Relationship between alloy composition, microstructure and exfoliation corrosion in Al–Zn–Mg–Cu alloys

The exfoliation corrosion (EFC) susceptibility of several 7000 Aluminium alloys has been studied after a variety of heat treatments using two independent corrosion tests (standard EXCO test and an electrochemical test based on potential transients analysis), together with detailed microstructural examinations. It is proposed that depending on heat treatment EFC may occur via two different mechanisms: inter-granular dissolution induced damage (IDD) or inter-granular fracture induced damage (IFD). The coexistence of these two mechanisms, leading to EFC, and their relative predominance explain the influence of alloy composition and heat treatment on EFC susceptibility via the confrontation of the two corrosion tests.     

Quantitative study of exfoliation corrosion: Exfoliation of slices in humidity technique

A new technique, exfoliation of slices in humidity (ESH), was developed for the determination of exfoliation corrosion (EFC) susceptibility and quantification of EFC kinetics. Two AA7178 plates taken from the wingskin of a retired KC135 airplane were used as test samples. Slices of the plate were pretreated by potentiostatic polarization in chloride solution to develop localized corrosion sites. Subsequent exposure to high humidity after pretreatment of properly oriented and unconstrained samples resulted in the development of EFC at the edges of the slices. The EFC kinetics were determined by measuring the width of the central unattacked region of the samples. The ESH results were representative of the different EFC behavior of the two plates during outdoor exposure. These results show the capability of the ESH test to discriminate between plates of varying susceptibility and to determine EFC rates quantitatively. The different susceptibility of the two plates to EFC was attributed to differences in microstructure and grain boundary chemistry.     

不同淬火转移时间处理的7050-T6铝合金剥落腐蚀行为

采用标准的剥落腐蚀浸蚀实验、剥落腐蚀后样品的强度损火测量以及电化学阻抗谱等技术,对固溶后经不同淬火转移时间处理的7050-T6态样品的剥落腐蚀行为进行研究。结果表明,7050-T6铝合金的抗剥落腐蚀性能随着淬火转移时间的延长而减小。背散射电子扫描连同透射电镜观察揭示,影响合金腐蚀性能的最主要因素是晶界的析出相覆盖率和析出相的微观组织,而晶界附近的贫溶质区对其不产生影响或影响较小。通过对合金进行静电势扫描发现,合金的剥落腐蚀敏感性与瞬态电势之间有很好的对应关系,即可以测试瞬态电势变化的数量来表征材料的剥蚀性能。     

Significantly changed intergranular corrosion and exfoliation corrosion behavior of the ultra‐fine grained Al–5 mass% Cu alloy fabricated by ECAP

Significantly changed intergranular corrosion (IGC) and exfoliation corrosion (EFC) behaviors of the equal‐channel‐angular‐pressed (ECAPed) Al–Cu alloy were discovered through immersion test, electrochemical measurements, and microstructure observation. The ECAPed alloys with ultra‐fine grained (UFG) α(Al) matrix and extremely refined θ‐phase particles displayed obvious decreased IGC sensitivity, but deteriorated susceptibility to EFC. The decreased IGC sensitivity of ECAPed alloys presented decreased IGC propagation depths in immersion test in NaCl + H₂O₂ solutions and increased polarization resistance in electrochemical impedance spectrum test in MIL‐H‐600 solution. The reason for the decreased IGC sensitivity was the breakage of the net structure of θ phase during ECAP process, which destroys the continuity of IGC propagation channel. The deteriorated susceptibility to EFC of ECAPed alloys in EXCO solution presented gradual evolution from serious IGC attack into obvious lamellar EFC, and finally complete dissolution of surface grains. Meanwhile, the EFC propagation depths were sharply decreased with the increasing ECAP passes. This phenomenon was caused by the aspects ratio evolution of deformed grains and the gradually decreased IGC sensitivity of the ECAPed alloys.     

Electrochemical aspects of exfoliation corrosion of aluminium alloys: The effects of heat treatment

Electrochemical approaches are used to investigate the exfoliation corrosion (EFC) of a 7XXX series aluminium alloy that has undergone different tempering treatments. EFC was produced under an artificial crevice at open circuit potential in neutral chloride solutions, and is found to be associated to current and potential transients. EFC was also produced under galvanostatic control conditions. Observations made through Scanning Electron Microscopy (SEM) suggest that these transients result from the progression of inter-granular cracks. Last, over-ageing heat treatments that are known to decrease both metal hardness and EFC sensitivity were found to decrease the number of transients.     

不同时效态对7150铝合金剥蚀行为的影响

针对老龄飞机7150合金飞机结构普遍存在的剥蚀问题,采用海洋性环境腐蚀试验、透射电子显微镜观测等手段,研究了T6、T73和T77时效态7150合金剥蚀行为。研究结果表明：T77时效态抗剥蚀性能最好,T6时效态抗剥蚀性能最差,T73 时效态介于T77和T6时效态之间。7150-T77合金晶界腐蚀产物的锲力,尚不足以提供其剥蚀扩展所需动力。7150合金时效后的晶界微观组织结构,是抗剥蚀性能的重要决定因素。     

正应力对7150铝合金剥蚀行为的影响

针对老龄飞机7150铝合金结构普遍存在的剥蚀问题,在海洋性盐雾环境下,通过T73时效态不受载和悬臂梁加载剥蚀试验,以及T77时效态波音737CL龙骨梁下缘条不受载和受载剥蚀试验,研究了正应力对7150铝合金剥蚀的影响。结果表明:T73时效态剥蚀,L轴向拉应力作用表面最轻,其次为不受载表面,L轴向压应力作用表面最严重。T77时效态龙骨梁下缘条剥蚀,在L轴向压应力作用下的产生和扩展速度,比不受载状态下快得多。由此认为:L轴向压应力可以加速7150铝合金剥蚀的形成和扩展,而L轴向拉应力可以抑制剥蚀的形成和扩展。     

Effects of Tafel slope,exchange current density and electrode potential on the corrosion of steel in concrete

A parametric study is carried out to investigate the effect of variations in anodic and cathodic Tafel slopes, exchange current densities and electrode potentials on the rate of steel corrosion in concrete. The main goal of this investigation is to identify the parameters that have significant influence on steel corrosion rate. Since there is a degree of uncertainty associated with the selection of these parameters, particularly during modelling exercises, it is intended that the results of this study will provide valuable information to engineers and researchers who simulate steel corrosion in concrete. To achieve this goal, the effect of a parameter on the corrosion rate of steel is studied while all other parameters are kept constant at a predefined base case. For each parameter, two extreme cases of anode‐to‐cathode ratio are studied. The investigation revealed that the variations in the anodic electrode potential have the greatest impact on the corrosion rate, followed by the variations in the cathodic Tafel slope.     

塔河油田机采井井筒腐蚀监测及缓蚀剂防护技术

随着塔河油田开发生产的进行,腐蚀问题已逐渐凸显并日趋严重,近年来油田井下管柱等部位腐蚀穿孔断裂事故频繁发生,严重影响了油田的正常生产,其中机采井腐蚀尤为严重,约占整个井下腐蚀的64%.机采井井筒腐蚀问题较突出,在所带来的经济损失最大,对油田生产的影响也最直接.开展机采井井筒腐蚀监测与防护,对防止和减缓油井生产系统腐蚀的危害,确保油田的安全、高效运行具有重要意义.本文通过对井筒腐蚀监测技术的研究应用,进而对缓蚀剂防腐技术进行了系统分析评价,确定了适宜塔河油田机采井的缓蚀剂.     

正应力在波音737CL飞机龙骨梁剥蚀中的作用

根据波音737CL飞机龙骨梁ADF环形天线组件固定孔区域的剥蚀特征,采用有限元分析和盐雾环境暴露试验研究了正应力在剥蚀中的作用.结果表明,纵向L方向及长横向LT方向压应力可加速7150铝合金的剥蚀的形成和扩展;L方向、LT方向拉应力以及短横向ST方向压应力抑制合金的剥蚀的形成和扩展.     

Development of databases and generation of stability diagrams pertaining to the modelling of processes during hot corrosion of heat exchanger components

The purpose of the project “Optimisation of In‐Service Performance of Boiler Steels by Modelling High Temperature Corrosion” (G5RD‐CT‐2001‐00593, acronym OptiCorr) was to establish a set of focused procedures, both in terms of applications of thermochemical standard software and in terms of dedicated new developments, which enable a user to investigate the behaviour of boiler components based on the application of rigorous thermodynamics. Thermodynamic databases which cover the materials involved had to be compiled and assessed in order to be able to apply the appropriate software. Particular new results coming from the databases work will be highlighted. The results of phase equilibrium calculations are shown in appropriate diagrams and compared with published experimental data. The thermochemical standard software FactSage permits the investigation of stoichiometric reactions, complex equilibria and phase diagrams. These calculational capabilities have been applied for the purposes of investigation of (1) the composition of complex combustion gases, (2) metal‐gas interactions and (3) metal‐gas‐molten salt interactions, since these have been established to be the key points for the understanding of the corrosion of heat exchanger components. Selected results from these calculations will be demonstrated and discussed. Application specific software has been developed using the approach of local chemical equilibrium calculated by the programmer's library ChemApp and the add‐in ChemSheet for Microsoft EXCEL™. Two key processes have been treated: The internal corrosion of the metallic material by diffusion of gases and metals and local phase formation as well as the corrosion of heat exchanger material under a molten salt layer which is in contact with an outer gas phase. The general principles of the code development will be outlined while the details of the programs are given in separate presentations in this volume.     

Modelling of reinforcement corrosion – Corrosion with extensive cathodes

Reinforcement corrosion is the most common reason for the premature deterioration of a concrete structure. In case of a partial depassivation of the reinforcement macrocells are formed with considerable metal removal rates. Thus an assessment of the macrocell current becomes of great concern. To find out, whether this can be achieved by numerical calculations, specimens have been fabricated and simulated by the use of a boundary element program. In this paper the results of the calculations are presented and compared to electrochemical measurements on the real specimens.     

辽宁大气腐蚀性研究——锌、铜、铝暴露两年试验结果

在辽宁省范围内约等距离地设置了192处挂片点,进行锌及铜、铝有色金属材料的大气暴露试验。两年后测量不同地点的腐蚀率,绘制成辽宁省大气腐蚀图。此外,根据各试验点的气象与大气污染数据,腐蚀形貌和腐蚀产物分析结果,讨论了锌等材料的大气腐蚀规律。     

埋地金属管道交流电腐蚀研究进展

分别从交流电腐蚀的特点、机理、影响因素以及对阴极保护和微生物腐蚀影响的角度,对近年来国内外开展的交流电腐蚀研究进行系统综述.通过对目前研究中存在的重点问题进行综合分析,展望这一领域的研究前景及发展趋势,为相关领域的研究人员提供新思路.     

Fluoride induced corrosion of steel rebars in contact with alkaline solutions, cement slurry and concrete mortars

Corrosion behaviour of mild steel rebars has been studied in contact with 0.01 N NaOH, saturated lime water, cement slurry and embedded mortars having different concentrations of fluoride ions. Weight-loss, electrochemical DC cyclic polarisation and polarisation resistance, surface topographic and X-ray diffraction (XRD) techniques have been used to investigate the effects of fluoride ion on the corrosion behaviour of the material. Under all the conditions of the exposure it is observed that a low content of fluoride (?25 ppm) in the corrodent has deleterious action on the performance of the steel, where as at its higher content (?100 ppm) the ion has rather an inhibiting effect on corrosion rate. XRD studies of the corrosion product accumulated on the steel surface in the presence of fluoride ion indicate the predominance of magnetite oxide phase. Accelerating effect of the ion is observed to be due to depolarisation of cathodic reaction of the corrosion process. Observations show that in accelerating range of fluoride (?25 ppm) it has almost double corrosive effect than noted for equal concentration of chloride ion.     

电厂蒸汽回路系统中腐蚀损伤的决定论预测

局部腐蚀,包括点腐蚀、应力腐蚀开裂和腐蚀疲劳是导致电厂发电装置损伤的重要原因,它们诱发50%以上的意外停机事故。迄今,腐蚀破坏的预测一直沿用经验和统计的方法,但是,由于已证实该方法的适用性和其结果的准确性欠佳,故不宜作为例行检修规程的基础。本文提出了预测局部腐蚀损伤的决定论方法,并使用这个方法说明点腐蚀如何引发低压蒸汽轮机涡轮盘Wilson线下游部位的应力腐蚀开裂(SCC),我们的计算表明SCC的萌发与扩展对蒸汽小氧含量、冷凝液膜的环境和涡轮盘所承受的应力这三个因素敏感。     

碳钢CO2腐蚀的缓蚀剂策略及缓蚀行为研究进展

从新型CO₂缓蚀剂合成制备、绿色动植物成分作为CO₂缓蚀剂开发、CO₂缓蚀剂协同效应研究、苛刻环境下的缓蚀剂性能探究、缓蚀剂构效分析及影响因素评价等5个部分对CO₂缓蚀剂的最新研究进展进行综述分析。针对现有部分缓蚀剂存在性能不足、污染大等问题，CO₂缓蚀剂的增效思路主要包括新型缓蚀剂分子合成、绿色缓蚀剂提取和缓蚀剂复配研究。新型缓蚀剂合成是通过有机化学反应，以杂环分子为原料进行结构设计、官能团接枝或修饰得到新型缓蚀剂分子。该部分同时介绍了纳米缓蚀剂的前沿发展及面临的瓶颈问题。绿色缓蚀剂提取是以天然动植物为原料，改善缓蚀剂的生态安全性，针对绿色缓蚀剂的快速发展提出“全流程”绿色控制理念，建议确立绿色定义标准。缓蚀剂协同效应研究旨在阐明不同缓蚀剂间复配增效的本质机理，当前需要建立快速评价体系，健全探寻最佳复配比的指导理论。另外，缓蚀剂在复杂或极端工况下的结构稳定性、缓蚀性能持久性和缓蚀机理变化对其实际应用至关重要，油气田开发苛刻环境下“防腐+”一体化试剂的需求增大。除上述制备与应用...     

Operational based corrosion analysis in naval ships

Life extension of ageing steel structures such as naval ships requires consideration of plate thickness losses due to corrosion, particularly when protective measures such as paint coatings and sacrificial protection are not entirely effective. Traditionally, corrosion prediction models for ships take no account of the operational profile. Consequently, the corrosion models have an inherently high variability with poor corrosion prediction capability. A new corrosion model for the prediction of corrosion loss in the seawater ballast tanks of naval vessels has been developed. The model incorporates previously available corrosion models for immersion corrosion and atmospheric corrosion and takes account of operational and environmental variables. Experimental validation is presented for a trial on an operational naval vessel.