The effects of annealing on the microstructure and mechanical properties of Al–Zn–Mg–Cu–Si alloys fabricated by high-energy ball milling (HEBM) and spark plasma sintering (SPS) were investigated. The HEBM-free sintered alloy primarily contained Mg₂Si, Q-AlCuMgSi, and Si phases. Meanwhile, the HEBM-sintered alloy contains Mg-free Si and θ-Al₂Cu phases due to the formation of MgO, which causes Mg depletion in the Al matrix. Annealing without and with HEBM at 500°C causes partial dissolution and coarsening of the Q-AlCuMgSi and Mg₂Si phases in the alloy and dissolution of the θ-Al₂Cu phase in the alloy, respectively. In both alloys, a thermally stable α-AlFeSi phase was formed after long-term heat treatment. The grain size of the sintered alloys with and without HEBM increased from 0.5 to 1.0 μm and from 2.9 to 6.3 μm, respectively. The hardness of the sintered alloy increases after annealing for 1 h but decreases significantly after 24 h of annealing. Extending the annealing time to 168 h improved the hardness of the alloy without HEBM but had little effect on the alloy with HEBM. The relationship between the microstructural factors and the hardness of the sintered and annealed alloys is discussed.

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• Microstructural evolution and thermal stability of Al–Zn–Mg–Cu–Si–Zr alloy fabricated via spark plasma sintering
  Junho Lee, Seonghyun Park, Sang-Hwa Lee, Seung Bae Son, Hanjung Kwon, Seok-Jae Lee, Jae-Gil Jung
  Journal of Materials Research and Technology.2024; 31: 205.     CrossRef

Inorganic-organic composites find extensive application in various fields, including electronic devices and light-emitting diodes. Notably, encapsulation technologies are employed to shield electronic devices (such as printed circuit boards and batteries) from stress and moisture exposure while maintaining electrical insulation. Polymer composites can be used as encapsulation materials because of their controllable mechanical and electrical properties. In this study, we propose a polymer composite that provides good electrical insulation and enhanced mechanical properties. This is achieved by using aluminum borate nanowhiskers (ABOw), which are fabricated using a facile synthesis method. The ABOw fillers are created via a hydrothermal method using aluminum chloride and boric acid. We confirm that the synthesis occurs in various morphologies based on the molar ratio. Specifically, nanowhiskers are synthesized at a molar ratio of 1:3 and used as fillers in the composite. The fabricated ABOw/epoxy composites exhibit a 48.5% enhancement in mechanical properties, similar to those of pure epoxy, while maintaining good electrical insulation.

This study investigates the melting point and brazing properties of the aluminum (Al)-copper (Cu)-silicon (Si)-tin (Sn) alloy fabricated for low-temperature brazing based on the alloy design. Specifically, the Al-20Cu-10Si-Sn alloy is examined and confirmed to possess a melting point of approximately 520°C. Analysis of the melting point of the alloy based on composition reveals that the melting temperature tends to decrease with increasing Cu and Si content, along with a corresponding decrease as the Sn content rises. This study verifies that the Al-20Cu-10Si-5Sn alloy exhibits high liquidity and favorable mechanical properties for brazing through the joint gap filling test and Vickers hardness measurements. Additionally, a powder fabricated using the Al-20Cu-10Si-5Sn alloy demonstrates a melting point of around 515°C following melting point analysis. Consequently, it is deemed highly suitable for use as a low-temperature Al brazing material.

Boron carbide (B₄C) is highly significant in the production of lightweight protective materials when added to aluminum owing to its exceptional mechanical properties. In this study, a method for fabricating Al-B₄C composites using high-energy ball milling and directed energy deposition (DED) is presented. Al-4 wt.% B₄C composites were fabricated under 21 different laser conditions to analyze the microstructure and mechanical properties at different values of laser power and scan speeds. The composites fabricated at a laser power of 600 W and the same scan speed exhibited the highest hardness and generated the fewest pores. In contrast, the composites fabricated at a laser power of 1000 W exhibited the lowest hardness and generated a significant number of large pores. This can be explained by the influence of the microstructure on the energy density at different values of laser power.

Aluminum alloys are widely utilized in diverse industries, such as automobiles, aerospace, and architecture, owing to their high specific strength and resistance to oxidation. However, to meet the increasing demands of the industry, it is necessary to design new aluminum alloys with excellent properties. Thus, a new method is required to efficiently test additively manufactured aluminum alloys with various compositions within a short period during the alloy design process. In this study, a combinatory approach using a direct energy deposition system for metal 3D printing process with a dual feeder was employed. Two types of aluminum alloy powders, namely Al6061 and Al-12Cu, were utilized for the combinatory test conducted through 3D printing. Twelve types of Al-Si-Cu-Mg alloys were manufactured during this combinatory test, and the relationship between their microstructures and properties was investigated.

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• Trends in Materials Modeling and Computation for Metal Additive Manufacturing
  Seoyeon Jeon, Hyunjoo Choi
  journal of Korean Powder Metallurgy Institute.2024; 31(3): 213.     CrossRef
• Microstructural Effects on the Mechanical Properties of Ti-6Al-4V Fabricated by Direct Energy Deposition
  Juho Kim, Seoyeon Jeon, Hwajin Park, Taeyoel Kim, Hyunjoo Choi
  Journal of Powder Materials.2024; 31(4): 302.     CrossRef
• Combinatorial Experiment for Al-6061 and Al-12Si alloy Based on Directed Energy Deposition (DED) Process
  Seoyeon Jeon, Suwon Park, Yongwook Song, Jiwon Park, Hyunyoung Park, Boram Lee, Hyunjoo Choi
  journal of Korean Powder Metallurgy Institute.2023; 30(6): 463.     CrossRef

Metal additive manufacturing (AM) has transformed conventional manufacturing processes by offering unprecedented opportunities for design innovation, reduced lead times, and cost-effective production. Aluminum alloy, a material used in metal 3D printing, is a representative lightweight structural material known for its high specific strength and corrosion resistance. Consequently, there is an increasing demand for 3D printed aluminum alloy components across industries, including aerospace, transportation, and consumer goods. To meet this demand, research on alloys and process conditions that satisfy the specific requirement of each industry is necessary. However, 3D printing processes exhibit different behaviors of alloy elements owing to rapid thermal dynamics, making it challenging to predict the microstructure and properties. In this study, we gathered published data on the relationship between alloy composition, processing conditions, and properties. Furthermore, we conducted a sensitivity analysis on the effects of the process variables on the density and hardness of aluminum alloys used in additive manufacturing.

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• Effect of Heat Treatment on Microstructure and Mechanical Properties of Al–Zn–Mg–Cu–Si Sintered Alloys with and Without High-energy Ball Milling
  Junho Lee, Seonghyun Park, Sang-Hwa Lee, Seung Bae Son, Seok-Jae Lee, Jae-Gil Jung
  journal of Korean Powder Metallurgy Institute.2023; 30(6): 470.     CrossRef

This study investigates the interfacial reaction between powder-metallurgy high-entropy alloys (HEAs) and cast aluminum. HEA pellets are produced by the spark plasma sintering of Al_0.5CoCrCu_0.5FeNi HEA powder. These sintered pellets are then placed in molten Al, and the phases formed at the interface between the HEA pellets and cast Al are analyzed. First, Kirkendall voids are observed due to the difference in the diffusion rates between the liquid Al and solid HEA phases. In addition, although Co, Fe, and Ni atoms, which have low mixing enthalpies with Al, diffuse toward Al, Cu atoms, which have a high mixing enthalpy with Al, tend to form Al–Cu intermetallic compounds. These results provide guidelines for designing Al matrix composites containing high-entropy phases.

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• Simultaneous enhancement of strength and ductility of Al matrix composites enabled by submicron-sized high-entropy alloy phases
  Chahee Jung, Seungin Nam, Hansol Son, Juyeon Han, Jaewon Jeong, Hyokyung Sung, Hyoung Seop Kim, Seok Su Sohn, Hyunjoo Choi
  Journal of Materials Research and Technology.2024; 33: 1470.     CrossRef

Aluminum-based powders have attracted attention as key materials for 3D printing owing to their low density, high specific strength, high corrosion resistance, and formability. This study describes the effects of TiC addition on the microstructure of the A6013 alloy. The alloy powder was successfully prepared by gas atomization and further densified using an extrusion process. We have carried out energy dispersive X-ray spectrometry (EDS) and electron backscatter diffraction (EBSD) using scanning electron microscopy (SEM) in order to investigate the effect of TiC addition on the microstructure and texture evolution of the A6013 alloy. The atomized A6013-xTiC alloy powder is fine and spherical, with an initial powder size distribution of approximately 73 μm which decreases to 12.5, 13.9, 10.8, and 10.0 μm with increments in the amount of TiC.

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• Influence of Curing Agent Amount on Properties of Dynamic Vulcanized Phenyl Silicone Rubber-SEBS-SBS System
  Chunxu Zhao, Bobing He, Xian Chen
  Polymers.2022; 14(24): 5443.     CrossRef

There is increasing demand for the development of a new material with high strength, high stiffness, and good electrical conductivity that can be used for high-voltage direct current cables. In this study, we develop aluminumbased composites containing C₆₀ fullerenes, carbon nanotubes, or graphene using a powder metallurgical route and evaluate their strength, stiffness, coefficient of thermal expansion, and electrical conductivity. By optimizing the process conditions, a material with a tensile strength of 800 MPa, an elastic modulus of 90 GPa, and an electrical conductivity of 40% IACS is obtained, which may replace iron-core cables. Furthermore, by designing the type and volume fraction of the reinforcement, a material with a tensile strength of 380 MPa, elastic modulus of 80 GPa, and electrical conductivity of 54% IACS is obtained, which may compete with AA 6201 aluminum alloys for use in all-aluminum conductor cables.

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• Synergistic strengthening of aluminum with SiC by grain refinement and dispersion hardening
  Kanhu C. Nayak, Juyeon Han, Suwon Park, Miran Joo, Kon‐Bae Lee, Donghyun Bae, Hyunjoo Choi
  Journal of the American Ceramic Society.2023; 106(12): 7340.     CrossRef
• Synergetic effect of milling speed and duration on particle morphology and mechanical properties of nanocrystalline Al matrix containing SiC
  K.C. Nayak, J.Y. Han, C.H. Jung, M.R. Joo, K.B. Lee, D.H. Bae, H.J. Choi
  Powder Metallurgy.2023; 66(5): 519.     CrossRef

The subject of this study is a zeolite generated as a by-product of recycling LAS (lithium-aluminum-silicate) resources, a kind of glass and ceramic produced by induction. The zeolite by-product is modified into Mg-zeolite using Mg as a cation to absorb Pb, a heavy metal generated from water pollution caused by recent industrial wastewater. An ion-exchange method is used to carry out the modification process, from zeolite byproduct to Mg-zeolite, and simultaneously absorb the Pb in the heavy-metal solution (99.032 mg/L). It is found that the sodium zeolite in the raw material residue can be modified to magnesium zeolite by reacting it with a mixture solution at 1 M concentration for 24 h. As a result, it is found that the residual Pb (0.130 mg/L) in the heavy metal solution is shown to be absorbed by 99.86%, with successful formation of a Mg-modified zeolite.

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• Y-Type Zeolite Synthesized from an Illite Applied for Removal of Pb(II) and Cu(II) Ions from Aqueous Solution: Box-Behnken Design and Kinetics
  Kinjal J. Shah, Jiacheng Yu, Ting Zhang, Zhaoyang You
  Water.2023; 15(6): 1171.     CrossRef

The powder manufacturing process using the gas atomizer process is easy for mass production, has a fine powder particle size, and has excellent mechanical properties compared to the existing casting process, so it can be applied to various industries such as automobiles, electronic devices, aviation, and 3D printers. In this study, a modified A4032-xSn (x = 0, 1, 3, 5, and 10 wt.%) alloy with low melting point properties is investigated. After maintaining an argon (Ar) gas atmosphere, the main crucible is tilted; containing molten metal at 1,000°C by melting the master alloy at a high frequency, and Ar gas is sprayed at 10 bar gas pressure after the molten metal inflow to the tundish crucible, which is maintained at 800°C. The manufactured powder is measured using a particle size analyzer, and FESEM is used to observe the shape and surface of the alloy powder. DSC is performed to investigate the change in shape, according to the melting point and temperature change. The microstructure of added tin (Sn) was observed by heat treatment at 575°C for 10 min. As the content of Sn increased, the volume fraction increased to 1.1, 3.1, 6.4, and 10.9%.

Aluminum nitride (AlN) has excellent electrical insulation property, high thermal conductivity, and a low thermal expansion coefficient; therefore, it is widely used as a heat sink, heat-conductive filler, and heat dissipation substrate. However, it is well known that the AlN-based materials have disadvantages such as low sinterability and poor mechanical properties. In this study, the effects of addition of various amounts (1-6 wt.%) of sintering additives Y₂O₃ and Sm₂O₃ on the thermal and mechanical properties of AlN samples pressureless sintered at 1850°C in an N₂ atmosphere for a holding time of 2 h are examined. All AlN samples exhibit relative densities of more than 97%. It showed that the higher thermal conductivity as the Y₂O₃ content increased than the Sm₂O₃ additive, whereas all AlN samples exhibited higher mechanical properties as Sm₂O₃ content increased. The formation of secondary phases by reaction of Y₂O₃, Sm₂O₃ with oxygen from AlN lattice influenced the thermal and mechanical properties of AlN samples due to the reaction of the oxygen contents in AlN lattice.

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• Effects of YH2 addition on pressureless sintered AlN ceramics
  Liang Wang, Wei-Ming Guo, Peng-Fei Sheng, Li-Fu Lin, Xiao Zong, Shang-Hua Wu
  Journal of the European Ceramic Society.2023; 43(3): 862.     CrossRef

To improve the mechanical properties of aluminum, graphene has been used as a reinforcing material, yielding graphene-reinforced aluminum matrix composites (GRAMCs). Dispersion of graphene materials is an important factor that affects the properties of GRAMCs, which are mainly manufactured by mechanical mixing methods such as ball milling. However, the use of only mechanical mixing process is limited to achieve homogeneous dispersion of graphene. To overcome this problem, in this study, we have prepared composite materials by coating aluminum particles with graphene by a self-assembly reaction using poly vinylalcohol and ethylene diamine as coupling agents. The scanning electron microscopy and Fourier-transform infrared spectroscopy results confirm the coating of graphene on the Al surface. Bulk density of the sintered composites by spark plasma sintering achieved a relative density of over 99% up to 0.5 wt.% graphene oxide content.

The aluminum (Al)/copper oxide (CuO) complex is known as the most promising material for thermite reactions, releasing a high heat and pressure through ignition or thermal heating. To improve the reaction rate and wettability for handling safety, nanosized primary particles are applied on Al/CuO composite for energetic materials in explosives or propellants. Herein, graphene oxide (GO) is adopted for the Al/CuO composites as the functional supporting materials, preventing a phase-separation between solvent and composites, leading to a significantly enhanced reactivity. The characterizations of Al/CuO decorated on GO(Al/CuO/GO) are performed through scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping analysis. Moreover, the functional bridging between Al/CuO and GO is suggested by identifying the chemical bonding with GO in X-ray photoelectron spectroscopy analysis. The reactivity of Al/CuO/GO composites is evaluated by comparing the maximum pressure and rate of the pressure increase of Al/CuO and Al/CuO/GO. The composites with a specific concentration of GO (10 wt%) demonstrate a well-dispersed mixture in hexane solution without phase separation.

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• Controlling Particle Size of Recycled Copper Oxide Powder for Copper Thermite Welding Characteristics
  Hansung Lee, Minsu Kim, Byungmin Ahn
  journal of Korean Powder Metallurgy Institute.2023; 30(4): 332.     CrossRef