• 열처리공학회지
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• 제28권5호
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• pp.229-238
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• 2015

The effects of Sn addition and solution treatment on corrosion behavior were studied in AZ91 magnesium casting alloy. The addition of 5%Sn contributed to the introduction of $Mg_2Sn$ phase, to the reduction in dendritic cell size and to the increase in the amount of secondary phases. After the solution treatment, trace amount of $Al_8Mn_5$ particles were observed in the ${\alpha}$-(Mg) matrix for the AZ91 alloy, while $Mg_2Sn$ phase with high thermal stability was additionally found in the AZ91-5%Sn alloy. Before the solution treatment, the AZ91-5%Sn alloy had better corrosion resistance than the Sn-free alloy, which is caused by the enhanced barrier effect of the (${\beta}+Mg_2Sn$) phases formed more continuously along the dendritic cell boundaries. It is interesting to note that after the solution treatment, the corrosion rate of both alloys became increased, but the Sn-added alloy showed higher corrosion rate than the Sn-free alloy. The microstructural examination on the corroded surfaces revealed that the remaining $Mg_2Sn$ particles in the solution-treated AZ91-5%Sn alloy play a role in accelerating corrosion by galvanic coupling with the ${\alpha}$-(Mg) matrix.

• 동력기계공학회지
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• 제20권5호
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• pp.29-36
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• 2016

Aluminum alloys have been widely used in engine materials, cold & hot-water storage vessels and piping etc., Furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston for various vehicles because of its properties of temperature, wear and corrosion resistance. Therefore, it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and to prolong its lifetime. In previous paper, the effect of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 16, 24, and 36 hrs)heat treatments to corrosion resistance and hardness were investigated using electrochemical method. In this study, in order to examine completely the effect of the tempering hours to hardness variation and corrosion resistance, the results of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 2, 4, 8 and 12hrs)heat treatments to hardness and corrosion resistance were investigated using electrochemical method. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment. Furthermore, the corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. And the tempering heat treatment temperature at $190^{\circ}C$ for 8 hrs exhibited the highest value of the hardness and also indicated the highest corrosion current density. However, the values of hardness and corrosion current density was again increasingly decreased with increasing of tempering hours than 8 hrs, Consequently, it is suggested that decision of the optimum. tempering hours is very important to improve the corrosion or wear resistance.

• Corrosion Science and Technology
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• 제3권1호
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• pp.6-13
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• 2004

The effect of inhibitors on the electrochemical behavior and the stress corrosion cracking resistance of Alloy 600(UNS N06600) was evaluated in 10% sodium hydroxide solution at $315^{\circ}C$. The specimens of a C-ring type for stress corrosion cracking test were polarized at 150 mV above the corrosion potential for 120 hours with and without inhibitors such as titanium oxide, titanium boride and cerium boride. The chemical compositions of the films formed on the crack tip in the C-ring specimens were analyzed using a scanning Auger electron spectroscopy. The cerium boride, the most effective, was observed to decrease the crack propagation rate more than a factor of three compared with that obtained in no inhibitor solution. It was found that the changes of the active-passive transition potentials and the film compositions were related to the resistance to stress corrosion cracking in high temperature caustic solution.

• 한국군사과학기술학회지
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• 제15권3호
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• pp.315-321
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• 2012

In the study, corrosion characteristics of AZ31 magnesium alloy under various environments exposed during machining(immersion in cutting oil, 5 % cutting oil aqueous solution and distilled water & contact with dissimilar metals, SPC4 and A5052-H32) were investigated. A corrosion test was performed AZ31 magnesium alloy was immersed in each electrolyte solution after contacting with each dissimilar metals, and the results were observed by an electron microscope. In immersion tests, corrosion of AZ31 magnesium alloy showed to be in the sequence of distilled water> 5 % cutting oil aqueous solution> cutting oil> air, and in the test of contact with dissimilar metals, corrosion showed to be in the sequence of SPC4> A5052-H32> AZ31. It can be concluded that to prevent corrosion during machining, AZ31 magnesium alloy must prevent contacting water and use magnesium alloy for raw material of Jig & Fixture.

• Journal of Welding and Joining
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• 제14권2호
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• pp.36-45
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• 1996

Fatigue strength of the spot welded lap joint is considerably influenced by corrosive environments. Particularly, the chloride and the sulfide are most injurious to strength of the spot welded lap joint. Therefore, there is a need to evaluate its effect to corrosion fatigue strength for safe life design of spot welded structures. In order to evaluate their corrosion fatigue strength, corrosion fatigue tests on the spot welded lap joints of the uncoated and the coated high strength steel sheets were conducted in air and in 10% NaCl solution. Corrosion fatigue strength of the uncoated specimens were entirely lower than the coated one in NaCl solution, but those of the coated specimens in NaCl solution were lower than in air. And stress distribution in single spon welded lap joint subjected to tension-shear load was investigated by the finite element method. Using these results, we tried to evaluate corrosion fatgue strength of the various spot welded lap joints with maximum stress $\sigma_{max}$ at edge on loading side of the spot welded lap joint. We could find that corrosion fatigue strength could be quantitatively and systematically rearranged by $\sigma_{max}$.

• Corrosion Science and Technology
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• 제3권6호
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• pp.251-256
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• 2004

Exposure of zinc samples in simulated acid rain solution (SARS) was investigated under a periodic wet-dry conditions using an AC impedance technique. The periodic wet and dry exposure consisted of the immersion of zinc samples in SARS for one hour followed by exposure to 7 hours drying at 60% RH. Phases of the corrosion products were indentified by X-ray diffraction (XRD). The influence of relative humdiity (RH), temperature, and surface inclination on the atmospheric corrosion of zinc is described. The reciprocal of polarization resistance (1/Rp) decreases rapidly during the initial stages then slowly and eventually attains a steady state as exposure time progresses. The average of reciprocal of polarization resistance per cycle, (ARPR) was calculated and found to decrease as number of exposure cycle increases. An increase of temperature enhances the corrsion rate of zinc. The values of ARPR, of a sample inclined at 30 o are lower than those for a sample oriented horizontally. The experiment result shows a pronounced dependence of reciprocal of polarization resistance on RH. Exposure in the presence of carbonate anions gives rise to more protective corrosion products than in nitrate anion solution. The corrosion mechanism during the initial stages of atmospheric zinc corrosion under wet-dry cyclic conditions is suggested.

• 오토저널
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• 제8권1호
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• pp.40-51
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• 1986

A study has been made of the corrosion fatigue of high strength low alloy steel in 3.5% NaCl solution under tension stress for solution temperature being 25.deg. C, 55.deg. C and 85 .deg. C. The main results obtained are as follows; 1) The corrosion fatigue crack growth rate curve could be divided into the First Region, the Second Region and the Third Region. 2) The corrosion fatigue crack growth rates in the First Region and the Second Region were Arrhenius temperature-dependent in this test range. The apparent activation energies for the corrosion fatigue cack growth rate were found to be 2000cal/mol in the First Region and 3700 cal/mol in the Second Region. 3) Hematite (Fe$_{2}$O$_{3}$) as the hexahedral crystal and magnetite (Fe$_{3}$O$_{4}$) as the octahedral crystal were observed in the corrosion products on the corrosion fatigue fracture surface at 85.deg. C and the anode fusion seem to be generated in the crack tip region at high temperature. 4) The complex environment effect ratio which was defined by the ratio of fatigue crack growth rate in corrosion environment to that in air might be considered not only a criterion estimating the effect of environment quantitatively but also an important parameter in the selection of the design stress for the fail safe design. The complex environment effect was not greater than ten in this test.

• 대한기계학회논문집A
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• 제25권6호
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• pp.965-971
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• 2001

To estimate the reliability of 12Cr alloy steel, the material of turbine blade in the steam power plant, Its corrosion susceptibility and fatigue characteristics in NaCl and Na$_2$SO$_4$solution with the difference of concentration and temperature was investigated. The polarization tests recommended in ASTM G5 standard for corrosion susceptibility in the various corrosive solutions was estimated. It showed that the higher temperature, the faster corrosion rates and corrosion rates were the fastest in 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution. From these results, the degradation conditions were determined in distilled water, 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution at room temperature, 60$\^{C}$ and 90$\^{C}$ during 3, 6 and 9 months. Its surface had a few pits for long duration. But, it was not susceptible in sulfide and chloride condition of several temperatures. If the degraded 12Cr alloy steel and non-degraded one were compared with fatigue characteristics, Any differences were not found regardless of temperature and degradation period.

• Corrosion Science and Technology
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• 제20권6호
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• pp.475-483
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• 2021

Additively manufactured titanium alloy is one of the promising materials in advanced medical industries. However, these additively manufactured alloys show corrosion properties different from those of conventional materials due to their unique microstructure. In this study, the effect of surface roughness and masking conditions on the results of the potentiodynamic polarization tests on additively manufactured or conventional Ti-6Al-4V alloys in artificial saliva solution with or without fluoride was investigated. The results showed that the corrosion potential was slightly lower with a flat cell with an O-ring than with masking tape. The corrosion rate was decreased with decreases in the surface roughness. Localized corrosion involving delamination of the surface layer occurred at 7 ~ 9 V (SSC) on the additively manufactured alloy in solution with or without fluoride when the samples were finished with 1000-grit SiC paper, whereas localized corrosion was not observed in the specimens finished with 1-㎛ alumina paste.

• Corrosion Science and Technology
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• 제23권4호
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• pp.310-314
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• 2024

The corrosion behavior of high chromium white cast iron was studied in 0.5 mol dm^-3 H₂SO₄ + 0.01 mol dm^-3 HCl solution over time through electrochemical and immersion experiments. Potentiodynamic and potentiostatic polarizations revealed active-passivation transition behavior, with critical current densities observed at -0.27 V_SSE and 0.00 V_SSE, repectively. The former potential showed preferential dissolution of primary γ phases, while the latter one showed preferential dissolution of eutectic γ phases. Immersion tests showed an exponential increase in corrosion rate, with significant acceleration observed around 1000 seconds due to the onset of eutectic γ phase dissolution. Over a 24-hour immersion period, both γ phases exhibited extensive corrosion, leaving carbides largely intact. These findings elucidate distinct corrosion behaviors of high chromium white cast iron in acidic environments, providing critical insights into material performance evaluation. Understanding these mechanisms is essential for predicting the longevity and durability of materials in corrosive conditions, thereby informing better material design and application strategies.