• 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 Welding and Joining
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• v.34 no.5
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• pp.19-25
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• 2016

Global warming is hot issue to keep the earth everlastingly. Despite the increase of the world population and the energy demand, the world oil supply and the oil price are hold the steady state. If we are not decrease the world population and the energy consumption, unforeseeable energy crisis will come in the immediate future. AMT acronym of Advanced Materials for Transportation is a non-profitable IEA-affiliated organization to mitigate the oil consumption and the environment contamination for the transportation. In recent, Annex X Multi-materials Joining was added to enhance the car body weight reduction cause the high fuel efficiency and the low emission of exhaust gas. Multi-materials are the advanced materials application technology to optimize the weight, the performance and the cost with the combination of different materials such as Al-alloy, Mg- alloy, AHSS and CFRP. In this study, the trends of AMT strategy and Al-alloy based multi-materials joining technology were review. Also several technologies for Al-alloy dissimilar joining were investigated.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.1
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• pp.41-49
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• 1992

The effects of alloying elements on the superplastic properties of Al-Li based alloys had been investigated. The intermediate thermo-mechanical treated (ITMT) Al-2.0wt%Li, Al-2.0wt%Li-1.0wt%Mg, Al-2.0wt%Li-0.12wt%Zr and Al-2.0wt%Li-1.2wt%Cu-1.0wt%Mg-0.12wt%Zr alloys were tested in tension at various temperature (400, 450, 500 and $550^{\circ}C$) and strain rate($6.7{\times}10^{-3}$, $1.0{\times}10^{-2}$, $1.6{\times}10^{-2}$ and $5.0{\times}10^{-2}/sec$). The results were as follows : The superplasticity in binary, ternary and pentanary alloys appeared at 500 to $550^{\circ}C$, and good strain rate for superplasticity. $1.6{\times}10^{-2}/sec{\sim}1.0{\times}10^{-2}/sec$ for a binary alloy and $1.0{\times}10^{-2}/sec{\sim}6.7{\times}10^{-3}/sec$ for ternary and pentanary alloys. A Zr-added ternary alloy had best value of elongation (730%) in four alloys at $550^{\circ}C$ of tension temperature and $1.0{\times}10^{-2}/sec$ of strain rate. The strain rate was greatly dependent on tension temperature and true strain rate was more than 1.0 at all test temperature and strain rate. In binary and Mg-added teranry alloys. the necks were slightly formed and their fracture surface had lips shape, but Zr-added ternary and pentanary alloy fractured along the grain boundary without necking. Their dislocations moved to grain boundary during superplasticity deformation and arranged perpendicular to grain boundary. Super plastic deformation was made by grain boundary slip of dislocation slip creep and model of core and mantle.

• Korean Journal of Metals and Materials
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• v.46 no.7
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• pp.412-419
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• 2008

Creep behavior of the squeeze infiltrated AS52 Mg matrix composites reinforced with 15 vol% of aluminum borate whiskers($Al_{18}B_4O_{33}w$) fabricated squeeze infiltration method was investigated. Microstructure of the composites was observed as uniformly distributed reinforcement in the matrix without any particular defects of casting pores etc.. Creep test was carried out at the temperature of 150 and $200^{\circ}C$ under the applied stress range of 60~120 MPa. The creep resistance of the composite was significantly improved comparing with the unreinforced AS52 Mg alloy. The creep behavior of composites might be interpreted with the substructure invariant model successfully for the composite. Threshold stress of the composite exist for the creep deformation of the composite. The analysis of the creep behavior of the composite with threshold stress indicated that creep deformation was controlled by the lattice diffusion process of AS52 Mg matrix at given effective stresses and temperatures. Activation energy was also calculated to check lattice diffusion controlled creep behavior of the composite.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.560-568
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• 1997

The dissolution behavior of secondary solidification phases in squeeze cast Al-3.9wt%Cu-1.5wt%Si-1.0wt%Mg has been studied using a combination of optical microscope, image analyzer, scanning electron microscope(SEM), energy dispersive spectrometer(EDS), X-ray diffractometer(XRD) and differential thermal analyzer (DTA). Special emphasis was placed on the investigation of the effects of the nonequilibrium heat treatment on the dissolution of the second solidification phases. Ascast microstructure consisted of primary solidification product of ${\alpha}-Al$ and secondary solidification products of $Al_2Cu$, $Mg_2Si$ and $Al_2CuMg$. Equilibrium and non-equilibrium solution treatments were carried out at the temperatures of $495^{\circ}C$, $502^{\circ}C$ and $515^{\circ}C$ for 3 to 5 hours. The amount of the dissolved secondary phases increased with increasing solution treatment temperature, for example, area fractions of $Al_2Cu$, $Mg_2Si$ and $Al_2CuMg$ were approximately 0%, 1.6% and 4.2% after solution treatment at $495^{\circ}C$ for 5hours, and were approximately 0%, 0.36% and 2% after solution treatment at $515^{\circ}C$ for 5hours. The best combination of tensile properties was obtained when the as-cast alloy was solution treated at $515^{\circ}C$ for 3hours followed by aging at $180^{\circ}C$ for 10 hours. Detailed DTA and TEM study showed that the strengthening behavior during aging was due to enhanced precipitation of the platelet type fine ${\theta}'$ phase.

• 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

• Korean Journal of Materials Research
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• v.28 no.9
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• pp.534-538
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• 2018

The annealing characteristics of a cold rolled Al-6.5Mg-1.5Zn alloy newly designed as an automobile material is investigated in detail. The aluminum alloy in the ingot state is cut to a thickness of 4 mm, a total width of 30 mm and a length of 100 mm and then reduced to a thickness of 1 mm (reduction of 75 %) by multi-pass rolling at room temperature. Annealing after rolling is performed at temperatures ranging from 200 to $400^{\circ}C$ for 1 hour. The tensile strength of the annealed material tends to decrease with the annealing temperature and shows a maximum tensile strength of 482MPa in the material annealed at $200^{\circ}C$. The tensile elongation of the annealed material increases with the annealing temperature, while the tensile strength does not, and reaches a maximum value of 26 % at the $350^{\circ}C$ annealed material. For the microstructure, recovery and recrystallization actively occur as the annealing temperature increases. The recrystallization begins to occur at $300^{\circ}C$ and is completed at $350^{\circ}C$, which results in the formation of a fine grained structure. After the rolling, the rolling texture of {112}<111>(Cu-Orientation) develops, but after the annealing a specific texture does not develop.

• Journal of Surface Science and Engineering
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• v.49 no.2
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• pp.119-124
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• 2016

Plasma electrolytic oxidation (PEO) is a promising coating process to produce ceramic oxide on valve metals such as Al, Mg and Ti. The PEO coating is carried out with a dilute alkaline electrolyte solution using a similar technique to conventional anodizing. The coating process involves multiple process parameters which can influence the surface properties of the resultant coating, including power mode, electrolyte solution, substrate, and process time. In this study, ceramic oxide coatings were prepared on commercial Al alloy in electrolytes with different KOH concentrations (0.5 ~ 4 g/L) by plasma electrolytic oxidation. Microstructural and electrochemical characterization were conducted to investigate the effects of electrolyte concentration on the microstructure and electrochemical characteristics of PEO coating. It was revealed that KOH concentration exert a great influence not only on voltage-time responses during PEO process but also on surface morphology of the coating. In the voltage-time response, the dielectric breakdown voltage tended to decrease with increasing KOH concentration, possibly due to difference in solution conductivity. The surface morphology was pancake-like with lower KOH concentration, while a mixed form of reticulate and pancake structures was observed for higher KOH concentration. The KOH concentration was found to have little effect on the electrochemical characteristics of coating, although PEO treatment improved the corrosion resistance of the substrate material significantly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1686-1694
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• 2003

The foam-filled tube beams can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision of vehicles. In the case of side collision where bending is involved in the crushing mechanism, the foam filler would be effective in maintaining progressive crushing of the thin-walled structures so that much impact energy could be absorbed. In this study, bending behaviors of the closed-cell-aluminum-alloy-foam-filled stainless steel tube were investigated. The various foam-filled specimens including piecewise fillers were prepared and tested. The aluminum-alloy-foam filling offered the significant increase of bending resistance. Their suppression of the inward fold formation at the compression flange as well as the multiple propagating folds led to the increase of load carrying capacity of specimens. Moreover, the piecewise foams would provide the easier way to fill the thin-walled shell structures without the drawback of strength.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.1
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• pp.12-19
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• 2022

The propellants used in the gas generator of the ducted rocket are fuel-rich propellants, which contain an excessive amount of metal fuel and a small amount of oxidizing agent compared to general solid rocket propellants. In this paper, boron powder and MgAl(Magnesium-Aluminium alloy) were applied to produce fuel-rich propellants. The optimum formulation was determined by characterizing these metal fuel-rich propellants. Analysis of combustion products in the gas generators confirmed that the fuel-rich propellants containing fine boron powder itself instead of boron-bead could be useful in gas generators.