• Journal of Korea Foundry Society
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• v.39 no.3
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• pp.33-43
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• 2019

In this study, the effects of Zn additions on the mechanical properties of Al-Si-Mg-Cu alloys were investigated by increasing the amount of Zn up to 8wt.%. As the Zn content was increased up to 6 wt.%, the yield strength and elongation changed linearly without any significant changes in the size and shape of the main reinforcement phase. However, it was confirmed by SEM observation that the Mg-Zn phase formed between the reinforcement phases when the amount of Zn added exceeded 7wt.%. A Mg-Zn intermetallic compound formed between the $Mg_2Si$ phase, becoming a crack initiation point under stress. Thus, the formation of the Mg-Zn phase may cause a sharp decrease in the elongation when Zn at levels exceeding 7 wt.%. It was also found that the matrix became more brittle with increasing the Zn content. From these results, it can be concluded that the formation of the Mg-Zn intermetallic compound and the brittle characteristics of the matrix are the main causes of the remarkable changes in the mechanical properties of this alloy system

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.176-179
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• 2005

Spray casting of hypereutectic Al-Si based 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. Hypereutectic Al-Si based alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, low coefficient of thermal expansion, high thermal stability, and good creep resistance. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. High temperature deformation behavior of the hypereutectic Al-Si based alloy has been investigated by applying the internal variable theory proposed by Chang et al. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.84-89
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• 2013

The demand of LNG tank and the constituting material, i.e., the Al5083 thick plate, increased due to the rapid growth LNG market. To weld the Al5083 thick plate, the gas metal arc welding (GMAW) of high current is necessary to increase manufacturing productivity incurred by the multi pass welding. However, the arc welding vaporizes the volatile element such as magnesium (Mg). This phenomenon changes the Mg composition of the weld metal and the mechanical properties. The study investigated the weldability of Al5083 alloys after conducting high current GMAW. The Al5083 alloy was welded by using different size of welding wires and high current (800-950A). As the arc current increased from 800A to 950A, the mechanical strength decreased and the secondary dendrite arm spacing (SDAS) increased. Even though the arc current increased SDAS, the mechanical strength decreased due to the Mg loss in the weldment. The large diameter of welding wire decreased the dilution of the weld, therefore increasing the Mg content and the strength of the weld. For the reason, the content of Mg in welds was a major parameter to determine the mechanical property for the high current GMAW. For the arc current between 800A and 950A, the yield strength of the weldments showed a relationship with the weight percent of Mg content ($X_{Mg}$): Y.S = 27.9($X_{Mg}$)-11.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.785-792
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• 2011

Equal channel angular(ECA) pressing is the established processing technique in which a polycrystalline metal is pressed through the die to achieve a very high plastic strain. Therefore, the capability to produce an ultra-fine grain size in the materials is provided. To investigate that mechanical properties at elevated temperature have the ultrafine grain ECA pressing, experiments were conducted on an Al-4.8% Mg-0.07% Mn-O.06% Si alloy. After having been solution treated at 773K for 2hrs, the billet for ECA pressing was inserted into the die. And it was pressed through two channel of equal to cross section intersecting at a 90 degree angle. The billet can be extrude repeatedly because of 1:1 extrusion ratio. Since the billet is passed through the cannel for 2 times, a large strain is accumulated in the alloy. The tensile tests on elevated temperature were carried out with initial strain rate of $10^{-3}s^{-1}$ at eight temperature distributed from 293K to 673K.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.5
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• pp.285-297
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• 2023

The effects of aging treatment sequence, specifically pre-aging and post-aging, on the microstructure and mechanical properties of Al-Zn-Mg-Cu aluminum alloys has been studied in comparison to symmetrically rolled specimens. In symmetrically rolled specimens, a straight-band precipitation distribution was observed, whereas asymmetrically rolled specimens exhibited a curved-band microstructure of fine precipitates. Notably, the asymmetrically rolled specimens displayed higher strengths. In the case of post-aging, the aging process occurred after rolling, and the dislocations generated during rolling acted as nucleation sites for precipitates during aging. This resulted in the formation of fine precipitates, contributing to improved mechanical properties compared to symmetric rolling. To enhance strength of the Al-Zn-Mg-Cu aluminum alloys, asymmetric rolling proves to be more effective than symmetric rolling, with post-aging showing greater efficacy than pre-aging.

• Journal of Powder Materials
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• v.16 no.1
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• pp.63-67
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• 2009

In order to investigate the effect of rapid solidification on the microstructure and the mechanical properties of Al-Zn-Mg system alloys, water atomization was carried out, since the water atomization beared the highest solidification rate among the atomization processes. The as atomized alloy powders consisted of fine grains less than 4 ${\mu}m$ in diameter, and the second particles were not detected on XRD. The microstructure as solidified was maintained even after the spark plasma sintering at the heating rate of 50 K/min. On the other hand, lower rate of 20 K/min induced a formation of $MgZn_2$ particles, resulting in strengthening of the matrix. The density was almost constant at the temperature above 698K. The sintering temperature above 698K had no effect on the strength of the sintered materials.

• Journal of Korea Foundry Society
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• v.41 no.3
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• pp.241-251
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• 2021

7000-series aluminum alloys are noted for their superior strength compared with other Al alloys, and their billets are generally fabricated by direct-chill (DC) casting. Surface defects in a DC-cast aluminum billet are mainly related to exudation and the meniscus freezing phenomenon, which are influenced by alloy compositions, casting speed, and casting temperature. 7000-series aluminum alloys have a wide freezing range during solidification, which makes it easy for casting defects to occur. In this study, we investigated surface defect evolution in casting billets of Al-8Zn-2Mg-2Cu alloy fabricated by a DC casting process. The billets showed "wavy" or "dotted" surfaces. The wavy surface was formed by meniscus freezing at a lower casting speed (200 mm/min) and temperature (655 ℃). In the wavy surface, refined dendritic cells were observed in a concave region due to the constitutional supercooling caused by meniscus freezing. Meanwhile, at a higher casting temperature (675 ℃), the dotted surface was formed by pore formation. In the dotted surfaces in the billet formed at a high casting speed (230 mm/min), an exudation layer was formed by the high metallostatic head pressure. The dotted region and the smooth region had a refined dendritic morphology and a columnar morphology at the exudation layer, respectively. This is attributed to the formation of gas pores in the dotted region.

• Journal of Korea Foundry Society
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• v.18 no.5
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• pp.439-449
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• 1998

Formation of oxide inclusions in the molten aluminium alloys during solidification is investigated. The oxidation tendency of both Al-4.5wt%Cu and Al-7wt%Si alloys is increased with melt temperature, particularly over $700^{\circ}C$. However, an Al-5wt%Mg alloy exhibits a decreasing mode over $800^{\circ}C$. The oxidation behavior with holding time shows the S curve shape for all of the alloys. It is shown that the mechanism of oxidation of Al-5wt%Mg alloy has a two step process different from that of Al-4.5wt%Cu and Al-7wt%Si alloys. The species and morphology of oxide inclusions in each alloy is also shown. The microstructure was more coarsened during solidification when the melt contains a large amount of oxide inclusion than when it doesn't. This result can be explained in terms of both the hindrance of heat extraction by oxide film formed on the aluminium melt and the difference of heat capacity between the aluminium melt and oxide inclusion during solidification.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.275-277
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• 2003

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.2
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• pp.109-115
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• 2022

The demand for metal 3D printing technology is increasing in various industries. The materials commonly used for metal 3D printing include aluminum alloys, titanium alloys, and stainless steel. In particular, for applications in the aviation and defense industry, aluminum alloy 3D printing parts are being produced. To improve the corrosion resistance in the 3D printed aluminum alloy outputs, a post-treatment process, such as chromate coating, should be applied. However, powdered materials, such as AlSi7Mg and AlSi10Mg, used for 3D printing, have a high silicon content; therefore, a suitable pretreatment is required for chromate coating. In the desmut step of the pretreatment process, the chromate coating can be formed only when a smut composed of silicon compounds or oxides is effectively removed. In this study, suitable desmut solutions for 3D printed AlSi7Mg and AlSi10Mg materials with high silicon contents were presented, and the chromate coating properties were studied accordingly. The smut removal effect was confirmed using an aqueous desmut solution composed of sulfuric, nitric, and hydrofluoric acids. Thus, a chromate coating was successfully formed. The surfaces of the aluminum alloys after desmut and chromate coating were analyzed using SEM and EDS.