Galvanic corrosion of bare and coated Al alloys coupled to stainless steel 304 or Ti-6Al-4V

The galvanic corrosion behavior of Al alloys 7075, 6061, 2024, bare or coated with the chemical conversion coating Alodine 600, coupled to stainless steel 304 or Ti-6Al-4V and immersed in aerated 3·5%NaCl solution, has been studied by continuous measurements of the galvanic current using a zero impedance ammeter and by weight loss measurements. Comparison of weight loss measurements for bare and coated uncoupled Al alloys shows that good corrosion protection is provided by the conversion coating. Data from weight loss and galvanic current measurements show that corrosion protection is also provided when coated Al alloys are coupled to stainless steel 304 or Ti-6Al-4V. Examination of potentiostatic polarization curves for the metals studied in 3·5%NaCl solution explains the protective action of the coating and also the higher dissolution rates of Al alloys coupled to stainless steel 304 instead of Ti-6Al-4V. Differences between dissolution rates calculated from galvanic current data and weight loss data are explained by theoretical considerations published recently by the authors taking into account the shapes of the individual polarization curves of the metals in the couple. After correction of galvanic current data, agreement between dissolution rates obtained by weight loss and galvanic current data is satisfactory. Continuous recording of the galvanic current reveals considerably more information than weight loss data.     

5383铝合金与907钢和铝青铜早期电偶腐蚀的平面分布

通过电偶电流测试和腐蚀形貌观察等方法,研究了5383铝合金分别与907钢和铝青铜组成的两种电偶体系的早期电偶腐蚀平面分布。研究结果发现,两种电偶对中5383铝合金为阳极,907钢和铝青铜则始终为阴极受到保护;5383铝合金的腐蚀形貌有亚稳点蚀、不规则点蚀和类丝状腐蚀;电偶电流随时间变化规律相似,即腐蚀初期电流迅速降低,之后趋于稳定;与偶接点的距离增大,电偶电流降低,且远端的电流分布较为均匀;5383铝合金与907钢偶接时比与铝青铜偶接时大部分区域电流密度更小,但电偶腐蚀更加集中于2 mm内的区域。     

0Cr13Ni8Mo2Al钢与铝合金和钛台金接触腐蚀与防护研究

通过测定0Cr13Ni8Mo2Al钢与铝合金（LY12）和钛合金（TC4）组成的电偶对的电偶电流的方法,研究了0Cr13Ni8Mo2Al钢在使用中与铝合金和钛合金接触时发生电偶腐蚀的敏感性。研究结果表明:0Cr13Ni8Mo2Al钢与铝合金接触时会产生严重的电偶腐蚀,必须进行防护处理方可使用;与钛合金接触时产生的电偶腐蚀很轻微,可以不进行防护。0Cr13Ni8Mo2Al钢表面进行镀镉钛防护后,与铝合金接触时的电偶电流密度大为减小,相差近10倍;采用环氧锌黄底漆、XM-33-4双组分密封胶防护可以有效地防止0Cr13Ni8Mo2Al钢与铝合金和钛合金接触产生的电偶腐蚀。     

The galvanic effect of high-strength weathering steel welded joints and its influence on corrosion resistance

ABSTRACT

The influence of the galvanic effects on the welded joints of A710 high-strength weathering steel with two different weld metals (80Ni1-H4 and WER70) under a simulated marine atmospheric environment was investigated by employing Scanning Kelvin Probe (SKP), galvanic current measurements, cyclic wet/dry accelerated corrosion testing, Field-Emission Scanning Electron Microscopy (FE-SEM) and other approaches. The results indicate that the average galvanic currents for the HAZ-BM and HAZ-WM couples of the two welded joints initially decreased and then gradually stabilised, which is related to the formation of a stable rust layer. In addition, the WER70 welded joints presented a higher average corrosion rate than for the 80Ni1-H4 welded joints. The significant galvanic effect of the WER70 welded joints and the formation of a compact rust layer are the dominant effects during the initial and later corrosion stages, respectively.     

Karbonatisierungszellen – Ein Beitrag zur Korrosion von Stahl in karbonatisiertem Beton

Carbonation cells – On the corrosion of steel in carbonated concrete Corrosion of steel in carbonated concrete involves the activity of active-passive galvanic couples (carbonation cells). Carbonation cells consisting of mortar electrodes in wet condition and subjected to wet-dry cycles have been investigated by means of current and potential measurements. The corrosion current can be explained in terms of oxygen diffusion through the mortar cover. The stationary current gives realistic values for the diffusion coefficient of oxygen in concrete. Changes from wet to dry and vice versa always increase the corrosion rate. Electrolytically and gravimetrically determined weight loss are in good agreement only for constant moisture conditions. In case of wetdry cycles oxidation and reduction reactions within the corrosion products are assumed to contribute to the total corrosion loss.     

CO2环境下油酸咪唑啉对X65钢异种金属焊缝电偶腐蚀的抑制作用研究

研究了X65管线钢与316L不锈钢、Inconel 625双金属复合管的异种金属焊缝在CO2环境下的电偶腐蚀行为,以及油酸咪唑啉的缓蚀作用。结果表明,随着电偶电位差的增大,异种金属焊缝的腐蚀速率明显升高,并且都显著高于母材。添加油酸基咪唑啉缓蚀剂能降低异种金属焊缝在CO2环境下的均匀腐蚀速率。但是,当缓蚀剂浓度添加较低时,异种金属焊接试样的碳钢一侧出现了严重的沟槽腐蚀或密集的点蚀坑;进一步增加缓蚀剂浓度才能消除沟槽腐蚀现象。讨论了缓蚀剂对异种金属焊缝电偶腐蚀的抑制机理,该项研究可为异金属焊接接头处的腐蚀防护提供借鉴。     

Experimental investigation of galvanic corrosion: Comparison between SVET and immersion techniques

In this work, two experimental techniques: (a) scanning vibrating electrode technique (SVET) and (b) immersion technique are used to calculate the corrosion rate of two galvanic couples, AE44 (Mg alloy) - mild steel and AE44 - AA6063 (Al alloy). The maximum corrosion rate estimated from these two widely different experimental techniques is found to be in a good agreement for both couples considered here. The maximum corrosion rate of AE44 in AE44 - mild steel couple is found to be approximately five times higher than that in AE44 - AA6063.     

Galvanic Corrosion of a Carbon Steel-Stainless Steel Couple in Sulfide Solutions

The galvanic corrosion behavior of carbon steel-stainless steel couples with various cathode/anode area ratios was investigated in S ²⁻-containing solutions, which were in equilibrium with air, by electrochemical measurements, immersion test, and surface characterization. It is found that the galvanic corrosion effect on carbon steel anode increases with the cathode/anode area ratios, and decreases with the increasing concentration of S²⁻ in the solution. A layer of sulfide film is formed on carbon steel surface, which protects it from corrosion. When the cathode/anode area ratio is 1:1, the potentiodynamic polarization curve measurement and the weight-loss determination give the identical measurement of the galvanic corrosion effect. With the increase of the cathode/anode area ratio, the electrochemical method may not be accurate to determine the galvanic effect. The anodic dissolution current density of carbon steel cannot be approximated simply with the galvanic current density.     

Automatische Ermittlung von Kontaktkorrosionsdaten und ihre Auswertung mittels Polarisationsdiagrammen

Automatic measuring of contact corrosion parameters and their interpretation by means of polarization diagrams To evaluate the danger of contact corrosion on coupled dissimilar metals, the corrosion potentials of the concerned metals, the mixed corrosion potential and the current between the galvanic couple are of interest. A test stand with 6 sets has been developed to determine these values simultaneously and automatically from 6 variations of metal couple electrolyte/electrolyte's condition/temperature. Every set is equipped with two electrolytic cells. One cell is for measuring the corrosion potentials of the two metal probes in an open circuit; in the other cell an identical metal couple is arranged in a short circuit, so that the mixed potential and the current of the contact couple can be monitored. The values are called in sequence in a pre-selected manner by a scanning unit and are then recorded. From couples obtained from combinations of mild steel, CrNiTi-steel, NiCrFe-alloy, and Molybdenum alloy (0,5 Ti and 0,1% Zr), the mild steel proved to be always the least noble whilst the Molybdenum alloy was the most noble; this was true in both alcaline and acid electrolytes. By plotting the measured values on a polarization diagram, a survey of the possible contact corrosion behaviour in several systems may be obtained together with information on the corrosion mechanisms occurring.     

Ti8LC钛合金与主要结构材料的电偶腐蚀及防护研究

通过测定表面防护处理前后,Ti8LC钛合金、7710铝合金、ZL59铝合金、30CrMnSiA高强钢的电极电位,以及Ti8LC钛合金与其余3种材料组成偶对后的电偶腐蚀电流-时间曲线,研究了表面防护处理前后3种偶对的电偶腐蚀行为,并评估了电偶腐蚀敏感性.研究结果表明:Ti8LC与7710铝合金、ZL59铝合金、30CrMnSiA钢偶接时,会产生严重的电偶腐蚀,必须进行表面防护处理才能使用;采用涂层前处理+有机涂层防护的方法,可有效阻止Ti8LC钛合金与铝合金和高强钢的电偶腐蚀.     

Influence of geometry on galvanic corrosion of AZ91D coupled to steel

The influence of geometric factors on the galvanic current density distribution for AZ91D coupled to steel was investigated using experimental measurements and a BEM model. The geometric factors were area ratio of anode/cathode, insulation distance between anode and cathode, depth of solution film covering the galvanic couple and the manner of interaction caused by two independent interacting galvanic couples. The galvanic current density distribution calculated from the BEM model was in good agreement with the experimental measurements. The galvanic current density distribution caused by the interaction of two independent galvanic couples can be reasonably predicted as the linear addition of the galvanic current density caused by each individual galvanic couple.     

Evaluation of atmospheric galvanic aluminum corrosion in electrical transmission towers at different sites in the Valparaíso region,Chile. Wire-on-Bolt Test (CLIMAT)

This study evaluates environmental aggressiveness and atmospheric galvanic corrosivity categories in Chile (Classification of Industrial and Marine ATmospheres test) by installing bolts in electrical transmission towers in the Valparaiso region across four exposure sites: Playa Ancha, San Sebastián, Las Vegas, and San Felipe. Classifications of marine corrosion index (MCI), industrial corrosion index (ICI), and atmospheric corrosion index (ACI) used different galvanic couples: aluminum/steel for MCI, aluminum/copper for ICI, and aluminum/polyethylene for ACI. Corrosion indices varied by season (summer, autumn, winter, and spring), for which couples were exchanged every 3 months. Intraseason variation depended mainly on the meteorochemical variables of the zone, the Cl⁻/SO₂ ratio, and the presence of general and pitting corrosion in the aluminum. The results indicate that, regardless of environmental condition, the aluminum in Al/steel (MCI) and Al/copper (ICI) couples presented a higher corrosion rate than when not forming a galvanic couple (ACI). Moreover, under higher environmental chloride, these differences increase. The Playa Ancha station presented the highest ACI.     

高流速海水中金属材料的腐蚀行为

<正> 一、前言 金属材料在自然海水中的腐蚀数据通常是在自然海流(0.1～1米/秒)条件下获得的,但滨海的电站、石油、化工系统中的高流速管道、泵、热交换器、阀门以及高速舰船中的管道以至船体等,都处在较高流速(5～30米/秒)海水的环境中。因此,各国相继开展了高流速海水中金     

Galvanic corrosion of gas tungsten arc repair welds in 17-4PH stainless steel in 3·5% NaCl solution

Abstract

In this paper, the galvanic corrosion of individual components of a 17-4PH repair welded stainless steel in 3·5% NaCl solution was investigated using various dc electrochemical measurements and microscopy. Open circuit potential measurement of the regions in the vicinity of a repair weld [i.e. parent metal, weld metal and heat affected zone (HAZ)] in 17-4PH stainless steel in 3·5% NaCl solution indicated that the most likely galvanic couple was between HAZ and weld with the HAZ acting as the anode and weld metal as the cathode. Slow scan rate potentiodynamic polarisation measurement of pitting potentials revealed a lower passive current density and a higher pitting potential in the weld region, while the HAZ showed the highest passive current density and the lowest pitting potential. Observation of the material after applying an anodic potential close to the pitting potential of the individual weld parts also confirmed the formation of several stable pits in the HAZ but only a few metastable pits in the weld and parent metal zones. Galvanic coupling using a zero resistance ammeter also showed a higher current density in the weld metal/HAZ as compared with the parent metal/HAZ and parent metal/weld galvanic couples. Although, the current densities in all measurements were in the range of a few to tenths of nanoampere per square centimetre, it can still be concluded that the weld metal/HAZ couple has the highest risk of galvanic corrosion among the three individual galvanic couples.     

常用牺牲阳极合金在NaCl溶液中的接触腐蚀行为

研究了作为牺牲阳极材料的ＭｇＡｌＺｎＭｎ、ＡｌＺｎＩｎＳｉＭｇ和ＺｎＡｌＣｄ合金与Ａ３钢偶接时，溶液中Ｃｌ－浓度和电偶对中阴阳极面积比变化对三种合金接触腐蚀行为的影响。偶对阳极电偶电流密度ｊｇ随Ｃｌ－浓度增大而增大，ｊｇ与面积比成正比关系。偶对电偶电势Ｅｇ随Ｃｌ－浓度增大和面积比减小向负向变化。当偶对中阴极金属材料为３０２不锈钢和紫铜时，ｊｇ随Ｃｌ－浓度增大有不同的变化趋势。     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

Corrosion inhibitor control in aqueous solutions evaluated with galvanic couples

An electrochemical method was evaluated for obtaining measurements to determine the effectiveness and the type of control exerted by corrosion inhibitors in galvanic systems. Anode and cathode potentials and corrosion currents were measured on zinc-platinum and iron-platinum galvanic couples in test solutions before and after addition of potassium chromate as an inhibitor. The measurements were then plotted as galvanic polarization diagrams which indicate a comparative corrosion rate and the type of inhibitor control, as anodic, cathodic, or mixed. Some of the results were also compared with weight loss data. Experimental variables such as inhibitor concentration, sodium sulfate concentration, corrosion current density, spacing between the anode and the cathode of the couple, and external resistance of the test circuit were investigated.The method gave a good evaluation of the behavior and the type of control of an inhibitor in galvanic systems in dilute aqueous solutions. The results show that it possibly could be used to identify the inhibitor behavior in ordinary corrosion provided the corrosion current generated by the galvanic couple is adjusted to approximate that generated by local cell action. The inhibiting effectiveness of chromate ions was lowered by the presence of the other anions such as the sulfate ion. When the initial corrosion current started at low values, the chromate tended to develop greater anodic polarization and better inhibition than higher initial corrosion currents.     

Galvanic corrosion of A1 alloys — II. Effect of solution composition

Galvanic corrosion of the A1 alloys 1100, 2024, 2219, 6061 and 7075 coupled to Cu, stainless steel 304L, Ti-6A1-4V, 4130 steel or zinc has been studied in 3·5% MaCl, tapwater and distilled water using electrochemical and weight loss data. In 3·5% NaCl the galvanic effect decreases in the order Cu > 4130 steel > SS304L > Ti-6A1-4V for A1 alloys coupled to one of these metals, while in tapwater and distilled water the ranking is Cu > SS304L ～ Ti-6A1-4V > 4130 steel. Zinc, although being the anode in all galvanic couples, can sometimes accelerate corrosion rates of A1 alloys. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3·5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing galvanic corrosion behaviour of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of A1 6061 is, for example, higher in tapwater with Cu as cathode than in 3·5% NaCl with SS304L or Ti-6A1-4V as cathode.     

Effect of Al additions in WC-(Cr1−xAlx)N coatings on the corrosion resistance of coated AISI D2 steel in a deaerated 3.5 wt.% NaCl solution

Multilayered WC-(Cr_1−xAl_x)N coatings were deposited on AISI D2 steel using cathodic arc ion plating (CAIP) process. Five kinds of WC-(Cr_1−xAl_x)N coatings were prepared: WC-Cr_0.6Al_0.4N, WC-Cr_0.57Al_0.43N, WC-Cr_0.53Al_0.47N, WC-Cr_0.48Al_0.52N and WC-Cr_0.45Al_0.55N. The Al concentration could be controlled by using evaporation source for Al targets and fixing the evaporation rate of the other metals (WC alloy and Cr). In this study, the corrosion behavior in deaerated 3.5 wt.% NaCl solution was investigated by electrochemical corrosion tests (potentiodynamic polarization test, galvanic corrosion test, electrochemical impedance spectroscopy (EIS)) and surface analyses (glow discharge optical emission spectroscopy, X-ray diffractometry, scratch adhesion test, scanning electron microscopy, electron probe micro-analyzer).

The results of potentiodynamic polarization test showed that the WC-Cr_0.48Al_0.52N coating with lower porosity exhibited the lower corrosion current density. The galvanic corrosion current between the coating and the substrate showed low values. In EIS measurements, the charge transfer resistance (R_ct) value of WC-Cr_0.48Al_0.52N coating only increased with the immersion time, when compared to the other coatings. It can be due to the corrosion products plugging the pores and increasing the pathway resistance.     

CORROSION PROTECTION OF Al CATHODES IN ZINC ELECTROLYSIS

1.IntroductionAlthoughthecomputerizedpredictionofalloyphasediagramsbythermodynamicmethodhasmadegreatachievements,thelackofthermodynamicdataisoneoftheobstaclesforthecomputationofalloyphasediagrams.Manymethodsforcomputerizedalloyphasediagramshavebeenproposedinordertoovercometheobstacle.Forexample,thereareHume--Rotherytheory[']forsolidsolutiollofbinaryalloysystemandMiedema'stwoparameters.oded2](Ark*,A.;/sa)forthethermodynamicpropertyestimationofalloysystems.Che.[3--5]hajsappliedatomicparameter-…