Effective corrosion protection of AA6061 aluminum alloy by sputtered Al-Ce coatings

Al-Ce coatings were deposited on silicon and AA6061 aluminum alloy substrates by DC magnetron sputtering using aluminum in combination with pure cerium targets. The materials were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electrochemical impedance spectroscopy (EIS) in order to consider their application as high corrosion resistance coatings. The corrosion behavior of the films was studied using a NaCl aqueous solution (3.5 wt%). As for the characterization results, an apparent amorphous phase of aluminum oxide with small cerium compounds embedded in the matrix was detected by the X-ray diffraction patterns and HRTEM on the deposited films at 200 W and 4 Pa. At these conditions, AFM and SEM images evidenced crack-free coatings with low-roughness nanometric structures and columnar growth. EIS and Tafel results converged to indicate an inhibition of the corrosion reactions. The film displayed good stability in the aggressive medium and after 1 day of exposure underwent very little degradation. The variations in the impedance and Tafel characteristics were found to occur as a function of cerium content, which provokes important changes in the film protective properties.     

LY12铝合金表面钒–钛复合转化膜的制备与耐蚀性研究

为解决单一钒酸盐转化膜表面因存在裂纹而耐蚀性不佳的问题,采用由硫酸氧钛(Ti OSO4)、偏钒酸钠(Na VO3)组成的转化液,在LY12铝合金表面制备出钒–钛复合转化膜。通过中性盐雾(NSS)测试讨论了Ti OSO4和Na VO3质量浓度、时间、温度、p H等工艺条件对转化膜耐蚀性的影响,并通过单因素试验得到了最佳转化条件:Ti OSO4 0.5 g/L,Na VO3 0.4 g/L,p H 4.0,温度25°C,转化时间10 min。用扫描电镜和能谱分析了转化膜的表面形貌及元素组成。结果表明,由O、Ti、V、Al、Mg等元素组成的钒–钛复合转化膜无裂纹。LY12铝合金经转化处理后,在3.5%Na Cl溶液中的腐蚀电位较转化前正移56 m V,腐蚀电流密度减小约1/5,耐盐雾时间达到91 h,耐蚀性得到显著提高。     

铝合金上低温钛锆转化膜快速成膜工艺

采用正交试验和单因素试验研究了在6063铝合金上低温快速制备钛锆转化膜的工艺,得到的最佳转化液配方为:H₂TiF₆2.0 g/L,H₂ZrF₆ 0.8 g/L,氧化剂(偏钒酸钠)3.0 g/L,配位剂(单宁酸)4.0 g/L,pH=3.2。X射线光电子能谱的分析结果显示,膜层的主要组分为金属氧化物(Al₂O₃、VO₂、V₂O₅、ZrO₂、TiO₂)、金属氟化物(AlF₃、ZrF₄)及金属有机配位化合物。不同低温条件下工艺的最佳成膜时间为:5℃,300～350 s;10℃,150～200 s;15℃,100～150 s;20℃,60～120 s。     

氯离子对6063铝合金铈-锰转化膜耐蚀性的影响

在Ce-Mn稀土钝化液中添加Cl-作为促进剂,以6063铝合金为基体制备了Ce-Mn转化膜。分别采用扫描电镜(SEM)和能谱仪(EDS)研究了转化膜的表面形貌及元素组成,并采用硫酸铜点滴腐蚀实验、动电位极化曲线以及电化学阻抗谱(EIS)研究了Ce-Mn转化膜的耐蚀性。结果表明,Ce-Mn转化膜主要由Ce、Mn、O等元素组成,往稀土钝化液中添加Cl-可使膜层更平整、致密,转化膜的平均耐点滴时间从50s提高至100s,在NaCl质量分数为3.5%的腐蚀介质中的腐蚀电流密度明显降低,转化膜极化电阻增大,铝合金的耐蚀性显著提高。     

Development of a solar reflector coating on AA6061 alloy by plasma electrolytic oxidation

Journal of Applied Electrochemistry - A spacecraft consists of various components which will function with maximum efficiency only when their operating temperature is maintained within certain...     

铝合金无铬化学转化膜工艺研究

以单宁酸和氟钛酸盐为主体原料,加入硝酸铜,在铝合金表面形成化学转化膜,以硫酸铜点滴试验为依据,通过单因素实验优化了铝合金非铬转化膜工艺条件:乙二胺四乙酸二钠0.5 g/L,氟钛酸钾1.0 g/L,氟硼酸铵0.25 g/L,单宁酸0.8 g/L,马日夫盐0.5 g/L,A液(含Cu(NO3)2·3H2O和氟钛酸)25 m L/L,化学转化液的p H 2.5~3.5,温度35°C,浸渍时间15 min。该工艺可在铝合金表面形成完整致密的金黄色非晶态化学转化膜,硫酸铜点滴时间达到6 min,具有较好的抗蚀性能。     

Influence of buffering on the spontaneous deposition of cerium conversion coatings for corrosion protection of AA2024-T3 aluminum alloy

Cerium-based conversion coatings were spontaneously deposited on AA2024-T3 alloy at 60 °C using buffered and non-buffered CeCl₃ solutions in the presence of H₂O₂. Malonic acid or amino-acetic acid (glycine) was used as buffering additives. The deposition process and the properties of the coatings obtained were followed by linear voltammetry and electrochemical impedance spectroscopy. The surface morphology was studied by scanning electron microscopy. It was found that buffering complicates the conversion process and hampers the deposition rate. The coatings deposited using buffered baths had lower barrier ability and corrosion durability in 3.5 % NaCl corrosive medium compared to those deposited in the absence of buffers.     

新型铝合金三价铬复合转化膜工艺研究

为克服非六价铬铝合金转化膜耐蚀性能不佳的问题,以Cr(NO_3)_3·9H_2O、Na_2MoO_4·2H_2O、NaH_2PO_4·2H_2O为主要成膜物质,采用单因素法对转化液组分及转化条件进行优化,在5052铝合金表面制备三价铬复合转化膜。利用扫描电镜、能谱仪分析了复合膜的形貌及成分,并通过硫酸铜点滴试验、中性盐雾试验和动电位极化曲线测量研究其耐蚀性能。结果显示:以15 g/L Cr(NO_3)_3·9H_2O、10 g/L Na_2MoO_4 2H_2O、10 g/L NaH_2PO_4·2H_2O、0.15 g/L NH_4HF_2组成转化液,在pH为3.3、温度为40℃的条件下反应10 min,所得复合膜的耐蚀性较佳。该复合膜由Cr、Mo、P、O、Al、Mg等元素组成,在3.5%Nacl溶液中的腐蚀电位较基体正移了196 mV,腐蚀电流密度远小于基体。经此钝化液处理的样品在中性盐雾试验168 h后才发生点蚀。     

HMMM cured corrosion resistance waterborne ormosil coating for aluminum alloy

Due to the exceptional advantages of sol–gel process, organically modified silane (ormosil) coating has been applied to study the corrosion protection of aluminum alloy. In the present work, GPTMS/MTMS sol–gel solution was prepared by hydrolysis and condensation of 3-glycidoxypropyltrimetoxysilane (GPTMS) and methyltrimethoxysilane (MTMS) in aqueous solution of 0.05 M acetic acid in molar ratios 3:1. To prepare the ormosil coating solutions, a crosslinking agent hexamethoxymethylmelamine (HMMM) and a blocked acid catalyst p-toluenesulphonic (p-TSA) were combined with the sol–gel solution. Aluminum substrates were dip coated and cured at 130 °C for 45 min. Effectiveness of HMMM as a crosslinking agent was analyzed by evaluating corrosion resistance, chemical resistance and hydrophobicity of coating using potentiodynamic polarization method, immersion test and water contact angle, respectively. UV stability of sol–gel solution, ormosil coating formulation and coated substrate was also studied using UV–vis spectroscopy and UV-weatherometer to see performance of coating in outdoor application. Thermal behavior of ormosil was characterized using TGA and DSC. Surface morphology and structural characteristics were also characterized using SEM, AFM and FT-IR-RAS (reflection absorption spectroscopy). Pencil hardness, impact test and bend test were carried out to determine the adhesion, hardness and flexibility of coating.     

The influence of EDTA-2Na on microstructure and corrosion resistance of PEO coating for AA1060 alloy

In this study, plasma electrolytic oxidation (PEO) process was applied to AA1060 aluminum alloy in an alkaline-based electrolyte with different concentrations of EDTA-2Na. The investigation of coatings was concentrated on sparks, phase, structure, morphology, and corrosion resistance. The whole process presented a “soft spark” regime which proved by the reduction of light and acoustic emission with increase of current. The results of SEM and EDS showed that more discharge channels were found under surface and the proportion of silicon in the inner layer increased for the sample treated in solution with 5 g/L EDTA-2Na, which was attributed to D type discharge causing some light emission invisible on sample surface. The polarization test presented a better corrosion resistance with the increase of EDTA-2Na. However, EIS measurement showed a bigger corrosion resistance for outer layer of sample prepared with the addition concentration up to 3 g/L that meant outer layer played a more critical role in terms of corrosion resistance.     

变形铝合金表面锆基化学转化膜的研究现状

化学转化膜是金属表面主要的处理方法之一,具备良好的附着力和耐蚀性,能为铝合金提供一定的临时防护。传统的六价铬酸盐化学转化膜在日渐严苛的环保压力下已经逐渐淘汰,取而代之的是近几年发展迅猛的三价铬及无铬锆基化学转化膜。铝合金可分为铸造铝合金和变形铝合金,按照所含主要合金元素和热处理状态可分为若干个系列和型号。本文选取几种典型的变形铝合金,综述了不同铝合金微观组织对转化膜成膜过程的影响,化学转化液添加剂、预处理和后处理工艺对转化膜性能的调控及作用机理,以及几种典型商业钝化剂在变形铝合金表面的应用。总结了目前变形铝合金表面锆基化学转化膜仍面临的问题和发展趋势,未来化学转化膜需在满足新型铝合金发展要求的基础上,通过不同有机、无机添加剂以及外场作用对转化膜的成膜均一性、完整性进行调控,以提高转化膜的综合性能。     

Wear behavior of silicone rubber/carbon black coatings on 6061 aluminum alloy surfaces

In this paper, the effects of structural and process variables on wear resistance of silicone rubber/carbon black coatings on 6061 aluminum alloy surfaces are studied. Testing parameters have been optimized for maximum wear resistance based on taguchi orthogonal design with six important parameters, viz. polydimethylsiloxane (PDMS) molecular weight, oxime/OH ratio, catalyst weight percent, pigment weight percent, surface preparation method and adhesion promoter type. The analysis of variance showed that the wear resistance strongly depends on oxime/OH ratio and catalyst weight percent. PDMS molecular weight and pigment weight percent also have intermediate effects. Neither the surface preparation method nor adhesion promoter type had any effects on wear resistance in this study. The optimum sample was prepared according to the best levels of each factor and the wear resistance in optimum conditions was reasonably in agreement with the experimental data. Scanning electron microscopy analysis of wear surface and debris showed two mechanisms: cohesive wear with fatigue mechanism and interfacial wear with adhesion mechanism.     

Improvement in corrosion resistance of micro-arc oxidation coating on PVD Ti-coated aluminum alloy 7075

Surface treatments are always needed to enhance corrosion-resistant performance of aluminum (Al) alloys when they are used in seawater environments. The paper aimed to prepare the composite oxide ceramic coating on Al alloy 7075 by combining micro-arc oxidation (MAO) and magnetron sputtering technology. The Al substrate was precoated with titanium (Ti) layer by using the magnetron sputtering technology and then treated by MAO in the alkaline aluminate electrolyte, resulting in a composite MAO coating, which is composed of Al₂O₃ and TiO₂ along with the complex oxide (Al₂TiO₅). The potentiodynamic polarization and electrochemical impedance spectroscopy were carried out to evaluate the corrosion performance of the MAO coatings in 3.5 wt% NaCl solution. Better corrosion resistance was observed for composite oxide coating than the reference MAO coating on the bare Al, as evidenced by the higher corrosion potential of −0.664 V versus Ag/AgCl and the lower corrosion current density of 4.41 × 10^-6 A/cm².     

The kinetics and mechanisms of filiform corrosion on aluminium alloy AA6111

Scanning Kelvin Probe (SKP) potentiometry is used to investigate the effect of surface abrasion and heat treatment on the open-circuit potential (OCP) of AA6111 in humid air. SKP is also used to follow the kinetics of filiform corrosion (FFC) and to determine characteristic potentials associated with FFC filaments. Simply abrading with 180 grit SiC produces a near surface deformed layer (NSDL) with OCP >0.2 V lower than the bulk alloy. When the abraded sample is overcoated with a 30 μm layer of PVB (polyvinyl butyral) and exposed to HCl a fast, superficial, surface-active FFC is observed in which metal loss is limited to the thickness of the NSDL (approximately 2 μm). Filiform head OCP values are similar to that of the NSDL and filiform tail OCP values are similar to the bulk. A mechanism is proposed in which the ultra-fine grain structure of the NSDL produces an anodic activation, and the potential difference between the NSDL and the bulk provides an increased driving force for corrosion. When the NSDL has been removed through surface-active FFC or by caustic etching, a slower, deeper, successive-pitting form of FFC affects the bulk alloy. The rates of both surface-active and successive-pitting FFC reach a maximum after post-abrasion heat treatment at 180 °C.     

Electrochemical synthesis of poly(o-anisidine) and its corrosion studies as a coating on aluminum alloy 3105

The synthesis of poly(o-anisidine) coatings on aluminum alloy 3105 (AA3105) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by reflection absorption infrared (RAIR) spectroscopy, UV–visible absorption spectrometry and scanning electron microscopy (SEM). Optical absorption spectroscopy reveals the formation of the emeraldine form of poly(o-anisidine). The anticorrosion performances of poly(o-anisidine) coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarization technique Tafle and electrochemical impedance spectroscopy (EIS). The corrosion rate of poly(o-anisidine)-coated AA3105 was found ∼330 times lower than bare AA3105 and potential corrosion increases from −0.85 V versus SCE for uncoated AA3105 to −0.65 V versus SCE for poly(o-anisidine)-coated AA3105 electrodes. The results of this study clearly ascertain that the poly(o-anisidine) has outstanding potential to protect the AA3105 against corrosion in a chloride environment.     

Erosion corrosion control of 6061 aluminum alloy in multi-phase jet impingement conditions with eco-friendly green inhibitor

Erosion corrosion performance of 6061 aluminum alloy in simulated sea water slurry was investigated under multi-phase jet impingement conditions. The main objective of the work is to study erosion–corrosion of a material with engineering application and mitigate it using eco-friendly green inhibitor. Experiments were performed with the sand concentration of 0.3% and 0.3 μm size. The effect of temperature and flow rate on the performance of inhibitor was explored. Electrochemical methods were adopted for erosion-corrosion measurements. Experiments revealed that starch could mitigate erosion-corrosion with a maximum reduction efficiency of 58% at temperature of 303 K and flow rate of 4 L·min~(–1). Inhibition efficiency decreased with increase in flowrate and temperature. EIS spectrum demonstrated that the corrosion process in the presence on inhibitor was both charge transfer and mass transfer controlled. A key role of hydrodynamics in the performance of corrosion inhibitor was confirmed by the present study.     

硫酸铈改性磷酸–硫酸铝合金阳极氧化膜耐腐蚀性研究

研究了稀土盐硫酸铈改性磷酸–硫酸阳极氧化处理对2A50铝合金表面耐腐蚀性能的影响。通过滴碱试验和铜加速乙酸盐雾(CASS)试验对改性前后阳极氧化膜的耐蚀性进行了研究,采用扫描电镜观察了不同阳极氧化膜的表面和截面形貌,测试了氧化膜的厚度,并对铈盐改性后的氧化膜进行了能谱分析,探讨了铈盐的作用机理。结果表明,稀土改性后得到的阳极氧化膜上孔分布均匀,孔隙率较高,其组成为Al2O3,氧化膜厚度由改性前的4.2μm提高到改性后的49.2μm,滴碱时间由35.9 s提高到186.9 s,CASS试验24、72和168 h的腐蚀评级分别由9、7和5级提高到10、9和8级。认为稀土盐的加入使氧化膜多孔层生长速率加快,阻挡层厚度增加,多孔部分结构更致密,从而提高了铝合金阳极氧化膜的耐蚀性能。     

Effect of graphene on the microstructure and corrosion resistance of PEO coating formed on D16T aluminum alloy

Incorporated graphene coating was successfully prepared on D16T aluminum alloy by plasma electrolytic oxidation (PEO) technology, and the effect of graphene on the microstructure, corrosion resistance, and wettability of the coating was investigated. Microstructure, composition, and morphology were studied by transmission electron microscope, confirming that graphene was successfully incorporated into the coating with pancake-like and embedded mode. The thickness and microhardness of the coating with graphene (G2) increased, whereas roughness and porosity reduced due to the incorporation of graphene, compared to the coating without graphene (G0). The resistive arc radius of G2 is obviously increased. The real impedance value of G2 is four times than that of G0. The resistance (R₁) of G0 and G2 are 3708 and 7533 Ω cm², respectively. The resistance (R₂) of G0 and G2 are 2.508E5 and 7.752E5 Ω cm², respectively. The contact angle of G2 under three liquid droplets was maximum, showing minimal surface-free energy (36.8 mJ/m²). Formation water showed the most obvious effect on the wettability of the coating compared to the distilled water and sodium chloride solution. Results verified that graphene in PEO coating significantly improved the microstructure of the coating and enhanced the hydrophobic performance and corrosion resistance of the coating.     

Comparison of single and multilayer coatings based on ormosil and conversion layers for aluminum alloy corrosion inhibition

Corrosion resistance behavior of single and multilayer coatings based on ormosil, trivalent chromium conversion coating (tccc) and hexavalent chromium conversion coatings (hccc) on the surface of 2024-T3 aluminum alloy (AA) was investigated using potentiodynamic polarization curves and accelerated salt spray testing. The magnitude of the corrosion resistance for single layer coatings increased tccc < ormosil < hccc. Multilayer ormosil/ormosil coatings are subject to phase separation, leading to poor performance in the electrochemical and accelerated salt spray testing. The presence of either hccc or tccc in the multilayer film was found to augment the inherent corrosion resistance of the ormosil barrier film. Multilayer coatings composed of either tccc/ormosil or hccc/ormosil were found to exhibit R_corr values in the range 158–177 kΘcm². This implies that the environmentally-benign and nontoxic trivalent chromium conversion coating used in combination with an ormosil film may be a potential alternative for hexavalent chromium conversion coatings. Environmental Institute, 003, Life Science East, Stillwater, OK 74078.     

Preparation of a thick sponge-like structured amorphous silica ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in TEOS solution

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si₃N₄ friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10⁻⁵A·cm⁻² to 1.239 × 10⁻⁷A·cm⁻², while extending the passivation region from 0.322 V to 1.032 V.