• 한국표면공학회지
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• 제41권3호
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• pp.121-128
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• 2008

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% $H_2O_2$ and 0.6M $Na_2SO_4$ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% $H_2O_2$ + 0.6M $Na_2SO_4$ solution. When the strain rate was below $2{\times}10^{-6}$, the stress corrosion cracking induced fracture start to be observed.

• 한국융합학회논문지
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• 제9권11호
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• pp.285-290
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• 2018

강은 자동차 제조업체 및 전기 제품에 많이 사용되고 있으나 부식으로 많은 문제점이 발생한다. 이러한 부식문제를 해결하기 위해 강 위에 아연전기도금을 두껍게 하고 있다. 그러나 아연 도금의 두께가 두꺼워지면 부품 제조 시 크렉이 발생하기 쉬우며, 이로 인해 부식이 더욱더 악화될 수 있다. 이러한 부식 문제를 해결하기 위해 아연과 크롬합금도금에 관심이 집중되고 있다. 본 연구에서는 염화욕에서 합금도금의 조성에 미치는 전해조건의 영향을 조사하였다. 전류밀도가 증가함에 따라 Zn함량이 감소하고 Cr함량은 증가하였다. 전해액 온도가 증가함에 따라 Zn함량이 감소하고 Cr함량은 증가하였으며, 그 결과는 음극분극곡선으로 가지고 해석되었다.

• 한국재료학회지
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• 제31권12호
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• pp.704-709
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• 2021

In the flux used in the batch galvanizing process, the effect of the component ratio of NH₄Cl to ZnCl₂ on the microstructure, coating adhesion, and corrosion resistance of Zn-Mg-Al ternary alloy-coated steel is evaluated. Many defects such as cracks and bare spots are formed inside the Zn-Mg-Al coating layer during treatment with the flux composition generally used for Zn coating. Deterioration of the coating property is due to the formation of AlCl_x mixture generated by the reaction of Al element and chloride in the flux. The coatability of the Zn-Mg-Al alloy coating is improved by increasing the content of ZnCl₂ in the flux to reduce the amount of chlorine reacting with Al while maintaining the flux effect and the coating adhesion is improved as the component ratio of NH₄Cl to ZnCl₂ decreases. Zn-Mg-Al alloy-coated steel products treated with the optimized flux composition of NH₄Cl·3ZnCl₂ show superior corrosion resistance compared to Zn-coated steel products, even with a coating weight of 60 %.

• 연구논문집
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• 통권29호
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• pp.163-171
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• 1999

A new titanium alloy system. Ti-xFe-ySi (x,y=0-4 wt%). was designed and characterized with the point at low cost and high strength for casting applications. Fe improved room and elevated temperature mechanical properties owing to solid solution hardening and beta phase stabilization. Si yielded titanium silicides and Si addition over 1 wt% resulted in poor ductility due to coarse silicide chains at prior beta boundaries. The optimum composition was found to be Ti-4Fe-(0.5-1)Si in the viewpoint of tensile strength and ductility which are comparable to the Ti-6Al-4V. The metal-mould reaction was also examined for Ti-xFe and Ti-xSi binary alloy system. The thickness of surface reaction layer w as not affected significantly with Fe content, while it was decreased with Si content. In the Ti-4Si alloy, no reaction layer was found. The depth of surface hardening layer was about $200\mum$ regardless of the mould materials.

• Corrosion Science and Technology
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• 제10권6호
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• pp.194-198
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• 2011

This is the first release of an interim report on the development of coating technology of Zn-Mg alloy layers on steel strip by EML-PVD (electromagnetic levitation - physical vapor deposition) process in an air-to-air type continuous PVD pilot plant. It intends to introduce a basic principle of the EML-PVD process together with the high speed PVD pilot plant built in Posco. Due to the agitation effect provided by the high frequency induction coil, simultaneous evaporation of Zn and Mg from a droplet could produce alloy coating layers with Mg content of 6% to 12% depending on the composition of the droplet inside the coil. For its superior corrosion resistance, Zn-Mg alloy coated steel would be a very promising material for automotive, electrical appliances, and construction applications.

• Journal of Magnetics
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• 제4권2호
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• pp.55-59
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• 1999

In an attempt to find an effective production way of the$ Sm_2Fe_{17}N_{x-}type material, the Sm_2Fe_{17-}$type alloy with chemical composition of Sm 22.7 wt.%, Fe72.3 wt.% Nb 5.0wt.% was subjected to a HD (hydrogen decrepitation) treatment prior to a nitrogenation, and its effect on the formation of the nitride material was investigated. The nitrogenation behaviours of the alloy were investigated using a TPA(thermopiezic analysis), TMA, and DTA under nitrogen gas, and XRD. It has been found that the previous HD treatment significantly facilitated the formation of $Sm_2Fe_{17}N_{x-}$type nitride, and this was accounted for by the clean surface and the finer particle size of the powder caused by the HD treatment. It has also been found that the hydrogen atoms existing in the initial HD-treated alloy were removed almost completely during the nitrogenation. The heat output associated with the nitrogenation of the previously HD-treated alloy was found to be significantly smaller than that of the as-cast alloy.

• E2M - 전기 전자와 첨단 소재
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• 제10권2호
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• pp.113-118
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• 1997

For the amorphous F $e_{78}$ $B_{13}$S $i_{9-x}$G $e_{x}$ alloy, thermal analysis and measurements of the magnetic properties were carried out. As the content of Ge increased, the crystallization temperature was decreased and the Curie temperature was increased, and the tendencies were almost linear. The core loss of the amorphous alloy for x=1.7, field annealed at optimized condition, was 0.057 W/kg(l.0T, 60Hz), which was about 30% lower than that of no Ge added amorphous alloy (basic composition). Such a low core loss characteristics was thought to be caused by the lower coercive force and good squareness of B-H loop of the alloy.y.y.

• 한국자기학회지
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• 제5권5호
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• pp.451-455
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• 1995

The composition and thickness dependence and the ferromagnetic under- and overlayer effect on the magnetoresistance ratio and saturation field of the Co-Ag nano-granular films were investigated. The maximum magnetoresistance (23% at R.T.) in the as-deposited state was obtained in the $3000{\AA}$ $Co_{30} Ag_{70}$ bare alloy film. As the thickness of the alloy films decreased below $500{\AA}$, the MR ratio decreased because of the resistivity increase and the non-uniform film formation. We showed that the ferromagnetic over- and underlayer could reduce the saturation field of the nano-granular films via exchange coupling effect. The magnetoresistance and the saturation field of the $100{\AA}$ alloy film were 3.65 % and 2.85 kOe respectively and those of the under- and overlayered alloy films with $200{\AA}$ Fe were 3.3 % and 1.23 kOe respectively.

• 한국분말재료학회지
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• 제22권5호
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• pp.362-366
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• 2015

The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at $-25^{\circ}C$. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at $300^{\circ}C$ and sintering at $850^{\circ}C$ for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.

• 한국재료학회지
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• 제14권12호
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• pp.846-850
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• 2004

NiCo silicide films have been fabricated from $300{\AA}-thick\;Ni_{1-x}Co_{x}(x=0.1\sim0.9)$ on Si-substrates by varying RTA(rapid thermal annealing) temperatures from $700^{\circ}C\;to\;1100^{\circ}C$ for 40 sec. Sheet resistance, cross-sectional microstructure, and chemical composition evolution were measured by a four point probe, a transmission electron microscope(TEM), and an Auger depth profilemeter, respectively. For silicides of the all composition and temperatures except for $80\%$ of the Ni composition, we observed small sheet resistance of sub- $7\;{\Omega}/sq.,$ which was stable even at $1100^{\circ}C$. We report that our newly proposed NiCo silicides may obtain sub 50 nm-thick films by tunning the nickel composition and silicidation temperature. New NiCo silicides from NiCo-alloys may be more appropriate for sub-0.1${\mu}m$ CMOS process, compared to conventional single phase or stacked composit silicides.