Papers by Author: In Gon Kim

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Authors: In Gon Kim, Yang Do Kim, In Bae Kim
Abstract: The effects of pre-strain and aging treatment on the mechanical properties of hot rolled steel sheet containing 1.0wt.%Cu were investigated. As the amount of pre-strain increased, the maximum hardness increased and the time to reach its peak hardness decreased. Tensile strength of 10% pre-strained steel was 600MPa. This value was about 150MPa higher than that of hot rolled steel. In case of 30% pre-strained steel, the strength was further increased to 657MPa. Such a strength increase was due to the strain hardening and enhanced precipitation reaction of Cu-clusters. TEM study revealed that fine Cu-clusters were uniformly dispersed throughout the grain. This means that the precipitation of Cu-clusters was mainly controlled by the vacancies introduced during the pre-straining process. The size of Cu-clusters was about 10~20nm at peak aged condition and they had spherical shape.
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Authors: In Bae Kim, Yong Su Park, Kyung Hyun Kim, In Gon Kim
Abstract: Effects of Si and Cr additions on the fatigue properties of Al-Zn-Mg-Cu cast alloy were investigated by low and high cycle fatigue tests. It was found that in the low cycle fatigue test, fatigue life of base alloy showed the maximum value of 3,075 cycles, whereas in Si and Cr containing alloys, it was 2,993 and 1,413 cycles, respectively. The same trend was obtained in high cycle fatigue test, i.e., the fatigue strength in base alloy showed the highest value of 104MPa and decreased to 100MPa for Cr containing alloy and 81MPa for Si containing alloy. The fatigue ratio was about 0.20 for all three alloys. The tensile strength of base alloy also showed the maximum value of 513MPa, and decreased with the addition of Si and Cr to 400 and 500MPa, respectively. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary.
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Authors: In Bae Kim, Kwang Nyeon Kim, Kyung Hyun Kim, In Gon Kim
Abstract: Effects of Si and Cr additions and aging treatment on the stress corrosion cracking(SCC) resistance of Al-Zn-Mg-Cu cast alloys were investigated by C-ring test and electrical conductivity measurement. The SCC resistance of Al-Zn-Mg-Cu cast alloys decreased in the order of Cr containing alloy, Si containing alloy and base alloy. The lowest electrical conductivity of Cr containing alloy exhibited the best SCC resistance and this is probably due to an improved corrosion resistance by forming a passive film on the surface. The over-aged alloys showed the better SCC resistance. This is due to the increased distance between coarse particles at grain boundary. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of Al-Zn-Mg-Cu cast alloys was found to be the anodic dissolution model.
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Authors: Young Ha Kim, Uoo Chang Chung, Byungwook Nam, Won Sub Chung, In Gon Kim
Abstract: Mg2Ni powder was heated up to 880°C which is higher than the melting point of Mg2Ni alloys (760°C) for 30 minutes and immediately cooled into water (14°C). And then, mechanical ball milling was conducted for 1,4,8,10,12,24 hours respectively. As milling time increased discharge capacity was increased to maximum of 700mAh/g at 12hours then decreased with increasing milling time. The best high rate dischargeability (HRD) characteristic also obtain at the 12 hours ball milling time. Therefore, the ball milling time could be shorten to 12 hours by heat treatment and rapid cooling. Praseodymium (0,0.2,0.5,0.7,1.0%Pr) was added to Mg2Ni alloys. These alloys were ground for 12 hours to investigate the improvement of cycle life. The cycle life was remarkably improved with increasing the amount of Pr. The best amount of Pr was 0.7 wt%.
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