• Korean Journal of Materials Research
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• v.13 no.6
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• pp.352-359
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• 2003

In order to control the grain size, the spark plasma sintering technique is applied for the manufacturing of Cu-26.7Al-4.05AI(wt.%) shape memory alloy with pure Cu, Zn, and Al element powders. The sintering processes were carried out under different atmospheres. The sintered bodies were denser under Ar or Ar＋4%$H_2$gas atmosphere than under vacuum. With use of small-sized powders, a very small average grain size of 2∼3 $\mu\textrm{m}$ was obtained, but the single phase was not formed. With the large-sized powders the single austenitic phase was observed with the average grain size of $70∼72\mu\textrm{m}$. When the different size of raw powders was mixed, it is confirmed that the average grain size of the manufactured alloys was 15 $\mu\textrm{m}$ with single austenitic phase, but the distribution of grain size was not uniform.

• Journal of the Korean institute of surface engineering
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• v.22 no.4
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• pp.179-184
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• 1989

This study seeks to the morphological changes in the oxide skin of the Al-10wt.%si alloy melts. These changes depend on the oxidation time and the temperature of the molten alloy, as well as the effects of adding Mg, Cu and Ni. Thess affects observed by X-ray diffractometer(XRD) and scanning electron microscope(SEM)' Very litte oxide skins on Al-10wtwt.%Si alloy melts can be detected by XRD because it is less than the measuring capabillity of the XRD, or the formation of noncrystalline oxide skins oxide skins canbe deteced by SEM. The addition of 1%Mg and 1%Cu-1%Mg-2.5%Ni to this base alloy crystallized the structure of the oxide skins and increased the oxidation in proportion to the length of time, but adding 3% had hardiy anyaffect at all on the crystal structure of the oxide skins.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.237-241
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• 2000

The effects of Si addition on the precipitation processes of in Al-Cu-Si alloy films were studied by the transmission electron microscopy. Deposition of an Al-1.5Cu-1.5Si (wt. %) film at $305^{\circ}C$ resulted in formation of fine, uniformly distributed spherical $\theta$-phase particles due to the precipitation of the $\theta$ and Si phase particles during deposition. For deposition at $435^{\circ}C$, fine $\theta$-phase particles precipitated during wafer cooldown, while coarse Si nodules formed at the sublayer interface during deposition. The film susceptibility to corrosion is discussed in relation to the film microstructure and deposition temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1818-1832
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• 1994

Transport process during solidification of an AI-CU alloy in a vertical annular mold of which inner wall is cooled is numerically simulated. A model which can take account of local density dependence on the solute concentration is established and incorperated in the analysis. Results show that thermally and solutally induced convections are developed in sequence, so that there is little interaction between them. Thermal convection effectively removes the initial superheat from the melt and vanishes as solidification proceeds from the cooling wall. On the other hand, solutal convection which is developed later over the meshy and the pure liquid regions leads to large-scale redistribution of the consituents. The degree of the initial superheating hardly affects overall solidification behavior except the early stage of the process, when the cooling rate is kept constant. Macrosegregation is reduced remarkably with increasing cooling rate, because not only the liquidus interface advances so quickly that time available for the solute transport is not enough, but also the interdendritic flow is strongly damped by rapid crystal growth within the mushy region.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.4
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• pp.244-252
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• 1994

The morphological changes of primary solid particles as a fuction of process time on Al-Si alloys during semi-solid state processing with a shear rate of 200s were studied. In hypereutectic Al-15.5wt%Si alloy, it was observed that primary Si crystals are fragmented in the early stage of stirring and morphologies of primary Si crystals change from faceted to spherical during isothermal shearing for 60 minutes. In quaternary Al-12.5wt%Si-2.9wt%Cu-0.7wt%Mg alloy system, it was observed both primary silicon and ${\alpha}$-alumunum particles. Microstructural evolution of primary Si crystals was similar to that of the hypereutectic Al-Si alloy but equiaxed ${\alpha}$-Al dendrites are broken into nearly spherical at the early stage of shearing and later stage of the isothermal shearing ${\alpha}$- Al particles are slightly coarsoned by Ostwald ripening. Mechanical properties of Al-Si-Cu-Mg alloy were compared to those from other processes (squeeze casting and gravity casting). After T6 heat treatment, comparable values of hardness were obtained while slightly lower compressive strength values were observed in rheocast alloy. The elongation, on the other hand, exhibited significant increasement of 15% over gravity cast alloy.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.2
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• pp.90-96
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• 2003

The effect of betatizing temperature on microstructure and transformation characteristics in a Cu-AI-Ni based pseudoelastic alloy fabricated by heated mold continuous casting by using metallography, XRD and calorimetry. The microstructure of cast rod betatized at $600^{\circ}C$ revealed a ${\beta}_1$ parent phase and a ${\gamma}_2$ phase precipitated along the casting direction. When the cast rod was betatized at the elevated temperature above $600^{\circ}C$, the ${\gamma}_2$ phase is completely dissolved into the matrix so that the volume fraction of the ${\gamma}_2$ phase was decreased. The parent phase was stabilized by betatizing at $600^{\circ}C$. However, the ${\beta}_1$ parent phase was transformed to both ${{\beta}_1}^{\prime}$ and ${{\gamma}_1}^{\prime}$ martensites with increasing betatizing temperatures above $600^{\circ}C$, while $M_s$ and $A_s$ temperatures were decreased. The stress-strain curves for compression test were not same with betatizing temperature; the stress-strain curves of the specimen betatized at $600^{\circ}C$ and $700^{\circ}C$ were linear but those of the specimen betatized at $800^{\circ}C$ and $900^{\circ}C$ were not linear.

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.556-565
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• 1994

Effects of Ag addition to 2090 and CP 276 Al-Li alloy systems on the microstructure and mechanical properties have been investigated. The addition of silver up to 0.16wt.% reduced the grain size of the alloys, and was responsible for the formation of finer and more uniform $\delta$'($AI_{3}Li$) and $T_{1}(AI_{2}CuLi$) precipitates in 2090 alloys, even though no variation of precipitates was found in CP 276 alloys. The addition of 0.16wt.% Ag improved the tensile strength of 2090 alloys about 40MPa with the expense of small reduction of percent elongation. However, the small addition of Ag to CP 276 containing Mg did not show any variation of tensile strength and elongation. The aging treatment of these alloys at $150^{\circ}C$ for 70 or 90 hours, depending on alloy systems, showed peak hardness value of about 92 $H_rB$.

• Journal of Powder Materials
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• v.9 no.2
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• pp.116-123
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• 2002

The characteristics of two commercial 2xxx series Al alloy powders, AMB2712 and 201AB, were evaluated and their compacting and sintering characteristics were discussed in tems of compacting pressure. The particle shapes of both two powder mixtures were irregular and their particle size distributions were broad. The compactibility of AMB2712 was superior to that of 201AB because of better fluidity. The sintered density was higher than the green density at low compacting pressure, however, it was lower than the green density when the samples were compacted at higher pressure due to the selling during sintering. The sintered density was alomost the same as the green density at the "homogeneous deformation" stage. It was observed that pores were created at the triple points due to the rapid diffusion of Cu in Al. Cu in Al.

• Journal of Korea Foundry Society
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• v.22 no.5
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• pp.257-264
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• 2002

Effects of Ca content on the refinement of primary Si of Aluminum B390 alloy have been examined. Ca was found to have an effect on the refinement of primary Si particle. Primary Si particle size has been refined as Ca content of the melts decreased and cooling rate increased. A control of Ca content by the addition of $CuCl_2$ to the melt was the most efficient in the refinement of primary Si particles. The minimum size of primary Si particles in this study was $15.0\;{\mu}m$ when a residual content of Ca element in the alloy was 5ppm, Primary Si particle size was refined as primary Si crystallization temperature increased, which was attributed to the decrease of Ca content in the melts.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.145-156
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• 1999

The distribution of the second phase, the change of transformation temperature and mechanical properties with thermomechanical treatment conditions were investigated by metallography, calorimetry, EDS, tensile test and fractography in a Cu-Al-Ni-Ti-Mn alloy. The cast structure revealed Ti-rich precipitates($X_L$ phase) between dendrite arms, which have been identified as $(Cu,Ni)_2TiAl$ intermetallic compounds. By homogenizing above $900^{\circ}C$, the $X_L$ phase was melted in the matrix, while the Xs phase was precipitated in matrix and the volume fraction of it was increased. When hot-rolled specimen was betatized below $750^{\circ}C$, recrystallization could not be observed. However, the specimen betatized above $800^{\circ}C$ was recrystallized and the grain size was about $50{\mu}m$, while Xs phase was precipitated in matrix. With raising betatizing temperature, $M_s$ and $A_s$ temperatures were fallen and transformation hysteresis became larger. The strain of the specimen betatized at $800^{\circ}C$ was 8.2% as maximum value. The maximum shape recovery rate could be obtained in the specimen betatized at $800^{\circ}C$ but it was decreased due to the presence of Xs phase with increasing betatizing temperature.