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Optimizing Fabrication of Plasma-Driven CuO Shell Over Porous Al2O3 Substrate to Meet Coating Issues
(2026-07-01)
Kaentown, Sasithon
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Wang, Wei Cheng
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Lin, Yi Cheng
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Chankitmunkong, Suwaree
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Diewwanit, Onnjira
A plasma-driven in situ conversion strategy was developed in which Cu<inf>2</inf>O nanoparticles introduced into an alkaline phosphate–hydroxide electrolyte undergo oxidative transformation to CuO within plasma micro-discharge channels during plasma electrolytic oxidation (PEO) of AA6061 aluminum alloy. The positive duty cycle was systematically varied from 10% to 40% under constant mean current density to regulate dielectric breakdown behavior, discharge energy input, and interfacial oxidation conditions. Voltage transient analysis, X-ray diffraction, field emission scanning electron microscopy, and scratch adhesion testing were employed to correlate discharge characteristics with phase evolution and coating integrity. A progressive increase in the duty cycle was found to reduce the dielectric breakdown transition voltage, promote more spatially distributed microdischarges, and facilitate charge-transfer-driven oxidation of Cu<inf>2</inf>O to CuO within the active oxide growth zone. This plasma-assisted redox mechanism enables CuO to form co-spatially with Al<inf>2</inf>O<inf>3</inf> melting and rapid re-solidification, producing a CuO shell structure distributed over the porous alumina matrix rather than as a passively entrapped particulate phase. The resulting microstructural densification suppresses discharge-crater porosity, reduces surface roughness, and improves coating–substrate adhesion by nearly twofold relative to particle-free PEO coatings. These findings establish that duty-cycle-controlled discharge behavior provides a mechanistically grounded and dispersant-free route for fabricating CuO-modified oxide coatings with enhanced structural integration and interfacial adhesion on aluminum alloys.
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Effect of Nitrocarburizing and Tempering on Microstructure and Wear Performance of SKH51 High-Speed Tool Steel
(2026-06-01)
Jornsanoh, Pijarn
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Chankitmunkung, Suwaree
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Taweejun, Nipon
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Praditja, Tanabodee
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Diewwanit, Onnjira
Traditional heat treatment of high-speed tool steels requires multiple thermal cycles, increasing processing time and energy costs. This study investigates an integrated approach combining tempering and nitrocarburizing processes to optimize both processing efficiency and surface properties of SKH51 high-speed tool steel. Various heat treatment sequences were examined: quenching–double tempering (Q2T), austenitizing at a temperature of 1220 °C for a duration of 15 min. Subsequently, the specimen underwent tempering at 570 °C for 3 hours and was cooled to room. In addition, it is a combination of quenching followed by single (QNC) or double (Q2NC) nitrocarburizing at 570 °C for 3 hours, and quenching–double tempering followed by single (Q2TNC) or double (Q2T2NC) nitrocarburizing. Microstructural analysis revealed that carbon and nitrogen atoms can diffuse into the martensite matrix when the steel is heated at 570 °C for 3 hours in a nitrocarburizing atmosphere. However, the thickness of the nitrocarburized layer was slightly greater for pre-tempered steel compared to direct tempering in the nitrocarburizing atmosphere. XRD analysis confirmed the formation of both ε-nitride (Fe<inf>2-3</inf>(N,C)) and γ′-nitride (Fe<inf>4</inf>(N,C)) phases in the compound layer, with the substrate microstructure influencing phase development. While double nitrocarburizing increased compound layer thickness from 4 to 8 μm, it also generated continuous porosity, particularly in pre-tempered specimens, which compromised mechanical performance. All heat treatment sequences effectively reduced the retained austenite content from 24.0 to 1.5-2.1%. Tribological properties were assessed using microhardness depth profiling, scratch test, and ball-on-disk wear test. The wear volume of the QNC specimen was close to that of the Q2TNC specimen. Additionally, the connected porosity in the compound layer developed after two nitrocarburizing cycles led to a decrease in scratch resistance and wear resistance, despite the high surface hardness. These findings establish that a single cycle of direct tempering in the nitrocarburizing atmosphere (QNC) offers a practical pathway for reducing processing steps while maintaining desired surface properties in tool steel manufacturing.
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Improvement in the Uniformity of Bismuth Distribution in an Al-Bi Alloy by Ultrasonic Processing and Hydrogen Melt Enrichment
(2026-01-01)
Chankitmunkong, Suwaree
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Eskin, Dmitry G.
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Diewwanit, Onnjira
Manufacturing of immiscible metallic alloysMetallic alloys, such as aluminumAluminum-bismuth, faces challenges in achieving uniform distribution of secondary phase droplets/particles due to their higher density and tendency to agglomerate/coalesce, which negatively affects mechanical propertiesMechanical properties. Recent studies on emulsification of immiscible liquids showed that ultrasonic treatment (UST) of gas-saturated systems improved the droplet distribution. In this work we tested this approach on Al-Bi alloys with melts saturated with hydrogenHydrogen. It was demonstrated that this combination resulted in the uniform distribution of fineFines Bi droplets in the aluminumAluminum matrix. UST had a dual role in the process: (a) increased cavitation facilitated by dissolved hydrogenHydrogen improved the efficiency of droplet formation and distribution and (b) ultrasonic degassing eliminated the adverse effects of gas porosity. Finer and evenly distributed Bi particles enhanced the wear resistance of the alloy.
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Enhancing the properties of a hypereutectic Al-Fe alloy through recycled aluminum scrap and ultrasonic melt processing
(2025-10-01)
Tangsuksan, Tawatchai
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Pandee, Phromphong
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Diewwanit, Onnjira
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Limmaneevichitr, Chaowalit
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Tyurnina, Anastasia V.
This paper focuses on the effects of using recycled aluminum beverage cans and ultrasonic melt processing (USP) on the microstructure and properties of a hypereutectic Al-Fe alloy that has potential in structural and electric applications. The proportion of recycled aluminum scrap used as the starting material varied, and its influence on grain refinement, intermetallic phase formation, precipitation hardening, and mechanical performance was examined. Ultrasonic melt processing (USP) was applied to refine the microstructure and improve phase distribution. The experimental results showed that both the addition of recycled aluminum scrap and USP significantly increased the hardness and tensile strength of the alloys, with further improvements observed after optimal aging treatments, although ductility slightly decreased. Additionally, the presence of alloying elements from the recycled scrap, such as Mg, Mn, Si, and Cu, led to a reduction in electrical conductivity while improving the precipitation hardening response. This study highlights the potential of using recycled materials and advanced processing techniques to develop sustainable, high-performance aluminum alloys for various industrial applications.
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Aging-induced enhancement of corrosion resistance in Al-4Ni-1Mn alloys through Al3(Sc, Zr) precipitates
(2025-05-05)
Masthong, Anuchit
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Eskin, Dmitry
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Limmaneevichitr, Chaowalit
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Pandee, Phromphong
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Diewwanit, Onnjira
Al-Ni-Mn alloys are attractive for high-temperature, corrosive environment due to the formation of stable intermetallic compounds that can reduce corrosion susceptibility. This study showed that the additions of Mn, Sc, and Zr in Al-4 % Ni alloys significantly enhanced hardness and thermal stability through the simultaneous effect of transformation of the Al + Al<inf>3</inf>Ni to Al + Al<inf>9</inf>(Ni, Mn)<inf>2</inf> eutectic and precipitation of Al<inf>3</inf>(Sc, Zr). The thermal stability of an Al-4 % Ni-1 % Mn alloy was very good when exposed to 350 °C for 60 h. Additionally, the hardness substantially increased in an Al-4 % Ni-1 % Mn alloy with the addition of Sc and Zr, showing an approximate increase of 30 %. The highest hardness achieved was approximately 50 % higher with the optimal Sc and Zr content as compared to the Al-4Ni-1Mn alloy. Addition of 1 % Mn to an Al-4 % Ni alloy decreased the current density (I<inf>corr</inf>) and increased the corrosion potential (E<inf>corr</inf>), indicating better corrosion resistance. The effects of Sc and Zr additions on corrosion were also investigated, revealing that the increased Sc and Zr content led to more aggressive corrosion in the as-cast condition due to the eutectic coarsening and a high solid solution concentration of Sc and Zr that led to microstructural instability and electrochemical effects. However, after aging at 350 °C, the corrosion resistance significantly improved due to the Al<inf>3</inf>(Sc, Zr) precipitates that interrupted the corrosion path.
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Effect of Zr and Sc on Intermetallic Morphology and Hardening of an Al–Fe Alloy
(2023-01-01)
Chankitmunkong, Suwaree
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Eskin, Dmitry G.
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Limmaneevichitr, Chaowalit
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Pandee, Phromphong
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Diewwanit, Onnjira
We studied the effect of zirconium and scandium on an Al-7 wt% Fe cast alloy with potential heat- and wear-resistant applications. An addition of 0.2% Zr resulted in thinning of primary Al<inf>3</inf>Fe particles, while an addition of 0.15% Zr and 0.15% Sc changed the morphology of primary intermetallics from needles to flower-like shape. While the addition of Zr did not affect the properties, the Zr + Sc joint additions increased the hardness of the as-cast Al–Fe alloy. The hardness of the base alloy increased upon annealing from 40 to 80 HV (450 °C, 2 h) and to 110 HV (350 °C, 20 h). The wear resistance of the Al–Fe alloy was also improved by Zr and Sc addition, especially after annealing. The observed effects are likely to be linked to the supersaturation of Zr and Sc in the aluminum solid solution during solidification and precipitation of dispersoids during annealing.
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Characterization of the Anodic Film and Corrosion Resistance of an A535 Aluminum Alloy after Intermetallics Removal by Different Etching Time
(2022-07-01)
Chankitmunkong, Suwaree
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Eskin, Dmitry
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Limmaneevichitr, Chaowalit
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Kengkla, Nattarat
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Diewwanit, Onnjira
The objective of this study was to improve the corrosion resistance of an A535 alloy by removing intermetallics on the alloy surface by alkaline etching to improve the morphologies and properties of the anodic film that was sealed with different sealants. It was found that alkaline etching for 4 min was suitable for dissolving intermetallic particles and simultaneously providing sufficient roughness for the adhesion of an oxide film to the Al matrix. The effect of alkaline etching revealed that a decrease in the intermetallic fraction from 21% to 16% after etching for 2 and 4 min, respectively, corresponded to the increase in the surface roughness, thickness, and consistency of the anodic film. It was also demonstrated that the surface morphology of the anodic films after stearic acid sealing was more uniform and compact than that after nickel fluoride sealing. The electrochemical polarization curves and salt spray test proved that the alloy etched for 4 min and sealed with stearic acid had better corrosion resistance as compared with the aluminum alloy sealed with nickel fluoride.
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Effect of Homogenization on Anodic Film and Electrochemical Behavior of an A535 Alloy After Sealing with Stearic Sealant
(2022-01-01)
Chankitmunkong, Suwaree
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Eskin, Dmitry G.
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Limmaneevichitr, Chaowalit
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Pandee, Phromphong
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Kengkla, Nattarat
Almag 35 (A535) is a commercial aluminum alloy intended for a number of marine components, which is mainly justified by its excellent castability and corrosion resistance. However, the most important factor for corrosion resistance is the formation of intermetallics that can lead the defects in the oxide film and substrate, as well as activate the corrosion reaction. The characteristics of a sealant on the anodic film were investigated in this work. The alloy was subjected to homogenization at 400 °C for 5 h to improve the uniformity of the anodic oxide film due to the decreased number of intermetallics as a result of dissolving in the matrix. It also improved the hardness of this alloy. Electrochemical measurements were conducted to investigate the corrosion behavior. The effects of intermetallics and stearic sealing on the characteristics of the oxide layer are discussed. The decrease in the number of intermetallics can lead to reduced corrosion current density (I<inf>corr</inf>) and increased potential corrosion (E<inf>corr</inf>), which results in a lower corrosion rate of this alloy.

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