Faculty Profiles - OTSUBO Fumitaka

Papers - OTSUBO Fumitaka

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Structure and Hardness of Al-Cu and Sn-Cu-Sb Alloys Obtained by Casting While Hammering on Mold Reviewed

Otsubo Fumitaka, Hidenori Era

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 97 ( 3 ) 163 - 168 2025.03

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)

Vibration and stirring of molten metals during the solidification process has positive effects on the casting such as refinement of grains, reduction of segregation, and promotion of degassing. Therefore, in this study, vibration due to hammering was applied to a casting mold, and the effects of hammer vibration on the cast structure, hardness and porosity were investigated.
The hammer vibration device was custom-made. Two kinds of alloys with different solidified forms and specific gravities（ρ） were used in the casting experiments. In the Al-Cu alloy（ ρ=2.7）, the morphology of columnar crystals changed,and the size of the equiaxed grain regions varied with the vibration conditions. On the other hand, the Sn-Cu-Sb alloy（ ρ=7.4）showed a broken lath-shaped to become granular crystals lead to an increase in hardness, a suppression in segregation and a
decrease in porosity when vibration was applied.

DOI： 10.11279/jfes.97.164

Manufacturing Techniques Estimated from Microstructures of Iron Objects in Central Anatolia in the Late Bronze Age and the Early Iron Age Reviewed

Otsubo Fumitaka, Mariya Masubuchi, Hidenori Era, Hidenori Kuroki

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 97 ( 3 ) 184 - 188 2025.03

Microstructure and Mechanical Properties of YAG Laser Welded Spheroidal Graphite Cast Iron Reviewed International journal

Otsubo Fumitaka, Fukumatsu Kiyotaka

MATERIALS TRANSACTIONS ( The Japan Institute of Metals and Materials ) 65 ( 6 ) 665 - 671 2024.05

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

Cast iron welding improves the performance of joints using welding rods for cast iron. However, such rods are more than twice as expensive as those for mild steel. The authors found that when spheroidal graphite cast iron is melted and rapidly solidified, spherical graphite nodules aggregate and moved to the surface. If the spherical graphite nodules in the fusion zone moved to the surface, the carbon concentration may reduce, thereby suppressing the generation of ledeburite. In this study, by irradiating with YAG laser, I-type butt-welded joints were fabricated using L materials (with an average spherical graphite nodule diameter of 52 µm) specimen without groove width. Ferrite and pearlite matrices joints were undermatch joints. Applying PWHT (Post Weld Heat Treatment) restored the joint strength to more than 90% that of the base metal. The impact value as-welded joint dropped to less than 15% of that for the base metal. However, it could be recovered up to about 40% of that for the base metal by PWHT. Ferrite matrix joints after PWHT exhibited similar level impact values as the as-welded pearlite matrix joints. Moreover, the surface of spheroidal graphite cast iron with different numbers and size of spherical graphite nodules was irradiated with YAG laser. As the result, at irradiation feed rates above 100 cm/min L materials specimen exhibited a much lower hardness in the fusion zone than S materials (with an average spherical graphite nodule diameter of 27 µm) specimen. The spherical graphite nodules in the fusion zone moved to the surface during rapid melting by laser irradiation. In the S materials specimen studied, more ledeburite, martensite and retained austenite formed near the fusion boundary than with the L materials specimen. This Paper was Originally Published in Japanese in J. Japan Foundry Engineering Society 95 (2023) 615–621.

DOI： 10.2320/matertrans.F-M2024807

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Microstructure and Mechanical Properties of YAG Laser Welded Spheroidal Graphite Cast Iron Reviewed

Otsubo Fumitaka, Fukumatsu Kiyotaka

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 95 ( 11 ) 615 - 621 2023.11

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)

Cast iron welding improves the performance of joints using welding rods for cast iron. However, such rods are more than twice as expensive as those for mild steel. The authors found that when spheroidal graphite cast iron is melted and rapidly solidified, graphite nodules aggregate and move to the surface. If the graphite nodules in the fusion zone move to the surface, the carbon concentration may reduce, thereby suppressing the generation of ledeburite. In this study, by irradiating with YAG laser, I-type butt-welded joints were fabricated using L materials (with an average nodule diameter of 52 μm) specimens without groove width. Ferrite and pearlite matrices joints were undermatch joints. Applying PWHT (Post Weld Heat Treatment) restored the joint strength to more than 90 % that of the base metal. The impact value for the as-welded joint dropped to less than 15 % of that for the base metal. However, it could be recovered up to about 40 % of that for the base metal by PWHT. Ferrite matrix joints after PWHT exhibited similar level impact values as the as-welded pearlite matrix joints. Moreover, the surface of spheroidal graphite cast iron with different numbers and size of graphite nodules was irradiated with YAG laser. As a result, at irradiation feed rates above 100 cm/min L, materials specimen exhibited a much lower hardness in the fusion zone than S materials (with an average nodule diameter of 27 μm) specimen. The graphite nodules in the fusion zone moved to the surface during rapid melting by laser irradiation. In the S materials specimen studied, more ledeburite, martensite and retained austenite formed near the fusion boundary than with the L materials specimen.

DOI： 10.11279/jfes.95.615

CiNii Research

Structures and hardness of materials formed by melting and liquid diffusion of Mg alloy substrate with pure Al surface+ Reviewed International journal

Fumitaka Otsubo

Materials Transactions ( The Japan Institute of Metals and Materials ) 61 ( 8 ) 1657 - 1662 2020.08

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

In this study, pure Al powder was compression molded on the surface of flame-retardant Mg alloy plate, and integration of pure Al and Mg alloy was attempted by melting and solidification in air. In order to integrate different materials by liquid diffusion of metal elements, the structure, composition phase and hardness of the formed integrated materials were investigated.It was found that heating the specimens for 180 s results in melting and liquid diffusion between Al and Mg. When heated and melted with pure Al down and Mg alloy up (Type B), shrinkage cavity was formed on the former Mg alloy side of the former Al/former Mg alloy interface. When heated at 450 s, the specimen was composed of Al–Mg system stable phases of Al3Mg2 and Al12Mg17, and Al–Mg system metastable phases of Al0.37Mg0.63 and Al0.1Mg0.9. In Type A with pure Al up and Mg alloy down and Type B, stable phases of Al3Mg2 and Al12Mg17 were formed on the former Al side. The constituent phase of the former Mg alloy side was composed of metastable phases of Al0.37Mg0.63 and Al0.1Mg0.9, but the structure morphologies of Type A and B differed near the surface of the former Mg alloy side, and the primary phase was Al0.37Mg0.63 and Al0.1Mg0.9 respectively. The final solidification phase consisted of eutectic phases of Al0.37Mg0.63 and Al0.1Mg0.9. The hardness on the former Al side was about 250 HV, and the hardness on the former Mg alloy side had decreased. Type B was evaluated to be lower than Type A. This Paper was Originally Published in Japanese in J. JFS 92 (2020) 69–74.

DOI： 10.2320/matertrans.F-M2020830

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TEM analysis of whiskers formation over tin-plated films "jointly worked" Reviewed International journal

Fumitaka Otsubo, Hidenori Era, Yutaka Tsuru, Shigeru Hirano

Materials Chemistry and Physics 251 (2020) 122985 2020.04

Structures and Hardness of Materials Formed by Melting and Liquid Diffusion of Mg Alloy Substrate with Pure Al Surface Reviewed

Otsubo Fumitaka

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 92 ( 2 ) 69 - 74 2020.01

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)

In this study, pure Al powder was compression-molded on the surface of a flame-retardant Mg alloy plate, and integration of pure Al and Mg alloy was attempted by melting and solidification in air. In order to integrate different materials by liquid diffusion of metal elements, the structure, composition phase and hardness of the formed integrated materials were investigated. It was found that heating the specimens for 180s results in melting and liquid diffusion between Al and Mg. When heated and melted with pure Al down and Mg alloy up (Type B), shrinkage cavity was formed on the former Mg alloy side of the former Al/former Mg alloy interface. When heated at 450s, the specimen was composed of Al-Mg system stable phases of Al3Mg2 and Al12Mg17, and Al-Mg system metastable phases of Al0.37Mg0.63 and Al0.1Mg0.9. In Type A with pure Al up and Mg alloy down and Type B, stable phases of Al3Mg2 and Al12Mg17 were formed on the former Al side. The constituent phase of the former Mg alloy side was composed of metastable phases of Al0.37Mg0.63 and Al0.1Mg0.9, but the structure morphologies of Type A and B differed near the surface of the former Mg alloy side, and the primary phase was Al0.37Mg0.63 and Al0.1Mg0.9 respectively. The final solidification phase consisted of eutectic phases of Al0.37Mg0.63 and Al0.1Mg0.9. The hardness on the former Al side was about 250HV, and the hardness on the former Mg alloy side had decreased. Type B was evaluated to be lower than Type A.

DOI： 10.11279/jfes.92.69

CiNii Article

CiNii Research

Other Link： https://ci.nii.ac.jp/naid/130007804110

Cladding of Al Layer onto Mild Steel Substrate Using Al Powder and Its Structure and Properties Reviewed

59 ( 10 ) 1585 - 1590 2018.10

Columnar Ferrite Structure in Cast Iron Formed by Decarburization of White Cast Iron Reviewed

59 ( 8 ) 1326 - 1332 2018.08

Columnar Ferrite Structure in Cast Iron Formed by Decarburization of White Cast Iron Reviewed

Otsubo Fumitaka, Matsuki Kousuke, Era Hidenori, Kuroki Hidenori

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 90 ( 2 ) 61 - 67 2018.01

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)

Cast iron objects such as axes and other artifacts excavated from ancient sites generally have a layered structure with columnar ferrite on the outside, changing to pearlite and ledeburite with increasing depth, together with a minor fraction of dispersed graphite; this structure is the result of the heat treatment used in the decarburization process. The formation of the columnar ferrite structure has previously been explained by assuming that cast iron was produced using a metal mold and then decarburized. In this study, in order to clarify this issue, decarburization experiments were performed on white cast iron. Part of a white cast iron block, containing the surface that had been in contact with the mold during casting, in addition to a cut surface, was heated to 1273K, held at that temperature for 96h, and then slowly cooled to 873K at 67K/h (for 6h). It was found that columnar ferrite crystals grew in the direction perpendicular to the surface regardless of the solidification direction. The ferrite structure did not have a uniform crystal orientation, similar to the case for partially decarburized ancient cast iron. Therefore, this clarified that the issue was a misunderstanding without materials scientific grounds. In addition, when white cast iron was decarburized at 1123K for 48h and cooled to 873K at 42K/h, the overall thickness of the decarburized layers was close to that for ancient artifacts. Therefore, it is likely that in ancient times, the same type of cast iron and heat treatment conditions were used.

DOI： 10.11279/jfes.90.61

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CiNii Research

Other Link： https://ci.nii.ac.jp/naid/130006407089

鋳鉄中に生成した球状黒鉛の構造と物性 Invited

坪田俊樹，大坪文隆，佐野秀明，吉元昭二，梅谷拓郎，吉澤徳子

炭素材料科学の進展 ( 日本学術振興会炭素材料第117委員会 ) 2018.11

溶射による表面改質技術 Invited

大坪文隆

月刊トライボロジー ( （株）新樹社 ) 32 ( 8 ) 43 - 45 2018.08

白鋳鉄の脱炭により形成された鋳鉄の柱状フェライト組織 Reviewed

大坪文隆、松木康祐、恵良秀則、黒木英憲

鋳造工学 90 ( 2 ) 61 - 67 2018.02

Mg合金基板とその表面に成形したAl 圧粉層の溶融凝固材の組織と特性 Reviewed

大坪文隆, 大森百合香, 佛木大亮

鋳造工学全国講演大会講演概要集 ( 公益社団法人日本鋳造工学会 ) 172 ( 0 ) 31 - 31 2018.01

Columnar ferrite structure in cast iron formed by decarburization of white cast iron+ Reviewed

Otsubo F., Matsuki K., Era H., Kuroki H.

Materials Transactions 59 ( 8 ) 1326 - 1332 2018.01

Cladding of al layer onto mild steel substrate using al powder and its structure and properties Reviewed

Otsubo F., Era H.

Materials Transactions 59 ( 10 ) 1585 - 1590 2018.01

高周波誘導加熱による球状黒鉛鋳鉄の表面焼入れ性（共著） Reviewed

徳永辰也、若菜凌、濱口主税、浦濱大地、岩川風、福永修大、丸山栄三郎、大坪文隆、恵良秀則

溶射 54 ( 1 ) 8 - 11 2017.01

Al粉末を用いた軟鋼基材へのAl層のクラッド加工およびその組織と特性 Reviewed

大坪文隆, 恵良秀則

塑性と加工 58 ( 678 ) 582 - 586 2017.01

Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal)

Pure aluminum powder with grain sizes of 45 to 10μm preformed on aluminum (A1050) and mild steel (SPCC)<tt> </tt>substrates were rolled to form cladding materials at room temperature in air. The partial rolling reduction of the Al cladding layer was smaller than that of the A1050 substrate in an Al powder/A1050 cladding sheet. In contrast, the partial rolling reduction of the Al cladding layer was larger than that of the SPCC substrate in an Al powder/SPCC cladding sheet. The difference in the partial rolling reduction of the cladding layers and SPCC substrates became smaller with increasing total rolling reduction of the Al powder/SPCC cladding sheets. The shear adhesion strength of the Al powder/SPCC cladding sheet was about 40MPa, which decreased to about 10MPa after heat treatment at 773K for 3.6ks. The intermetallic compounds were formed between the cladding layer and the substrate after heat treatment at 773K for 3.6ks. Also, the cladding layer showed excellent oxidation resistance compared with cast iron after heat treatment at 1073K for 36ks in air, though light oxidation occurred in specimens after heat treatment at 773K for 36ks in air.

DOI： 10.9773/sosei.58.582

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130005858702

Change in Eutectic Structure of AC4C Aluminum Alloy Castings Obtained by Solidification after Electric Current Melting by Use of Spot Welding Machine Reviewed

Journal of Japan Foundry Engineering Society 87 ( 10 ) 695 - 701 2015.10

Change in Eutectic Structure of AC4C Aluminum Alloy Castings Obtained by Solidification after Electric Current Melting by Use of Spot Welding Machine Reviewed

Otsubo Fumitaka, Matsunaga Yuuki, Era Hidenori

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 87 ( 10 ) 695 - 701 2015.01

Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal)

The structure and hardness of aluminum alloy (JIS : AC4C) obtained by solidification after electric current melting by use of a spot welding machine were investigated focusing on structure formation through the loss of homogeneity and its properties. The molten area of the sample increased with increasing heat input and the columnar sample melted with further heat input. The center and outside areas of the samples exhibited a granular α-Al structure and fine eutectic structure, respectively. The fine structure with α-Al and eutectic phases of α-Al and Si formed in the whole area of the sample under a maximum heat input of 400J. The hardness of the outside area was generally higher than that of the center area, except when the heat input was maximum. It is found that the change in hardness with heat input was caused by the change in the area of the eutectic phase of α-Al and Si. The hardness of the outside area of the sample solidified under an appropriate heat input, e. g., 270J was twice as high as that of the as-cast ingot. Furthermore, the outside area of the appropriately solidified sample further hardened with the T5-heat treatment and the hardness was 50% higher compared to the center area. Thus the outside of the appropriately solidified sample, achieved by suitable heat input, markedly enhanced its hardness, bringing about the potential for wear resistant improvement.

DOI： 10.11279/jfes.87.695

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130005529567

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Papers - OTSUBO Fumitaka