• Korean Journal of Materials Research
• /
• v.27 no.11
• /
• pp.597-602
• /
• 2017

In this study, an Al-0.7wt%Fe-0.2wt%Mg-0.2wt%Cu-0.02wt%B alloy was designed to fabricate an aluminum alloy for electrical wire having both high strength and high conductivity. The designed Al alloy was processed by casting, extrusion and drawing processes. Especially, the drawing process was done by severe deformation of a rod with an initial diameter of 12 mm into a wire of 2 mm diameter; process was equivalent to an effective strain of 3.58, and the total reduction in area was 97 %. The drawn Al alloy wire was then annealed at various temperatures of 200 to $400^{\circ}C$ for 30 minutes. The mechanical properties, microstructural changes and electrical properties of the annealed specimens were investigated. As the annealing temperature increased, the tensile strength decreased and the elongation increased. Recovery or/and recrystallization occurred as annealing temperature increased, and complete recrystallization occurred at annealing temperatures over $300^{\circ}C$. Electric conductivity increased with increasing temperature up to $250^{\circ}C$, but no significant change was observed above $300^{\circ}C$. It is concluded that, from the viewpoint of the mechanical and electrical properties, the specimen annealed at $350^{\circ}C$ is the most suitable for the wire drawn Al alloy electrical wire.

• Clean Technology
• /
• v.13 no.4
• /
• pp.237-243
• /
• 2007

Phase behavior of the ternary systems of water-insoluble simvastatin drug, which is well known to be effective drugs for hypercholesterolemia therapy, in solvent mixtures of dimethyl ether (DME) and supercritical carbon dioxide was investigated to present a guideline of establishing operating conditions in the particle formation of the drugs by a supercritical anti-solvent recrystallization process utilizing DME as a solvent and carbon dioxide as an anti-solvent. The solubilities of simvastatin in the mixtures of DME and carbon dioxide were determined as functions of temperature, pressure and solvent composition by measuring the cloud points of the ternary mixtures at various conditions using a high-pressure phase equilibrium apparatus equipped with a variable-volume view cell. The solubility of the drug increased as the DME composition in solution and the system pressure increases at a fixed temperature. A lower solubility of the drug was obtained at a higher temperature.

• Journal of the Korean Society for Heat Treatment
• /
• v.18 no.1
• /
• pp.18-23
• /
• 2005

Effect of cold rolling on microstructural changes has been investigated for a Zn-15%Al alloy to elucidate the reason for its work softening behavior. Fully annealed microstructure of the Zn-15%Al alloy is characterized by ${\eta}$ grains and (${\eta}+{\alpha}$) lamellar colonies, where ${\eta}$ and ${\alpha}$ are Zn-rich HCP and Al-rich FCC phases, respectively. The hardness decreases continuously with increasing cold rolling degree, exhibiting work softening behavior. It is revealed that during the cold rolling, (${\eta}+{\alpha}$) lamellar colonies gradually change into equiaxed ${\eta}$ and ${\alpha}$ grains due to dynamic recrystallization at room temperature, while pre-existing ${\eta}$ grains are only deformed without recrystallization. Furthermore, cold rolling causes the precipitation of dissolved Al solutes in ${\eta}$ grains. In view of these results, change of (${\eta}+{\alpha}$) phases from lamellar to equiaxed morphology, which results in structural softness and increase in equiaxed ${\eta}/{\alpha}$ grain boundaries with higher mobility, and deterioration of solution hardening by precipitation of Al solutes from ${\eta}$ grains, are thought to contribute to the work softening of Zn-15%Al alloy.

• Nuclear Engineering and Technology
• /
• v.25 no.1
• /
• pp.71-79
• /
• 1993

Positron annihilation characteristics and microhardness of 25% cold worked and isochronally annealed hafnium specimens were measured to study recovery and recrystallization stages of hafnium specimens. The annihilation lifetime of positrons in hafnium has been measured for the distinct cases of annihilation in the annealed lattice and annihilation after trapping at lattice defects generated by cold deformation at room temperature. The annihilation lifetime in the annealed lattice was 187 $\pm$3.7 psec, whereas it was 217 $\pm$ 4.2 psec for positrons trapped at deformation-induced defects (mostly dislocations). The changes in Doppler broadening and hardness showed similar trend in the recrystallization range, however, the measured value of Doppler broadening variation were quite sensitive to changes in the recovery region in which the variation in hardness value was completely insensitive. Recovery of cold worked hafnium initiated at about 623 K and recrystallization occurred at around 1023 K.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.163-167
• /
• 2003

The large deformation at cryogenic temperature would be one of the effective methods to produce large bulk UFG materials. The effects of annealing temperature 150∼300$^{\circ}C$, on microstructure and mechanical properties of the sheets received 85% reduction at cryogenic temperature were investigated. In comparison with those at room temperature. Annealing of 5083 Al alloy deformed 85%, at 200$^{\circ}C$ for an hour, results in the considerable increase of tensile elongation without the great loss of strength and the occurrence of equiaxed grains less than 300nm in diameter.

• Transactions of Materials Processing
• /
• v.13 no.2
• /
• pp.137-141
• /
• 2004

The large deformation at cryogenic temperature is expected as one of the effective methods to produce large bulk ultrafine grained materials. The effects of annealing temperature, 150∼$300^{\circ}C$, on microstructures and mechanical properties of the sheets received 85% reduction at cryogenic temperature were investigated, in comparison with those at room temperature. Annealing of 5083 Al alloy deformed 85%, at $200^{\circ}C$ for an hour,. resulted in the considerable increase of tensile elongation without the great loss of strength and the occurrence of equiaxed grains less than 300nm in diameter.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.139-141
• /
• 2007

Compression tests were carried out to investigate morphologies of compressed specimen, deformation microstructure and stress-strain relation in high-nitrogen austenite stainless steel. Tests were performed under a wide range of temperature and, with true strain rates up to $\dot{\varepsilon}$ =0.05, 0.1, 0.5 and $1.0s^{-1}$. The activation energy of loading force was equal to plastic deformation energy within the temperature range of $900^{\circ}C$ to $1250^{\circ}C$. Dynamically recrystallized grain size decreased with an increasing strain rate and temperature. Flow stresses and deformation microstructures, were used to quantify the critical strain rate and recrystallized grain size. The grain size versus strain rate-temperature map obtained in the study was in good agreement with the deformation microstructures of compressed specimens.

• Journal of the Korean Society for Precision Engineering
• /
• v.6 no.4
• /
• pp.103-107
• /
• 1989

The effects of annealing temperature on the magnetic properties (maximum permeability, coercive force and remanence) and mechanical properties (hardness, tensile strength and elongation at rupture) were analyzed using the nondestructive impulsive magnetic analyzer in a medium carbon cold rolled steel sheet. This nondestructive method was very useful for the analysis of magnetic and mechanical properties of materials. As it was known in the literature, the three distinct processes that indicate the recovery, recrystallization, and grain growth of a metal were measured with the non-destructive analyzer.

• Journal of Powder Materials
• /
• v.10 no.2
• /
• pp.103-107
• /
• 2003

Aluminum-based $Al/Al_2O_3$ composites were fabricated by a powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. A mixture of aluminum powder and $Al_2O_3$ particles of which volume content was varied from 5 to 20%, was filled in the tube by tap filling and then rolled by 75% reduction in thickness at ambient temperature. The rolled specimen was then sintered at 56$0^{\circ}C$ for 0.5 h. The mixture of Al powders and $Al_2O_3$ particles was successfully consolidated by the sheath rolling. The $Al/Al_2O_3$ composite fabricated by the sheath rolling showed a recrystallized structure, while unreinforced Al powder compact fabricated by the same procedure showed a deformed structure. The unreinforced Al powder compact was characterized by a deformation (rolling) texture of which main component is {112}<111>, while the $Al/Al_2O_3$ composite showed a mixed texture oi deformation and recrystallization. The sintering resulted in recrystallization in Al powder compact and grain growth in the composite.

• Journal of the Korean Society for Heat Treatment
• /
• v.13 no.6
• /
• pp.412-419
• /
• 2000

There has been a considerable attention on Invar alloys due to its low thermal expansion property. A low thermal expansion property of Invar alloys, lower than $10^{-6}$ near the room temperature, is attractive for electric transmission lines and precision machine tools. However, the expansion property of Invar alloys is limited below about 520K, and mechanical properties are relatively low to apply to electric transmission line. In order to improve mechanical properties in this alloy, Ti alloying element was added to the $Ni_{38}-Mo_2-Cr_1-Fe$ invar alloy. The microstructure Ti added alloy showed finer than that of the unalloyed one. It was found that the (Mo, Ti), Mo carbide formed by Ti addition obstacled grain growth by pinning effect and supplyed recrystallization sites during heat-treatment. Optimum heat-treatment conditions with Ti addition were also discussed in the modified Invar alloy.