• Transactions of Materials Processing
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• v.28 no.3
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• pp.123-129
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• 2019

Hypereutectic Al-Si alloys have been widely utilized for wear-resistant components in the automotive industry. In order to expand the application of Hypereutectic Al-Si alloys, the addition of alloying elements forming a stable precipitate at high temperature is required. Thermally stable inter metallic compounds can be formed through the addition of transition elements such as Fe, Ni to Al alloys. However, the amount of transition element to be added to Al alloys is limited due to their low solid solubility. Also, hypereutectic Al-Si-Fe alloys form coarse primary Si phases and needle-shaped intermetallic compounds during solidification in the general casting processes. In this study, the effects of the destruction of Intermetallic compound and Si phase are investigated via hot extrusion. Both the microstructure and mechanical properties are discussed under different extrusion conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.88-91
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• 2003

The forging of Al 6061 has been studied by using finite element analysis and real forging experiment to find out the effect of strain rate and strain on the final forged product. It seems to be well known that the mechanical properties depend on the microstructures of forged products. The hot deformation of Al alleys including Al 6061 has been researched quite a long period on the various aspects. However, the forging of Al alloys seem to have few information, especially the recrystallization, recovery and grain growth. To elucidate the process variables to control those microstuctual aspects the specially designed model was used for finite element simulation and forging experiments, in which the variation of strain and strain rate could be obtained. The effect of strain md strain rate has been related with the microstructures of forging stocks.

• Journal of the Korean institute of surface engineering
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• v.32 no.1
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• pp.21-30
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• 1999

Coating adherance behavior of low carbon steels, produced by POSCO, Korea, was studied in order to study the characteristics of hot rolled galvanized iron(HGI) manufactured without pickling line and the development of its process. Galvanizing experiments were carried out in zinc pot with 0.2wt% Al after hot rolled plates with scale were reduced at $550~750^{\circ}C$ in 10~30% hydrogen gas atmosphere during 60~400seconds. The reduced plates and coated products were examined by SST, XRD, SEM and EPMA on their surfaces and cross sections. Coating layer of HGI manufactured with pickling line was composed of retained scale, Fe-Zn-Al compound, Fe-Zn compound ($\delta_1\;and\;\zeta$ Phase) and pure zinc. It was superior to HGI in coating adhesion. It seems to be due to forming of Fe-Zn-Al compound in interface of matrix and retained porous scale.

• Journal of Powder Materials
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• v.9 no.6
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.158-163
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• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.

• Transactions of Materials Processing
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• v.19 no.2
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• pp.127-131
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• 2010

Carbon-epoxy prepreg has been introduced in the forming of the upper and lower swash plates that control the pitch of rotor blade of unmanned helicopter because of its lightweight. Taguchi experimental method has been used by introducing the variables such as arrangement angle, laminated number and forming temperature, in order to obtain the proper forming method by using prepreg satisfying the required strength of the swash plate. In the evaluation of structural safety for the swash plates, three kinds of models are considered by using FE-analysis. In comparison of the hot forged products with Al6061-T6 and the formed products with prepreg, it was found that ultimate tensile strength of the products with prepreg is three times higher than that of the Al6061-T6, and the weight reduction of 68.5g can be achieved by using prepreg swash plates.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.277-280
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• 2001

The effects of a -phase morphology on the static and dynamic deformation behavior of a Ti-6Al-4V alloy was investigated in this study. Static tension test, static and dynamic tension test and hot compression test were conducted on three microstructures of Ti-6Al-4V alloy, i.e., equiaxed, widmanstatten and bimodal microstructures. Fracture surfaces of all three microstructures represented ductile fracture appearance, though the formation of adiabatic shear bands was noticed at dynamic torsion test. The susceptibility of forming adiabatic shear bands was greatest in the equiaxed microsoucture and lowest in the bimodal microstructure, which was evidenced by hot compression test.

• Journal of the Korean institute of surface engineering
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• v.50 no.1
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• pp.42-45
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• 2017

The magnesium-base AZ61 alloy was cast while adding 1% CaO powder into the melt. It was hot extruded, and oxidized at $550-650^{\circ}C$ in air in order to study its microstructure and oxidation behavior. Initially added CaO powder reacted with Al in the melt to $Al_2Ca$ particles that aligned along the extrusion direction. The formed $Al_2Ca$ particles increased the oxidation resistance through forming the superficial CaO scale at the upper part of the thin MgO oxide scale.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.299-302
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• 2003

The interface heat transfer coefficient was measured for non-isothermal bulk forming of Ti-6Al-4V. FE analysis and experiments were conducted. Equipment consisting of AISI H13 die was instrumented with thermocouples located at sub-surface of the bottom die. Die temperature changes were investigated in related to the process variables such as reduction, lubricant and initial die temperature. The calibration approach based on heat conduction and FE analysis using an inverse algorithm were used to evaluate the interface heat transfer between graphite-lubricated die and glass-coated workpiece. The coefficients determined determined were affected mainly by the contact pressure. The validation of the coefficients was made by the comparison between experimental data and FE analysis results.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.370-375
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• 2003

Determination of the interface heat transfer coefficient was investigated in non-isothermal bulk forming of glass-coated Ti-6Al-4V. FE analysis and experiments were conducted. Equipment consisting of AISI Hl3 die was instrumented with thermocouples located at sub-surface of the bottom die. Die temperature changes were investigated in related to the process variables such as reduction, lubricant and initial die temperature. The calibration approach based on heat conduction and FE analysis using an inverse algorithm were used to evaluate the interface heat transfer between graphite-lubricated die and glass-coated workpiece. The coefficients determined were affected mainly by the contact pressure. The validation of the coefficients was made by the comparison between experimental data and FE analysis results.