Papers by Author: Joon Pyo Park

Abstract: By imposing a high frequency magnetic field, the surface quality and macro/micro structure of the direct chill cast billets are improved. The casting speed can also be improved by simultaneous applying mold and electromagnetic coil, especially for the alloys with a wide freezing range such as Al-Cu-Mg alloy. The extent of macrosegregation in the Al-Cu-Mg alloy is reduced by application of the magnetic field. Moreover, the inverse segregation layer usually observed in the direct chill cast billet is eliminated by the effect of the electromagnetic field. The microstructure of the hot-rolled and heat treated billets cast under the high frequency field also show better characteristics.

Abstract: The objective of this study was to optimize the casting design of gamma titanium aluminde automotive turbocharger rotor by means of the practical experiment and numerical simulation. Gamma titanium aluminide rotors were produced by centrifugal casting methods on a laboratory scale. Based on the metal-mold reaction of gamma titanium aluminide, the investment molds were manufactured by an electro-fused Al2O3 mold. The experimental results showed that the castings failed to reach the end of the cavities due to insufficient centrifugal force and a lower fluidity compared to the other metals. Although the satisfactory results were not obtained in the numerical simulation, it was concluded that numerical simulation aided to achieve understanding of the casting process and defect formation in gamma titanium aluminide turbocharger rotor castings.

Abstract: 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.

Abstract: In this study, the electromagnetic vibration process is adopted for modifying the eutectic Si phase and reducing its size. The higher the current density and frequency of electromagnetic vibration (EMV), the finer the size of the eutectic Si phase. The tensile strength and elongation of EMVed alloys were highly improved. Measured twin probability of EMVed alloy at a frequency of 1000Hz was approximately six times as high as that of the normal alloy and half of that of Sr modified alloy. The mechanism for the increase in twin density due to EMV during solidification could be suggested from the fact that the preferential growth along <112> in silicon was suppressed by preventing the Si atom from attaching to the growing interface of the Si phase and by changing the solid/liquid interfacial energy of silicon.

Abstract: The separation system including a DC electric field with steady magnetic field was adopted for removal of inclusion in molten Al alloy. But, very small inclusions, which less than 10 ㎛ are not eliminated. So, firstly, small inclusions are agglomerated by low frequency electromagnetic vibration. And then, we adopting the previously used electromagnetically inclusion removal process. Experiments were carried out on commercial die casting aluminum alloy A380 (JIS: ADC 10). Inclusion was separated continuously. XRF was used for compositional test and PoDFA for cleanliness test. Chemical composition of specimen was not changed and UTS, elongation and cleanliness were increased.