• Journal of Korea Foundry Society
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• v.31 no.1
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• pp.11-17
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• 2011

The effect of CaO addition to AM60B Mg alloy on tensile properties has been investigated, with focus on strength and ductility at room and elevated temperatures. The 0.25-0.65wt% CaO added AM60B Eco-Mg diecastings were prepared by high pressure die casting using Buhler 1,450-ton cold chamber machine without $SF_6$ and $SO_2$ gases. The microstructures and tensile properties of each alloy were tested. The results show that the grains of AM60B are refined and the mechanical properties increase with CaO addition at room temperature. The improvement of strength and ductility is prominent at 0.45-0.55wt% CaO addition. Also, improved mechanical properties are maintained at elevated temperature of $150^{\circ}C$. CaO addition results in $Al_2Ca$ phase formation mostly on the grain boundaries. This phase leads to the refinement of grain structures and improvement of ductility as well as strength. The suppression of ${\beta}-Mg_{17}Al_{12}$ phase as well as the decrease of fracture surface porosity and other casting defects caused by melt cleanliness also contribute to the enhancement of mechanical properties of AM60B Eco-Mg at room and elevated temperature.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.129-135
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• 2021

Recently, additive manufacturing (AM) technology such as powder bed fusion (PBF) and directed energy deposition (DED) are actively attempted as consumers' needs for parts with complex shapes and expensive materials. In the present work, the effect of processing parameters on the mechanical properties of 316L stainless steel coupons fabricated by PBF and DED AM technology was investigated. Three major mechanical tests, including tension, impact, and fatigue, were performed on coupons extracted from the standard components at angles of 0, 45, 90 degrees for the build layers, and compared with those of investment casting and commercial wrought products. Austenitic 316L stainless steel additively manufactured have been well known to be generally stronger but highly vulnerable to impact and lack in elongation compared to casting and wrought materials. The process-induced pore density has been proved the most critical factor in determining the mechanical properties of AM-built metal parts. Therefore, it was strongly recommended to reduce those lack of fusion defects as much as possible by carefully control the energy density of the laser. For example, under the high energy density conditions, PBF-built parts showed 46% higher tensile strength but more than 75% lower impact strength than the wrought products. However, by optimizing the energy density of the laser of the metal AM system, it has been confirmed that it is possible to manufacture metal parts that can satisfy both strength and ductility, and thus it is expected to be actively applied in the field of electric power section soon.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.21 no.3
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• pp.257-265
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• 1999

To investigate the sequential changes in microvascular architecture and osseous regeneration during the bony healing after an application of the guided tissue regeneration method, we made artificial defects measuring $0.7cm{\times}0.3cm$ in size on femoral bones of rats measuring about 200gm and applied non-absorbable TEFE membrane at experimental sites but not at control sites. Then we observed the sequential changes and correlations between new vacuolation and bony regeneration using microvascular corrosion cast method and routine light microscopic observation at 1, 2 and 3 weeks after operation, respectively. The results showed that there were close relationships between regeneration of microvasculature and bone. In early phase, the invasion of granulation tissue at control sites delayed bony regeneration, however, in later phase, there was no remarkable differences in bony regeneration between control and experimental sites. The placement of barrier also affected in revascularization of regenerating bony defects. This is, the experimental sites showed parallel arranged nutritional vessels along long axis with well developed retiform plexus whereas the control revealed vertical invasion of microvasculature from outside of marrow space through bony defects which was also rearrange with time into parallel pattern with a vertical plexus but lesser organized than that of experimental sites. These findings suggest that the reconstruction of regenerating vasculature within the marrow cavity only may be sufficient and/or more be efficient in regeneration of bony defects.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.482-489
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• 2020

This study conducted a prototype development and evaluation by performing die-casting mold design, mold manufacturing, and injection condition optimization based on flow and solidification analysis to meet the needs of the coupling parts produced by die casting. Through flow analysis, the injection conditions suitable for 100% filling in the cavity were found to be a molten metal temperature of 670 ℃, injection speed of 1.164 m/s, and filling pressure of 6.324~18.77 MPa. In addition, solidification close to 100 % occurred in all four cavities when the solidification rate was 69.47 %. A defect inspection on the surface and inside the product revealed defects, such as poor molding and pores. In addition, the dimensions of the injected product were within the target tolerance and showed good results. Through the feedback of the results of flow and solidification analysis, it was possible to optimize the mold design, and the injection optimization conditions were confirmed to be a total cycle time of approximately 6.5 seconds. Good quality carrier parts with an average surface hardness of approximately 45 mm from the gate measured at 97.48(Hv) could be produced.

• Journal of Korea Foundry Society
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• v.12 no.4
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• pp.305-316
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• 1992

Steel and iron castings made with expandable polystylene (referred to hereafter as EPS) patterns are often affected by distinctive defects associated with incomplete decomposition of the EPS as the molds are filled with metal. The effects of practical factors on carbon pick-up were investigated on the specimens, by taking successive layers of swarf and analysis, whereas the lustrous carbon is determined by using combustion analysis. The quality of the castings, with particular reference to carbon pick-up in low carbon steel and lustrous carbon on gray iron, is further influenced to a significant extent by such practical factors as reduced pressure, the pouring temperature, the density of EPS pattern, the additive in coating and in pattern and the casting thickness. The rate at which carbon pick-up and lustrous carbon deposites are formed can be reduced by reducing the density of the pattern and also reducing pressure, especially by adding $Na_2CO_3$ in coating and in pattern to promote $CO_2$ evolution. The upper parts of castings obtained using EPS patterns are slightly higher in carbon pick-up and in lustrous carbon than other parts.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.544-550
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• 2018

The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from $0.9{\mu}m$ to $0.1{\mu}m$ and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

• Journal of Welding and Joining
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• v.8 no.4
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• pp.35-45
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• 1990

Casting are widely used nodays as complicated and diversified forming materials due to its superior castability. However the welding of cast iron has not been accompaniced satisfactory resulting in an microstructure change happened in the heat affected zone (HAZ), especially the graphite are formed and shaped consecutively in the area and it has great impact on the crack occuring and growth together with martensite forming in this area. It case of gray cast iron welding, it is required for pre-heat treatment or specific welding consumables to restrain forming the martensite in the HAZ. In this study, by applying the plasma surface overlaid welding. Fe-Mn-Al steel powder has been used for improvement of anti-crackability in the HAZ and much attention has been paid to establish the overlaid welding method for gray cast iron so that optimum welding conditions may prevent the cracking. With our experiments, we have found that to prevent defects which may occur in the HAZ, the overlaid welding technique for gray cast iron has been developed.

• Transactions of Materials Processing
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• v.15 no.6 s.87
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• pp.421-427
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• 2006

Drawing process of Al-1%Si bonding wire considering fine Si particle is analyzed in this study using FE-simulation. Al-1%Si boding wire requires electric conductivity because Al-1%Si bonding wire is used for interconnection in semiconductor device. About 1% of Si is added to Al wire for dispersion-strengthening. Distribution and shape of fine Si particle have strongly influence on the wire drawing process. In this study, therefore, the finite-element model based on the observation of wire by continuous casting is used to analyze the effect of various parameters, such as the reduction in area, the semi-die angle, the aspect ratio, the inter-particle spacing and orientation angle of the fine Si particle on wire drawing processes. The effect of each parameter on the wire drawing process is investigated from the aspect of ductility and defects of wire. From the results of the analysis, it is possible to obtain the important basic data which can be guaranteed in the fracture prevention of Al-1 %Si wire.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.566-571
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• 2010

Dispersion behavior of the slurries consisted of bimodal-type AlN powders was examined in non-aqueous solvent system. Azotropic solvent system and copolymer acidic dispersant were applied to the slurries. Measurements of the sedimentation height and the viscosity of the each slurry, and the test of particle size distribution of the each powder sample were conducted as examinations for the dispersion behavior at the various dispersant contents. The bimodal-type particle size distribution was continued after addition of the dispersant and small particle portions were increased as the dispersant content increases. The density of the green sheet was also increased as the dispersant content increases and a green density of $2.114\;g/cm^3$ was obtained at the sample prepared from 2.4 wt% dispersant content. The increase of large particle portions resulted in the surface defects of the green sheets.

• Journal of Korea Foundry Society
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• v.13 no.3
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• pp.248-258
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• 1993

A semi-solid alloy in which solid and liquid phase are co-existing is obtained by stirring of A17075 molten metal. A semi-solid alloy is dependent on the corresponding temperature within the solid-liquid range, and the process parameters should be controlled accurately to obtain the homogeneous semisolid alloy. The fabrication possibility of fiber-reinforced aluminum alloy containing $Al_2O_3$ short fibers with vigorous agitation of short fibers were obtained by control of stirring time, solid fraction and impeller speed in extrusion billet fabrication processes. The microstructure to extrusion billet fabricated by low pressure casting was investigated for fiber dispersion state. The relationship between the extrustion force and velocity at hot extrustion, the flow strain and extrusion ratio were theoretically described. The surface defects with lubricants and without lubricant after hot extrusion were investigated. The composites materials after hot extrusion were measured by vickers hardness with extrusion ratio. It has become clear that the secondary working such as hot extrusion was very useful to obtained improved the mechanical properties of metal matrix composites.