• Transactions of Materials Processing
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• v.14 no.4 s.76
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• pp.319-326
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• 2005

In this study, the nano-deformation behavior of semi-solid Al-Si alloy was investigated using a molecular dynamics simulation as a part of the research on the surface crack behavior in thixoformed automobile parts. The microstructure of the grain-size controlled Al-Si alloy consists of primary and eutectic regions. In eutectic regions the crack initiation begins with initial fracture of the eutectic silicon particles and inside other intermetallic phases. Nano-deformation characteristics in the eutectic and primary phase of the grain-size controlled Al-Si alloy were investigated through the molecular dynamics simulation. The primary phase was assumed to be single crystal aluminum. It was shown that the vacancy occurred at the zone where silicon molecules were.

• Journal of the Korean institute of surface engineering
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• v.29 no.4
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• pp.278-285
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• 1996

The structure of coating layer formed by hot dip Al-Cu alloy coating on Monel 1400 metal was studied. The coating layer consists of alloyed layer adjacent to the Monel 400 substrate and Al-Cu alloy. It was found that the hardness of coating increased with dipping time and heat treatment associated with the diffusion and the formation of intermetallic compound at the interface. However the thickness of coating layer was decreased at high dipping temperature due to tile higher viscosity of liquid coating alloy. Diffusion heat treatment at $600^{\circ}C$ after coating resulted in the disappearence of adhered Al(Cu) and $CuAl_2$ phases, and then they transformed into the new phases of CuAl and Al7Cu4Ni at coating layer.

• Transactions of Materials Processing
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• v.13 no.4
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• pp.374-381
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• 2004

In this study, the deformation behavior of semi-solid Al-Si alloy was investigated by nanoindenter as a part of the research on the surface crack behavior in thixoformed automobile component. The microstructure of semi-solid Al-Si alloy consists of primary and eutectic regions. In eutectic regions the crack initiation begins with initial fracture of the eutectic silicon particles and inside other intermetallic phases. Nano-deformation characteristics in the eutectic and primary phase of semi-solid aluminium alloy were investigated through the nano-indentation experiments and the AFM observation. In addition, mechanical properties of each region were investigated and compared with each other.

• 연구논문집
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• s.25
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• pp.163-168
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• 1995

The intermetallic compound $Ni_3Al$ causes a peritectic reaction at the composition and temperature very close to the eutectic reaction in Ni-Al system. Although the phase diagram accepted for this system by ASM Handbook has the eutectic forming between the $\gamma$ and $\gamma$ phases, directional solidification study has shown that the eutectic occurs between $\beta$ and $\gamma$. This work examines the liquidus region using quenched, directional solidification experiments that preserve the microstructrues formed at the solidification front. It is also shown that under certain composition and growth conditions a metastable eutectic between the $\beta$ and $\gamma$ phases forms in this system. Finding of the metastable eutectic provided an important information to understand the phase equilibria near the $Ni_3Al$ composition.

• Advances in materials Research
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• v.13 no.2
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• pp.141-151
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• 2024

The aim of this work was to determine the behavior of alloy elements and compounds formed during solidification in the manufacturing process of the CuAgZrCr alloy under an oxidizing environment. Bulk and surface analysis techniques, such as Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman and X-ray diffraction (XRD) were used to characterize the phases obtained in the solidification process. In order to focus the analysis on the on grain boundary interface, partial removal of the matrix phase by acid attack was performed. The compositional differences obtained by SEM-EDX, Raman and XPS on post-manufacturing materials allowed us to conclude that the composition of grain boundaries of the alloy is directly influenced by the oxidizing environment of alloy manufacturing.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.4
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• pp.172-181
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• 2024

In this study, the effect of addition of Ti and Co elements on microstructural evolution and characteristics of vacuum-casted Cu-25%Cr electrical contact material was investigated. The coarse and insoluble Cr phases with an average size of 300 ㎛ in commercial Cu-25%Cr alloy were reduced to tens of micrometers in vacuum casted Cu-25%Cr-X(X=Ti, Co) alloy, which can be interpreted as result controlling coarsening and the work-frame structure of the insoluble Cr phase by the formation of intermetallic compounds such as Cr₂Ti or Cr_0.5Co_1.5Ti around the Cr phase As a result, the electrical properties such as weight loss and fusion resistance against the repeated arc generation of the electrical contact material as well as the mechanical properties were greatly improved.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.6
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• pp.281-287
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• 2014

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for engine mount bracket prepared by gravity casting (as-cast) and die-casting (as-diecast) process have been investigated. For the microstructural characterization, the inductively coupled plasma mass spectrometry (ICP-MS), optical microscope (OM), scanning electron microscope (SEM) and electron probe microanalysis (EPMA) analyses are conducted. For the intermetallic phases, the X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are also conducted with quantitative and qualitative analysis. Micro Vickers hardness and static tensile test are achieved in order to measure mechanical properties of alloys. Secondary dendrite arm spacing (SDAS) of as-cast and as-diecast show 37um and 18um, respectively. A large amount of coarsen eutectic Si, $Al_2Cu$ intermetallic phase and Fe-rich phases are identified in the Al-6Si-2Cu alloy. Mechanical properties of gravity casting alloy are much higher than those of die-casting alloy. Especially, yield strength and elongation of gravity casting alloy show 2 times higher than die-casting alloy. After shot peening, shot peening refined the surface grains and Si particles of the alloys by plastic deformation. The surface hardness value shows that shot peening alloy has higher value than unpeening alloy.

• Transactions of Materials Processing
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• v.30 no.1
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• pp.5-15
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• 2021

The effects of heat treatments (T6 and T73) on the microstructure, mechanical properties, and high cycle fatigue behavior of modified AA7075 alloys were investigated. A modified 7075 alloy was manufactured using modified-Mg (Mg-Al2Ca) instead of the conventional element Mg. Based on the microstructure, the average grain size was 4.5 ㎛ (T6) and 5.2 ㎛ (T73). Regardless of heat treatment, the modified AA7075 alloys consisted of Al matrix containing homogeneously distributed Al2CuMg and MgZn2 phases with reduced Fe-intermetallic compound. Room temperature tensile tests showed that the properties of modified 7075-T6 (Y.S.: 622MPa, T.S: 675MPa, elongation: 15.4%) were superior to those of T73 alloy (Y.S.: 492MPa, T.S: 548MPa, elongation: 12.8%). Experimental data show that the fatigue life of T6 was 400 MPa, about 64% of its yield strength. However, the fatigue life of T73 alloy was 330 MPa and 67%. Irrespective of the stress level, all crack initiation points were located on the specimen surface, and no inclusions acting as stress concentrators were seen. Superior mechanical properties and high cycle fatigue behavior of modified AA7075-T6 alloy are attributed to the fine grains and homogeneous distribution of small second phases such as MgZn2 and Al2CuMg, in addition to reduced Fe-intermetallic compounds.

• Corrosion Science and Technology
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• v.9 no.2
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• pp.98-103
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• 2010

In order to further reduce the cost without reducing the corrosion resistance, a high-manganese austenitic alloy for sink roll or stabilizer roll in continuous hot-dip coating lines was developed. A systematic study of corrosion behavior of the high-manganese austenitic alloy in pure zinc bath at $490^{\circ}C$ was carried out. The results shows that, the high-manganese austenitic alloy shows better corrosion resistance than 316L steel. The corrosion rate of the high-manganese austenitic alloy in pure zinc bath is calculated to be approximately $6.42{\times}10^{-4}g{\cdot}cm^{-2}{\cdot}h^{-1}$, while the 316L is $1.54{\times}10^{-3}g{\cdot}cm^{-2}{\cdot}h^{-1}$. The high-manganese austenitic alloy forms a three-phase intermetallic compound layer morphology containing ${\Gamma$}, ${\delta}$ and ${\zeta}$ phases, while the 316L is almost ${\zeta}$ phase. The ${\Gamma}$ and ${\delta}$ phases of the high-manganese austenitic alloy contain about 8.5 wt% Cr, the existence of Cr improve the stabilization of phases, which slow down the reaction of Fe and Zn, improve the corrosion resistance of the high-manganese austenitic alloy. So substitute the nickel with the manganese to manufacture the high-manganese austenitic alloy of low cost is feasible.

• Journal of Korea Foundry Society
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• v.30 no.3
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• pp.100-110
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• 2010

The solidification sequence and formation of intermetallic phase of Fe-rich Al-Si-Cu alloy were investigated by using real-time imaging of synchrotron X-ray radiation. Effects of cooling rate during uni-directional solidification on the resultant solidification behavior was also studied in a specially constructed vacuum chamber in the SPring-8 facility. The series of radiographic images were complementarily analyzed with conventional analysis of OM and SEM/EDX for phase identification. Detailed solidification sequence and formation mechanisms of various phases were discussed based on real-time image analysis. The growth rates of $\alpha$-AlFeMnSi and ${\beta}-Al_5FeSi$ were measured in order to understand the growth behavior of each phase. It is suggested that real-time imaging technique can be a powerful tool for the precise understanding of solidification behavior of various industrial materials.