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Mg-5wt%Al-0.6wt%Zr 합금의 용탕단조시 주조결함의 형성 및 방지
황영하,허승호,홍준표 ( Young Ha Hwang,Seung Ho Huh,Chun Pyo Hong ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.3
N/A The squeeze casting of a Mg-5wt%Al-0.6wt%Zr alloy was carried out to investigate the conditions for the formation and the prevention of macrodefects, such as macrosegregation and shrinkage defects. The effects of the process parameters, the applied pressure, the die temperature, and the pouring temperature on the formation of macrodefcts were investigated in correlation with the evolution of macrostructure. Three types of macrodefects were found; macrosegregation only, shrinkage defects only, both macrosegregation and shrinkage defects. It was found that the pouring temperature, the die temperature, and the applied pressure are closely related to the formation of macrodefects. Sound castings without macrosegregation and shrinkage defects can be obtained under the conditions of 80 MPa < P < 110 MPa, 730˚C < Tp < 760˚C, and 180˚C < Tp < 250˚C. (Received April 15, 1998)
오상섭(Sang Sub Oh),황영하(Young Ha Hwang),김도향(Do Hyang Kim),홍준표(Chun Pyo Hong),박익민(Ik Min Park) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.1
N/A Microstructural characteristics and strengthening behavior in Mg-5wt%Zn-0.6wtZr alloys have been investigated by a combination of optical, secondary electron and transmission electron microscopy, differential thermal analysis, and hardness and tensile, creep property measurements. The result have been compared with those of Mg-5wt%Zn alloys. The as-squeeze cast microstructure consisted of dendrite α-Mg, interdendrite or intergranular Mg_7Zn₃ and fine dispersoids of ZnZr₂. The size of secondary solidification phases in Mg-5wt%Zn-0.6wtZr alloys was significantly smaller than that of the Mg-5wt%Zn alloys due to the existence of fine dispersoid of ZnZr₂ which also effected the refinement of grain size. TEM study showed that the main cause of age hardening is formation of fine rodlike β₁` precipitates as well as fine ZnZr₂ dispersoids. Due to the observed microstructural characteristics mechanical propeties of Mg-5wt%Zn-0.6wtZr alloys was found to be superior to those of Mg-5wt%Zn alloys. (Received June 22, 1998)
융탕단조한 Mg-10 wt % Li-3 wt % Al 합금의 연화형상에 미치는 Si 영향
홍준표,김도향,황영하 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4
Effects of Si on the softening of the squeeze cast Mg-10wt%Li-3wt%Al allay have been investigated as functions of Si content, solution treatment, aging temperature and time. Microstructures of as-cast Mg-10wt%Li-3wt%Al-Xwt%Si(X:0.2, 0.4, 0.6, 1.0, 1.2) alloys consist of a mixture of α, β, AlLi and Mg₂Si phases. The hardness increased with the addition of Si due to the formation of polygon and Chinese script type Mg₂Si in the α and β phase and due to the decrease of the amount of AlLi phase. In the case of alloys having Si content lower then 0.4wt%, two types of Mg₂Si became much finer, and the volumes of ㎦ and AlLi phases decreased with the increase of the aging temperature and time which resulted in the improvement of hardness. It Can be concluded that the combined effects of fine dispersion of Mg₂Si, disolving of Al into the matrix, and decreased volume of α and AlLi effectively lead to the prevention of softening.
용탕단조한 Mg-Li-Al 합금의 기계적 성질에 미치는 열처리 영향
Han, Chang Haw,황영하,김영우,김도향,홍준표,Cho, Bum Jin 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.12
Effects of heat treatment on the mechanical properties in squeeze cast Mg-10wt%Li-3wt%Al and Mg-10wt%Li-5wt% Al alloys have been ivestigated. The as-cast microstructure consists of a mixture of α, βand AlLi. The best combination of hardness and tensile strength were obtained after solution treatment at 350℃ for 1 hour for Mg-10wt%Li-3wt%Al and 370℃ for 1 hour for Mg-10wt%Li-5wt%Al, respectively. Various microstructural features such as the ratio of α/βvolume fraction, the orientation relationship between α and β grains and shape change of α phase were observed after heat treatment. Strengthening of the Mg-Li-Al alloys is due to the precipitation of AlLi in the β phase matrix, dissolving of Al into the matrix during heat treatment and reprecipitation of α platelets during cooling after heat treatment.