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AZ91합금의 조직과 시효특성에 미치는 Ca 및 Si의 영향
지태구 ( T. G. Jhee ),김용규 ( Y. K. Kim ) 한국열처리공학회 2002 熱處理工學會誌 Vol.15 No.6
N/A The effects of calcium and silicon on microstructure and aging characteristics of AZ91 magnesium alloy during T5 treatment was investigated. The addition of 0.88% calcium or 0.25% silicon to AZ91 alloy made dendrite cell smaller. Especially, silicon is more effectively acted as refinement of the dendrite cell than calcium. It is due to that Mg_2Si precipitated at the dendrite cell boundary or in the matrix during T5 treatment of Si added AZ91 alloy retarded the growth of the secondary phase. In the mean while, without inducing the precipitates containing calcium, calcium was segregated mainly around secondary phase such as Mg_17Al_12 and partially dissolved in ternary eutectic (Mg-Al-Ca) structure. In the AZ91 alloy containing both silicon and calcium, more finely distributed Mg_2Si in matrix homogeneously and much finer microstructure were obtained than those containing silicon or calcium. Hence, An AZ91 containing both silicon and calcium was more effective to retarding the growth of the secondary phase than the other AZ91 alloy such as AZ91 alloy containing silicon or AZ91 alloy containing calcium.
급속냉각한 Al-(1 , 3 , 5)Cr 합금의 조직에 미치는 기계적 합금화의 영향
지태구,김완철 ( T . G . Jhee,W . C . Kim ) 한국열처리공학회 1993 熱處理工學會誌 Vol.6 No.4
Rapid solidified splats Al-(1, 3, 5Cr) Alloys were produced by atomization-splat quenching method. Effects of mechanical alloying on the structure and mechcanical properties of rapidly solidified Al-(1, 3, 5)Cr alloys were studied. Degree of mechanical alloying of Al-(1, 3, 5)Cr alloys can be determined by observing the microstructural refinement, microhardness and microstructure of Al-(l, 3, 5)Cr splats during processing. In the initial stage of mechanical alloying of the Al-(1, 3, 5)Cr splats fracturing of the grain boundaries occured first, followed after fracturing of zone A regions. Saturation hardness of Al-(1, 3, 5)Cr alloys increased proportionally with increasing concentration of the solute (Cr). Age hardening was not observed in these alloys. Decomposition temperature of Al-1Cr splats after mechanical alloying was higher than that of Al-5Cr splats. The density of Al_7 Cr precipitates increased proportionally with increasing chromium content, as a result, there was a transition to finely and spherically dispersed phase after mechanical alloying.
급속냉각한 Al-(1 , 3 , 5) Cr 합금 압출재의 조직과 기계적 성질에 미치는 기계적 합금화의 영향
지태구,김완철 ( T . G . Jhee,W . C . Kim ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.1
The structure and mechanical properties of the extruded specimens were investigated in rapid solidified Al-(1, 3, 5) Cr alloys after mechanical alloying. Finer lamellar microstructure could no longer be resolved in the bars obtained by extrusion of the spherical particles after 200min. of processing time. The structure of extruded bars are highly depended on the processing time of splats. The isothermal annealing of the extruded bars showed that all the alloys had good thermal stability up to 400℃ and did not show the recrystallization phenomena. Severe working of Al-(1, 3, 5)Cr splats produced a very fine grain size and substructural strengthening (high dislocation density and fine grain size). Effects of mechanical alloying on the thermal stability of the extruded bars Al-(1, 3, 5) Cr alloys decreases, with increasing Cr content. But the ultimate tensile Strength in the extruded bars increases with increasing Cr content.