Kwon Hoo Kim

Effect of Large Strain on Texture Formation Behavior of AZ80 Magnesium Alloy during High Temperature Deformation

In previous study, the formation behavior of texture and microstructure in AZ80 magnesium alloy under high temperature deformation was investigated. It was found that the basal texture was formed at stress of more than 15-20MPa and the non-basal texture was formed at stress of less than 15-20MPa. This means that stress of 15-20MPa is the change point of deformation mechanism. Therefore, in this study, uniaxial compression deformation of AZ80 magnesium alloy was carried out at high temperature deformation (stress of 15-20MPa). Behaviors of microstructure and texture development are experimentally studied. The material used in this study is a commercial magnesium alloy extruded AZ80. The uniaxial compression deformation is performed at temperature of 723K and strain rate 3.0×10-3s-1, with a strain range of between-0.4 and-1.3. Texture measurement was carried out on the compression planes by the Schulz reflection method using nickel filtered Cu Kα radiation. EBSD measurement was also conducted in order to observe spatial distribution of orientation. As a result of high temperature deformation, the maximum value of the flow stress is observed at the true stress-strain curves, and the main component of texture and the accumulation of pole density vary depending on deformation condition.

The Effect of Frequency of Electromagnetic Vibration on the Primary Silicon Size in Hypereutectic Al-Si Alloy

In this study, the electromagnetic vibration is adopted for control of the size of primary Si phase. The higher the current density and frequency of electromagnetic vibration (EMV), the finer the size of primary Si phase. The higher the current density but the lower frequency of EMV, the bigger the size of primary Si phase. This phenomenon considered to be related the collision, agglomeration and diffusion of silicon atoms.

Effect of Bubbling on the Primary Silicon in Hypereutectic Al-Si Alloy

This paper investigates the effect of bubble on the primary Si size in Al-18wt.%Si alloy. The primary Si size observed was varied with bubble size and bubbling time in bubble process. The effect of the holding temperature of the melt in bubbling process was also investigated. In water model, as the injecting bubble size decreases, the residual bubble size in the water decreases and the residual bubble conservation time in the water increases. Also in the experiment of Al melt, the primary Si size decreases, as the injecting bubble size decreases and as the bubble processing time increases. Pore was observed at the center of primary Si. This pore was observed at many Si phases. So, this experiment suggests that the bubble can be used as nucleation sites of primary Si.

Effect of Prior Strain on Damping Capacity and Mechanical Property during Heat Treatment

In previous study, it was investigated damping capacity on various deformation and heat treatment conditions in order to study damping capacity that was influenced by grain size and dislocation motion in detail. Magnesium alloy AZ31 was rolled at 673K with different rolling reduction, respectively. Specimens were machined out parallel to the rolled direction and annealed on various temperature and time. Then, damping capacity, microstructure and hardness was measured at room temperature. Factors affected on damping capacity are grain size, crystal orientation, dislocation motion, and so on. It was found that damping capacity has been affected by grain size and crystal orientation. Grain size and hardness is not examined obvious difference after annealing. In large prior strain, however, low damping capacity is appeared and damping capacity increases with increasing of heat treatment temperature. The reason is that resolved shear stress factor is influenced by damping capacity.

Effect of Aluminum Content on Texture Formation Behaviors in Magnesium Alloy

In order to understand the effects of the solute element and its concentration on the formation of texture, uniaxial compression tests were carried out at various deformation conditions with different aluminum solute concentration in rolled AZ magnesium alloy (AZ31, AZ61, AZ91). To clarify the texture measurements and crystal orientation distribution, X-ray diffraction methods were conducted on mid plane section of the specimens. As a result in this study, the formation of fiber texture and occurrence of dynamic recrystallization were observed in all case of specimens. The main components and its sharpness of texture were varied depending on deformation conditions and Al concentrations. Especially, accumulation of basal texture was developed with an increasing of Al concentration.

Derivation of Optimum Treatment Conditions per Heavy Metal Contamination for Electrical Membrane and Convergent Process Apparatus in Electromagnetic Field

Objective of the present study is to derive appropriate study factors upon introduction of purification technique with mounting of multi-type of electrical membranes in an industrial combined with contaminated underground water. For reaction times of 540mins, removal rates according to the strength of voltages were calculated and optimum operating factors of the electrical membrane were derived according to treatment conditions per concentration of electrode liquid using electrical membranes. The removal rates as a function of voltages were shown to be 88% at 15V for Ni, 65% and 68% at 15V and 20V, respectively, for Cr. In the comlex modulation electromagnetic field, Cr showed the removal rates of 80% and 85% at 15V and 20V, respectively, while Ni showed the removal rates of 94% and 97% at 10V and 15V, respectively. When the concentrations of electrode liquid (Na2SO4) were varied upon electrode membrane treatment, the removal concentration for 0.5% was 1.8mg/l in the case of 20V resulting in the removal rate of 91%. In case of 1% of electrode liquid (Na2SO4), the final concentrations at 15V and 20V were shown to be below 1mg/l in both cases, and high removal tates above 98.9% could be obtained in the treatement with combined application of the electromagnetic field.

Study on the Removal of Cadmium from Underground Water Using a Complex Modulation Electromagnetic Device Based on Correlation of Electromagnetic Field and Electrical Conductivity

The objective of this study was to increase flux and decomposition speed through the development of a multi-type electrical field decomposition facility that employs a more complex modulated electromagnetic field than that used in existing decomposition facilities where recalcitrant organics or heavy metals are combined together. Further, in this study, optimized foundational data was derived from the results obtained following field work. As a result, when an electrical field was applied to an electrolyzer, decomposition of the electrolyzer was carried out quickly, thereby showing higher efficiency because an electrical field was permeated to the contaminant faster compared to the case where an electrolyzer was not added. Keywords: Electromagnetic field, Heavy metal, Electrolyzer, Electrical field

Microstructure Characterizations of Hypereutectic Al-Si Alloys with Different Undercooling Levels

Microstructural variation is quantitatively characterized by measured undercooling. For neareutectic Al-13wt%Si alloys, microstructure transitions, which include a phase change from eutectic to primary α-Al dendrite plus eutectic and a morphological change from α-Al dendrite to equiaxed Al grains, were observed with increasing undercooling levels. For hypereutectic Al-Si alloys, microstructure transitions, which include a morphological change of primary and eutectic Si crystals, were also obtained quantitatively by increasing undercooling.