Corrosion resistant performances of Al‐rich epoxy resin based paint on arc‐sprayed Al coating

Electrical conductive Al‐rich epoxy resin based paint with an acceptable surface was for the first time prepared on an arc‐sprayed aluminium coating surface successfully. Adhesion test and salt solution immersion test (SSIT) with complementary measurements including electron probe microanalysis (EPMA) and Raman spectroscopy were employed. Adhesion properties of the epoxy resin pigmented with Al particles did not degrade. Besides, because of the close Al particle–resin integration and the tight adhesion in the paint–coating interface, the strong adherence of corrosion products on Al particles, as well as probable passivation of Al particles, the paint showed no worse corrosion resistance properties than the epoxy resin and corroded at a similar rate to the epoxy resin, uniformly, slowly and slightly, protecting the coating base as a barrier type film.     

The influence of cerium ion concentrations on the characteristics of hybrid films obtained on AA2024‐T3 aluminum alloy

This work aimed to study the corrosion behavior of AA2024‐T3 aluminum alloy substrates pre‐treated with 3 glicidoxypropyltrimethoxysilane (GPTMS) silane layers doped with different cerium ion concentrations. The withdrawal speed of substrates from the sol was 20 cm · min^?1. The hybrid films were obtained by dip‐coating process and analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy, Rutherford scattering spectroscopy (RBS), salt spray test, and electrochemical analyses. The correlation among the results obtained from different analyses was very good and indicated that the addition of Ce ion in the hybrid coating contributed to the corrosion resistance; however, for the high Ce ion concentration, the barrier effect of the hybrid films was deteriorated. The results obtained by RBS showed that the concentration of Ce ion in the hybrid film increased linearly with the concentration of Ce ion in the sol. Moreover, it was verified that, for the nominal concentration of 0.05 M Ce ion in the sol, the Ce atomic fraction increased in the hybrid film, while the Si atomic fraction reduced, indicating the possible modification on the silane network due to the incorporation of Ce ions.     

The electrochemical corrosion behavior of TiN and (Ti,Al)N coatings in acid and salt solution

In this study, the corrosion properties of TiN and (Ti,Al)N coatings fabricated by Hollow Cathode Ionic Plating (HCIP) were studied by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) measurement and potentiodynamic measurement in acid and salt solution. It was found that both coatings showed an excellent corrosion resistance in acid and salt solutions at the beginning of long-term immersing test. The corrosion resistance of TiN coating deteriorated rapidly after nearly 100 h immersion in both acid and salt solutions. In the contrast, the corrosion rate of (Ti,Al)N coating decreased a little and then kept at a stable value. For the TiN coating, the corrosion initiated from pinholes and the underlying corrosion was very similar to pitting corrosion. With the addition of aluminum to the TiN coating, the corrosion resistance was improved, especially in salt solution. The test results demonstrated that the (Ti,Al)N coating seemed to posses certain self-repairing function. The corrosion mechanism took the form of denudation corrosion, owing to deterioration of the adhesion of the coating.     

Electrochemical corrosion behavior of plasma sprayed Al2O3‐13%TiO2 coatings in aqueous hydrochloric acid solution

One kind of conventional and two kinds of nanostructured Al₂O₃‐13%TiO₂ coatings were prepared by plasma spray process. The phase composition and microstructure of coatings were examined by means of scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the corrosion behavior of coatings in aqueous hydrochloric acid solution. The results showed that nanostructured coatings had superior corrosion resistance compared to conventional Metco 130 coating. The corrosion resistance of coatings was mainly related to their microstructure and defects density. The EIS measurement for long time immersion in hydrochloric acid solution revealed that the corrosion resistance of coatings decreased with the increasing of immersion time. During the immersion period, electrochemical corrosion mainly occurred on the carbon steel substrate under NiCrAl coatings. In addition, the Al₂O₃‐13%TiO₂ coatings were also failed during corrosion in aqueous hydrochloric acid solution.     

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

Ultrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.     

高速电弧喷涂铝涂层在模拟深水下的腐蚀行为

目的探究高速电弧喷涂铝涂层在深水压力环境下的腐蚀行为。方法利用电化学阻抗谱、扫描电镜微观形貌观察、物相衍射和红外光谱等锈层分析手段,分析高速电弧喷涂铝涂层在不同实验条件下的腐蚀行为,并对实验结果进行了对比研究。结果 3 MPa高压浸泡72 h的铝涂层表面腐蚀产物呈现疏松粉状,并出现了腐蚀坑洞,铝涂层快速失效。常压浸泡72 h后的铝涂层表面腐蚀较轻,常压浸泡720 h后的铝涂层表面则已被腐蚀产物完全覆盖。经XRD分析,三种条件下的铝涂层腐蚀产物基本一致。进一步利用傅里叶变换红外光谱(FTIR)分析可知,3 MPa高压条件下,压力加速了碱式氯化铝水合物Al9Cl6(OH)21·18H_2O、Al5Cl3(OH)12·4H_2O等腐蚀产物的形成。这些腐蚀产物在高压下不能有效结合,且易于流失,致使涂层耐蚀性能快速下降。结论铝涂层在高压条件下形成的腐蚀产物不能有效覆盖在涂层表面阻止腐蚀介质侵入,导致铝涂层的耐蚀性能下降。     

5A06/T2异种材料搅拌摩擦焊接头的耐蚀性

为了研究Al/Cu异种材料搅拌摩擦焊焊缝的耐腐蚀性能,对4mm的5A06和T2搅拌摩擦焊焊接接头进行了浸泡腐蚀试验。结果表明,焊缝区的耐腐蚀性能比铝合金母材要差,而焊缝铝铜结合过渡区耐腐蚀性能最差,并在该区域产生了腐蚀沟。电子能谱和X射线衍射物相分析结果发现,在过渡区Mg含量比其它区域高,而且有少量Al4Cu9产生,它的自腐蚀电位比铝高,这是导致该区域严重腐蚀的主要原因。     

原位微锻造冷喷涂制备高致密铝基涂层及耐腐蚀性能

目的提出一种基于原位微锻造冷喷涂制备高致密度金属沉积体的新方法,旨在为镁合金腐蚀防护提供一种低成本的涂层制备方法。方法通过在Al喷涂粉末中混入20%～60%(体积分数)的大粒径喷丸颗粒,借助其在喷涂过程中对已沉积Al涂层的原位微锻造效应,实现Al涂层制备中的实时致密化,研究了原位微锻造强度对涂层显微组织及耐腐蚀性能的影响规律。采用SEM分析了涂层的显微结构,采用电化学测试及长期浸泡试验测试了涂层的耐腐蚀性能。结果随着微锻造强度的提高,金属沉积体的致密度逐渐增加,当混合粉末中的喷丸颗粒含量高于40%时,可获得孔隙率低于0.3%的高致密度Al涂层。电化学测试及长达1000 h的Na Cl溶液浸泡腐蚀结果显示,高致密度Al涂层包覆后的镁合金表现出与冶金块材铝相当的耐腐蚀性能,比无保护镁合金腐蚀速率降低两个数量级以上;在1000h的盐雾腐蚀后,涂层与基材界面无腐蚀产物生成,表明涂层可完全对腐蚀介质进行物理隔绝。同时,致密铝涂层表面形成了微米级的钝化膜,可进一步提高耐腐蚀性能。结论通过原位微锻造辅助冷喷涂技术,可在较低的气体温度和气体压力条件下在镁合金表面获得完全致密的Al腐蚀防护涂层。该技术还有望用于诸如高导热、高导电涂层的制备,金属构件修复及增材制造等其他对金属沉积体有致密度要求的领域。     

EIS study on 2024‐T3 aluminum alloy corrosion in simulated acid rain under cyclic wet‐dry conditions

The wet‐dry cycle corrosion processes of 2024‐T3 aluminum alloys under different pH environments were investigated using electrochemical impedance (EIS) technique in conjunction with SEM method. The results show that, during the dry period of each cycle, the electrode potential was relatively stable and the corrosion processes can be studied using EIS technique. In the case of pH 3.5 and during the entire corrosion process, the Nyquist plot was composed of a high‐frequency capacitive arc due to corrosion reaction and a low‐frequency capacitive arc due to the formation of corrosion products layer, and the corrosion rate during the same cycle was almost the same. In the case of pH 4.5 and during the first several cycles, the Nyquist plot was composed of nearly only one capacitive arc due to the corrosion reaction, and the corrosion rate during the same cycle increased with time. Additionally, the EIS features of the entire corrosion processes of 2024‐T3 aluminum alloy were interpreted theoretically.     

Corrosion behavior of Fe‐Si metallic coatings added with NiCrAlY in an environment of fuel oil ashes at 700°C

Electrochemical potentiodynamic polarization curves and immersion tests for 300 h at 700°C in a furnace have been used to evaluate the corrosion resistance of Fe‐Si metallic coatings added with up to 50 wt.% of NiCrAIY. The corrosive environment was fuel oil ashes from a steam generator. The composition of fuel oil ashes includes high content of vanadium, sodium and sulfur. The results obtained show that only the addition of 20 wt.% NiCrAlY to the Fe‐Si coating improves its corrosion resistance. The behavior of all tested coatings is explained by the results obtained from the analysis of every coating using electron microscopy and energy dispersive X‐ray analysis.     

Effect of anodizing on galvanic corrosion behavior of T300 CFRP/5083P-O Al bolted joints

T300 carbon fiber reinforced polymer (CFRP) and 5083P-O aluminum (5083P-O Al) alloy bolted joints have been used in high-speed trains due to the advantages of light weight and high strength. However, high potential difference between the CFRP and 5083P-O Al will induce galvanic corrosion and result in accelerating corrosion rate of 5083P-O Al, which is a potential risk for its engineering applications. In this work, combination with the electrochemical analysis, surface and cross-section corrosive morphologies analysis, the galvanic corrosion behavior between CFRP/5083P-O Al bolted joints with and without anodizing in 3.5 wt.% NaCl spray was investigated. Results indicated that severe corrosion occurred on unanodized 5083P-O Al in the coupled regions of the CFRP/5083P-O Al bolted joint due to galvanic corrosion. With the content of sulfuric acid increasing, the thickness of each Al₂O₃ layer and atomic oxygen content increases significantly. 5083P-O Al anodized by the 135 g/L H₂SO₄ + 8 g/L H₃BO₃ mixed solution had the favorable Al₂O₃ film, which increased the resistance of 5083P-O Al by roughly three orders of magnitude, effectively improving the corrosion resistance of 5083P-O Al.     

Effect of nano Al (Scx−1Zrx) precipitates on the mechanical and corrosion behavior of Al‐2.5 Mg alloys

Microanalytical, mechanical, and corrosion studies were undertaken to investigate the effect of nano‐precipitates of Al(Sc_x−1Zr_x) on the mechanical and corrosion characteristics of Al 2.5 alloy containing 0, 0.15, 0.3, 0.6, and 0.9 wt% of Sc with 0.15 wt% Zr. Addition of 0.3% Sc significantly increased the yield strength due to small precipitates sizes (5–19 nm) and the high coherency of the nano‐particles. Largest contributor to the strength was grain boundary strengthening caused by pinning of grain boundary precipitates. The alloys showed a good resistance to corrosion in 3.5 wt% neutral chloride solution. The alloy offered a high passivation tendency because of homogeneous coherent nano Al(Sc_x−1Zr_x) precipitates. The nano precipitates interfaces and homogeneously distributed Al₃Sc precipitates offer a high degree of corrosion resistance to Al 2.5 Mg Sc alloys compared to conventional aluminum alloys, such as Al 6061 and Al6013.     

Evaluation of different sealing methods for anodized aluminum‐silicon carbide (Al/SiC) composites using EIS and SEM techniques

Electrochemical impedance spectroscopy (EIS) and the scanning electron microscope (SEM) have been used in an investigation of the effectiveness of various sealing methods that can be used to improve the corrosion resistance of an anodized aluminum‐silicon carbide (Al/SiC) composite. Anodic oxide films were grown on Al7075‐T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate. Other samples were sealed using the traditional method of boiling water or hot nickel acetate for comparison. The results revealed a uniform anodized layer on Al7075‐T6 that resisted pitting corrosion for more than 2 weeks exposure to NaCl, whereas a cracked oxide film with variations in thickness was observed on the composite material. Pit initiation occurred in less than 5 days on the anodized Al/SiC that was sealed in the hot solutions. This study suggests that the traditional hot sealing methods did not provide sufficient corrosion protection for aluminum metal–matrix composites (MMCs) because the reinforcing SiC particles deteriorated the surface film structure. However, this defective film can be repaired by nickel hydrate precipitation during cold sealing or by applying a thick polyurethane coating.     

Surface treatment of Cf/Al composites with immersion in aqueous solution containing Ce ions for corrosion barrier

In this study, Ce‐rich coating is investigated as corrosion inhibitor of carbon fibers reinforcement aluminum matrix (Cf/Al) composites. The coatings are obtained by immersion in aqueous solution containing Ce(NO₃)₃ onto composite surface, whereas the Ce‐rich coating process produces a coating with highly heterogeneous nature of the surface, but micro‐cracked layer with “dry‐mud” morphology. The coatings were composed of Ce‐rich nano‐particles, Ce‐rich particles with a sphere‐like morphology, which are agglomerated particles with diameter 4 ～ 8 nm and piled up for this coating. TEM observation for Ce conversion coating of the corresponding ring‐like SAED patterns could not be matched to any of the previously reported structures of cerium compounds. Results of high‐resolution XPS spectra of Ce3d obtained for Ce conversion coating show that the Ce3d spectra has several components with binding energies characteristic of Ce³⁺ and Ce⁴⁺. The Ce‐rich coating process produces effective corrosion protecting of Cf/Al composites, which is verified by electrochemical measurement results. The R_t values of coated sample are higher than those of uncoated sample, this confirms the better corrosion resistance of coating obtained after immersion treatment for Cf/Al composites.     

Nanostructured surface pre‐treatment based on self‐assembled molecules for corrosion protection of Alclad 7475‐T761 aluminum alloy

Coatings based on self‐assembled molecules (SAMs) for corrosion protection of aircraft aluminum alloys have been studied to evaluate their potentialities as replacements to yellow chromate conversion coatings (CCC), due to the toxicity of these leading to environmental problems. In this work, the influence of alkane diphosphonates self‐assembling molecules on the corrosion resistance of the AA7475‐T761 cladded with AA7072 was investigated by electrochemical impedance spectroscopy and cathodic and anodic polarization curves, in naturally aerated 0.5 mol/L Na₂SO₄ aqueous solution, with pH adjusted to 4. Corrosion accelerated experiments (salt spray tests) were also carried out to examine the resistance of the SAM treated samples against corrosion. The results suggested that the development of boehmite (aluminum oxide) layer with incorporation of SAM was beneficial to the corrosion resistance of the tested aluminum alloy. Samples surface treated with SAM or aluminum oxide/SAM (without and with subsequent polyester layer) showed better corrosion resistance results than samples with CCC, indicating that this last type of coating containing hexavalent chromium could be replaced by the environmentally friendly pre‐treatment corresponding to boehmite growth followed by incorporation of SAM.     

无铬纳米锌铝涂层的微观组织及腐蚀性能

向无铬锌铝涂层中分别加入3种纳米微粒ZnO,TiO₂和SiO₂制备纳米复合涂层,通过盐水浸泡实验和电化学测试研究其耐蚀性,结合SEM等手段观察纳米复合涂层显微组织及其在盐水中的腐蚀情况,分析纳米微粒在涂层中所起作用。结果表明,3种纳米微粒的加入能够加强涂层的阴极保护作用,并能延缓涂层金属粉末的消耗,较无铬锌铝涂层更易减慢腐蚀速率。其中,纳米SiO₂复合涂层耐蚀性最佳,纳米TiO₂复合涂层略次,ZnO纳米复合涂层耐蚀效果较差,3种纳米复合涂层耐蚀性均优于无铬锌铝涂层。     

Q235上电弧喷涂Zn55Al涂层在3.5wt%溶液中的腐蚀行为研究

本文使用电弧喷涂通过包套挤压+拉拔的方法制备的Zn55Al伪合金丝材成功的在Q235钢上喷涂出了Zn55Al涂层。通过扫描电镜和微区XRD研究了Zn55Al 伪合金丝材的显微结构。通过浸泡腐蚀实验和电化学方法研究了Zn55Al涂层、Zn15Al涂层和 Al涂层的腐蚀行为,并对比了三种涂层之间的差异。结果表明Zn55Al伪合金丝材由纯锌和纯铝组成,在整个成型过程中没有产生合金化。Zn55Al涂层由层片状的富锌相和富铝相组成。经过20天的浸泡实验,Zn55Al涂层形成了一层致密的钝化膜,比其他两种涂层有更好的耐腐蚀性。Zn55Al涂层的自腐蚀电位大约是-1.25v,高于Zn15Al涂层低于纯Al涂层和Q235基体.电偶腐蚀实验表明,Zn55Al涂层比Zn15Al涂层具有更好的点虎穴保护作用。这些结果说明Zn55Al涂层具有更好的耐腐蚀性和可以给Q235基体提供更强的电化学保护.本文也讨论了Zn55Al涂层的的腐蚀机理。     

U上Al，Ti／Al镀层研究

用循环Ar^ 轰击-磁控溅射离子镀（MSIP）法在U表面上镀Al,Ti/Al,并采用俄歇电子能谱仪（AES）、扫描电镜（SEM）、电化学实验和平面磨耗实验，研究了其表面、剖面形貌和耐磨耐蚀性能，以及Al/U和Ti/Al镀层界面。结果表明：U上循环Ar^ 轰击-磁控溅射离子度Al,Ti/Al界面存在较宽的原子共混区，且Ti/Al镀层的耐磨蚀性能明显优于单一磁控溅射离子镀Al层。     

Study on localized corrosion mechanism of 2195 Al‐Li alloy in 4.0% NaCl solution (pH 6.5) using a three‐electrode coupling system

Localized corrosion morphologies of 2195 Al‐Li alloy with various heat treatment in 4.0% NaCl solution (pH 6.5) were investigated, and its corrosion mechanism was studied using a three‐electrode coupling system of α (Al) substituting for the precipitate‐free zone (PFZ), simulated bulk θ′ (Al₂Cu) and T1 (Al₂CuLi). θ′ acts as cathodic zone in the alloy. At the initial stage, T1 phase is active with respect to θ′ and α (Al), and endures the main anodic current, indicating that anodic dissolution occurs on T1. However, its potential moves to positive direction with immersion time, due to dealloying of Li from T1. As a result, the main anodic dissolution occurs on α (Al) at a later stage. At this stage, as only T1 and α (Al) are coupled, T1 is cathodic to α (Al). In real 2195 alloy, T1 phase is very tiny, and anodic dissolution of T1 and PFZ occurs alternately. These results show that its intergranular corrosion or intersubgranular corrosion is caused by alternate anodic dissolution of T1 phase and PFZ along grain and subgrain boundaries.     

铝合金上电弧离子镀(Ti,Al)N膜的腐蚀特性

研究铝合金上电弧离子镀(Ti,Al)N膜层的腐蚀性能。通过对3种N2气分压下沉积膜层的阳极极化曲线、电化学阻抗谱、盐雾腐蚀失重曲线以及表面形貌的分析表明:沉积过程氮分压较低时,膜层中含有富金属相,耐腐蚀性能较低;增加氮分压使膜层中金属与非金属呈理想配比时,膜层的耐腐蚀性明显增加;膜层在缺陷处产生点蚀、电偶腐蚀,并通过形成裂纹、碎屑脱落使质量显著减小。