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Intergranular Corrosion (intergranular + corrosion)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Intergranular corrosion on Nd:YAG laser-welded A653 steel for automotive application

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2004
Y. M. Looi
Abstract Laser welding techniques produce a narrower heat-affected zone than other conventional welding methods. However, laser welding is not exempt from high heat input during the welding process. This high heat input results in changes of the material properties including its corrosion behaviour; the formation of the heat affected zone increases the susceptibility of the material to intergranular attack. The residue of zinc at the weld due to condensation and splashing during the welding process may also influence adversely the corrosion behaviour of the material. The degree of susceptibility to corrosion strongly depends on the welding parameters. Electrochemical and microstructure characterisation were employed to study the influence of Nd:YAG (neodymium yttrium aluminium garnet) laser-welding on an A653 galvanized steel at different welding parameters. [source]

Influence of heat flux and surface temperature on the intergranular corrosion of stainless steel

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2005
T. Pro
Abstract The exposure tests followed by metallographic evaluation and the electrochemical reactivation measurements in double-loop (DL-EPR) modification were used for investigation of the influence of non-boiling heat transfer on initiation and rate of propagation of intergranular corrosion (IGC) of sensitized austenitic stainless steel EN 1.4301 (AISI 304) in sulfuric acid solutions. The influence of heat flux and surface temperature was ascertained separately. The susceptibility to IGC and the rate of crack propagation increased with the surface temperature. Heat flux from metal to solution at constant surface temperature facilitated the IGC initiation, but at the same time it caused a drop of the corrosion attack depth in the metal. The increase of the heat flux by 10 kW m,2 in a range from 0 to 42 kW m,2 led to a drop of the maximum depth of cracks formed after subsequent bending the specimen, in average by 8%. The overall danger of corrosion was lower at positive heat flux between metal and solution than under isothermal conditions at constant surface temperature of the metal. The intensification of heat flux by 10 kW m,2 had the same effect on the IGC as a change of the surface temperature by less than 2 K. Therefore, the effect of the heat flux on IGC of the heat exchangers operating under non-boiling conditions may be considered as relatively less important than the effect of the surface temperature. [source]

EBSD investigation of intergranular corrosion attack on low interstitial stainless steel

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2004
T. Kuníková
Abstract Grain boundary effect on corrosion behaviour of low interstitial AISI 316LN austenitic stainless steel after homogenization and heat treatment at 700 and 800°C was investigated by means of Electron Backscattered Diffraction (EBSD) technique. Rapid oxalic acid etch test (ASTM A262- practice A) was used to determine steel susceptibility to intergranular corrosion. An attempt to quantify oxalic acid etch test results was also made. Beneficial effect of low carbon and nitrogen content on grain boundary precipitation and corrosion was observed. No changes neither in grain orientations nor in grain boundary types between sensitised and non-sensitised steel states using orientation measurements were recorded. Twin boundaries were found in all samples with highest amount and only small occurrence changes. CSL categorizations showed only little increase of special boundary fractions with increasing time and temperature of heat treatment. Irrespective to annealing conditions a continued network of random boundaries was retained. Additionally, based on misorientation measurement of 50 grooved grain boundaries, a tendency for preferred attack of high angle boundaries (30,55°) was noted. [source]

Exfoliation corrosion of aluminum alloy AA7075 examined by electrochemical impedance spectroscopy

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2004
F.-H. Cao
Abstract A typical aluminum alloy, AA7075, was immersed in the EXCO solution, and its corrosion properties during different immersion time were measured repetitively using electrochemical impedance spectroscopy technique (EIS). The EIS data a were simulated using equivalent circuit with ZView program. The results show that once the exfoliation occurs, the low frequency inductive loop in the Nyquist plot associated with the relaxation phenomenon of reaction intermediates disappears, and the Nyquist plane is mainly composed of two capacitive arcs in the high frequency range and low frequency range respectively. The former originates from the original corroded surface, while the latter from the newly formed interface by exfoliation corrosion (EXCO). With the increased immersion time, the high frequency capacitance arc decreases gradually, while the low frequency capacitance arc increases gradually. From the beginning of immersion up to 9 hours, charge transfer resistance gradually decreases, illustrating the acceleration of the corrosion rate, whereas the proton concentration decreases steeply, indicating the cathodic process is pre-dominant. Then the corrosion rate decreases gradually corresponding to the exhausting of proton ions. The results also show that the exfoliation corrosion is developed from pitting corrosion through intergranular corrosion to general corrosion at the end. [source]

Improving the properties of aluminium alloys by retrogression and reageing

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2003
J. S. RobinsonArticle first published online: 11 APR 200
Abstract Retrogression and reageing heat treatments offer the potential of improved tensile properties in combination with greatly increased resistance to stress corrosion cracking. The potential of this technique is reviewed with respect to the current application in the European and North American Aerospace Industry. To illustrate the performance increase associated with RRA treatments, the stress corrosion cracking performance of the established aerospace plate and forging alloy 7010 has been evaluated using an alternate immersion constant load tensile type test (ECSS-Q-70-37A) Specimens were cut from a large aerospace rectilinear forging and tested in three different tempers, T652, T7452 and a retrogressed and reaged condition (RRA). In the T652 condition the material has been shown to be highly susceptible to intergranular corrosion and stress corrosion cracking. In the T7452 and RRA conditions 7010 showed much improved resistance to SCC but pitting corrosion resulted in failure of some specimens within the 30day requirement of the test standard. [source]