• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.365-370
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• 1997

The effects of changes in microstructure of Si phase on the thermal expansion coefficients(CTEs) and tensile properties of the hypereutectic Al-Si foundry alloy(A390) were investigated experimentally. Specimens were prepared by various fabrication processes, such as a permanent mold casting, a squeeze casting and a spray casting process, and subsequently hot-extruded. CTEs of the spray-cast specimen were found to be about 10% lower than those of the permanent mold-cast specimen, and the CTEs of the hypereutectic Al-Si alloy(A390) were changed proportionally with the size of Si phase. Ultimate tensile strength of the spray-cast and hot-extruded specimen was dramatically improved about 100% with improved elongation, compared to that of permanent mold-cast specimen. These improvements are mainly attributed to the reduction in size and aspect ratio of the brittle Si phase, and the elimination of the microvoids/porosities formed during casting.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.129-135
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• 1997

This study has investigated the effects of aging treatment on thc nlechanical propcrries of blg-iiAl-x%nix - 0.1.2) alloys fabricated by the squeeze castmg process. The microstructurcs of as-squeeze cast were composed of pro eurectic $\alpha$ magnesium solid solution, super saturated $\alpha$ solid solution and $\beta(Mg_{17}AI_{12}$) compund. Agcd at both $200^{\circ}C$ and $240^{\circ}C$, Mg--6AixZn alloys showed the peak hardness due to the formation of $\beta(Mg_{17}AI_{12}$) precipitates. The tiiscontinuous precipitates of the lamella r\.pe are predominant at $200^{\circ}C$ aging tredrment. tvhilc. the finely dispersed continu ous precipitates were major type at $240^{\circ}C$ treatment. Mg-- GAI-xZn a1loi.s fabricated hy the squeeze casting process had the hetter combination of tensile strength and elongation compared to the conventionally cast alloys. As increascci zinc: contents. the tensile strength was increased 11y the soiid solutirin strengthening effect of zinc,.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.797-810
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• 2009

A study was made of the effects of a Sn addition on the microstructure and microfracture mechanism of squeeze cast AZ51-xSn magnesium alloys. Microstructural observation, in situ fracture testing, and fractographic observations were conducted on these alloys to clarify the microfracture process. The microstructural analyses indicated that $Mg_2Sn$ particles as well as $Mg_{17}Al_{12}$ particles precipitated mainly along the solidification cell boundaries; the volume fraction of these hard particles increased as the amount of added Sn increased, with increased the strength. From in situ fracture observations of the AZ51-7Sn alloy, coarse precipitates located on the cell boundaries worked as easy crack propagation sites and caused abrupt intercellular fracturing. On the other hand, the overall fracture properties of the AZ51-3Sn alloy improved because crack propagation proceeded into the Mg matrix rather than into the cell boundaries as twins developed actively, as confirmed by an R-curve analysis. These findings suggest that the addition of 3~5 wt.% Sn is effective in improving both the tensile and fracture properties on the basis of well-developed twins, the blocking of crack propagation, and crack blunting.

• Journal of Korea Foundry Society
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• v.14 no.3
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• pp.258-266
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• 1994

AC4A $Al/Al_2O_3+SiC_p$ hybrid composites were fabricated by the squeeze infiltration technique. Effect of applied pressure, volume fraction of reinforcement($Al_2O_3$ and SiC) and SiC particle size($4.5{\mu}m$, $6.5{\mu}m$ and $9.3{\mu}m$) on the solidification microstructure of the hybrid composites were examined. Mechanical properties were estimated preliminarly by fractographic observation, hardness measurement and wear test. Results show that the microstructure of the hybrid composites were quite satisfactory, namely revealing relatively uniform distribution of reinforcements and refined matrix. Some aggregation of SiC particle caused by particle pushing was observed especially in the hybrid composites containg in fine particle($4.5{\mu}m$). Refined matrix was attributed to applied pressure and increased nucleation sites with addition of reinforcements. Fractured facet also revealed finer for the hybrid composites possibly due to refined matrix. Hardness and wear resistance increased with volume fraction of reinforcements. For hybrid composites with $9.3{\mu}m$ SiC, hardness was somewhat lower and wear resistance higher than other composites.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.537-549
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• 1996

This study aims at investigating the correlation of microstructure and mechanical properties of the AZ91 Mg/Al borate whisker composites fabricated by squeeze csting technique with a variation of applied pressure. Microstructure observation and in-situ fracture tests were conducted on the composites to identify the microfracture process. Detailed microstructural analyses indicated that the grain refinement could be achieved with applied pressure and the little change in volume fraction on reinforcing whiskers could be carried out. It was also found clearly from in-situ observation of crack initiation and propagation that in the composite processed by the lower applied pressure, microcracks were initiated earily at whisker/matrix interfaces, thereby resulting in the drop in strength. In the composite processed by the higher applied pressure, on the other hand, planar slip lines were well developed in the matrix, and then propagated through whiskers without whisker/matrix decohesion. Thus, the effect of the applied pressure on microstructure and mechanical properties can be explained by grain refinement, increased amounts of reinforcements, and improvement of whisker/matrix interfacial strength as the applied pressure in increased.

• Journal of Korea Foundry Society
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• v.28 no.6
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• pp.268-272
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• 2008

Interfacial characteristics of aluminum borate whisker reinforced AS52 matrix composite was investigated. Peak hardness of AS52 composite was obtained aging at $170^{\circ}C$ for 15h and the aging process was accelerated by the presence of the aluminium borate whisker. The MgO layer, which was the interfacial reaction product between the reinforcement and the Mg matrix, was produced with 20 nm thickness in as-cast condition. As the aging time increased, the thickness of the interfacial reaction layer increased to 50 nm in peak aged condition. The nano-indentation test results indicated that the strength of interface was improved by the aging but over-aging degraded the reinforcement and decreased the interfacial strength which resulted in the decrease of overall composite strength.

• Journal of Korea Foundry Society
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• v.28 no.3
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• pp.136-140
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• 2008

A new concept of salt core, a melting temperature of which is lower than the solidus temperature of cast alloy, was introduced to produced an integrated casting part having a complicated inner shape or requiring under-cut in high pressure die casting or squeeze casting process. The main goal of this study is to develop a new integrated net-shape forming technology using fusible core of lower melting temperature than that of a casting alloy. This integrated net-shape forming technology would be very successful and cost-effective for producing the integrated products having a complicated inner shape or requiring under-cut. The technology for measuring and evaluating a various property of fusible core such as a thermal conductivity and thermal expansion coefficient, melting temperature was established. Also, the work space can be cleaned without a pollution inducing products.

• Journal of Korea Foundry Society
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• v.14 no.5
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• pp.455-463
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• 1994

Aluminum matrix composites reinforced by fine steel wires were fabricated by squeeze casting process. Preforms made of fine steel wires were prepared with different surface conditions, namely uncoated(TN), carbo-nitriding treated(TT), and brass coated(TA). Squeeze casting were performed under the pressure of $1500kg/cm^2$ for 3min. during solidification, and pouring temp. of the melt being $750^{\circ}C$ and the steel mold being preheated at $250^{\circ}C$. Microstructural characteristics were evaluated, particularly concerned with the effect of the surface conditions of the preforms. The results obtained from this study are like these. TN specimens show partially non-wetted regions, due to easy formation of oxides on the surface of the fine steel wires. TT specimens show no interfacial reaction between the steel wires and the aluminum alloy matrix, possibly due to the formation of carbo-nitrided zone on the surface of the steel wires. TA specimens show excellent wettabillity between the reinforced steel wires and the aluminum alloy matrix and very thin interfacial zone is formed between them. During the solution hardening treatment of TA specimens, thickness of the interfacial reaction zones were increased with the solution treating time. TA specimens show typical ductile fracture in tensile test, but TT specimens show brittle fracture possibly due to the formation of the brittle hard surface on the steel wires during carbo-nitriding treatments. TA specimens which were reinforced with 40 vol.% of the fine steel wires exhibit high tensile strength of $77.1kgf/mm^2$ and impact value of $8.1kgf-m/cm^2$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.273-276
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• 2004

A356 alloy is one of the most popular casting aluminum alloys due to its good castability. It is well known that the mechanical properties of A356 alloy strongly depend on its characteristic microstructure, such as the size of eutectic Si, primary $\alpha$ dendrite and so on. These microstructural features are determined during the casting and solidification process, which implies the strong relationship with mechanical properties with solidification methods. In the present study, the mechanical characteristics of A356 alloy was investigated by using squeeze cast control arm in terms of the microstructural features, such as the size of eutectic Si, primary a dendrite. By doing so, the most favorable microstructure of A356 could be determined for Al control arm that should be one of the most reliable parts in automobile.

• Journal of Korea Foundry Society
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• v.20 no.4
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• pp.269-276
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• 2000

So far, the study on semi-solid process has been carried out to develop and research new advanced materials without some casting defects. In this study, A356 billets consisted of various dendritic shapes were prepared using electro-magnetic stirring process continuously. As-cast respectively has liquidus temperature of $625.6^{\circ}C$ and solidus temperature of $573.55^{\circ}C$ A356 slugs were reheated homogeneously at different temperatures of 580, 590 and $605^{\circ}C$, followed by squeezing in a mold insulated with applied pressures(0, 25, 50 and 70 MPa). In order to investigate on aging responce for casts, 50 MPa squeezed specimen among all specimens was prepared in aging treatments, which conditions are aging temperature of $160^{\circ}C$ and holding times of 0, 45, 90, 270, 360, 720, 1440 and 2880 min after solution treatment ($540^{\circ}C$ for 10 hr). SSM ingot with the output velocity of 150mm/min appeared more spheroidal shape and fine structure than that with the output velocity of 250 mm/min. According to increasing in reheating temperature, numbers of fatigue cycles, U.T.S and elongation increased at same time.