• Journal of the Korean Society for Heat Treatment
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• v.15 no.5
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• pp.213-218
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• 2002

In order to develop the economic and environmental water-soluble black coloring agent, some adequate chemical mixtures were mixed and this solution was applied to coat quenched and tempered 51B20 steel bolt. Some basic properties of the solution and characteristics of the coated film in addition to the corrosion resistance were investigated. The developed 100 kg of water-soluble black coloring agent solution was a chemical mixture consisted of 10 kg of aqueous coloring agent, 40 kg of surface active agent, 0.3 kg of anti-foam agent and $50{\ell}$ of water. The coated film of the bolt was composed of hard layer of about $2{\mu}m$ and the disbondable soft layer of about $4{\mu}m$ above the hard layer. Many surface active agents peaks and a few hydrophilic peaks were observed in the coated film. Surface roughness value of the coated bolt was lower than that of the non-coated bolt. Corrosion resistance of the coated bolt considerably improved and also relatively showed a good polarization resistance at test condition of $40^{\circ}C$ colorizing temperature and 5% the solution concentration in 3% NaCl anodic polarization test. Initial appearance time of the surface rust was greatly retarded owing to the coated film in salt spray test.

• Corrosion Science and Technology
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• v.14 no.5
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• pp.213-217
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• 2015

Recently, household electronic industries require environmentally-friendly and highly functional steels in order to enhance the quality of human life. Customers especially require both excellent corrosion and abrasion resistant anti-fingerprint steels for digital TV panels. Thus POSCO has developed new functional electro-galvanized steels, which have double coated layers with organic-inorganic composites on the zinc surface of the steel for usage as the bottom chassis panel of TVs. The inorganic solution for the bottom layer consists of inorganic phosphate, magnesium, and zirconium compounds with a small amount of epoxy binder, and affords both improved adhesion properties by chemical conversion reactions and corrosion resistance due to a self-healing effect. The composite solution for the top layer was prepared by fine dispersion of organic-inorganic ingredients that consist of a urethane modified polyacrylate polymer, hardener, silica sol and a titanium complex inhibitor in aqueous media. Both composite solutions were coated on the steel surface by using a roll coater and then cured through an induction furnace in the electro-galvanizing line. New anti-fingerprint steel was evaluated for quality performance through such procedures as the salt spray test for corrosion resistance, tribological test for abrasion resistance, and conductivity test for surface electric conductance regarding to both types of polymer resin and coating weight of composite solution. New composite coated anti-fingerprint steels afford both better corrosion resistance and abrasion properties compared to conventional anti-fingerprint steel that mainly consists of acrylate polymers. Detailed discussions of both composite solutions and experimental results suggest that urethane modifications of acrylate polymers of composite solutions play a key role in enhanced quality performances.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.32-32
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• 2015

Electrophoretic paint (E-paint) was investigated on four different magnesium substrates: as-extruded AZ61 (AZ61), heat-treated AZ61 (AZ61-H), as-extruded TZ61 (TZ61) and heat-treated TZ61 (TZ61-H), to elucidate the effect of heat treatment and alloying elements on the deposition and corrosion resistance of E-paint. It was found that, a rapid increase of voltage, indicating that the deposition of E-paint had started, was observed after an induction time of 0.39 min for AZ61-H, 0.43 min for AZ61, 0.51 min for TZ61-H and 0.58 min for TZ61. The amount of E-paint deposited on the four samples was approximately similar, but the electrical charge used for the deposition process on the heat-treated samples was smaller than that on the as-extruded samples. The current efficiencies of E-paint on AZ samples (AZ61 and AZ61-H) were higher than those of TZ samples (TZ61 and TZ61-H), and on the heat-treated samples were higher than on as-extruded samples. All E-paintings on the four magnesium substrates had an excellent adhesion without any paint detached by tape peel-test. However, many large blisters were formed on the surface of AZ samples, and none, or very small blisters were observed on TZ samples after immersion test in DI-water for 500 h at $40^{\circ}C$. Under salt spray test (SST) conditions, E-paint on AZ samples showed blistering adjacent to scribes, while blistering of E-paint occurred on intact areas of TZ samples. The E-paint on heat-treated samples showed much better corrosion resistance than that on as-extruded samples. The ranking of greater to lesser corrosion resistance of the E-paint on these four different magnesium substrates is indicated by the order: AZ61-H > AZ61 > TZ61-H > TZ61.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.43-49
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• 2005

This paper is to investigate the effect of corrosion by acoustic emission method in tensile loading and the adhesiveness between substrate and coating layer. The powders used are Zn and Amdry625, respectively. They are coated on brass alloy substrate. AE signals of Zn and Amdry625 coating layer increase drastically in strain $2\%$. However, those of Zn specimen have more than those of Amdry625 specimen. When the specimens executed the corrosion test under $3.5\%$ NaCl solution for 500, 1000 hours, the salt solution penetrated into the surface of the substrate through the pores of the coating layer. As a result, corrosion production formed on the surface of the substrate. The adhesiveness between coating layers is weakened by the polarization and corrosion itself. The AE event, count, and energy of corroded coating specimens decrease, compared to specimens without corrosion. The results are summarized as follows : 1. In the tensile tests, the time that it took to start and develop the cracks and exfoliations between the surface of the substrates and the plasma spray coatings were different according to the type of plasma sprayed material, which are Zn and Amdry625. These phenomena were obvious at the strain rate 1 to $5\%$, and few available data were found after that stage. 2. The specimens with Zn coating showed the characteristics of crack, according to the changes of the tensile strength applied on the substrates while those with Amdry625 showed exfoliation as a result of low adaptation to the tensile strength. 3. The anti-corrosion specimens showed that the adhesive properties between the substrate and the plasma spray coating were strong in the order of Zn, Amdry. It showed that Corroded specimens cracked or exfoliated easily, even with the small energy, because those had a comparatively weakened adhesive property, due to corrosion. 4. Zn specimen showed no corrosion phenomena on the surface of the substrates, because they had the function of sacrifice anode however, Amdry625 specimen showed the corrosion, because it did not have that function.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.296-302
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• 2007

A trivalent chromate conversion coating solution which is composed with $KCr_2(SO_4)$ as main component was investigated to test a feasibility of use as an alternative six-valent chromate conversion coating for improvement of anti-corrosion of zinc plating. The proposed trivalent convesion coating was consisted of $KCr(SO_4)$ 35~45 g/L as trivalent chromium source, $NaH_2PO_4$ 20~30 g/L as phosphate, $CoSO_4$, 10~20 g/L, $ZnSO_4$ 10~20 g/L as metallic sulfates. This trivalent chromate films which are coated by this chromate conversion coating solution under pH 2.0~2.2, immersion time of 20~25 s at room temperature are able to achieve over 120 h in neutral salt spray test to 5% white rust.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.26-33
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• 2014

The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.61-68
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• 2016

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.201-207
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• 2018

Infrared(IR) heating has many advantages, such as energy efficiency, reduced heating time, cleanliness, equipment compactness, high drying rate and easy automation. These features of IR heating provide widely industrial applications, such as surface heat treatment in semiconductor fabrication, thermoforming of polymers, drying and disinfection of food products, heating to metal forging, and drying of wet materials. In this study, the characteristics of a protected gold mirror were examined by spectrophotometer and the lifetime of the coating layers were evaluated by a cross-cutting method and salt spray test. The effects of manufacturing conditions on the protected gold mirror were seen and remedies for these effects were noted in order to improve the properties of the protected gold mirror in the drying process. The reflectance and lifetime of the protected gold mirror was influenced by manufacturing conditions, such as surface roughness and forming conditions of the anti-oxide layer, the adhesion layer, the reflecting layer and the protection layer. The results of this study showed that the protected gold mirror manufactured using a buffing method for pre-treatment resulted in the most effective reflectance. In addition, $Al_2O_3$ coating on an Al substrate as an anti-oxide layer was more effective than the anodizing process in the test of reflectance. Furthermore, the protected gold mirror manufactured by layers forming of various materials resulted in the most effective reflectance and lifetime when coated with $Al_2O_3$ as the anti-oxide layer, coated Cr as the adhesion layer, and coated $MgF_2$ as the protection layer.

• Corrosion Science and Technology
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• v.6 no.3
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• pp.120-127
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• 2007

In any developing nation major investment goes for infrastructure and it is not exception in India. Good numbers of buildings, bridges, shopping malls, car parks etc. are coming up with steel for sustainable development. Thus protecting the structures from corrosion are the challenges faced by professionals for all types of steel structures. About 3% of GDP is accounted for loss due to corrosion. To combat this up to date corrosion map is called for as the country has wide variation of climatic zones with vastcoastline. Logically organic paint system can be prescribed based on the corrosion rate on bare steel with respect to environment. Present paper will emphasis on the study conducted on two types of structural steel coated with organic paint located in twomarine environment having been exposed for three years, Test coupons made from steels both bare and coated are deployed at two field stations having marine (Digha) and industrial marine (Channai) environments. Various tests like AC impedance DC corrosion, polarisation, salt spray test, $SO_2$ chamber and Raman spectroscopy were carried out both in laboratory on fresh as well as coupons collected from exposure sites. Rust formed on the bare and scribed coated coupons are investigated. It is found that normal marine environment at Digha exhibits higher corrosion rate than polluted marine environment in Channai. Rust analysis indicates formation of ${\propto}$-FeoOH protects or reduces corrosion rate at Channai and formation of non-protective ${\gamma}$-FeoOH increases corrosion rate at Digha. The slower corrosion rate in Channai than at Digha is attributed due to availability of $SO_2$, in the environment, which converts non‐protective rust ${\gamma}$-FeoOH to protective rust ${\propto}$-FeoOH. While comparing the damage on the coated panels it is found that low alloy structural steel provides less damage than plain carbon steel. From the experimentations a suitable paint system specification is drawn for identical environments for low medium and high durability.

• Journal of the Korean institute of surface engineering
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• v.42 no.2
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• pp.86-94
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• 2009

Various types of multilayer coatings including Al/$Al_2O_3$ structure have been prepared on Nd-Fe-B permanent magnet to modify the morphology of the coating and to enhance the corrosion resistance of the magnet. Magnetron sputtering has been employed to make the multilayer coatings. $Al_2O_3$sputtering conditions were optimized in reactive sputtering by varying the deposition parameters. The formation of $Al_2O_3$ film was confirmed from the binding energy shift measured by electron spectroscopy for chemical analysis. 3 types of coating structures were designed and prepared by magnetron sputtering. The coating structures consist of (1) single Al coating, (2) modified coatings having oxide or plasma treated layer in the middle of coating structure, and (3) Al/$Al_2O_3$ multilayer coatings. Surface and cross-sectional morphologies showed that Al/$Al_2O_3$ multilayer grew as a layered structure, and that very compact Zone 3 like structure were formed. X-ray diffraction peak showed that the crystal orientations of multilayer coatings were similar to that of the bulk powder pattern. Hardness increased drastically when the Al thickness was around 1im in the Al/$Al_2O_3$ multilayer. From the salt spray test and pressure cooker test, it has been shown that the multilayer coatings showed good corrosion resistance compared to Al single or modified layer coatings.