Papers by Author: Young Hee Cho

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Authors: B.S. Moon, S.H. Han, I.K. Hwang, Young Hee Cho, C.E. Chung
2273
Authors: Jae Hyung Cho, Jong Soo Cho, Jung Tak Moon, J. Lee, Young Hee Cho, Anthony D. Rollett, Kyu Hwan Oh
499
Authors: Young Hee Cho, Dae Heon Joo, Chul Hyun Kim, Hu Chul Lee
Abstract: The role of alloying elements in the improvement of the high temperature strength of Al-12Si(CuNiMg) cast alloys used for automotive piston applications was investigated. The addition of alloying elements such as Mn, Cr, Ti and Ge was studied and the detailed characterization of the composition and morphology of the constituent phases after over aging at 350 for 1000 hrs was performed. The compositions and volume fractions of the equilibrium phases determined by thermodynamic calculation were compared with the experimental results. The addition of transition elements, including Mn, Cr and Ti, increased the volume fraction of the intermetallic phases, which effectively enhanced the high temperature strength of the alloys. Among these transition elements, Mn turned out to be the most effective alloying element. After adding up to 0.5wt% of Mn, a large number of intermetallic phases, α-Al(Mn,Fe)Si as well as fine Al6(Mn,Fe) particles were precipitated and a significant improvement in the elevated temperature properties was achieved. The addition of Ge promoted the precipitation of the θphase (metastable phase, θ-Al2Cu), due to the formation of GeSi precipitates, thereby improved the mechanical properties of the alloy after T6 heat treatment. However, the presence of these GeSi precipitates did not affect the coarsening of the θ phase to form Qphase( Al5Cu2Mg8Si6) during aging and, thus, the elevated temperature properties were not improved by the addition of Ge.
461
Authors: Young Hee Cho, Young-Roc Im, Soon-Woo Kwon, Hu Chul Lee
339
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