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김대환 ( Dae Hwan Kim ),정현주 ( Hyun Ju Jung ),심성용 ( Sung Yong Shim ),임수근 ( Su Gun Lim ),이상용 ( Sang Yong Lee ) 한국주조공학회 2014 한국주조공학회지 Vol.34 No.4
This work presents the results of a thixo-extrusion process applied to aluminum alloy and and reheating characteristics of semisolid A356 Alloy using have been discussed. The reheating experiment was performed using an electric resistance furnace and multistage heating for uniform reheating. The thixo-extrusion was performed at the optimal reheating conditions of the semi-solid A356 alloy, the the extrusion conditions were an extrusion ratio of 33 and ram speed of 6 mm/sec. The results showed that the thixoextrusion of semi-solid A356 alloy fabricated by the cooling slope reduced the extrusion pressure by 180% in comparison with hot extrusion, and that a sound extrusion could be obtained in spite of the same extrusion ratio and strain rate.
반응고 Al-Zn-Mg계 합금의 반용융 압출을 위한 재가열 시 결정립 성장 억제에 미치는 Ca 첨가의 영향
박형원 ( Hyung Won Park ),김대환 ( Dae Hwan Kim ),심성용 ( Sung Yong Shim ),김희경 ( Hee Kyung Kim ),성봉학 ( Bong Hak Seong ),최창옥 ( Chang Ock Choi ),임수근 ( Su Gun Lim ) 한국주조공학회 2011 한국주조공학회지 Vol.31 No.6
There is thixo-extrusion to form high strength aluminum alloy. But, it is a problem that grains become grain coarsening during reheating process because the alloy was exposed at high temperature. In order to solve grain growth during reheating process, calcium was added in Al-Zn-Mg alloys. Primary a grain sizes of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca were measured with image analyzer after reheating. Measured primary a grain sizes were applied to LSW(Lifshitz-Slyozov and Wagner) equation to check the effect of Ca on grain coarsening. Coarsening rate constant K values of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca alloys were 371 mm3s-1, 247 mm3s-1, 198 mm3s-1 and 166 mm3s-1, respectively. As increasing calcium content, K value decreased which means grains are refined. Also, grains of calcium addition were more spherical than that of calcium free.
Mg 첨가에 따른 A356 합금의 열처리 및 기계적 특성 변화
조재찬 ( Jae-chan Jo ),김광삼 ( Kwang-sam Kim ),임인택 ( In-taek Im ),김대환 ( Dae-hwan Kim ),심성용 ( Sung-yong Shim ),임수근 ( Su-gun Lim ) 한국주조공학회 2016 한국주조공학회지 Vol.36 No.6
The effects of Mg addition on heat treatment and mechanical properties of A356 alloy were investigated. With increased amounts of Mg addition to A356 alloy, the grain size decreased and eutectic Si was refined. And, this process can improve the mechanical properties. Solid solution heat treatment causes the spheroidizing of eutectic Si. In this study, although eutectic Si was refined with Mg addition, solid solution time increased from 2 hours to 6 hours with Mg addition, and aging time also increased, from 4 hours to 8 hours. After heat treatment, Mg2Si remained in a formation of Chinese script. And, Chinese script Mg2Si formed with Mg addition caused a reduction of the elongation of the alloys according to the stress concentration.