Corrosion behavior of magnesium and magnesium alloys

The automotive industry has crossed the threshold from using magnesium alloys in interior applications such as instrument panels and steering wheels to unprotected environment such as oil pan, cylinder head and wheels. The expanding territory of magnesium leads to new challenges.mainly environmental degradation of the alloys used and how they can be protected. The present critical review is aimed at understanding the corrosion behavior of magnesium and magnesium alloys in industrial and marine environments, and the effect of microstructure, additive elements and inhibitors on the corrosion mechanism.     

Corrosion resistance of electroplated Zn-Co alloy coating

By the NSS test and the test in SO2 gas atmosphere and detecting the φcorr-t curves, Rp-t curves and the cyclic voltammogram curves, the corrosion resistance of the electroplated Zn-Co alloy coating was studied. The corrosion resistance of the electroplated Zn-Co alloy coating is three times higher than that of the galvanized coating. Because the corrosion resistance of the Zn-Co alloy coating is especially remarkable in SO2 gas atmosphere, it is particularly fit to be used as a protective coating in industrial atmosphere. The reason why the Zn-Co alloy coating has such a high corrosion resistance is that its corrosive product has a comparatively great role in depressing the corrosive process.     

NACE International Corrosion／2003大会概况

美国腐蚀工程师协会 (NACE)Corrosion/2 0 0 3学术年会和展览会于 2 0 0 3年 3月 16日～ 2 0日在美国加州的SanDiego举行。每年在美国举行的NACE年会和展览会 ,是当今世界规模最大的材料与腐蚀领域的学术盛会 ,集中展现了美国和世界各国在腐蚀与防护领域的最新科研成果和技术动态。本次大会共收到正式会议论文近 5 0 0篇 ,其中中国大陆学者有三篇 ,即中国石油公司的“中国在役油气管线的安全评价的实践和展望”、“N80管道钢CO2腐蚀垢的离子通道选择性” ,上海电力学院的“吗啉齐聚物气相缓蚀剂的研究”。另外中国台湾、香港的学者也…     

Corrosion Behaviour of Annealed Cn_x/Tin_y Multilayers

IN RECENT YEARS,there has been great interest instudies of carbon nitride(CNX)coating because it wasproposed by Liu and Cohen that would have abulk modulus comparable to or even higher thandiamond due to its small bond length and lowionicity[l].The research on multiplayer CNx/TiNycoatings has been processed for more than ten years inWuhan University,and the coatings can be successfullyproduced with a hardness higher than45GPa underproper deposition conditions.This was achieved usinga…     

Corrosion characteristics of copper in magnetized sea water

The corrosion characteristics of copper in magnetic action system were investigated by mass loss method, electrochemical test, scanning electron microscopy （SEM） and energy analysis. It is found that the corrosion process of copper is influenced by magnetic field. The flow corrosion rate of copper decreases at the initial segment, then drives to gentle stage at the final segment. From electrochemical test, the corrosion rate of copper in the magnetized sea water is minimal compared with that in 3.5% NaCl solution and sea water. Electlochemical impedance spectroscopy （EIS） plots of copper in 3.5% NaCl, sea water and magnetized sea water are similar. However, EIS plot of copper in magnetized sea water shifts rightwards due to the effect of magnetic field on sea water. The corrosion process of copper in magnetized sea water is pitting corrosion. The surfaces of samples are finer in magnetized sea water relative to those in 3.5% NaCl solution and sea water. The corrosion products of copper include large amount of Cu element, O element and Cl element. Cu2O and CuCl2 are the primary products. This suggests that electromagnetic treatment has remarkable effect on the corrosion of copper.     

Corrosion of titanium in supercritical water oxidation environments

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Corrosion behavior of CuCrNiAl alloy in HCl solutions

1 Introduction Cu alloy has become a kind of important materials for ocean construction as its excellent anti-corrosion performance. Though this kind of alloy has been applied for a long time, it often undertakes serious corrosion, low strength and leakag…     

Corrosion behavior of an Al-6Mg-Sc-Zr alloy

The corrosion behavior of an Al-6Mg-Sc-Zr alloy was studied and compared with that of an Al-6Mg-Zr alloy. The addition of scandium into the Al-6Mg-Zr alloy reduced the susceptibility to exfoliation corrosion. By using the constant load tensile method in a 3.5 wt.% NaCl solution, the resistance to SCC of the Al-6Mg-Sc-Zr alloy was higher than that of the Al-6Mg-Zr alloy. When the specimens were not applied with an anodic current, the Al-6Mg-Sc-Zr alloy was resistance to SCC and no brittle cracking was found on the fracture surface. When an anodic current was applied, the Al-6Mg-Sc-Zr alloy specimens failed as a result of accelerated corrosion rather than SCC. It was believed that the addition of scandium re- sulted in （Al3Sc, Zr） particles that greatly refined grains and promoted the formation of homogeneous discontinuous distribution of β-phase in the alloy base, which much contributed to good corrosion resistance of the Al-6Mg-Sc-Zr alloy.     

Corrosion Resistance of Deformed Cu-Ni Alloy in Seawater

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Corrosion Behaviour of Annealed Cnx／Tiny Multilayers

The corrosion behaviour of annealed CNx/TiNy multilayers have been investigated using potentiodynamic test in a 0.5MH2SO4 solution. The coating has been deposited on W6MoSCr4V2 steel by reactive magnetron sputtering and then annealed at different temperature. The annealed multilayers showed superior corrosion resistance as compared to the as-deposited coating, The corrosion model of annealed CNx/TiNy multilayers has been set up.     

Corrosion and fatigue in micro-sized Ni cantilever beams

The Ni microcantilevers were fabricated by femtosecond laser. The corrosion behavior of the micro-sized Ni cantilever beams was studied by electrochemical noise and a newly developed fatigue testing method. The results show that the micro-sized specimens exhibit general corrosion behavior under the studied corrosion condition, whereas the ordinary-sized plates exhibit the localized corrosion behavior. The critical load amplitude of the micro-sized Ni specimens under corrosion fatigue status was determined to be 15 mN. The maximum bending loads, which were measured by fatigue tests, decrease gradually prior to final fracture. Corrosion fracture first occurs in the range of notch with a higher tensile bending stress, and exhibits clear evidence of trans-columnar fracture. The variation of maximum bending loads with time agrees with that creep deformation of the micro-sized Ni specimens can easily occur at room temperature, which implies that the micro-sized Ni specimens appear to have an improved resistance towards total crack as compared with the ordinary-sized Ni specimens.     

Corrosion 2000: V International Conference–Exhibition

Problems of Corrosion and Corrosion Protection of Materials (Corrosion 2000), V International conference–exhibition was held in Lviv (Ukraine) on June 6–9, 2000. The conference was organized by the Ukrainian Association of Corrosion Scientists and the Karpenko Physicomechanical Institute of the National Academy of Science of Ukraine (PMI NASU) with a support of the European Corrosion Federation, the National Academy of Science of Ukraine, and the Ministry of Education and Sciences of Ukraine. More than two hundred participants were involved in the conference work. Fifteen companies and organizations presented their advances. Next to 170 oral reports and posters were presented by scientists from Azerbaijan, Croatia, England, Germany, Italy, Japan, Kazakhstan, Libya, Lithuania, Poland, Russia, Switzerland, Turkey, Ukraine, and other countries.     

High-Temperature Corrosion Behaviour of Aluminized-Coated and Uncoated Alloy 718 Under Cyclic Oxidation and Corrosion in NaCl Vapour at 750 °C

To evaluate the suitability of HR3C and 22Cr–25Ni–2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 °C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr₂O₃ healing layer on the HR3C was formed at the temperature of 700 or 800 °C, but the Cr₂O₃ oxide film on HR3C was unstable and partly converted into a less protective MnCr₂O₄ with the increase in temperature to 900 or 1000 °C. The composition and structure of oxide film of 22Cr–25Ni–2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr₂O₃ to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 °C compared to HR3C. Further, the oxide films consist of internal Al₂O₃ and AlN underneath the outer loose layer after 22Cr–25Ni–2.5Al AFA oxidized at 900 or 1000 °C. It can be proved that the internal oxidation and nitrogen would make 22Cr–25Ni–2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 °C.     

Corrosion of titanium in phosphoric acid at 250℃

Corrosion studies of a commercially pure titanium in phosphoric acid solutions at 250 ℃ were carried out by immersion test in an autoclave. At lower phosphoric acid concentration (0.1 mol/L), the corrosion was mild. At higher phosphoric concentration (1.0 mol/L) corrosion, a 25 μm-thick white corrosion products layer was formed on the samples after 24 h immersion. XRD analysis shows that the white layer consists mainly of titanium oxide phosphate hydrate (π-Ti2O(PO4)2·2H2O). The corrosion product shows the morphology of fiber bundles. A thermodynamic analysis of the formation of the corrosion product is presented.     

Corrosion behavior of pure aluminum in FeCl_3 solution

1Introduction Some in-situ imaging technologies such as video camera[1,2]and CLSM(confocal laser scanning microscopy)[3]have been used in corrosion studies,but the detailed morphological characteristics of surfaces can not be obtained from these methods b…     

Corrosion behavior of sintered zinc-aluminum coating in NaCl solution

Sintered zinc-aluminum coating (SZAC) was prepared using zinc flakes,aluminum flakes and CrO3 as main raw materials,The corrosion behavior of SZAC in 3.5NaCl solution was Studied by means of SEM,EDS,EIS and so on.Results indicate that aluminum corroded in advance of zinc to produce speculate or spherical substances,which attaches to SZAC and adds mass to it.Corrosion production passivates metal powders in SZAC.causes Ecorr of SZAC to increase gradually,and causes the arising of the third time constant in EIS,which corresponds to the insulation of corrosion production.     

Corrosion behavior of Cu-Ni-Ag-Al alloy anodes in aluminium electrolysis

The behavior of Cu-Ni-Ag-Al alloy used as anode for aluminum electrolysis was directly visualized in a two-compartment see-through cell during electrolysis, and its performances were tested at 850℃ in acidic electrolyte molten salts consisting of 39.3%NaF-43.7%AlF3-8%NaCl-5?F2-4%Al2O3 for 40 h in a laboratory cell. The results show that nascent oxygen oxidizes the anodic surface to form oxide film at the beginning of electrolysis. X-ray diffraction analysis of alloy surface show that the oxide film on the anodic surface consists of CuO, NiO, Al2O3,CuAl2O4 and NiAl2O4. However, SEM image shows the oxide film is porous, loose and easy to fall into electrolyte and to contaminate aluminum. The corrosion mechanism of metal anodes was analyzed.     

Corrosion Characteristics of Multilayer Vacuum-Arc Ti–C Coatings

The behavior of multilayer Ti–C coatings formed by pulsed arc plasma streams are studied by means of electrochemical and XPS methods. The results on the steady-state potentials of multilayer Ti–C coatings are compared with those for single-layer coatings of titanium and carbon. It is shown that irrespective of the substrate material (structural and stainless steels) the multilayer Ti–C coatings enhance the corrosion stability of steel by inhibiting the active dissolution and facilitating the passivation.     

Corrosion behavior of NiCrBSi coatings deposited by HVOF spraying

The corrosion resistance of NiCrBSi coating deposited on steel substrate by HVOF was examined using electrochemical tests and immersion tests so as to offer an experimental basis to expand a promising applied field of HVOF in aqueous medium, comparing with those of coatings deposited by oxyacetylene flame spraying and flame cladding. The results show that the general corrosion rate of HVOF sprayed coatings is quite bigger than that of clad coatings, bat it is less sensitive to local corrosion. There is less and smaller porosity in the coatings deposited by HVOF than that in flame sprayed coatinlgs. The effects of porosity on the corrosion current density was indistinctive, bat the existence of large amount of defects in the coatings damaged the cohesion of the coatings, causing the metallic particles drop off from the coatings under the influence of corrosive medium. Improving the quality and reducing the porosity of coatings is the key to get the coatings with high corrosion resistance.     

Corrosion and high-temperature oxidation of AM60 magnesium alloy

The corrosion and high-temperature oxidation characteristics of AM60 Mg alloy in different environments were investigated by immersion test, electrochemical polarizing analysis and differential thermal analysis （DTA）/thermo gravimetric （TG） experiments. The influence of aging heat treatment on the corrosion resistance of AM60 Mg alloy was studied. AM60 Mg alloy shows better corrosion resistance in sea water than in 3.5%（mass fraction） NaCI solution. The corrosion resistance after aging for 24 h is better than that of both as-cast and aging for 48 h. Corrosion resistance of Mg alloy is controlled by microstructure, composition of a-matrix. Precipitation offl phase along the grain boundaries acts as a barrier that decreases corrosion rate, whereas the decrease of aluminum content of a phase causes an increase in the corrosion rate. The DTA and TG curves of heating process in air are characterized with combustion after 590℃. When heated in helium, the curves show two endothermic peaks and a remarkable evaporation of magnesium. As for isothermal DTA and TG experiments, mass increment caused by oxidation does not happen till 520 ℃.