• Korean Journal of Materials Research
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• v.7 no.6
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• pp.453-459
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• 1997

용탕단조법에 의해 제조된 Mg-9AI-2Zn 합금을 미세조직관찰, 미소경도측정, 인장시험 등을 행하여 시효거동과 기계적 성질을 조사하였다. 용탕에 가압을 한 결과 주조결함이 제거된 미세한 주조조직을 얻었으며 미세조직은 초정 $\alpha$(Mg 고용체), 과포화고용체 $\alpha$상 및 $\beta$(Mg$_{17}$AI$_{12}$)화합물의 3가지 상으로 구성되어 있었다. 16$0^{\circ}C$및 20$0^{\circ}C$에서 시효열처리한 결과 $\beta$석출물에 의한 피크 경도값이 나타났으며 피크경도에서의 석출물의 형태는 lamella 형태의 불연속 석출물이 대부분이었고 과시효에 따라 불연속석출물의 조대화와 함께 연속석출물의 분율이 증가하였다. 용탕단조방법에 의해 제조된 Mg-9AI-2Zn 합금의 인장특성은 인장강도 261.4MPa, 연산율 7.6%로서 상용 AZ 92 합금보다 인장강도 및 연신율에서 우수한 기계적 성질을 가졌는데 이는 Zn의 고용강화 및 용탕의 가압에 의한 효과였다.다.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.3
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• pp.115-120
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• 2014

Microstructural features were comparatively investigated in AZ91 (Mg-9%Al-1%Zn) and AZ91-0.5%Sn alloys, in order to clarify the reason for the enhancement in room temperature tensile properties by the addition of small amount of Sn in Mg-Al-based alloy. In as-cast state, the Sn-containing alloy showed increased YS, UTS and elongation than the Sn-free alloy. The microstructural examination revealed that various factors including finer cell size, reduction of lamellar (${\alpha}+{\beta}$) phase and morphological change of bulky ${\beta}$ phase from partially divorced shape to fully divorced shape, are likely to be responsible for the improvement in tensile properties for the Sn-containing alloy. It is noted that two alloys showed similar tensile properties after solution treatment. This implies that microstructural evolution related to the ${\beta}$ phase plays a key role in better tensile properties in the Sn-containing alloy.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.62-68
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• 2016

A chromium-free Ce-based conversion coating formed by immersion in a solution containing cerium chloride and nitric acid on AZ31 magnesium alloy has been studied. The effects of acid pickling on the morphology and the corrosion resistance of the cerium conversion coating were investigated. The corrosion resistance of the conversion coating prepared on AZ31 Mg alloy after organic acid pickling was better than that of inorganic acid pickling. The morphology of the conversion-coated layer was observed using optical microscope and SEM. Results show that the conversion coatings are relatively uniform and continuous, with thickness 1.0 to $1.1{\mu}m$. The main elements of the conversion coating of AZ31 Mg alloy are Mg, O, Al, Ce and Zn by EDS analysis. The electrochemical polarization results showed that the Ce-based conversion coating could reduce the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions.

• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.110-115
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• 2000

In this study, the powders of Mg-3wt%Al-1wt%Zn-1wt%MM alloy were produced under vacuum condition by the inert gas atomization and the rapidly solidified powders were consolidated by the vacuum hot extrusion. Then the structural change of powders during extrusion was investigated. The effects of misch metal addition to AZ31 on mechanical properties of extruded bars were also examined. During extrusion of the rapidly solidified powders, their dendrite structure was broken into fragments and remained as grains of 2 ${\mu}m$ size in extruded bar. The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were broken finely, too. The yield stress, tensile strength and ductility obtained in as-extruded Mg-3wt%Al-1wt%Zn-1wt%MM alloy were ${\sigma}_{0.2}=325$ MPa, ${\sigma}_{T.S.}=417$ MPa and ${\varepsilon}=16.8%$. All of these improvements on mechanical properties result from the refined micostructure and second-phase dispersions.

• Journal of Korea Foundry Society
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• v.33 no.1
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• pp.22-31
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• 2013

In order to develop an aluminum alloy, that can combine high thermal conductivity and good castability and anodizability, aluminum alloys with low Si content, such as Al-(0.5~1.5)Mg-1Fe-0.5Si and Al-(1.0~1.5)Si-1Fe-1Zn, were designed. The developed aluminum alloys exhibited 170~190% thermal conductivity (160~180 W/mK), 60~85% fluidity, and equal or higher ultimate tensile strength compared with those of the ADC12 alloy. In each developed alloy system, the thermal conductivity decreased and the strength increased with the increment of Mg and Si, which are the significant alloying elements. The fluidity was in reverse proportion to the Mg content and in proportion to the Si content. The Al-(0.5~1.5)Mg-1Fe-0.5Si alloys exhibited better fluidity in thick-wall castings, while the Al-(1.0~1.5)Si-1Fe-1Zn alloys were better in thin-wall castability due to their lower surface energies. The fluidity behavior was complexly affected by the heat release for the solidification, viscosity, solidification range, and the type, quantity, and formation juncture of the main secondary phase.

• Journal of Powder Materials
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• v.17 no.3
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• pp.190-196
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• 2010

In this paper, rapid solidified Mg-4.3Zn-0.7Y (at.%) alloy powders were prepared using an inert gas atomizer, followed by a severe plastic deformation technique of high pressure torsion (HPT) for consolidation of the powders. The gas atomized powders were almost spherical in shape, and grain size was as fine as less than $5\;{\mu}m$ due to rapid solidification. Plastic deformation responses during HPT were simulated using the finite element method, which shows in good agreement with the analytical solutions of a strain expression in torsion. Varying the HPT processing temperature from ambient to 473 K, the behavior of powder consolidation, matrix microstructural evolution and mechanical properties of the compacts was investigated. The gas atomized powders were deformed plastically as well as fully densified, resulting in effective grain size refinements and enhanced microhardness values.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.145-152
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• 2011

Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of ${\alpha}$-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26~30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding ${\alpha}$-Mg matrix. The presence of I-phase having higher corrosion potential than ${\alpha}$-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between ${\alpha}$-Mg and I-phase.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.37-37
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• 2015

합금 조성 및 열-기계적 처리 조건에 따라 제2상의 종류, 분율, 크기 등이 변화하였으며, 이러한 미세조직적 인자의 변화에 따라 부식거동이 변화하였다. 또한 부식환경에 따라 부식거동에 영향을 미치는 여러 인자들의 상호작용이 변화하였으며 이로 인하여 서로 다른 부식환경에서 합금 조성에 따른 부식거동의 차이가 발생하였다.

• Journal of Korea Foundry Society
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• v.18 no.3
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• pp.283-288
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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. In this study, Mg-Zn alloys have been produced as continuous strips by melt overflow technique. In order to evaluate the influence of additional elements on the grain refinement and mechanical properties, Th and Zr were added in rapidly solidified Mg-5wt%Zn alloy. Then the microstructual observations were undertaken with the objective of evaluating the grain refinement as function of the cooling rate and the additional elements. The tremendous increase in hardness of Mg-Zn base alloys was mainly due to the refinement of the grain structure by the effect of rapid solidification and alloying elements. The formation of intermetallic phases on the grain boundaries may have a positive effect on the corroion resistance. Therefore, despite competition from many other developments, the rapid solidification processing of magnesium alloys emerges as a valuable method to develop superior and commercially acceptable magnesium alloys.

• Journal of Korea Foundry Society
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• v.19 no.5
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• pp.403-409
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• 1999

Mg-Zn-Zr ternary alloys containing 6wt% Zn and (0, 0.4, 0.6)wt% Zr, which is added for grain refinement, can be cast into complex shape by squeeze casting. The influence of Zn and Zr as additional elements on microstructure and mechanical characteristics is investigated by OM, SEM, WDX, XRD and microvickers hardness measurement. The microstructure of Mg-Zn-Zr alloys consists of primary ${\alpha}-Mg$ and MgZn eutectic compound between dendrites. The grain size is decreased from $136{\mu}m$ to $97\;{\mu}m$ by Zr addition, resulting in that the hardness is increased from 42Hv to 59Hv. Furthermore, the grain size is changed to $83{\beta}$ and the hardness is increased to 65Hv by additional infiltration pressure. These results indicate that the Zr addition and additional infiltration pressure are effective for grain refinement acting as an important factor to increase the hardness. The increment in hardness by the Zr addition is slightly larger than that by the additional infiltration pressure.