• Journal of Korea Foundry Society
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• v.35 no.6
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• pp.147-154
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• 2015

The effects of Sc and Sr elements on the modification of the eutectic $Mg_2Si$ phase and the castability were investigated in the Al-4wt%Mg-0.9wt%Si-0.3wt%Mn-0.15wt%Fe alloy. Measurements of the cooling curve and microstructure observations were performed to analyze the additional effects of Sc and Sr minor elements during the solidification process. A prominent effect found on the modification of the eutectic $Mg_2Si$ phase with additions of the Sr and Sc elements. Here, a fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident with an addition of Sc element up to 0.2 wt%. The growth temperature of the eutectic $Mg_2Si$ phase decreased and the effect on the modification of the eutectic $Mg_2Si$ phase increased with the addition of Sr element up to 0.02 wt%. The addition of 0.02wt%Sr had the strongest effect on the modification of the eutectic $Mg_2Si$ phase, and the resulting microstructure of the eutectic $Mg_2Si$ phase was found to have a fibrous morphology with a decreased aspect ratio and an increased modification ratio. Fluidity and shrinkage tests were conducted to evaluate the castability of the alloy. The addition of 0.02wt%Sr effectively increased the fluidity of the alloy, while an addition of Sc did not show any effect compared to when nothing was added. The maximum filling length was recorded for 0.01wt%TiB-0.02wt%Sr owing to the effect of the fine ${\alpha}$-Al grains. The macro-shrinkage ratio decreased, while the micro-shrinkage ratio increased with the addition of various eutectic modifiers. The highest ratio of micro-shrinkage was recorded for the 0.02wt%Sr condition. However, the total shrinkage ratio was nearly identical regardless of the amounts added in this study.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.6
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• pp.391-397
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• 2000

Addition of Ca element and nonequilibrium heat treatment which promotes shape modification of eutectic Si and ${\beta}$ intermetallic compound were conducted to improve the mechanical properties of Al-Si-Cu alloy. Modification of eutectic Si and dissolution of needle-shape ${\beta}$ intermetallic compounds were possible by nonequilibrium heat treatment in which specimens were held at $505^{\circ}C$ for 2 hours in Al-Si-Cu alloy with Fe. Owing to the decrease in aspect ratio of eutectic Si by the heat treatment of the alloy with 0.33wt.% Fe, the increase in elongation was prominent to be more than double that in the as-cast specimen. Dissolution of needle-shape ${\beta}$ intermetallic compounds in the alloy with 0.85wt.% Fe led to the improvement of tensile strength as the length of ${\beta}$ compounds decreased to 50%.

• Journal of Korea Foundry Society
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• v.24 no.3
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• pp.145-152
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• 2004

The eutectic Si in Al-8.5wt.%Si alloy was changed from large flake to fine lemellar(or fibrous) shape when the Sc amount in the Al-Si alloy reaches 0.2wt.%. The optimum amount of Sc for the best modification effect was 0.8wt.% and slight decrease of modification effect occurred over this value. The study on the distribution of the modifiers(Sr, Na, and Sc) and the measurement of the surface tension of the Al-8.5wt.%Si alloy melt added with Sr, Na, and Sc modifier, respectively, reveals that Sc modifies the eutectic Si by the decrease of surface tension, while Sr and Na modify the eutectic Si mainly by impurity induced twinning mechanism.

• 한국기계연구소 소보
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• s.20
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• pp.71-78
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• 1990

This investigation was undertaken to establish the technologies of grain refinement and modification, and to characterize material properties, essential for high quality aluminum alloy castings. Grain refinement seldom changed DAS and eutectic Si size, but largely decrease grain size. The variations of grain size induced by grain refinement had a great influence on the elongation without changes in the tensile strength or yield strength. The optimum Ti level lies between 0.1% and 0.16% to achieve the best possible mechanical properties. DAS and grain size were little affected, but eutectic Si size was greatly refined by modification. The variation of eutectic Si size had a great effect on the elongation, impact value, fracture toughness and fatigue crack propagation rate without changes in the tensile strength or yield strength. The Sr content of 0.015% is optimum to modification.

• Journal of Korea Foundry Society
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• v.34 no.5
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• pp.156-161
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• 2014

This study is focused on the effect of $Al_2Ca$ as a modifier on eutectic Si modification of A356 alloy. Microstructural observation was carried out for as-cast, as-solution treated and as-aged samples. Solution treatment and aging were performed for 2, 4, 6 and 10 hrs at $540^{\circ}C$ and $170^{\circ}C$, respectively. Although A356 alloy, which $Al_2Ca$ was added, has no significant difference in as-cast phases with normal A356 alloys, it shows much more modified eutectic Si, grain refinement and improved tensile property both in as-cast and as-heat treated conditions. TGA result shows that $Al_2Ca$ added A356 alloy has a certain improvement in oxidation resistance.

• Journal of Korea Foundry Society
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• v.24 no.2
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• pp.79-84
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• 2004

In this study, the electromagnetic vibration is adopted for modifying eutectic Si phase and reducing its size. The higher the current density and frequency of electromagnetic vibration(EMV), the finer the size of eutectic Si phase. The tensile strength and elongation of EMVed alloy were highly improved. Measured twin probability of EMVed alloy at a frequency of 1000 Hz was approximately six times as high as that of the normal alloy. The mechanism for the increase in twin density due to EMV during solidification could be supposed from the fact that the preferential growth along <112> in silicon was suppressed by preventing Si atom from attaching to the growing interface of Si phase and by changing the solid/liquid interfacial energy of silicon. According to the result of UTS test, because of modification of eutectic Si, UTS and elongation are highly increased.

• Journal of Korea Foundry Society
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• v.38 no.6
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• pp.121-131
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• 2018

The effect of additives on the castability of the AC2BS aluminum alloy, which contains 35% recycled scrap, was investigated. For the wide utilization of the recycled scrap AC2BS aluminum alloy, the research results were compared to those with the AC2B virgin alloy, which is typical Al-Si-Cu alloy system. It was confirmed that the addition of Al-5%Ti-1%B increased the ${\alpha}$-Al nucleation temperature during solidification and decreased the grain size through cooling curve and microstructural observations of the recycled alloy. It was also found that an addition of Al-10%Sr decreased the eutectic Si growth temperature during the solidification process and modified the shape of the eutectic Si of the recycled alloy. The characteristics of fluidity, shrinkage and solidification crack strength were evaluated. For the AC2BS aluminum alloy containing 35% recycled scrap, both ${\alpha}$-Al grain refinement due to Ti-B and eutectic Si modifications due to Sr contributed to the improvement of the fluidity. The macro- shrinkage ratio increased with additions of both Al-10%Sr and Al-5%Ti-1%B and the micro-shrinkage ratio increased with the addition of Al-10%Sr but decreased with the addition of Al-5%Ti-1%B. The casting characteristics of TiB and Sr-treated AC2BS aluminum alloy containing 35% recycled scrap are similar to those of AC2B virgin alloy. The improvement of the solidification crack strength of the AC2BS aluminum alloy was possible by the reduction of the grain boundary the stress concentration through the enhancement by both ${\bullet}{\cdot}$-Al refinement and eutectic Si modification. More extensive use of the AC2BS aluminum alloy containing 35% recycled scrap can be expected in the future.

• Korean Journal of Materials Research
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• v.15 no.7
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• pp.480-485
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• 2005

Sc has been known to be an very effective ppt-hardening element in Al and Al alloys and also to be effective in modification of eutectic Si in hypoeutectic Al-Si alloys. The modification mechanism of Sc is different from that of the traditional modifier Sr in Al-Si alloys. In the present study the effects of Sc on the primary and eutectic Si in hypereutectic Al-Si alloys were investigated with evaluating the microstructures with OM, EPMA and EBSD methods. The results represent that Sc has only a small effect on primary Si when added less than $0.8wt\%$. However, when Sc addition leading to the precipitation of metallic Sc within primary Si reaches $1.6wt\%$, very coarse primary Si occurs.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.3
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• pp.150-158
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• 2022

The effects of scandium addition on the Al-6Si-2Cu Alloy were investigated. The Al-6Si-2Cu-Sc alloy was prepared by gravity die casting process. In this study, scandium was added at 0.2 wt%, 0.4 wt%, 0.8 wt%, and 1.0 wt%. The microstructure of Al-6Si-2Cu-Sc alloy was investigated using Optical Microscope, Field Emission Scanning Electron Microscope, Electron Back Scatter Diffraction, and Transmission Electron microscope. The microstructure of Al-6Si-2Cu alloy with scandium added changed from dendrite structure to equiaxed crystal structure in specimens of 0.4 wt% Sc or more, and coarse needle-shape eutectic Si and β-Al₅FeSi phases were segmented and refined. The nanosized Al₃Sc intermetallic compound was observed to be uniformly distributed in the modified Al matrix.

• International Journal of Advanced Culture Technology
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• v.3 no.2
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• pp.132-137
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• 2015

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy. It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si, $Cu_3NiAl_6$ and $Mg_2Si$ phases in the ${\alpha}$-Al matrix but different in size and morphology. Both size and inter-particle spacing of Si particles were significantly changed by increasing of the solution treatment time. After a short solution treatment, the coarse acicular plate of the eutectic Si appears to be fragmented. Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time to shorter compared to unmodified alloy. The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys. Compared to 10 h solution treatment, the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.