采用大气腐蚀检测技术 (ACM)、零电阻电流技术 (ZRA) 以及电化学阻抗谱技术 (EIS) 对2024铝合金与316L不锈钢在薄液膜下的电偶腐蚀行为进行了实时监测。结果表明,电偶腐蚀的过程可分为诱导期、加速期和减速期3个阶段。随着两电极之间距离的减小,电偶腐蚀会快速诱发,且腐蚀速率迅速增加,但电偶腐蚀的加速期变短。
Atmospheric corrosion monitor (ACM), zero resistance amperemeter (ZRA) and electrochemical impedance spectroscopy (EIS) were applied to detect deeply the real-time galvanic corrosion of the couple of 2024 Al-alloy and 316L stainless steel beneath a thin electrolyte film. The galvanic corrosion process could be divided into three phases: initial phase, acceleration phase and deceleration phase. The smaller the insulative space between the two different materials is, the shorter the initial and acceleration phases are.
将尺寸为20 mm×10 mm×3 mm的AA 2024铝合金与316L不锈钢 (其成分如
将制备好的试样置于CCT 600循环腐蚀试验箱内进行加速腐蚀实验。腐蚀溶液为3.5% (质量分数) NaCl溶液,实验条件如
进入高湿阶段后,将AA 2024铝合金与2273电化学工作站的工作电极相连接,316L不锈钢与辅助电极和接地电极相连接,并在软件中选择ZRA测试模式,开始测量。ZRA测试之后,将316L不锈钢与电化学工作站的辅助电极和参比电极相连接,开始进行EIS的测量,电化学阻抗测试的频率区间为105 ~10-2 Hz,扰动电位为10 mV。
The authors have declared that no competing interests exist.
Abstract Galvanic corrosion induced by plastic composite materials (graphite-epoxy-composite-materials) coupled to metallic materials (ferrous and nonferrous) in neutral and air-saturated aqueous 3.5% NaCl solution has been investigated. Two types of composites, manufactured by Fiberite and Ciba-Geigy, were electrically coupled to aluminum alloys, to stainless steels, to steels, and to an Al-Ni-Bronze alloy. The galvanic corrosion behavior was studied by continuous measurement of the galvanic current, by weight loss measurements, and by potentiostatic polarization curves for the metallic and nonmetallic materials investigated. Experimental results show that the galvanic corrosion current decreases with the nature of the metal in a certain order. The potential difference of uncoupled dissimilar materials was found to be a poor predictor of galvanic corrosion rates. Dissolution rates calculated from galvanic data and weight loss data have been analyzed according to a theoretical computation reported in the literature based on mixed potential theory. A satisfactory agreement between theory and experimental findings was found. Galvanic corrosion can be increased by increasing the temperature.
ABSTRACT Purpose - This paper aims to investigate the galvanic corrosion of titanium/L 316 stainless steel, by electrochemical noise (EN), electrochemical impedance spectroscopy (EIS), and anode/cathode area ratio effect on the galvanic behavior of the couple. Design/methodology/approach - The EN measurement was employed to examine effects of anode to cathode area ratio on the galvanic corrosion behavior between stainless steel L 316 and titanium in artificial seawater. Current noise and potential noise were monitored simultaneously using a three-electrode configuration under open-circuit condition. The noise resistance was evaluated as the ratio of the standard deviation of the potential to that of the current noise after removing the DC component. The time-series noise patterns were transformed into frequency domain by fast Fourier transformation and then their power spectrum densities (PSDs) at specified frequency were determined and compared with the EIS and polarization results. Findings - The EN, EIS and polarization results were in agreement. Galvanic corrosion density increase and galvanic potential moved slowly to negative direction with decrease in anode/cathode area ratio. The results showed that the slope of PSD of the current (i.e the "roll off") was rising slowly where the anode/cathode area ratio was declined. The relationship between polarization resistance (Rp) and noise resistance (Rn) was investigated. Rt was determined by EIS for samples, and its value compared with Rp and Rn. The result indicates that galvanic corrosion has an inversely relation with anode/cathode area ratio that exposed to aggressive environment. Originality/value - This paper presents the application of noise analysis to demonstrate galvanic corrosion and the effect of area ratio anode/cathode on current density and galvanic potential.
Abstract The effect of variations of the area of two metals in a galvanic couple is discussed for three common cases. In Case 1, it is assumed that the only significant process on the more active metal (A) at the galvanic potential (蠒g) is metal oxidation (dissolution), while the only significant process on the more noble metal (C) is reduction of the oxidizer (H+, H2O, O2) and Tafel behavior is observed. Various possibilities to present the galvanic current as a function of electrode areas, which might have lead to some confusion in the literature, are discussed. In Case 2, it is assumed that metal (A), the anode in the galvanic couple, is polarized only slightly from its corrosion potential. It is shown that in this case the galvanic current density (igA) is not equal to the dissolution rate (idA) of the anode. A correlation between these two values is given. In Case 3, it is assumed that the cathodic process on both metals is entirely diffusion controlled. In this case, the dissolution rate of the anod...
An experimental setup was developed for the validation of a finite element model (FEM) for simulating galvanic corrosion occurring under very thin electrolyte for bi-material combination composed of aluminium AA2024 and carbon-fibre reinforced polymer (CFRP). The validation approach is explained and the results obtained are presented. The main outcomes of the model are electric current density and potential distribution on the electrode surface. Good agreement has been obtained between measured and modelled data. Further parameter studies are discussed to show the effect of different physical properties of the electrolyte on corrosion rates and total current changes in the materials involved.
A numerical analysis of galvanic corrosion of a Zn/Fe interface beneath a thin layer electrolyte is presented. Specifically, a circular defect, where the zinc coating has been removed, is considered. It is assumed that both oxygen reduction and iron oxidation can occur on the Fe surface, while only zinc oxidation occurs on the Zn surface. The importance of electrolyte thickness and conductivity and defect radius is considered. It is assumed that the iron and zinc oxidation rates are described by a Tafel relationship. If the kinetic parameters of the oxidation reactions are known, the cathodic protection of Fe is a function of a Wagner number, the ratio of the electrolyte thickness to the defect radius, and the ratio of the radius of the defect to the outer radius of the zinc layer.
An investigation was carried out into the galvanic corrosion of magnesium alloy AZ91D in contact with zinc, aluminium alloy A380 and 4150 steel. Specially designed test panels were used to measure galvanic currents under salt spray conditions. It was found that the distributions of the galvanic current densities on AZ91D and on the cathodes were different. An insulating spacer between the AZ91D anode and the cathodes could not eliminate galvanic corrosion. Steel was the worst cathode and aluminium the least aggressive to AZ91D. Corrosion products from the anode and cathodes appeared to be able to affect the galvanic corrosion process through an “alkalisation”, “passivation”, “poisoning” effect or “shortcut” effect.
The galvanic corrosion behaviour of a rivet joint of two sheets of the aluminium alloys EN AW-6014-T4 and EN AW-6082-T5 joined by an electrogalvanized steel blind rivet was investigated. The potentiodynamic polarization curves in a 5 wt.% NaCl solution show a potential reversion of the anodic and cathodic regions of the rivet joint. The surface potential was investigated with a capillary electrode before and after corrosion. From the measurements by the capillary electrode and SEM-observations an improved resistance against galvanic corrosion is expected after the dissolution of the zinc layer of the blind rivet.Research highlights? Electrochemical corrosion behaviour of a rivet joint. ? Contact corrosion and surface potential. ? Polarization curves including a reverse scan. ? SEM observation.
ABSTRACT A test sample incorporating a painted Al alloy panel, uncoated through-hole fasteners, and scribes has recently been shown to provide an accelerated response during atmospheric corrosion testing in the field and in laboratory chambers. In this paper the galvanic current between Type 316 (UNS S31600) stainless steel (SS316) or Ti-6Al-4V (UNS R56400) fasteners and painted and scribed AA7075-T6 (UNS A97075) panels was examined during exposure in a salt fog chamber using a zero-resistance ammeter. The anodic current of the AA7075-T6 panel and the cathodic current of each of the four fasteners were monitored using different connection schemes. The anodic current of the panel depended on the number of fasteners connected. The total cathodic current of fasteners was approximately equal to the anodic current of the AA7075-T6 panel, which validates the accuracy of the current measurement. Furthermore, galvanic interaction between the fasteners was observed such that the cathodic current of other fasteners was decreased when a new fastener was added. Scribes on a panel can interact with distant fasteners, not just the closest ones. The amount of corrosion as determined by charge and optical profilometry were close and indicated SS316 fasteners caused more corrosion attack than Ti-6Al-4V fasteners, which also is explained by differences in the cathodic current of the fasteners.
The Kelvin vibrating-capacitor technique has been used to measure the corrosion potential and the oxygen-consumption method has been applied to measure the corrosion rate of a low-alloy steel under very thin layers of electrolyte in air. The layer thickness dependencies of the corrosion rate and of corrosion potential are due to kinetic control by oxygen diffusion, and the latter dependence permits the Tafel slope of the anodic dissolution reaction to be evaluated. The anomalously large value of the Tafel parameter may be understood in terms of partial passivation of the metal surface by the intermediate reaction product, FeOH. This signifies a distinct difference from corrosion in the same system under bulk solutions.
The galvanic corrosion risk of metal/SiC-based ceramic coupling in 3.5wt% NaCl aqueous solution is investigated. Electrochemical measurements as linear sweep voltammetry and galvanic corrosion tests according to DIN-50919 were used. The results clearly show that the resistivity of the SiC-based ceramic plays the key role in the understanding of galvanic corrosion between metal and ceramic. In all cases the ceramic represents the cathodic site of the coupling. The corrosion rate is dominated by the electrical resistance of the ceramic.
A finite element model (FEM) was developed to calculate the potential distribution in the electrolyte in the case of bimetallic corrosion between iron and zinc electrodes, taking into account mass transport of oxygen in the solution. This model was first compared with experimental results obtained by scanning vibrating electrode technique (SVET) on a galvanized steel cut-edge in immersion conditions in a 0.03聽M NaCl electrolyte. A good agreement was obtained between the calculated and experimental current densities. The model predicted the evolution of the galvanic coupling as function of the electrolyte thickness and for various iron鈥搝inc surface area ratios. Different coupling regimes were highlighted when the electrolyte thickness was decreased: from a kinetic (cathodic) control in full immersion conditions, to an ohmic control for very thin electrolyte films, leading to a decrease of the protection efficiency. The evolution of the critical electrolyte thickness limiting these different regimes as function of the conductivity and geometrical conditions was also studied.
The corrosion behavior of aluminum alloy 7075-T6 dependent of the thin electrolyte layers in 102M sodium sulfate solution has been investigated using cathodic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The oxygen reduction current is measured to be maximum at 611.102V by cathodic polarization test when the thickness of the electrolyte layer is 11002μm. The EIS results show that the corrosion rate increases with the increase of the immersing time independent of thickness of the electrolyte layer although 11002μm thick electrolyte layer produces the largest corrosion rate over the immersing time between 002h and 9602h. However, with the longer immersing time, corrosion rate of the sample in bulk solution becomes higher. This result can be explained that the diffusion of the corrosion product and the metal ions from the electrode in the case of the thicker layer is easier. SEM morphologies reveal that corrosion products on the surface of the samples are distributed unhomogenously, with their amount near edges being more than the center area. In addition, XPS analysis demonstrates that corrosion products are mainly composed of Al(OH) 3 and Al 2 (SO 4 ) 3 .