• Journal of the Korean Society for Heat Treatment
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• v.15 no.6
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• pp.260-268
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• 2002

The effects of calcium and silicon on microstructure and aging characteristics of AZ91 magnesium alloy during T5 treatment was investigated. The addition of 0.88% calcium or 0.25% silicon to AZ91 alloy made dendrite cell smaller. Especially, silicon is more effectively acted as refinement of the dendrite cell than calcium. It is due to that $Mg_2Si$ precipitated at the dendrite cell boundary or in the matrix during T5 treatment of Si added AZ91 alloy retarded the growth of the secondary phase. In the mean while, without inducing the precipitates containing calcium, calcium was segregated mainly around secondary phase such as $Mg_{17}Al_{12}$ and partially dissolved in ternary eutectic (Mg-Al-Ca) structure. In the AZ91 alloy containing both silicon and calcium, more finely distributed $Mg_2Si$ in matrix homogeneously and much finer microstructure were obtained than those containing silicon or calcium. Hence, An AZ91 containing both silicon and calcium was more effective to retarding the growth of the secondary phase than the other AZ91 alloy such as AZ91 alloy containing silicon or AZ91 alloy containing calcium.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1078-1079
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• 2006

The paper presents the possibilities of obtaining new composite materials based on sintered porous ceramics with particles and fibre of $Al_2O_3$ infiltrated by aluminum alloy. The EN AC - AlSi12 alloy features the matrix material, whereas the RF50AX-301 preform, of Saffil Automotive, was used as the reinforcement. Examinations of ceramics preforms permeability were made. Metallographic examination of composite materials made on light microscope and in scanning electron microscope show that aluminum alloys fill micropores in the matrix. New composite materials show twice higher value of hardness in comparison with matrix. Results indicate that it is possible to infiltrate porous ceramic with liquid aluminum alloy to obtain new composite materials were advantageous properties of each component are connected.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.49-56
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• 2010

This study investigated how the surface of Al-12wt.%Si alloy modified by the plasma electrolytic oxidation process (PEO). The PEO process was performed in an electrolyte with sodium hexametaphsphate as a conducting salt, and the effect of ammonium metavanadate on variations in the morphology of electrochemically generated oxide layers on the alloy surface was investigated. It is difficult to form a uniform passive oxide layer on Al alloys with a high Si content due to the differences in the oxidation behavior of the silicon-rich phase and the aluminum-rich phase. The oxide layer covered the entire surface of the Al-12WT.%Si alloy uniformly when ammonium metavanadate was added to the electrolyte. The oxide layer was confirmed as a mixture of $V_2O_3$ and $V_2O_5$ by XPS analysis. In addition, the oxide layer obtained by the PEO process with ammonium metavanadate exhibited a black color. Application of this surface modification method is expected to solve the problem of the lack of uniformity in the coloring of oxide layeres caused by different oxidation behaviors during a surface treatment.

• Korean Journal of Materials Research
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• v.17 no.12
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• pp.648-653
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• 2007

Plasma electrolytic oxidation (PEO) treatment was performed on cast Mg-6 wt%Al alloy solution-treated at 693K for 16h and aged at 498K. The surface roughness, thickness, micro-hardness, wear and corrosion properties of coatings on solution-treated and aged Mg-6 wt%Al alloy were investigated. The coatings on aged Mg-6 wt%Al alloy had thinner layer and lower micro-hardness and wear resistance than the solution-treated Mg-6 wt%Al alloy. As the aging time increased, the thickness of coatings decreased while the surface roughness was almost no changed. In addition, the micro-hardness and wear property of coatings decreased with increasing the aging time unlike the uncoated Mg-6 wt%Al alloy showing the peak micro-hardness and the best wear property after aging for 16 h. However, the coatings on Mg-6 wt%Al alloy peak-aged for 16h revealed the best corrosion resistance in 3.5% NaCl solution, which was explained based on the microstructural characteristics.

• Advanced Composite Materials
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• v.18 no.4
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• pp.339-350
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• 2009

Al-Fe-V-Si alloys reinforced with SiC particles were prepared by multi-layer spray deposition technique. Both microstructures and mechanical properties including hardness and tensile properties development during hot exposure process of Al-8.5Fe-1.3V-1.7Si, Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$ and Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ were investigated. The experimental results showed that an amorphous interface of about 3 nm in thickness formed between SiC particles and the matrix. SiC particles injected silicon into the matrix; thus an elevated silicon concentration was found around $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids, which subsequently inhibited the coarsening and decomposition of $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids and enhanced the thermostability of the alloy matrix. Moreover, the thermostability of microstructure and mechanical properties of Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ are of higher quality than those of Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.6
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• pp.20-26
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• 1995

With the recent development of light and high efficient automobiles and aircraft, demand of the A1-Si alloy is rapidly increasing. However, there is an inclination that as the content of silicon increases it becomes more difficult to machine. Accordingly, the present study intends to analyse and study the cutting resistance and surface roughness of A1-Si alloy with Si contents of 8%, 12%, 17%, and 20%. The A1-Si alloy specimens were turned by a poly- crystalline diamond tool under selected cutting conditions, and results are here described and discussed.

• Corrosion Science and Technology
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• v.5 no.6
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• pp.218-221
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• 2006

Influence of microstructure on the corrosion property of Mg-Al-Zn alloy was investigated using potentiodynamic polarization experiments, galvanic coupling experiments, and scanning electron microscopy in sodium chloride solutions. Pitting was the most common form of attack in chloride solution, and filiform corrosion was also occurred in AZ91D-T4 alloy. On the contrary, filiform attack in the bulk matrix was predominant corrosion form in AZ91D-T6 alloy, and the number and size of pit were decreased than those of AZ91D-T4 alloy. Galvanic coupling effect between $Mg_{17}Al_{12}$ and matrix was existed, but the propagation of galvanic corrosion was localized only near the $Mg_{17}Al_{12}$ phase in AZ91D-6T alloy. The corrosion resistance of Mg-Al matrix increased with decreasing Al content in the matrix. And, it could be regarded that Al content in the matrix is decreased by precipitation of $Mg_{17}Al_{12}$ during the aging treatment and it decreases the anodic reaction rate of the matrix and galvanic effect in AZ91D-T6 alloy. It could be considered that the composition and microstructure of surface protective layer would be varied by precipitation of $Mg_{17}Al_{12}$ and subsequent decreasing of Al content in the matrix. And it would contribute the corrosion resistance of AZ91D-T6 aging alloy.

• Journal of Powder Materials
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• v.12 no.4 s.51
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• pp.296-302
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• 2005

In order to improve mechanical properties, the hypereutectic Al-20 wt%Si based prealloy powder was prepared by gas atomization process. Microstructure and compressibility of the atomized Al-Si powder were investigated. The average powder size was decreased with increasing the atomization gas pressure. Size of primary Si particles of the as-atomized powder was about $5-8\;\mu{m}$. The as-atomized Al-Si powder such as AMB 2712 and AMB 7775 to increase compressibility and sinterability. Relative density of the mixed powder samples sintered at $600^{\circ}C$ was reached about 96% of a theoretical density.

• Journal of Korea Foundry Society
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• v.15 no.4
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• pp.377-387
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• 1995

Partial squeeze die casting is a special die casting process which combines squeeze technique to conventional die casting. The influence of squeeze pressure $(1500-3000kg/cm^2)$ and time-lags(0.5-2.0sec) on defect control, density and microstructure of ADC12 alloy die casts has been studied by appling partial squeeze die casting to air compressure front housing production. Defect free, maximum density of $2.736kg/cm^3$ with sound microstructure of ADC12 alloy die cast has been obtained by partial squeeze die casting technique at the pressure of $2000-2500kg/cm^2$ and time-lags of 1.0-2.0sec.

• Journal of Korea Foundry Society
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• v.33 no.1
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• pp.8-12
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• 2013

Although aluminum-silicon based commercial casting alloys have been used in applications that demand high electrical or thermal conductivity, new aluminum casting alloys that possess higher conductivities are currently required for advanced applications. Therefore, there is much research into the development of new high conductivity aluminum casting alloys that contain lower amounts of or no silicon. In this research, the properties and casting characteristics of Al-Zn-Fe-Si alloys with various Fe and Si contents were investigated. Two types of AlFeSi phases were formed depending on the Fe and Si contents. As the silicon content increased, the tensile strength of the Al-Zn-Fe-Si alloy increased slightly, while the electrical conductivity decreased slightly. It was also observed that both the fluidity and hot cracking susceptibility of the investigated alloys were closely related to the formation of the AlFeSi phases.