• 소성∙가공
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• 제21권7호
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• pp.447-452
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• 2012

This paper is concerned with forming of Al-Zn-Mg-Sc aluminum alloy bolts, focusing on the effects of heat treatment and age-hardening on the formability and ductile damage evolution. Both experimental and finite element studies were performed. From the experiments, it is observed that the heat treatment or the normalization of Al-Zn-Mg-Sc aluminum alloy increases its formability dramatically resulting in successful bolt forming, while the effects of age-hardening at room temperature on the stress-strain relationship and formability are not very critical. Deformation characteristics such as distribution of effective stress and strain, material flow, and ductile damage evolution during bolt forming are examined using a commercial finite element package, Deform-2D. It should be noted that the extrusion load predicted by the finite element method matches well the experiment results. The finite element predictions on the deformation characteristics support the experimental observations such as fracture of bolt head flange, material flow, and distribution of hardness.

• 한국표면공학회지
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• 제47권6호
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• pp.330-334
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• 2014

In this study, the Zn-Mg alloy coatings with various Mg contents were deposited using an unbalanced magnetron sputtering process. Their surface microstructure, chemical composition, phase, and corrosion property were investigated. The microstructure of the Zn-Mg coatings changed from porous microstructure to dense one with increasing Mg contents in the coatings. As Mg contents in coatings increased, intermetallic phases such as $Mg_2Zn_{11}$ and $MgZn_2$ were detected from X-ray diffraction (XRD) results. The corrosion resistance of the Zn-Mg alloy coatings was investigated quantitatively using electrochemical impedance spectroscopy (EIS) measurement with 3.5% NaCl solution. The results of EIS measurement showed that the charge transfer resistance and the phase angle of the Zn-Mg alloy coatings were increased from $162.1{\Omega}{\cdot}cm^2$ to $558.8{\Omega}{\cdot}cm^2$ and from about $40^{\circ}$ to $60^{\circ}$ with increasing Mg contents from 5.1 wt.% to 15.5 wt.% in the coatings. These results demonstrate that the Zn-Mg coatings with increasing Mg contents showed an enhanced corrosion resistance.

• 한국주조공학회지
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• 제22권2호
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• pp.82-88
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• 2002

Al-5.5Zn-2.5Mg-l.5Cu semi-solid slurry was prepared by cooling the liquid metal with a low superheat to a solid and liquid co-existing temperature. Relatively round solid particles could be obtained in the slurry through the simple process. The prepared slurry was deformed into the metallic mold by a press and the mechanical properties of obtained specimens were investigated. Mold filling ability of the alloy slurry was also investigated and compared with that of A356 alloy. Al-Zn-Mg-Cu alloy showed lower mold filling ability than A356 alloy probably because small amount of eutectic phase is present and the heat of fusion generated during solidification is smaller than that of A356 alloy.

• 한국주조공학회지
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• 제30권4호
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• pp.137-141
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• 2010

The effects of Zn amounts on the castability and tensile properties of Al-Zn-Mg-Cu alloys were investigated for development of high strength die casting aluminium alloys. Al-Zn-Mg-Cu alloys with 3.5% Zn showed high cast cracking tendency and poor mold filling behaviour. Al-Zn-Mg-Cu alloys with 5wt% Zn and 7wt% Zn had the tensile strengths of 300~400MPa and the elongations of 2~18%. The effect of Zn on the tensile strength of Al-Zn-Mg-Cu alloys was insignificant, but Al-Zn-Mg-Cu alloy with high Zn amount had lower elongation.

• 열처리공학회지
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• 제22권2호
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• pp.75-79
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• 2009

Precipitate formations and grain size variations in various Mg-Sn-Zn alloys have been investigated and their effects on the tensile properties and sheet metal formability were evaluated. MgSn and MgZn precipitates were observed in the alloy sheets, however any clear difference in morphology or size for the precipitates could not be found even though MgSn precipitates tend to be larger than MgZn. The highest formability in terms of conical cup value was found in the Mg-4 wt%Sn-2 wt%Zn where the high tensile elongation and the reduced grain coarsening at elevated temperatures were observed.

• 한국주조공학회지
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• 제37권3호
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• pp.63-70
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• 2017

In the present study, effects of an addition of Sn on the microstructure and corrosion behavior were investigated in Mg-4%Zn-(0-3)%Sn casting alloys. With an increase in the Sn content, the ${\alpha}-(Mg)$ dendritic cell size was reduced, whereas the total amount of precipitates increased due to the formation of the $Mg_2Sn$ phase. It was found in immersion and electrochemical corrosion tests that the addition of Sn has a detrimental effect on the corrosion resistance of the Mg-4%Zn alloy. Microstructural examinations of the corrosion product and the corroded surface indicated that an accelerated micro-galvanic effect by the $Mg_2Sn-phase$ particles and a less protective corrosion product on the surface were responsible for the increased corrosion rate at a higher Sn content.

• 한국재료학회지
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• 제21권3호
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• pp.168-173
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• 2011

Precipitation of the ordered icosahedral quasicrystal in Mg-6wt%Zn-1wt%Y alloy has been characterized by transmission electron microscopy observations. The lamellar-type icosahedral qusicrystal phases (I-phase) with the face-centered icosahedral (FCI) structure are observed in alloy after solution treatment at $550^{\circ}C$. In the alloy annealed at $400^{\circ}C$, polygon-shaped I-phases are observed in the ${\alpha}$-Mg matrix. The interfaces of the I-phase with the matrix are facetted and the facets are on five-fold and two- fold plane of the I-phase. The orientation relationship of the I-phase with the matrix is determined to be $[I5]_I//[001]_{Mg}$, $(2f)_I//(2\overline{1}0)_{Mg}$ and $[I2]_I//[311]_{Mg}$, $(5f)_I//(0\overline{1}1)_{Mg}$. The icosahedral grains are occasionally found to be twinned with one of the five-fold axis as the twin axis. The twin boundaries appear to be fairly straight and perpendicular to the fivefold twin axis. The icosahedral twin can be expressed as a rotation of $63.4^{\circ}$ or $116.62^{\circ}$ around two fold zone axis.

• Metals and materials international
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• 제24권6호
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• pp.1315-1326
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• 2018

In this work, ultrasonic vibration (UV) and rheo-squeeze casting was first applied on the Mg alloy reinforced with long period stacking ordered (LPSO) structure. The semisolid slurry of Mg-Zn-Y alloy was prepared by UV and processed by rheosqueeze casting in succession. The effects of UV, Zr addition and squeeze pressure on microstructure of semisolid Mg-Zn-Y alloy were studied. The results revealed that the synergic effect of UV and Zr addition generated a finer microstructure than either one alone when preparing the slurries. Rheo-squeeze casting could significantly refine the LPSO structure and ${\alpha}-Mg$ matrix in $Mg_{96.9}Zn_1Y_2Zr_{0.1}$ alloy without changing the phase compositions or the type of LPSO structure. When the squeeze pressure increased from 0 to 400 MPa, the block LPSO structure was completely eliminated and the average thickness of LPSO structure decreased from 9.8 to $4.3{\mu}m$. Under 400 MPa squeeze pressure, the tensile strength and elongation of the rheocast $Mg_{96.9}Zn_1Y_2Zr_{0.1}$ alloy reached the maximum values, which were 234 MPa and 17.6%, respectively, due to its fine ${\alpha}-Mg$ matrix (${\alpha}1-Mg$ and ${\alpha}2-Mg$ grains) and LPSO structure.

• 한국재료학회지
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• 제17권6호
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• pp.337-341
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• 2007

[ $Mg_{97}Zn_1Y_2$ ] alloy powders were prepared from gas atomization process, followed by consolidation using spark plasma sintering (SPS) process. The atomized $Mg_{97}Zn_1Y_2$ alloy particles were entirely spherical in shape and dendritic microstructure. The compacts sintered by SPS process had theoretical density more than 99%. The compressive yield strength was decreased as sintering temperature increased. It was found that the compressive strength showed the maximum value of 303MPa at the $Mg_{97}Y_2Zn_1$ specimen sintered under load of 255 MPa at $350^{\circ}C$.

• 한국주조공학회지
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• 제18권5호
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• pp.462-466
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• 1998

Interest in rapid solidification of magnesium alloys stems from the fact that conventional ingot metallurgy alloys exhibit poor strength, ductility, and corrosion resistance. Such properties can be improved by microstructural refinement via rapid solidification processing. Mg-5wt%Zn alloys have been produced as continuous strips by melt overflow technique and the strips were consolidated by hot extrusion. The yield stress, tensile strengh and ductility obtained in asextruded Mg-5wt%Zn alloy were ${\sigma}_{0.2}=152\;MPa$, ${\sigma}_{T.S{\cdot}}=263\;MPa$ and ${\varepsilon}=21.8%$. In order to evaluate the influence of additional elements on mechanical properties, Th and Zr were added in rapidly solidified Mg-5wt%Zn alloy. An 130% increase in yield stress of as-extruded Mg-5wt%Zn-3wt%Th-1wt%Zr alloy was attributed to grain refinement by rapid solidification and elemental addition.