• Journal of the Korean Society for Heat Treatment
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• v.22 no.4
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• pp.217-222
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• 2009

The effects of severe plastic deformation by equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue behaviors of Al-Mg-Si alloy were investigated. The specimens which were peak aged at $175^{\circ}C$ after solution treatment showed cyclic hardening at all strain amplitudes, while the specimens ECAPed after solution treatment showed cyclic softening at all strain amplitudes during fatigue. The specimens aged at $100^{\circ}C$ after ECAP showed slight cyclic hardening. Various changes of cyclic fatigue behavior after severe plastic deformation and/or heat treatment were discussed in terms of the microstructural changes and precipitation conditions.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.1
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.4
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• pp.85-96
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• 1988

The optimum cutting condition for rake angle in turning was investigated in (6-4) Brass and Al alloy. Results of experiments in (6-4) Brass and Al alloy are as follow. Specific cutting resistance becames higher as the depth of cutting, feed or cutting velocity decreases at same rake angle and resistance appear low value 20.deg., 25.deg.(6-4)brass, 0.deg. 20.deg.(Al alloy). The optimum cutting condition for(6-4) Brass is depth of cutting 0.5mm, rake angle 25.deg., cutting velocity 80m/min, feed 0.1mm/rev and for Al alloy is depth of cutting 0.1mm, rake angle 0.deg., cutting velocity 200m/min, feed 0.5mm/rev. The rake angle for good roughness is 20.deg. at (6-4) Brass, and that for Al alloy is 15.deg. The roughness is influenced by feed and it has the lowest value at 0.1mm/rev and the cutting condition is influenced by rake angle only.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.5
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• pp.257-261
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• 2006

Scandium(Sc) in Al-Zn-Mg-Cu based Al alloy on precipitation phenomenon was compared to a 7001(Al-7.2%Zn-3.2%Mg-1.8%Cu) Al alloy. GP zone and ${\eta}^{\prime}$ phases were the main strengthening phases at low aging temperature under $100^{\circ}C$, but ${\eta}^{\prime}$ and $Al_3Sc$ phases were the main strengthening phases at high aging temperature above $1600^{\circ}C$ in Sc added 7000(Al-7.7%Zn-2.0%Mg-1.9%Cu-0.1%Zr) Al alloy. With the addition of 0.1%Sc in 7000 Al alloy, the activation energy for the GP zone, ${\eta}^{\prime}$ and ${\eta}$ phase decreased compared to the 7001 Al alloy. This result indicates that the Sc accelerated the precipitation for the GP zone, ${\eta}^{\prime}$ and ${\eta}$ phases in 7000 Al alloy. Al-7.7%Zn-2.0%Mg-1.9%Cu-0.1%Zr-0.1 Sc alloy has higher strength than 7001 Al alloy, which has high strength.

• Journal of Korea Foundry Society
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• v.31 no.1
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• pp.18-25
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• 2011

Effect of Fe and Mn contents on the tensile properties has been studied in Al-9wt%Si-0.3wt%Mg alloy. As Fe content of Al-9wt%Si-0.3wt%Mg-0.5wt%Mn alloy increased from 0.15wt% to 0.45wt%, tensile strength of as-cast alloy decreased from 192 MPa to 174 MPa, and elongation of the alloy also decreased from 4.8% to 4.2%. Decrease of these properties can be explained as the formation of plate shape, ${\beta}-Al_5FeSi$ phase with high Fe/Mn ratio of the alloy. However when Mn content of Al-9wt%Si-0.3wt%Mg-0.45wt%Fe alloy increased from 0.3wt% to 0.5wt%, tensile strength of T6 aged alloy increased from 265 MPa to 275 MPa, and elongation of the alloy increased from 2.3% to 3.6%. These improvements attribute to chinese script, ${\alpha}-Al_{15}(Mn,Fe)_3Si_2$ phase shape-modified from ${\beta}-Al_5FeSi$ phase with low Fe/Mn ratio of the alloy.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.82-87
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• 2003

Stress corrosion cracking of Alloy 600 and Alloy 690 has been studied with a C-ring specimen in 1%, 10% and 40% NaOH at $315^{\circ}C$. SCC test was performed at 200 mV above corrosion potential. Initial stress on the apex of C-ring specimen was varied from 300 MPa to 565 MPa. Materials were heat treated at various temperatures. SCC resistance of Ni-$_\chi$Cr-10Fe alloy increased as the Cr content of the alloy increased if the density of an intergranular carbide were comparable. SCC resistance of Alloy 600 increased in caustic solution as the product of coverage of an intergranular carbide in grain boundary, intergranular carbide thickness and Cr concentration at grain boundary increased. Low temperature mill annealed Alloy 600 with small grain size and without intergranular carbide was most susceptible to SCC. TT Alloy 690 was most resistant to SCC due to the high value of the product of coverage of an intergranular carbide in grain boundary, intergranular carbide thickness and Cr concentration at grain boundary. Dependency of SCC rate on stress and NaOH concentration was obtained.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2299-2305
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• 2020

Zr alloy specimens were coated with Cr-Al alloy to enhance their resistance to oxidation. The coated samples were oxidized at 1200 ℃ in a steam environment for 300 s and showed extremely low oxidation when compared to uncoated Zr alloy specimens. The microstructure and elemental distribution of the oxides formed on the surface of Cr-Al alloys have been investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A very thin protective layer of Cr₂O₃ formed on the outer surface of the Cr-Al alloy, and a thin Al₂O₃ layer was also observed in the Cr-Al alloy matrix, near the surface. Our results suggest that these two oxide layers near the surface confers excellent oxidation resistance to the Cr-Al alloy. Even after exposure to a high temperature of 1200 ℃, inter-diffusion between the Cr-Al alloy and the Zr alloy occurred in very few regions near the interface. Analysis of the inter-diffusion layer by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) measurement confirmed its identity as Cr₂Zr.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.294-297
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• 2007

Due to their low densities and high specific strength and stiffness, magnesium alloy sheets are very attractive lightweight materials for automotive and electrical products. However, the magnesium alloy sheets are usually formed at elevated temperature because of their poor formability at room temperature. To use of the magnesium alloy sheets for an industrial, their mechanical properties at elevated temperature and appropriate forming process conditions have to be developed. In this study, non-isothermal simulations of a square cup drawing from magnesium alloy sheets have been conducted to evaluate a proper forming process conditions such as the tool temperature, the tool shoulder radius, friction between the blank and the tools. According to this study, appropriate forming process conditions of square cup drawing at elevated temperature from magnesium alloy sheets are suggested.

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.401-405
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• 2007

Due to the low densities and high specific strength and stiffness, magnesium alloy sheets are very attractive lightweight materials for automotive and electrical products. However, the magnesium alloy sheets should be usually formed at elevated temperature because of their poor formability at room temperature. For the use of the magnesium alloy sheets for an industrial, their mechanical properties at elevated temperature and appropriate forming process conditions have to be developed. In this study, non-isothermal simulation of a square cup drawing of magnesium alloy sheets have been conducted to evaluate a proper forming process conditions such as the tool temperature, the tool shoulder radius, friction between the blank and the tools. According to this study, appropriate forming process conditions of square cup drawing at elevated temperature from magnesium alloy sheets are suggested.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.813-819
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• 2001

The microstructure and the distribution of hardness of Co and A1 alloy powder cladding layer in high carbon 9CrSi alloy steel for roll materials cladded by laser surface cladding were investigated. And, for the evaluation of soundness as the roll materials, we examined the wear resistance of the cladding materials with the wear appratus of pin on disc type. The experimental results showed that the microstructure of laser cladding layer was constituted with the clad surface layer, the alloy layer, the heat treatment layer with base metal. The wear resistance of Ni alloy Powder cladding material was superior to that of Co alloy powder cladding material both at the low speed (0.46m/s) and the high speed(0.92m/s). It seemed that the behavior of wear showed the abrasive wear at the early stage and the adhesive wear at the late stage.