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Compocasting 법에 의한 AZ91D/SiC_pMMCs(metal matrix composites)제조
이경태,김세광,구형찬,김달식,김영직 成均館大學校 科學技術硏究所 1994 論文集 Vol.45 No.2
Metal matrix composites have toughness, machinability and heat conductivity, which can be obtained in metals, as well as hardness, high temperature stability, which can be obtained in ceramics. The purpose of this study is to find the optimum production condition of a compocasting method which is composed of stirring SiC particles inside a matrix which is presented as a solid or liquid state. During the compocasting method. SiC particles are mechanically incorporated into the matrix. From this study, sound AZ91D/SiC_p composites were obtained when stirring the matrix for 60minutes between 583-588℃.
반용융 성형가공된 AZ 91 HP Mg 합금의 아연치환도금에 관한 연구
김세광,김영직,한혜준,한범석 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3
Magnesium alloys have received an increasing amount of attention in recent years due to their exceptionally low densities and high specific strengths. Among various manufacturing methods for magnesium alloys, semi-liquid forming has advantages of near net shape and the safety over inflammable magnesium alloys. The objective of this paper was to produce a electroplating base for semi-liquid formed AZ91HP magnesium alloy, consisting of activations and zinc immersion deposition. The variations of the surface potentials with time were conducted both during activations and zinc immersion deposition. The results indicate that oxalic/chromic activation sequence can produce a good foundation for zinc immersion deposition and by the double-dip technique, thin and homogeneous zinc immersion deposits can be obtained in shorter time compared with the normal single-dip technique. The growth mode of zinc immersion deposits largely depends on the surface potential deviations caused by the differences of microstructures and phases.
Ti 주물표면의 반응성에 미치는 주형재료 및 점결제의 영향
김세광,김영직,김명균,김태경,홍태환 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.4
Attempts have been made to evaluate the relative stability of surface layer reactions of cast metal with mold material in commercially pure titanium and Ti-6Al-4V alloy castings. For melting of titanium alloys, plasma arc melting process was used and the extent of the surface reaction of castings was determined by optical metallography and microhardness profiles. The mold materials being examined included ZrO₂, Al₂O₃, CaO stabilized ZrO₂, CaZrO₃ and CaO. The machined graphite mold was used for comparison. Moreover, it was to investigate the effect of the binder on metal-mold reaction in case of Al₂O₃ mold. The results showed that titanium castings with ZrO₂, Al₂O₃ mold had clear reaction layer(α-case), whereas negligible reaction with titanium occurred in CaO stabilized ZrO₂, CaO, CaZrO₃ and graphite mold. The grading of thermal stability of mold material does not follow the free energy data of the formation of these oxide. CaZrO₃ is regarded as a promising mold material for titanium investment castings. In additions, metal-mold reaction of titanium castings was affected sufficiently by the binder as well as the mold material.
SiCp/AZ91HP Mg 복합재료의 반용융 가압성형에 관한 연구
김세광,김영직,김명균,홍태환 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11
Thixoforming process is a novel forming process that has some advantages compared to die casting. In this study, thixoforming process was selected for net shape of magnesium composites. This present work was mainly concerned with the formability and the mechanical properties of thixoformed silicon carbide particulate reinforced AZ91HP magnesium composites, which were manufactured by Rotation-Cylinder Method. The fulfilling behaviors of the composite slurries with thixotropic microstructures showed that the complete fulfilling was achieved over 0.5 effective liquid fraction regardless of the fraction of the reinforcement. Moreover it was observed that all slugs filled the die cavity with essentially laminar flow, unique flow behavior of thixoforming, even in incomplete mold filling at lower temperature. The results of mechanical properties of the composites showed significant improvement in YS and a slight increase in UTS had been achieved in the composite with 5 ㎛ SiC particulate, and wear properties of them were dependent on the size of particulate compared to the fraction of reinforcement.
교반관법을 이용한 Mg-Ni 수소저장합금의 제조 및 수소화 특성평가
김세광,김영직,김명균,홍태환,하원 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
Mg -1, 5, 10 mass%Ni hydrogen absorbing alloys were fabricated by Rotation-Cylinder Method(RCM) and their hydrogenation properties were evaluated by PCI(Pressure-Composition Isotherm) measurement. The microstructure of as-cast Mg-10mass%Ni alloy is consisted of an island-like hydride forming α-Mg phase and the eutectic phase. The composition of the eutectic phase is measured about 80 mass%Mg and 20 mass%Ni by EPMA. Nickel has a catalytic effect on hydrogen dissociated reaction and the eutectic phase is rich in nickel composition compared with a phase. So the eutectic phase may act as a hydrogen dissociation site and a channel of diffusion of protium. This microstructure may promote the hydrogenation behaviors. The results of the maximum hydrogen storage capacity and reversible capacity of Mg-10 mass%Ni alloy were measured about 6.3 mass% and 4 mass% at 623K, respectively.
SiCp/AZ91D Mg 복합재료의 반용융 가압성형을 위한 조직제어
김세광,김영직,김명균,홍태환 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11
The purpose of this study was to evaluate the microstructure evolution during partial remelting as a function of isothermal holding temperature and time in the semisolid state. SiC particle reinforced magnesium composites were manufactured by Rotation-Cylinder method(RCM) and fully solidified as the billet, and then the microstructure evolutions of them were evaluated through simple reheating procedure. The results showed that the presence of SiC particles led to the fine solid globules compared to those of unreinforced magnesium alloys, and the finer solid globules were achieved with increasing SiC particle fraction. Coalescence was reduced since the solid globules were more isolated with respect to each other by the presence of the particle in grainboundary regions, and Ostwald ripening was also altered by the reduction of the effective diffusion coefficient in the liquid. The average diameters of the solid globules were independent of holding temperature but the standard deviation of the average diameters and the number of the solid globules per area were reduced as temperature increased, mainly due to high liquid fraction. Based on the previous results, it might be suggested that thixoforming of the particle reinforced composites should be performed after short isothermal holding at a relatively high temperature.