• 소성∙가공
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• 제27권6호
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• pp.379-385
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• 2018

This study investigated the effect of extrusion conditions on microstructures and mechanical properties of AM80 magnesium alloys. The billets of magnesium alloy used for hot extrusion were prepared by permanent mold casting method, and its extrusion was hot direct extrusion with different extrusion conditions. The results of microstructural analysis showed that the main phases in the as-casted alloys were ${\alpha}-Mg$, ${\beta}-Mg_{17}Al_{12}$, and lamella $Mg_{17}Al_{12}$. Hot extrusion results, The tensile strength of the most soundly manufactured extruded bars (extrusion temp: $350^{\circ}C$, extrusion ratio: 27:1, ram speed: 2mm/s) was approximately 327MPa at room temperature. The increase in the mechanical properties of hot-extruded alloys was as a result of grain refinement by dynamical recrystallization during hot extrusion.

• 열처리공학회지
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• 제33권5호
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• pp.219-225
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• 2020

The objective of this study was to investigate the tensile properties and thermal conductivities of Mg9.3%Al alloy in as-cast state and heat-treated state consisting of fully discontinuous precipitates (DPs), respectively. The fully DPs microstructure was obtained by solution treatment at 405℃ for 24 h, followed by furnace cooling to RT. The as-cast alloy showed a partially divorced eutectic β(Mg₁₇Al₁₂) phase particles formed along the α-(Mg) cell boundaries. The DPs had various apparent (α+β) interlamellar spacings, which is related to different transformation temperatures during the furnace cooling. The DPs microstructure exhibited better tensile strength than the as-cast one, resulting from the higher value of elongation in response to its more homogeneous microstructure. It is noticeable that the DPs microstructure had 12.4% higher thermal conductivity in average than the as-cast one between RT and 200℃. The XRD analyses revealed that the lower Al concentration in the α-(Mg) matrix may well be responsible for the better thermal conductivity of the DPs microstructure.

• 한국재료학회지
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• 제22권10호
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• pp.499-503
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• 2012

The present study is intended to comparatively investigate the changes in microstructure and tensile properties at room and elevated temperatures in commercial AM50(Mg-5%Al-0.3%Mn) and 0.3 wt%CaO added ECO-AM50 alloys produced by permanent mould casting. The typical microstructure of AM50 alloy was distinctively characterized using two intermetallic compounds, ${\beta}(Mg_{17}Al_{12})$ and $Al_8Mn_5$, along with ${\alpha}$-(Mg) matrix in an as-cast state. The addition of a small amount of CaO played a role in reducing dendrite cell size and quantity of the ${\beta}$ phase in the AM50 alloy. It is interesting to note that the added CaO introduced a small amount of $Al_2Ca$ adjacent to the ${\beta}$ compounds, and that inhomogeneous enrichment of elemental Ca was observed within the ${\beta}$ phase. The ECO-AM50 alloy showed higher hardness and better YS and UTS at room temperature than did the AM50 alloy, which characteristics can be mainly ascribed to the finer-grained microstructure that originated from the CaO addition. At $175^{\circ}C$, higher levels of YS and UTS and higher elongation were obtained for the ECO-AM50 alloy, demonstrating that even 0.3 wt%CaO addition can be beneficial in promoting the heat resistance of the AM50 alloy. The combinational contributions of enhanced thermal stability of the Ca-containing ${\beta}$ phase and the introduction of a stable $Al_2Ca$ phase with high melting point are thought to be responsible for the improvement of the high temperature tensile properties in the ECO-AM50 alloy.

• 열처리공학회지
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• 제28권3호
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• pp.126-133
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• 2015

The aim of this study is to investigate the effect of solution treatment on the corrosion behavior of Mg-8%Al-(0-1)%Zn casting alloys in 1M NaCl aqueous solution. After the solution treatment, all alloys showed single ${\alpha}$-(Mg) phase microstructure by dissolution of ${\beta}(Mg_{17}Al_{12})$ phase into the ${\alpha}$-(Mg) matrix. The $H_2$ evolution volume decreased with an increase in Zn content, which indicates that the addition of Zn plays a beneficial role in decreasing corrosion rate of the Mg-Al-Zn alloy in solution-treated state. The microstructural evaluations on the corrosion products and corroded surfaces after the immersion test in 1 M NaCl solution revealed that the incorporation of more $Al_2O_3$ and ZnO into the corrosion product, by which the penetration of $Cl^-$ ions is impeded, are thought to be responsible for the better corrosion resistance in relation with the Zn addition.

• 한국재료학회지
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• 제7권2호
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• pp.129-135
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• 1997

용탕단조법에 의해 제조된 Mg-6AI-xZn(x=0,1,2)합금의 기계적 성질에 미치는 시효열처리의 영향을 조사하였다. 주조상태에서의 미세조직은 초정 Mg고용체, 과포화된 상태의 Mg상, 응고과정에서 형성된 $\beta(Mg_{17}AI_{12}$)화합물 등 3개의 상으로 구성되어 있었다. 용체화처리 수 $200^{\circ}C$및 $240^{\circ}C$에서 시효열처리한 결과 Mg-6AI-xZn(x=0,1,2)합금은 $\beta$ 석출물에 의한 피크 경도값이 나타났으며, 석출물의 형태는 $200^{\circ}C$에서는 lamella 형태의 불연속 석출물이, $240^{\circ}C$에서는 미세분산분포된 연속석출물의 형태를 보였다. 용탕단조방법에 의해 제조된Mg-6AI-xZn합금의 기계적 성질은 사형주조법에 비해 인장강도 및 연신율에서 우수한 특성을 보였으며 Zn의 첨가량이 증가함에 따라 Zn의 고용강화 효과에 따라 강도값이 증가되었다.

• 열처리공학회지
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• 제34권5호
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• pp.218-225
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• 2021

In this study, damping capacities were comparatively investigated for Mg-9%Al alloy with as-cast (AC) and fully discontinuous precipitates (DPs) microstructures, respectively. The DPs microstructure was obtained by solution treatment at 678 K for 24 h, followed by furnace cooling to RT. The AC microstructure was typically characterized by partially divorced eutectic β(Mg₁₇Al₁₂) phase particles distributed along the α-(Mg) matrix cell boundaries. The DPs microstructure showed lamellar morphology consisting of α and β thin layers with various interlamellar spacings. The DPs microstructure had better damping capacity than the AC microstructure in the strain-amplitude independent region, while in the strain-amplitude dependent region, the damping behavior was reversed. In view of the microstructural features of AC and DPs, the lower concentration of Al in the α-(Mg) phase for the DPs microstructure and the lower β phase number density for the AC microstructure would be responsible for the higher damping capacities in the strain-amplitude independent and strain-amplitude dependent regions, respectively.

• 한국주조공학회지
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• 제20권1호
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• pp.29-37
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• 2000

The purpose of this study is to investigate the effect of misch metal addition on the microstructure and mechanical property of rapidly solidified AZ91 alloy by melt spinning process. As the contents of misch metal(rare earth element:Ce,La, Nd, Pr)was increased, the microstructure of RS ribbons and extrudates became finer than those of AZ91, and RE related phases($Al_{11}RE_3$, $Al_2RE$) were formed. At room temperature, the rapidly solidified AZ91+1 wt%Mm alloy showed the highest tensile strength, 430 MPa due to precipitation strengthening of${\beta}(Mg_{17}Al_{12})$ phase and Al11RE3 phase. At the elevated temperature, the mechanical property of AZ01+3 wt%Mm alloy was higher than those of other Mg alloys. The reasons were that $Al_{11}La_3$ phase was thermally stable and suppressed the grain growth. In contrast with $Al_{11}La_3$ phase, ${\beta}$ phase was thermally unstable and could not suppress the grain growth at the elevated temperature. Therefore, Al11RE3 phase contributed to improve the thermal stability of RS AZ91 Alloy.

• 한국주조공학회지
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• 제20권6호
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• pp.386-394
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• 2000

In the present study, the effect of yttrium addition on the microstructure and mechanical property of rapidly solidified AZ91 alloy by melt spinning process is estimated. As yttrium was added, the microstructure of RS ribbons and extrudates became finer than those of AZ91, and RE related phases $(Al_2RE)$ were formed. In the case of the addition of 3wt%Y, the microstructure of extrude showed the finest grain size. At room temperature, the AZ91 + 3wt%Y alloy showed the highest tensile strength, 352 MPA due to precipitation of ${\beta}(Mg_{17}Al_{12})$ phase and $Al_2RE$ phase. At the elevated temperature, the mechanical property of AZ91 + 3wt%Y alloy was higher than those of other Mg alloys. The reasons were that $Al_2Y$ compound was thermally stable and suppressed the grain growth. In contrast with $Al_2Y$ compounds, ${\beta}$ phase was thermally unstable and could not suppress the grain growth at the elevated temperature. Therefore, $Al_2Y$ phase contributed to improve the thermal stability of RS AZ91 alloy.

• 열처리공학회지
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• 제28권4호
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• pp.190-199
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• 2015

The study is intended to investigate the effect of solution treatment on microstructure and corrosion behavior of AZ91(Mg-9%Al-1%Zn-0.3%Mn)-2%Ca casting alloy. In as-cast state, the AZ91-2%Ca alloy consisted of intermetallic ${\beta}(Mg_{17}Al_{12})$, $Al_8Mn_5$ and $Al_2Ca$ phases in ${\alpha}-(Mg)$ matrix. After the solution treatment, Al within the ${\alpha}-(Mg)$ matrix was distributed more homogeneously, along with the slight decrease in the total amount of intermetallic compounds. The corrosion resistance of the AZ91-2%Ca alloy was improved after the solution treatment. The microstructural examinations for the solution-treated samples revealed that the better corrosion resistance may well be related to the incorporation of more oxides and hydroxides such as $Al_2O_3$, $Al(OH)_3$, CaO and $Ca(OH)_2$ into the surface corrosion product without dissolution of the intermetallic phases along the grain boundaries.

• 한국재료학회지
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• 제7권6호
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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.