• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.337-343
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• 2018

The present study investigated the effect of heat treatment process on the surface wettability of an Al-Si-Mg alloy. After solution-treated at $525^{\circ}C$ and aged at $160^{\circ}C$, the alloy showed high hardness due to the formation of precipitates. In addition, surface wettability was improved in such a way that the contact angle of distilled water droplet on the flat surface decreased to $37.6{\sim}42.1^{\circ}$ after the heat treatment. The surface energy predicted by Owens-Wendt equation also confirmed the increase of surface energy after the heat-treatment. However, when the surface roughness increased, the positive effect of the heat treatment on wettability diminished due to the geometrical factors of the rough surface.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.306-309
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• 2009

The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

• Journal of Korea Foundry Society
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• v.37 no.6
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• pp.186-192
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• 2017

The lost foam casting method was used to fabricate Al-Si alloy thin sheet specimens; the effects of chemical composition and process variables on the mold filling and mechanical properties were investigated. The mold filling capability was observed to be proportional to the pouring temperature, and both the vibration imposed during the casting and the application of a pattern coating had rather negative effects. The mold filling capability also decreased with the addition of Mg or TiB. When the Mg content increased, the tensile strength of the cast alloy was enhanced, but the elongation decreased. However, after T6 heat treatment, both the strength and the elongation were improved. TiB addition for grain refining or pattern coating did not significantly affect the tensile properties.

• Journal of Korea Foundry Society
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• v.13 no.6
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• pp.547-554
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• 1993

Aluminum alloy matrix composites reinforced with various amounts of $Al_2O_3$ short fibers have been produced by rheo-compocasting accompanied by hot pressing. When composites reinforced with fibers are produced by rheo-compocasting, S-L process is the most effective method for homogeneous dispersion of fibers. A sound composites with the improved orientation(3 dimension${\rightarrow}$2 dimension) of the fibers and increased volume fraction of them have been fabricated through the hot pressing of the casted composites. Fibers are broken down when rheo-compocasting, hot pressing, and $T_6$ treating. Among them fibers are broken down most heavily in the hot pressing. And even in the case of the composite reinforced with 30 vol% fibers, which showed the hardest fiber break down, aspect ratio(11.6) is higher than critical aspect ratio(10.7). The fiber strengthening effect in the composites has showed upto 573K. As the test temperature increases to the range of 573K, the effect has been higher. The fracture of composites is controlled by fiber from room temperature to 473K, but the fracture of composites is controlled by interface between fiber and matrix alloy above 473K.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.65-73
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• 2000

Casting of metal matrix composites is an attractive process since it offers a wide selection of materials and processing conditions. Among the casting methods, melt-stirring technology is much attractive route in industrial application because it is more simple and inexpensive compared to squeeze casting or powder metallurgy. In the present work, effects of particle size, volume fraction of particles and mg addition on mechanical properties and thermal expansion coefficients of $\alpha$ -$Al_2O_{3(p)}$/LXA composites were studied. It is shown that $\alpha$ -$Al_2O_3$ particles formed at the interface of $\alpha$ -$Al_2O_3$ particles and matrix made an important role on mechanical properties. Ultimate tensile strength of most composite materials was not increased. But in the case of 5vol% addition of 16$\mu\textrm{m}$ $\alpha$ -$Al_2O_3$ Particle, Ultimate tensile strength of composite materials with 3wt.% Mg was increased. Volume fraction of reinforcements and mg content were thermal expansion coefficients of composite materials were decreased.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.236-242
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• 2014

Fabrication of reaction-bonded $Al_2O_3$ (RBAO) ceramics using Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processing using Al powder. The influence on reaction-bonding and microstructure, as well as on physical and mechanical properties, of the particulate characteristics of the $Al_2O_3$-Al alloy powder mixtures after milling, was revealed. Variation of the particulate characteristics of this $Al_2O_3$-Al alloy powder mixture with milling time was reported previously. To start, the $Al_2O_3$-Al alloy powder mixture was milled, reaction-bonded, post-sintered, and characterized. During reaction-bonding of the $Al_2O_3$-Al alloy powder mixture compacts, oxidation of the Al alloy took place in two stages, that is, there was solid- and liquid-state oxidation of the Al alloy. The solid-state oxidation exhibited strong dependence on the density of surface defects on the Al-alloy particles formed during milling. Higher milling efficiency resulted in less participation of the Al alloy in reaction-bonding. This was because of its consumption by chemical reactions during milling, and subsequent powder handling, and could be rather harmful in the case of over-milling. In contrast to very little dependence of oxidation of the Al alloy on its particle size after milling, the relative density, microstructure, and flexural strength were strongly dependent on particle size after milling (i.e., on milling efficiency). The relative density and 4-point flexural strength of the RBAO ceramics in this study were ~98% and ~365 MPa, respectively, after post-sintering at $1,600^{\circ}C$.

• 한국전자현미경학회:학술대회논문집
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• 2004.11a
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• pp.129-132
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• 2004

• Journal of Korea Foundry Society
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• v.28 no.1
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• pp.20-24
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• 2008

The characteristics, such as roughness, thickness, microhardness and corrosion resistance, of plasma electrolytic oxide coatings on AZ91D alloy were investigated under the processing condition of various coating times. The coatings on AZ91D alloy consisted of MgO, $MgAl_{2}O_{4}$ and $Mg_{2}SiO_{4}$ oxides. The surface roughness and thickness of coatings became larger with increasing the coating time. The microhardness in cross section of coatings was much higher than not only that in surface but that in the conventional anodic oxide coatings, which increased progressively as the coating time increased. After being immersed in 3.5%NaCl solution and methyl alcohol, the corrosion resistance of AZ91D alloy was markedly improved by plasma electrolytic oxidation coating treatment, and the AZ91D alloy coated for 50min revealed excellent corrosion resistance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.281-284
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• 2003

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment is investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) are hot extruded to make I-shape bars at 380$^{\circ}C$, then the bars are solution treated at 480$^{\circ}C$ for 2hrs followed by artificial aging at 120$^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consists of elongated grains, however, fine equiaxed grains are mainly observed around surface. The microstructural gradient suggests that different restoration process can proceed during the hot extrusion. For B1 and B2, different grain growth behaviors are found around the surface during the post heat treatment. Rapid grain growth behavior around the surface is discussed related with the crystallographic orientation of the grain.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.187-191
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• 2000

High temperature creep behaviour of Al-5 wt% Mg alloy reinforced with 7.5% BN flakes was studied. The composite specimens showed two main creep characteristics : (1) the value of the apparent stress exponent of the composite was high and varied with applied stress (2) the apparent activation energy for creep was much larger than that for self-diffusion in aluminum The true stress exponent of the composite was set equal to 5. Temperature dependence of the threshold stress of the composite was very strong. Which could not be rationalized by allowing for the temperature dependence of the elastic modulus change. AIN particles which were incorporated into the Al matrix during fabrication of the composite by the PRIMEXTM method were found to be effective barriers to dislocation motion and to give rise the threshold stress during creep of the composite