• Corrosion Science and Technology
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• v.9 no.2
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• pp.92-97
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• 2010

Many kinds of alternative fuels such as biodiesel, ethanol, methanol, and natural gas have been developed in order to overcome the limited deposits in fossil fuels. In some cases, the alternative fuels have been reported to cause degrade materials. The corrosion rates of metals were measured by immersion test, a kind of time consuming test because low conductivity of these fuels was not allowed to employ electrochemical tests. With twin two-electrode cell newly designed for the study, however, electrochemical impedance spectroscopy (EIS) test was successfully applied to evaluation of the corrosion resistance ($R_p$) of zinc, iron, aluminum, and its alloys in an oxidized biodiesel and gasoline/ethanol solutions and the corrosion resistance from EIS was compared with the corrosion rate from immersion test. In biodiesel, $R_p$ increased in the order of zinc, iron, and aluminum, which agreed with the corrosion resistance measured from immersion test. In addition, on aluminum showing the best corrosion resistance ($R_p$), the effect of magnesium as an alloying element was evaluated in gasoline/ethanol solutions as well as the oxidized biodiesel. $R_p$ increased with addition of magnesium in gasoline/ethanol solutions containing chloride and the oxidized biodiesel. In the mean while, in gasoline/ethanol solutions containing formic acid, Al-Mg alloy added 1% magnesium had the highest $R_p$ and the further addition of magnesium decreased $R_p$. It can be explained with the fact that the addition of more than 1% magnesium increases the passive current density of Al-Mg alloys.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.502-508
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• 2005

Hypereutectic Al-Si alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, high thermal stability, low thermal expansion coefficient and good creep resistance. Spray casting of hypereutectic Al-Si alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test. High temperature deformation behavior of the hypereutectic Al-Si alloy has been investigated by applying the internal variable theory proposed by Chang et al. Especially, the creep resistance of spray casted hypereutectic Al-Si alloy can be enhanced considerably by the accumulation of prestrain.

• Journal of Korea Foundry Society
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• v.18 no.5
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• pp.431-438
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• 1998

Microstructure of A356 aluminum alloys cast in the permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. Beryllium addition improved tensile properties and impact toughness of the A356 aluminium alloy, due to the formation of a script phase or a Be-rich phase instead of a needlelike ${\beta}-phase$. The DSC tests indicated that the presence of Be could increase the amount of Mg which is available for $Mg_2Si$ precipitate hardening, and enhance the precipitation kinetics by lowering the ternary eutectic temperature.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1830-1835
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• 2024

The current study aims to study the impacts of the substitution of magnesium with nickel concentrations on physical and γ-ray shielding capacity of magnesium alloys. The density of the magnesium alloys under study is varied from 3.677 g/cm³ to 5.652 g/cm³, with raising the nickel content from 26.7 wt% to 54.8 wt% and reducing the magnesium concentration from 72.6 wt% to 44.2 wt%, respectively. Additionally, the examination of the γ-ray shielding capacity using the Monte Carlo simulation code shows that the substitution of magnesium by nickel content in the magnesium alloys was associated with an enhancement in the γ-ray shielding capacity, where the linear attenuation coefficient for the studied alloys was enhanced by 53.22 %, 52.45 %, and 52.52 % at γ-ray energies of 0.662 MeV, 1.252 MeV, and 1.408 MeV, respectively, with raising the nickel concentration from 26.7 wt% to 54.8 wt%. Simultaneously, the half-value thickness for magnesium alloys was reduced from 2.47 cm to 1.62 cm (at gamma ray energy of 0.662 MeV), from 3.39 cm to 2.22 cm (at gamma ray energy of 1.252 MeV), and from 3.60 cm to 2.36 cm (at gamma ray energy of 1.408 MeV), raising the nickel concentration from 26.7 wt % to 54.8 wt%, respectively. The study shows that the substitution of magnesium for nickel greatly enhanced the radiation shielding capacity of the magnesium alloys.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.2
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• pp.41-48
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• 2018

In this study, microstructural changes due to extrusion, rolling and heat treatment were studied to fabricate Al-4.0wt%Zn-1.5wt%Mg-0.9wt%Cu alloys with homogeneous microstructure suitable for metal cases of smart phones and electronic products fabricated through plastic working. After extrusion microstructure and texture were developed very differently on the surface and inside. Inside, coarse grains were formed and a strong Cube component orientation was developed. On the surface, a weak texture was developed with small grains. After 72% cold rolling the intensity of the Cube component orientation was lower, and uniform texture was developed in all the layers and the R-value was uniformly predicted. After recrystallization, the grain size difference between at the surface and the inside is smaller, when 72% rolling was performed, indicating that a uniform structure is formed. Texture develops almost randomly after recrystallization and exhibits uniform R-values at all layers.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.797-810
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• 2009

A study was made of the effects of a Sn addition on the microstructure and microfracture mechanism of squeeze cast AZ51-xSn magnesium alloys. Microstructural observation, in situ fracture testing, and fractographic observations were conducted on these alloys to clarify the microfracture process. The microstructural analyses indicated that $Mg_2Sn$ particles as well as $Mg_{17}Al_{12}$ particles precipitated mainly along the solidification cell boundaries; the volume fraction of these hard particles increased as the amount of added Sn increased, with increased the strength. From in situ fracture observations of the AZ51-7Sn alloy, coarse precipitates located on the cell boundaries worked as easy crack propagation sites and caused abrupt intercellular fracturing. On the other hand, the overall fracture properties of the AZ51-3Sn alloy improved because crack propagation proceeded into the Mg matrix rather than into the cell boundaries as twins developed actively, as confirmed by an R-curve analysis. These findings suggest that the addition of 3~5 wt.% Sn is effective in improving both the tensile and fracture properties on the basis of well-developed twins, the blocking of crack propagation, and crack blunting.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.499-504
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• 2002

The microstructural change associated with the hardness profile in friction stir welded, age-hardenable 6005 Al alloy had been evaluated. Frictional heat and plastic flow during friction stir welding created the fine recrystallized grain (Stir Zone, SZ), the elongated and recovered grain (Thermo-Mechanical Affected Zone, TMAZ) in the weld zone. Heat affected zone (HAZ), which could be only identified by hardness test because there is no difference in the grain structure compared with that of the base metal, was formed beside the weld zone. A softened region had been formed near the weld zone during friction stir welding process. The softened region was characterized by the dissolution and coarsening of the strengthening precipitate during the friction stir welding. The sound joints of 6005 Al alloys were successfully formed under a wide range of the friction stir welding conditions.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.505-510
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• 2002

The Friction Stir Welding (FSW) is a new joining method that was developed at The Welding Institute (TWI) in England in 1991. It applied heating by the rotational friction and material plastic flow. It was developed as a new joining method to solve the problems of epochally in the welding of Al alloys. In the study, 6000series of Alloy composed of AI-Mg-Si, one of the Al alloys that are utilized for shipbuilding and construction, is selected as a specimen and the numerical is executed against the welded zone of FSW. The material used in this study had the unique properties of strength and anti-corrosion, but since the welded joint of this material is easily softened by the welding heat, FSW is executed and the numerical analysis is carried out around the joint. To examine the mechanical behaviors and properties, F.E.M analysis is executed and the developed thermal-elastic-plastic [mite analysis are used.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.10-18
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• 1996

Al합금과 경합을 하는 경량재료에는 금속재료로서는 Mg 및 Ti이 있는데, 이들 은 고가라는 단점이 있다. 또 비금속재료로는 플라스틱.수지등이 있는데, 산업폐기물 등의 문제가 있으나, Al합금은 재활용이 용이하다. 그러나 구조재료로서의 Al합금의 특성에는 아직 많은 결점을 가지고 있으며, 가장 큰 결점의 하나는 철강재료에 비하여 내마모성이 현저하게 떨어진다는 것이다. 그러므로 이 점이 개선된다면, Al합금은 경량구조용 재료로서 다양한 분야에서 철강재료를 대신할 수 있을 것으로 전망된다. Al합금에 대한 내마모특성을 부여하기 위한 종래의 표면경화기술로서는, 고경도합금 의 채용, 알루마이드처리등이 있는데, 충분한 경도가 얻어지지 않거나, 또는 고경도가 얻어져도 경화층의 깊이가 마이크론단위에 불과하여 고하중하에서의 내마모특성 등에 대한 문제가 있었다. 이들 방법 이외에도 PVD, CVD, 도금 등에 의한 표면피복 방법과 표면의 합금화에 의한 표면경화법 등에 있어서 여러 방법들이 있으나, 경도가 높고 또한 후막의 경화층으로서 박리의 위험이 적은 표면경화처리기술은 확립되어 있지 않다고 할 수 있다. 따라서, 이 분야에 대한 기술개발이 산업계로부터 강하게 요구되 고 있으며, 또한 이것과 관련된 연구가 활발하게 진행되고 있다. 본 해설에서는. 내마 모특성에 따른 Al후막기술의 현상과 그 대표적인 기술로서, 표면용융에 의한 합금화 를 이용하는 표면경화기술에 대하여 소개한다.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.5
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• pp.229-238
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• 2015

The effects of Sn addition and solution treatment on corrosion behavior were studied in AZ91 magnesium casting alloy. The addition of 5%Sn contributed to the introduction of $Mg_2Sn$ phase, to the reduction in dendritic cell size and to the increase in the amount of secondary phases. After the solution treatment, trace amount of $Al_8Mn_5$ particles were observed in the ${\alpha}$-(Mg) matrix for the AZ91 alloy, while $Mg_2Sn$ phase with high thermal stability was additionally found in the AZ91-5%Sn alloy. Before the solution treatment, the AZ91-5%Sn alloy had better corrosion resistance than the Sn-free alloy, which is caused by the enhanced barrier effect of the (${\beta}+Mg_2Sn$) phases formed more continuously along the dendritic cell boundaries. It is interesting to note that after the solution treatment, the corrosion rate of both alloys became increased, but the Sn-added alloy showed higher corrosion rate than the Sn-free alloy. The microstructural examination on the corroded surfaces revealed that the remaining $Mg_2Sn$ particles in the solution-treated AZ91-5%Sn alloy play a role in accelerating corrosion by galvanic coupling with the ${\alpha}$-(Mg) matrix.