In this study, AlSi10Mg powders with average diameters of 44 μm are additively manufactured into bulk samples using a selective laser melting (SLM) process. Post-heat treatment to reduce residual stress in the as-synthesized sample is performed at different temperatures. From the results of a tensile test, as the heat-treatment temperature increases from 270 to 320°C, strength decreases while elongation significantly increases up to 13% at 320°C. The microstructures and tensile properties of the two heat-treated samples at 290 and 320°C, respectively, are characterized and compared to those of the as-synthesized samples. Interestingly, the Si-rich phases that network in the as-synthesized state are discontinuously separated, and the size of the particle-shaped Si phases becomes large and spherical as the heat-treatment temperature increases. Due to these morphological changes of Si-rich phases, the reduction in tensile strengths and increase in elongations, respectively, can be obtained by the post-heat treatment process. These results provide fundamental information for the practical applications of AlSi10Mg parts fabricated by SLM.

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• Wear behavior of aluminum-matrix particle (TiH2 and ZrH2)-reinforced composite foam additively manufactured using directed energy deposition
  Hwa-Jeong Kim, Gwang-Yong Shin, Ki-Yong Lee, Do-Sik Shim
  Journal of Materials Research and Technology.2023; 25: 222.     CrossRef
• Effect of Microstructural Evolution on Mechanical Properties and Fracture Modes of AlSi10Mg Blocks Fabricated by Selective Laser Melting after Stress Relief Annealing
  Jianzhu Li, Yujie Li, Zhe Wang, Changguang Li, Hai Yuan, Yun Hao
  Advanced Engineering Materials.2022;[Epub]     CrossRef

Aluminum (Al) - based powders have attracted attention as key materials for 3D printing because of their excellent specific mechanical strength, formability, and durability. Although many studies on the fabrication of 3Dprinted Al-based alloys have been reported, the influence of the size of raw powder materials on the bulk samples processed by selective laser melting (SLM) has not been fully investigated. In this study, AlSi10Mg powders of 65 μm in average particle size, prepared by a gas atomizing process, are additively manufactured by using an SLM process. AlSi10Mg powders of 45 μm average size are also fabricated into bulk samples in order to compare their properties. The processing parameters of laser power and scan speed are optimized to achieve densified AlSi10Mg alloys. The Vickers hardness value of the bulk sample prepared from 45 μm-sized powders is somewhat higher than that of the 65 μm-sized powder. Such differences in hardness are analyzed because the reduction in melt pool size stems from the rapid melting and solidification of small powders, compared to those of coarse powders, during the SLM process. These results show that the size of the powder should be considered in order to achieve optimization of the SLM process.

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• Laser Soldering Process Optimization of MEMS Probe of Probe Card for Semiconductor Wafer Test
  Myeongin Kim, Won Sik Hong, Mi-Song Kim
  Journal of Welding and Joining.2022; 40(3): 271.     CrossRef
• Investigation on Interfacial Microstructures of Stainless Steel/Inconel Bonded by Directed Energy Deposition of alloy Powders
  Yeong Seong Eom, Kyung Tae Kim, Soo-Ho Jung, Jihun Yu, Dong Yeol Yang, Jungho Choe, Chul Yong Sim, Seung Jun An
  Journal of Korean Powder Metallurgy Institute.2020; 27(3): 219.     CrossRef

Ni hydroxides (Ni(OH)₂) are synthesized on Ni foam by varying the hexamethylenetetramine (HMT) concentration using an electrodeposition process for pseudocapacitor (PC) applications. In addition, the effects of HMT concentration on the Ni(OH)₂ structure and the electrochemical properties of the PCs are investigated. HMT is the source of amine-based OH⁻ in the solution; thus, the growth rate and morphological structure of Ni(OH)₂ are influenced by HMT concentration. When Ni(OH)₂ is electrodeposited at a constant voltage mode of -0.85 V vs. Ag/AgCl, the cathodic current and the number of nucleations are significantly reduced with increasing concentration of HMT from 0 to 10 mM. Therefore, Ni(OH)₂ is sparsely formed on the Ni foam with increasing HMT concentration, showing a layered double-hydroxide structure. However, loosely packed Ni(OH)₂ grains that are spread on Ni foam maintain a much greater surface area for reaction and result in the effective utilization of the electrode material due to the steric hindrance effect. It is suggested that the Ni(OH)₂ electrodes with HMT concentration of 7.5 mM have the maximum specific capacitance (1023 F/g), which is attributed to the facile electrolyte penetration and fast proton exchange via optimized surface areas.

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• Review of Domestic Research Trends on Layered Double Hydroxide (LDH) Materials: Based on Research Articles in Korean Citation Index (KCI)
  Seon Yong Lee, YoungJae Kim, Young Jae Lee
  Economic and Environmental Geology.2023; 56(1): 23.     CrossRef