• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.304-309
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• 2008

Magnesium alloys containing $Mg_2Si$ particles, as a promising cheap heat-resistant magnesium alloy for automobile power train parts applications, are attracting more attention of both material scientists and design engineers. Modification of the Chinese script shape $Mg_2Si$ particle is a key for using this alloy in sand or permanent mould casting. In the present work, the modification effect of Sr and Sb on the corrosion properties of the Mg-5Al-2Si alloy was investigated. Sr or Sb addition promoted the formation of fine polygonal shape $Mg_2Si$ particles by providing the nucleation sites. Sr was more effective element than Sb for shape modification of Chinese script shape $Mg_2Si$. Such improved microstructure of the modified alloy resulted in large improvement in corrosion resistance as compared to unmodified Mg-5Al-2Si alloy.

• Journal of Korea Foundry Society
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• v.13 no.6
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• pp.524-531
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• 1993

Dispersion behaviors of SiC particles and microstructures in Al-2%Si/SiCp composite prepared by Rheo-compocasting were studied with change of fabrication conditions(slurry temperature, agitation time) and additions of Mg($0{\sim}3wt.%$). Also, the microhardness change of matrix, interface and total in composites were examined with additions of Mg($0{\sim}3wt.%$). The dispersion of particles in the composites became relatively homogeneous with increase of Mg additions, agitation time and decrease of slurry temperature. Rate of occupied area by particle in matrix was increased as increase of Mg additions due to improvement of wettability between SiC particle and matrix. A favorable composites were obtained by melting under Ar atmospheric SiCp injection and bottom pouring system. According to the analysis of X-ray diffraction, $Mg_2Si$, $Al_4C_3$, $SiO_2$ and MgO, etc, intermetallic compounds were formed by chemical interreaction at interface of matrix and particles. The microhardness of interface is higher than that of matrix due to more strengthening of above intermetallic compounds. It was considered that the total hardness of the composites is improved by dispersing of SiCp and addition of Mg.

• Journal of Korea Foundry Society
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• v.20 no.4
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• pp.254-259
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• 2000

Metal matrix composites(MMCs) reinforced with hard particles have many potential application in aerospace structures, auto parts, semiconductor package, heat resistant panels, wear resistant materials and so on. In this work, the effect of SiC partioel sizes(50 and 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on the microstructure and the wear property of $Al-5Mg-X(Si,Cu,Ti)/SiC_p$ composites produced by pressureless infiltration method have been investigated using optical microscopy, scanning eletron microcopy(SEM) with EDS(energy dispersive spectrometry), hardness test, X-ray diffractometer(XRD) and wear test. In present study, the sound $Al-5Mg-X(Si,Cu,Ti)/SiC_p$(50 and 100 ${\mu}m$) composites were fabricated by pressureless infiltration method. The $Al-5Mg-0.3Si-O.1Cu-O.1Ti/SiC_p$ composite with $50 {\mu}m$ size of SiC particle has higher hardness and better wear property than any other composite with $100{\mu}m$ size of SiC particle produced by pressureless infiltration method. The hardness and wear property of $Al-5Mg/SiC_p$(50 and 100 ${\mu}m$) composites were enhanced by the addition of Si, Cu and Ti in Al-5%Mg matrix alloy.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.3
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• pp.56-59
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• 2005

Aluminum alloy casting is gaining increased acceptance in automotive and electronic industries and especially, squeeze casting is the most efficient method of mass manufacturing of such parts. In this study, the microstructures and mechanical properties of Al-7.0Si-0.4Mg(AC4C) alloy fabricated by squeeze casting process for development of fuel system parts (fuel rail) are investigated. The microstructure of squeeze cast specimen was composed of eutectic structure aluminum solid solution and $Mg_2Si$ precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg alloy was 298.5MPa. It was found that Al-7.0Si-0.4Mg alloy had good corrosion resistance in electrochemical polarization test.

• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.343-352
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• 2009

High-resolution Solid-state NMR provides element specific and quantitative information and also resolves, otherwise overlapping atomic configurations in multi-component non-crystalline silicates. Here we report the preliminary results on the effect of composition on the structure of CMAS (CaO-MgO-$Al_2O_3-SiO_2$) silicate glasses, as a model system for basaltic magmas, using the high-resolution 1D and 2D solid-state NMR. The $^{27}Al$ MAS NMR spectra for the CMAS silicate glasses show that four-coordinated Al is predominant, demonstrating that $Al^{3+}$ is network forming cation. The peak position moves toward lower frequency about 4.7 ppm with increasing $X_{MgO}$ due to an increase in $Q^4$(4Si) fraction with increasing Si content, indicating that Al are surrounded only by bridging oxygen. $^{17}O$ MAS NMR spectra for $CaAl_2SiO_6$ and $CaMgSi_2O_6$ glasses qualitatively suggest that NBO fraction in the former is smaller than that in $CaMgSi_2O_6$ glasses. As $^{17}O$ 3QMAS NMR spectrum of model quaternary aluminosilicate glass resolved distinct bridging and non-bridging oxygen environments, atomic structure for natural magmas can also be potentially probed using high-resolution 3QMAS NMR.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.233-238
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• 2010

Hot-dipped Al-Mg-Si coatings to alternate Zn and Zn alloy coatings for steel were examined on metallographic structure, corrosion resistance, sacrificial ability, formation and growth of inter-metallic compounds, and mechanical properties. Near the eutectic composition of quasi-binary system of Al-$Mg_2Si$, very fine eutectic structure of ${\alpha}$-Al and $Mg_2Si$ was obtained and it showed excellent corrosion resistivity and sacrificial ability for a steel in sodium chloride solutions. Formation and growth of Al-Fe inter-metallic compounds at the interface of substrate steel and coated layer was suppressed by addition of Si. The inter-metallic compounds layer was usually brittle, however, the coating layer did not peel off as long as the thickness of the inter-metallic compounds layer was small enough. During sacrificial protection of a steel, amount of hydrogen into the steel was more than ten times smaller than that of Zn coated steel, suggesting to prevent hydrogen embrittlement. Al-Mg-Si coating is expected to apply for several kinds of high strength steels.

• Journal of Korea Foundry Society
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• v.28 no.4
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• pp.179-183
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• 2008

Mechanical properties of the spray-cast Al 6061 alloy with variation of Mg/Si addition were investigated. After spray-cast, hot extrusion was performed at $460^{\circ}C$ then followed ageing treatment to the T6 condition. SEM, EDX, and XRD were used to characterize a ${\beta}(Mg_{2}Si)$ precipitate. The amount of ${\beta}$ precipitate was calculated from the XRD measurements. Hardness, ultimate tensile strength and elongation were tested then compared with those of the Al 6061 alloys made by ingot metallurgy (I/M) and powder metallurgy (P/M). The ultimate tensile strength and elongation of the spray-cast Al 6061 alloy were 318MPa and 16.5%, respectively. These properties were improved in the 2.2 wt%Mg and 1.3wt%Si addition up to 349MPa of UTS and 12.5% of elongation, mainly due to increased amount of a fine supersaturated ${\beta}(Mg_{2}Si)$ precipitate.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.556-564
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• 1996

Variation of shape and size of solid particles and solute redistribution in Mg-9wt.%Al, AI-4.5wt.% Cu, and AI-7wt.%Si alloys were investigated when they were heated to semi-solid temperatures and held without stirring. In the case of Mg-9wt.% Al and Al-4.5wt.%Cu alloys, the polygonal shaped solid particles were agglomerated with non-uniform distribution, and there were no disappearance of the solid/solid boundary until the end of melting. But in the case of an Al-7wt.%Si alloys, two or three spherical shaped particles were coalesced or separated individually, and the coalesced particles had no solid/solid interface on the contrary to the prevous case. The maximum size of solid particles during isothermal heating at high temperature was smaller than that at lower temperature, but the time required to reach the maximum size at high temperature was shorter than that at lower temperature. The concentrations of main solute atom whose distribution coefficient is lower than 1, decreased in the primary solid particles as the liquid fraction increased, and the gradient of solute concentration was steeper in Mg-9wt.%Al alloy and Al-4.5wt.%Cu alloy than that of Al-7wt.%Si alloy.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.37-42
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• 1983

An attempt was made to derive a possible synthetic mechanism of Fluoro-phlogopite (Mica, 4Mg.$Al_2O_3$.$6SiO_2$.$K_2O$.$2MgF_2$) The pevention of fluorine vaporization turned out to be the key in the synthesis of Mica in question.l Consequently the quinary system of Mica was seperately synthesized ; frist 4MgO.$Al_2O_3-6SiO_2$(ternary system) was sintered at 135$0^{\circ}C$ and $K_2O$ and $MgF_2$ were added and second 4MgO.$Al_2O_3-6SiO_2$.$K_2O$ (quarternary system) was heat-treated at 135$0^{\circ}C$ and $MgF_2$ was added. The ternary system resulted in Proto-enstatite Cordierite and Spinel phases while Forsterite and Leucite were shown in the quarternay system . In both methods Fluoro-phlogopite was systhesized but the solid state reactions to form Mica from the ternary system and the quarternary system were different. High temperature reactions in the formation of Mica were investigated employing XRD, DTA and SEM The study of the synthesis of Mica indirectly suggested a method of phase analysis of quinary system(MgO-$Al_2O_3-SiO_2-K_2O-MgF_2$) and quarternary system(MgO-$Al_2O_3-SiO_2-K_2O-MgF_2$) at various temperatures.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.29-33
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• 2014

The electrochemical characteristics of Al-Si casting alloys (Al-10%Si, Al-9%Si, Al-7%Si) in 3.5% NaCl solution at room temperature was studied using potentiodynamic techniques. The electrochemical values of corrosion potential($E_c$), corrosion current density($I_c$) and corrosion rate(mpy) were examined. The Al-Si alloys had several compounds such as $Mg_2Si$, ${\pi}$-$Al_8Si_6Mg_2Fe$ and $Al_2CuMg$ which could affect corrosion resistance significantly. The potentiodynamic polarization curve exhibited typical active behavior in anodic polarization curve. The major corrosion mechansim for the Al-Si alloys were pitting and grain boundary corrosion. As increasing Si and Cu contents, their corrosion resistance was decreased.