Je Sik Shin

Numerical and Experimental Study of the Electromagnetic Continuous Casting of Silicon

For the preparation of multi-crystalline Si ingot, an EMC (Electromagnetic Continuous Casting) technique using a segmented Cu cold crucible under a high frequency alternating magnetic field was utilized. Numerical and experimental works were systematically carried out in order to optimize the effect of Joule heating and electromagnetic pressure. A Si melt of 5.5 cm height was able to be kept non-contact with the crucible wall when the induction coil current of 970 A was applied. A segmented graphite crucible, which was attached at the upper part of the cold crucible, was introduced to enhance significantly the heating efficiency of Si melt keeping non-contact condition.

Manufacture of CNTs-Al Powder Precursors for Casting of CNTs-Al Matrix Composites

CNTs-Al matrix composites are considered to be promising heat dissipating materials because thermal conductivity can potentially be improved whilst their density is reduced. Although casting has many advantages in the fabrication of large, complex components, this process cannot be easily employed when manufacturing CNTs-Al composites. In order to produce CNTs-Al matrix composites by casting a CNTs-Al powder precursor was manufactured using mechanical milling and electroless plating processes. Aluminium powder with CNTs of 10 wt.% and 20 wt.% were mixed and ball milled using a horizontal mill. After milling for 3 hrs., the milled powder exhibits a flattened morphology with a band-type distribution of CNT clusters observed within the aluminium particles. Prolonged milling of up to 24 hrs. introduces an equiaxed particle shape for the milled powders with a uniform distribution of CNTs within the aluminium particles. However, as milling time increases, the CNTs become fractured by ball-to-ball collisions. There was no reaction evident between the aluminium and the CNTs at milling times up to 24 hrs. In order to improve the wettability between the CNTs-Al powder precursor and Al melt during the casting process, electroless Ni plating was performed. The processing time for the Ni-plating affects the uniformity of the coating layer. For a uniform coating condition, the average thickness of the coating was ~1.87 μm, with no evidence of gaps between the milled powders and coatings observed.

Optimization of Heat Treatment Parameters of Mo-Free High-Cr Cast Iron Mill Balls

A Mo-free high-Cr cast iron with superior impact-wear resistance was tried to develop for mill balls by alloy design and subsequent heat treatment. The Cr/C ratio was varied up to 7.7 in order to minimize and eventually eliminate Mo addition, still ensuring hardenability. For the proper balance between abrasion resistance and toughness, the combined effects of each heat treatment parameters on the mechanical properties were systematically investigated using Taguchi method and response surface method (RSM), well recognized as powerful tools of the designs of experiments (DOE). It was found that hardness and impact energy were mainly affected by tempering and destabilization conditions, respectively. It is noted that high impact energy of 5.2 J/cm2 was obtained without deteriorating hardness (54 HRc) during the verification experiments under the heat treatment condition optimized by the DOE analyses.

The Effect of Crucible Configuration on Joule and Pinch Effects in EMCC Process of Silicon

For the development of an economical production technology of multi-crystalline silicon, an EMCC (Electro Magnetic Continuous Casting) process using a segmented Cu cold crucible was practiced. In order to enhance significantly the heating efficiency of silicon melt keeping non-contact condition during continuous melting and casting processes, the effects of Joule heating and electromagnetic pressure in molten silicon were optimized by systematically varying crucible design and configuration. Throughout the present investigation, multi-crystalline silicon ingot was successfully produced at the casting speed of above 1.5 mm/min under a non-contact condition.

A Study on Surface Oxidation Coating Characteristic of Al-Si Casting Alloys

in this paper, it was aimed to improve understanding about the effects of physical melt treatment on the morphologies of eutectic silicon crystal size, and then the effects of these microstructural features on anodizing characteristics. A380 and A356 casting aluminum alloys were used in this experiment. A twin-screw melt-shearing process and an electro magnetic stirring process were utilized before high pressure die casting. In order to refine and homogenize the microstructure of the diecast Al-Si alloys, the melt-shearing process parameters were controlled and T6 heat treatment was carried out. A uniform microstructure over the whole thickness of the diecast specimens caused smaller difference in oxidation coating layer thickness between machined and non-machined surfaces. More uniform anodic coating layer was obtained by AC/DC coupled anodizing and PEO processes compared to conventional DC anodizing process.

Effects of Physical Melt Treatments on Microstructural Evolution and Anodizing Characteristics of Al-Si Casting Alloys

In order to investigate the effects of physical melt treatment on microstructural feature and anodizing characteristics of Al-Si system casting alloys, A380 and A356 aluminum alloys were chosen and a twin-screw melt-shearing process was utilized before high pressure die casting. In order to refine and homogenize the microstructure of the diecast Al-Si alloys, the melt-shearing process parameters were controlled and T6 heat treatment was carried out.

Fabrication and Properties of a Combined Structural Cu Sheet for Interconnect Material

In this study, it was aimed to develop a novel interconnect material simultaneously possessing high electrical conductivity and strength. Combined structural Cu sheets were fabricated by forming the high electrical conduction paths of Ag on the surface of high strength Cu alloy substrate by damascene electroplating. As a result, the electrical conductivity increased by 40%, while the ultimate tensile strength decreased by only 20%. When the depth of Ag conduction path was deep, fracture zone ratio as well as roll-over zone increased.

Tribological Behavior and Surface Chemistry Characteristics of Quasicrystal Coatings

The aim of this study was to investigate the effects of air plasma spraying process parameters on the tribological behavior and surface characteristics of quasicrystal coatings. For this purpose, the response surface method (RSM), one of the designs of experiment (DOE) was utilized to systematically investigate the combined effects of each process parameters. The RSM analysis revealed that the superior tribological performance of quasicrystal coatings was obtained by the optimized condition of specific micro-hardness and porosity level. It was specially quoted that the relatively low hardness of quasicrystal coatings caused the improvement of abrasive wear resistance during the current investigation.

Cold Workability and Magnetic Properties of 6% Si Steel

In order to develop an economical production method of high Si steel sheet, 6%Si (by weight percent, unless specified otherwise) steel was prepared by a combined process of conventional casting and hot- and cold-rolling. Tension and nano-hardness tests and TEM analysis were carried out to examine the effects of ordered phases, Si-content, and testing temperature on cold workability. By optimizing the successive processes of casting, hot-rolling, heat treatment, and cold-rolling, 0.5 mm thick 6%Si steel sheet was successfully produced without crack formation. As Si content increased from 3% to 6%, core loss (W10/50) of the 0.5 mm thick Si steel sheet decreased from 1.36 W/kg to 0.89 W/kg.

Development and Property Evaluation of Low-Si Aluminum Casting Alloys for Thermal Dissipation

To develop an aluminium alloy which may combine high thermal conductivity and good castability and anodizability, Al-(0.5~1.5)Mg-1Fe-0.5Si and Al-(1.0~1.5)Si-1Fe-1Zn alloys were assessed as potential candidates. The alloys exhibited 170~190% thermal conductivity, 60~85% fluidity, and equal or higher ultimate tensile strength compared to those of ADC12 alloy.