• Transactions of Materials Processing
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• v.9 no.4
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• pp.389-394
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• 2000

The studies on gram size refinement for rheocast processing of hypereutectic Al-18%Si alloys have been investigated in the present study. To increase the efficiency of mechanical stirring, sieve type stirrer are newly designed and implemented for rheocasting of hypereutectic Al-18%Si alloy. Mechanical stirring of semi-solid slurry by using sieve type mechanical stirrer results in morphological changes of the primary Si particles, from angular rod shape to near spherical shape and uniform distribution of proeutectic Si. The remarkable spheroidization of Primary Si Particles and distributional uniformity of proeutectic Si show well the efficiency of sieve type mechanical stirring method which can accelerate the coalescence-fracture-wear of the individual particles by strong turbulent flow between lattices during rotation of sieve type stirrer.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.120-126
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• 2010

It was known that the excellent wear resistance of hyper eutectic aluminum alloy is based on the primary Si particles which are distributed in the base metal. When the primary Si volume fraction increases, the smaller size have excellent wear resistance characteristics. However, this trend always does not match. There is no investigation result based on the materials and methods for real using parts. In this study, using the automotive parts manufacturer currently in use hyper eutectic Al alloy tensile test specimen type sample was fabricated by 350Ton high pressure die-casting machine. Then, fluidity, tensile, impact and wear resistance properties were evaluated. If the casting quality, primary Si size, fraction and distribution are similar, mechanical properties and wear resistance are equivalent.

• Journal of Korea Foundry Society
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• v.26 no.3
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• pp.140-145
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• 2006

Sr, added in the hypereutectic Al-Si alloys, is absorbed on the surfaces of primary Si as well as eutectic Si, and can change the growth mode of primary Si from non-faceted to faceted mode, as the amount of Sr increases larger than 0.04 wt.%, even though it cannot affect the grain size of primary Si, significantly. The EBSD analysis shows that the traction of ${\Sigma}3$ boundary(twin boundary) increases as the amount of Sr in the hypereutectic Al-Si alloys increase until the over-modification occurs at 1.6 wt.%Sr and proves that the change in growth mode of primary Si results from the change of TPRE growth to IIT growth.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.565-575
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• 1996

In this study, to gain the semi-solid alloy we employed the electromagnetic rotation by a induction motor of 3-phases and 2-poles for Al-7wt%Si alloy and observed the size of primary solid particle, distribution state of primary solid particle, the degree of sphericity, and fraction of primary solid for the evaluation of its results. The size of primary solid particle increases from $98{\mu}m$ to $118{\mu}m$ as solid fraction increases from 0.2 to 0.5. The degree of sphericity increased as the solid fraction increased. Solid particles obtained from the microstructures of isothermally held sample were coarsened and the degree of sphericity was enhanced as isothermal holding time increased. However, when the sample was stirred for more than 40min, solid particles merged together and liquid phase was entrapped within the cluster of solid particles. The size of primary solid particle was not changed significantly with the variation of input voltages by 160V over which solid particles began to merge together to be a large cluster of about $170{\mu}m$ at 180V. The standard deviation and the degree of sphericity were not changed significantly with the variation of input voltage.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.994-995
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• 2006

The microstructure of the extruded Al-20Si bars showed a homogeneous distribution of eutectic Si and primary Si particles embedded in the Al matrix. The grain size of ${\alpha}-Al$ varied from 150 to 600 nm and the size of the eutectic Si and primary Si in the extruded bars was about 100 - 200 nm. The room temperature tensile strength of the alloy with a powder size $<26{\mu}m$ was 322 MPa, while for the coarser powder ($45-106{\mu}m$) it was 230 MPa. With decreasing powder size from $45-106{\mu}m$ to $<26{\mu}m$, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The fracture mechanism of failure in tension testing and wear testing was also studied.

• Journal of Korea Foundry Society
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• v.36 no.2
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• pp.53-59
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• 2016

The effects of ultrasonic melt treatment on the microstructures of aluminum piston were examined at five observation parts having different cooling rates. The microstructure of aluminum piston consisted of primary Si, eutectic Si, and various types of intermetallic compounds. Regardless of cooling rate, the ultrasonic melt treatment transformed dendritic eutectic cells to equiaxed eutectic cells and it decreased the sizes of eutectic Si and intermetallic compounds that exist at eutectic cell boundaries. In the absence of ultrasonic treatment, coarse primary Si particles were severely segregated and its size was increased with decreasing the cooling rate. The ultrasonic treatment decreased the size of primary Si particles from $25.5{\sim}31.0{\mu}m$ to $17.6{\sim}23.1{\mu}m$, depending on the cooling rate. In the presence of ultrasonic treatment, relatively fine primary Si particles were homogeneously distributed throughout the piston. In addition, the ultrasonic treatment increased the population density and area fraction of fine primary Si particles.

• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.89-96
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• 2000

The effects of modification processing on the refinement of primary Si and the wear behavior of hyper-eutectic Al-Si alloys have been mainly investigated. Refining effects of primary Si in Al-17%Si alloy was more efficient than that of B.390 alloy. Optimum condition of getting the finest primary Si microstructure was when AlCuP modifier is added into the melt at $750^{\circ}C$ and held it at $700^{\circ}C$ for 30 minutes. Wear loss in the specimens of as-cast condition decreases as the size of primary Si decreases, in the order of B.390 alloy, B.390 alloy with AlCuP addition, Al-17%Si alloy and Al-17%Si alloy with AlCuP addition. Wear loss in the aged condition of Al-17%Si alloy, B.390 alloy and B.390 alloy with AlCuP addition decreased due to the increase of compressive residual stress in the matrix by the aging treatment. While, wear loss increased in the aged specimens of Al-17%Si alloy with AlCuP addition and Hepworth addition in which compressive residual stress decreases by the aging treatment. Therefore, it is assumed that higher compressive residual stress in the matrix can reduce the wear loss in composite materials such as hyper-eutectic Al-Si alloys.

• Journal of Korea Foundry Society
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• v.18 no.5
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• pp.474-480
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• 1998

Microstructural characteristics of semi-solid state processed hypereutectic Al-Si alloys have been investigated. Main concern of the present study is to investigate the effects of P and Sr addition on the size and morphology change of the primary Si particles. Refinement of the primary Si particles was observed with the addition of P and Sr at the early stage of semi-solid state processing, but such a refining effects became negligible resulting in Si particles with a near-spherical morphology with continuous stirring. This implies that the microstructural transformation mechanism became more dependent to stirring effects than to the alloying effects during semi-solid state processing. Brittle fracture and agglomeration were proposed as the mechanisms for microstructural alterations during semi-solid state processing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.355-358
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• 2004

In this study, the deformation characteristics of grain-size controlled rheology materials surfaces were investigated as a part of the research on the surface crack prediction in semi-solid formed automobile components. The microstructure of rheology Al-Si alloys consists of primary and eutectic regions. In eutectic regions the crack initiation begins with initial fracture of the eutectic silicon particles and inside other intermetallic phases. Nano-deformation characteristics in the eutectic and primary region of semi-solid aluminum alloys (356 alloy and 319 alloy) were investigated through the nanoindentation/scratch experiments and the AFM observation.

• Journal of Korea Foundry Society
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• v.26 no.3
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• pp.123-128
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• 2006

Mechanical and thermal properties of spray-cast hypereutectic Al-20wt.%Si-xwt.%Fe alloys (x=0, 1, 3, 5) were investigated. After the spray-casting, hot extrusion was performed at $400^{\circ}C$. Intermetallic compound (${\beta}-Al_5FeSi$) and primary Si are observed in the spray-cast aluminum alloys. The size of primary Si and intermetallic compound of the spray-aluminum alloys became finer and more uniformly distributed than that of the permanent mold cast ones. Ultimate tensile strength of the spray-cast aluminum alloys increased by increasing Fe contents, but that of the permanent mold cast aluminum alloys decreased by increasing Fe contents possibly due to increased amount of coarse intermatallic compound. The coefficient of thermal expansion (CTEs) of the aluminum alloys became lower with finer primary Si and intermetallic compound, and this is attributed to the increased amount of interfacial area between the aluminum matrix and the phases of finer Si and intermetallic compound.