification effect and the mechanism of its effect were examined and considered by analyzing of the treated surface. Results showed that a modified layer in which carbon elements were diffused was formed near the treated surface by the AIH-FPP treatment using MC particles. In addition, by examining the influence of the treatment conditions on the formation of the modified layer by the design of experiments, the treatment temperature showed the most significant influence among the treatment temperature, peening time, and gas flow rate. The higher the treatment temperature, the deeper the carbon diffused layer. In addition, when treated at ≥1273 K, the microstructure near the surface became pearlite, and Vickers hardness increased. The time required for carbon diffusion in the AIH-FPP carburizing process using MC particles of carbon/steel was approximately the same as that of a general carburizing treatment using a reactive gas. In the AIH-FPP carburizing process, carbon is considered to be transferred from the particles to the surface, and the grain boundaries and dislocations increased by fine particle peening (FPP) are used as channels to diffuse inside the specimen. This mechanism is entirely different from the conventional carburizing methods. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Jpn. 71 (2022) 787–794.

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