Improving corrosion resistance of aluminium metal matrix composites using cerium sealed electroless Ni–P coatings

Abstract

A conversion coating treatment using cerium salts was developed for the surface sealing of electroless nickel–phosphorus (Ni–P) coatings on carbon fibre reinforced aluminium (Cf/Al) composites. The corrosion resistances of uncoated and coated materials (i.e. the Ni–P coating, the Ce conversion coating and Ce sealed Ni–P coatings) were evaluated in 3·5 wt-%NaCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy. Ce sealed Ni–P coating showed the highest corrosion resistance and clearly improved the overall corrosion resistance of Cf/Al composites. Thus, the Ce sealed Ni–P coating had no obvious microcracks that were generally evident in the more conventional Ce conversion coatings. This is presumed to occur because the electroless nickel surface is relatively homogeneous, compared with the Cf/Al composite surface on which different local coating thicknesses would encourage increased microcrack formation. X-ray photoelectron spectroscopy analysis showed that the Ce conversion coating mainly contained both Ce³⁺ and Ce⁴⁺ species; however, Ce⁴⁺ species were the dominant oxidation state on Ce sealed Ni–P coatings.     

Preparation and corrosion resistance of titanium–zirconium–cerium based conversion coating on 6061 aluminum alloy

This paper aims to develop a chromium-free chemical conversion coating with good corrosion resistance. A novel chemical conversion coating was prepared on 6061 aluminum alloy by dipping in the treatment solution containing titanium/zirconium based-ions and sodium metaphosphate and cerium nitrate hexahydrate as additives. The morphology and composition of the conversion coatings were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The microarea structure of conversion coatings at different formation stages was analyzed by electron probe microanalyzer. The electrochemical polarization curve revealed that the corrosion potential of the conversion coating was −0.577 V and the corrosion current density was 0.1148 μA/cm². The equivalent circuit fitted by AC impedance showed that the film resistance reaches 68,140 Ω. The formation of coating preferentially grows on the Al (Fe) Si intermetallic to form oxides of Ti and Zr; then TiO₂ formed by a higher concentration of Ti⁴⁺ gradually covered ZrO₂. Ce³⁺ could adsorb on the intermetallic compound, the hydrolysis of which causes the local pH of the solution to decrease and promotes the aluminum alloy dissolved.     

A vanadium-based conversion coating as chromate replacement for electrogalvanized steel substrates

The vanadium conversion coating as chromate replacement was prepared on electrogalvanized steel (EG) plates previously treated in a solution mainly composed of vanadate. Corrosion behavior of these EG plates in contact with 3.5% NaCl solution was investigated using potentio-dynamic measurement and electrochemical impedance spectroscopy (EIS) measurement. The morphology and composition of the vanadium conversion coating were studied using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in conjunction with argon-ion sputtering. According to the results, the V-treated EG plate shows the best corrosion protection property compared with the untreated and Cr-treated EG plates. The vanadium-rich coating is composed of the closely packed particles. The coating mainly consists of vanadium and oxygen, which mainly exist as V₂O₅, VO₂, and its hydrates such as V₂O₅·nH₂O, VO(OH)₂.     

Pulse electroplating of Ni-W-P coating and its anti-corrosion performance

Ni-W-P coatings were electrodeposited on copper substrates by pulse electroplating. Effects of electrolyte pH (1-3), temperature (40–80 °C), average current density (1–7 A/dm²) and pulse frequency (200–1000 Hz) on deposition rate, structure and corrosion resistance performance of Ni-W-P coatings were studied by single factor method. Surface morphology, crystallographic structure and composition of Ni-W-P coatings were investigated by means of scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy, respectively. Corrosion resistance performances of Ni-W-P coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution (mass fraction) and soil-containing solution. It was found that the pulse electroplated Ni-W-P coatings have superior corrosion resistance performance and the electroplating parameters significantly affect the structure and corrosion resistance performance of Ni-W-P coatings. The optimized parameters of pulse electroplating Ni-W-P coatings were as follows: pH 2.0, temperature 60 °C, average current density 4 A/dm², and pulse frequency 600 Hz. The Ni-W-P coating prepared under the optimized parameters has superior corrosion resistance (276.8 kΩ) and compact surface without any noticeable defect.     

Effect of gelatin additions on the corrosion resistance of cerium based conversion coatings spray deposited on Al 2024-T3

The corrosion resistance of cerium based conversion coatings on Al 2024-T3 was improved by the addition of a water soluble gelatin to the coating solution. Auger electron spectroscopy depth profiling showed that coatings deposited from solutions containing 800-3200 ppm gelatin were ~ 400 nm thick, while coatings deposited from solutions with 0-200 ppm gelatin were ~ 850 nm thick. The thinner coatings exhibited reduced surface cracking and spalling. Open circuit potential measurements during deposition showed that adding gelatin to the coating solution resulted in a more negative and stable potential with increasing gelatin concentrations. Visually, increasing gelatin concentrations promoted the formation of stable bubbles that covered panel surfaces, which limited transport of cerium species to the surface and decreased the deposition rate. X-ray diffraction analysis revealed that only coatings deposited from solutions containing 400-3200 ppm gelatin could be converted to CePO₄H₂O during post-treatment, potentially improving the corrosion resistance compared to coatings deposited from solutions without gelatin.     

Corrosion resistance of the electro-galvanized steel treated in a titanium conversion solution

The conversion coating can be obtained by using a solution containing titanium tetrachloride, fluorosilicate acid and nitric acid. The results of X-ray photoelectron spectroscopy (XPS) showed that the titanium conversion coating consisted of ZnO, TiO₂ and Zn₄Si₂O₇(OH)₂. The formation process of the titanium conversion coating was studied. Effects of the immersion time, pH value and solution temperature on the corrosion resistance and the chemical composition of the titanium conversion coating were investigated by the salt spray test (SST) and XPS, respectively. The results of XPS and SST showed that the titanium conversion coating displayed better corrosion resistance with higher contents of Si and Ti. Results of corrosion tests (the salt spray and electrochemical test) indicate that the corrosion resistance of the conversion coating by titanium solution is better than that of the conversion coating using the traditional chromate solution.     

镁锂合金表面锌锰磷化膜的制备与性能表征

采用化学转化法在镁锂合金表面制备了外观深灰色、结构均匀致密、耐蚀性能良好的锌锰磷酸盐转化膜,并研究了磷化温度对磷化膜性能的影响。采用扫描电子显微镜(SEM)、能谱(EDS)仪、X射线光电子能谱(XPS)和X射线衍射(XRD)仪对膜层的表面形貌、化学组成及结构进行了表征。采用动电位极化曲线、电化学交流阻抗(EIS)和腐蚀失重实验对磷化膜的耐蚀性进行了研究。结果表明,锌锰磷化膜主要由Zn、Zn3(PO4)2、MnHPO4、Mn3(PO4)2组成。锌锰磷酸化膜起到了保护镁锂合金的作用,提高了镁锂合金的耐蚀性,当磷化温度为45℃时,磷化膜的腐蚀电流密度最低,腐蚀速率最小,耐蚀性能最好。     

Anticorrosive performance of epoxy/clay nanocomposites pretreated by hexafluorozirconic acid based conversion coating on St12

Abstract

In this research, epoxy composites were prepared using different loadings (0.5, 0.8, 1, 2 and 3 wt-%) of clay nanoparticles. Fourier transform infrared spectroscopy was utilised to investigate the curing behaviour of epoxy resin. The quality of dispersion and the distribution structure of nanoclays in coating were studied by visual observations and X-ray diffraction in detail. Corrosion resistance behaviour of epoxy coating containing various clay percentages was investigated on steel by electrochemical impedance spectroscopy. Moreover, the modification of substrate was accomplished using conversion coating based on hexafluorozirconic acid. The electrochemical results revealed that the pretreated coating with 3 wt-% nanoclays possesses the best anticorrosive performance (2.5×10⁸ Ω cm²) after 2 weeks immersion in 3.5 wt-%NaCl solution. The morphological properties of conversion coating were observed by a field emission scanning electron microscope. In addition, pull-off technique was employed to measure the adhesion strength of coatings to metallic substrate. Experimental results exhibited that optimum clay loadings and conversion coating impressively increased the corrosion resistance and coating adhesion as well.     

镁锂合金表面高锰酸盐转化膜的研究

采用化学转化法在镁锂合金表面制得了结构致密、耐蚀性能较好的高锰酸盐转化膜,研究了转化液中高锰酸盐溶液浓度对成膜效果的影响.实验采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和X射线光电子能谱(XPS)对所制得转化膜的表面形貌、结构和组成进行了测试.同时,使用动电位极化曲线、电化学交流阻抗谱和腐蚀失重3种方法对镁锂合金及其转化膜的耐腐蚀性能进行了深入研究.结果表明:高锰酸盐转化膜较均匀、平整,间隙较小,转化膜主要由锰的氧化物组成.提高了镁锂合金的耐腐蚀性能,当高锰酸盐溶液浓度为4.0 g/L时,转化膜的腐蚀电流密度小、容抗弧大、腐蚀速率低,耐腐蚀性能佳.     

Ecologically green conversion coating for zinc–cobalt alloy

Abstract

A phytic acid based conversion coating has been designed for Zn–Co alloys. The morphology of this coating was studied by SEM and showed that immersion of coatings for 15 min is smooth and compact. The composition of conversion coatings was analysed by X-ray photoelectron spectroscopy. The analysis data showed that the coating is composed of Zn, C, P, N and O. The presence of Co in the coating was not established. Corrosion protection provided by this coating was evaluated by electrochemical measurements (polarisation curves, electrochemical impedance spectroscopy) in a 0·5M NaCl solution. Electrochemical corrosion measurement showed that the corrosion resistance of the Zn–Co alloy has been improved by the conversion treatment with phytic acid.     

A study of conversion coatings on vanadium/galvanic zinc

The protective ability and corrosion resistance of conversion coatings on vanadium/galvanic zinc were assessed with chemical and electrochemical approaches. The conversion coatings were shown to possess high protective properties and corrosion resistance in a 3% NaCl solution. FT-IR and X-ray analysis data indicate that the conversion coatings on vanadium/galvanic zinc are complex systems consisting of ZnO and V₂O₅ oxides, as well as phosphorus-containing zinc and vanadium compounds, V(HPO₄)₂, Zn₃(PO₄)₂, and Zn(VO₃)₂, which are resistant throughout 13–19 h in a salt-spray chamber until the appearance of the first symptoms of white zinc corrosion.     

Molybdate based conversion coatings for zinc and zinc alloy surfaces: a review

Abstract

The replacement of chromate conversion coatings for Zn surfaces has been necessitated by industry due to the toxicity issues associated with Cr(VI) and the enforcement of 'WEEE' and 'ELV' directives by the European Union. Molybdate conversion coatings have been investigated by many researchers as possible 'non-chromate' alternatives due to their low toxicity. A significant amount of work has been undertaken in this area in the past 20 years and this review tries to bring together findings from this work. Although a direct replacement for Cr(VI) conversion coatings using molybdates does not appear to have been found, limited success has been gained with the addition of synergistic chemical species such as PO₄^3? and Al³⁺. Immersion time, pH, temperature and additives have been investigated by many researchers and the effects of these on molybdate systems have been contrasted. X-ray photoelectron spectroscopy characterisation data are included and shows coatings to contain Mo in the +2, +4, +5 and +6 oxidation states. ASTM B-117 neutral salt spray corrosion data suggests that the best performance of molybdate based coatings is around 24 h without white rust on electroplated Zn surfaces. Molybdate treatments on Zn–Ni alloy surfaces have given times to white rust of up to 360 h. In conclusion, the outlook for molybdate based conversion coatings on Zn surfaces is a promising one; with synergistic additions giving increased efficacy in corrosion tests.     

Characterization of calcium-modified zinc phosphate conversion coatings and their influences on corrosion resistance of AZ31 alloy

Two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc-calcium phosphate coating, were prepared on the surface of AZ31 alloy in phosphate baths. The morphologies of these coatings were observed using scanning electron microscopy. Their chemical compositions and structures were characterized using energy-dispersive X-ray spectrum, X-ray photoelectron spectroscopy and X-ray diffraction. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization technique. The results show that the flowerlike Zn-Ca phosphate conversion coatings are mainly composed of hopeite (Zn₃(PO₄)₂·4H₂O). They have a quite different morphology from the dry-riverbed-like Zn phosphate coatings that consist of MgO, MgF₂, Zn or ZnO and hopeite. Both of the zinc and zinc-calcium phosphate coatings can remarkably reduce the corrosion current density of the substrates. The Zn-Ca coating exhibits better corrosion resistance than the Zn coating. Introduction of calcium into the phosphate baths leads to the full crystallinity of the Zn-Ca coating.     

Effect of Cr3+- based conversion films on the corrosion behaviour of electrodeposited composite ternary zinc alloys with embedded carbon nanotubes

ABSTRACT

Composite ternary zinc-based alloys Zn-Ni-P and Zn-Fe-P containing embedded multi-walled carbon nanotubes (CNT) were obtained electrochemically. They were treated additionally in an environmentally friendly chemical conversion solution for passivation based on Cr³⁺-compound. The surface morphology, chemical and phase composition of the coatings after their treatment in the passivating solution were determined by SEM, EDS and XRD analysis respectively. The corrosion behaviour of composite alloy deposits both with or without additional conversion film (CF) was investigated in a model corrosion medium of 5% NaCl using selected methods such as potentodynamic polarisation (PD) curves, electrochemical impedance spectroscopy (EIS) and polarisation resistance (R_p) measurements. The changes in the surface morphology and phase composition of the corrosion tested samples were determined by SEM and XRD analysis. The corrosion studies indicated that the presence of a CF leads to a delay in the anodic dissolution process during the polarisation.     

Electrodeposition and Corrosion Properties of Zn-V2O5 Composite Coatings

Composite coatings were obtained by electrochemical codeposition of V₂O₅ nanoparticles with zinc, from an additive free acid sulfate bath. The corrosion behavior of electrodeposited Zn and Zn-V₂O₅ composite coatings was investigated in 3.5% NaCl solution using polarization and electrochemical impedance spectroscopy (EIS). The decrease in I _corr values and an increase in R _ct values show the higher corrosion resistant nature of Zn-V₂O₅ coatings. The observed textural modifications of composite coatings are associated with the specific structural modification of Zn crystallites provoked by the adsorption-desorption phenomena occurring on the metal surface, induced by the presence of V₂O₅ nanoparticles. It has been observed that the presence of V₂O₅ nanoparticles favors the [1 0 2] and [1 1 2] texture of zinc matrix. Moreover, the codeposition of V₂O₅ nanoparticles with zinc was found to be favored at pH 3.5 and applied current density 4?A?dm^?2. A considerable grain refinement of the deposit occurred due to incorporation of V₂O₅ nanoparticles and hence improved the preferred orientation of the zinc crystallites.     

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.     

Ni/Cu定向结构涂层在不同浓度H2SO4中的耐蚀性能

为了研究Cu元素对Ni基合金定向结构涂层耐腐蚀性能的影响,向Ni60合金粉末中添加了5%Cu(质量分数,下同),制备了定向结构Ni60/Cu复合涂层。采用电化学试验和浸泡试验,评估了涂层在不同浓度H₂SO₄溶液中的电化学腐蚀特性和浸泡腐蚀性能,探讨了涂层在不同浓度H₂SO₄溶液中的腐蚀行为。结果表明,涂层在不同浓度H₂SO₄溶液中的腐蚀均表现为活化-钝化-过钝化的过程,电化学阻抗谱在整个时间常数内具有典型的容抗特征,H₂SO₄溶液浓度从5%增至80%时,电荷转移电阻先减小后增大,涂层的耐腐蚀性呈现先降低后升高的趋势。随着H₂SO₄溶液浓度的增加,涂层表面的腐蚀程度先加剧后逐渐减缓,且在H₂SO₄溶液浓度为40%时,腐蚀电位移至最负,腐蚀电流密度增至最大。但在H₂SO₄溶液浓度达到80...     

Effect on Corrosion Resistance of Ce-Rich-Sealed Ni-P Coatings on Cf/Al Composite Surface

In this study, Ni-P coatings and sealing of the coatings by Ce-rich solution on Cf/Al composite surface for enhanced corrosion resistance are investigated. The corrosion resistance of uncoating sample in 3.5 wt.% NaCl solution was investigated and a comparison with Ni-P and Ce-sealed Ni-P coatings is given. Effect of Ce-sealing on Ni-P coating is discussed. The results of electrochemical measurements of corrosion performance of Cf/Al composites show that sealing of Ni-P coatings with Ce-rich solution can improve the corrosion resistance. The Ce-rich-sealed Ni-P coating has higher corrosion resistance than the coating without Ce, and the electroless plated Ni-P coating on composite surface has higher corrosion resistance than the bare sample, as evidenced by EIS and potentiodynamic polarization measurements. The microstructure of the Cf/Al composites and the two kinds of coatings (i.e., Ni-P coating and Ce-sealed Ni-P coating) were examined by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. The Ce-sealed Ni-P coatings on Cf/Al composite surface have a total thickness of ~11 μm of which 10 μm is the thickness of the Ni-P coating and ~1 μm is the thickness of the Ce-rich sealing. It shows that the selected area electron diffraction ring pattern of Ce-rich sealing on Ni-P plated composite is consistent with Ce₆O₁₁ or CeO₂. X-ray photoelectron spectroscopy results show that Ce⁴⁺ was the dominant oxidation state for Ce-rich sealing on Ni-P plated composite. The Ce-sealing treatment on Ni-P coating has improved the corrosion resistance over and above the corrosion resistance offered by the Ni-P mono-coating to the bare substrate.     

Influence of drying temperature on the corrosion performance of chromate coatings on galvanized steel

The influence of drying temperature on the corrosion performance of chromate coatings on electro‐galvanized (EG) steel has been investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements in 3.5% NaCl solutions. The chromate coatings were applied to the EG steel in a solution (pH 1.2) containing sodium dichromate and sulfuric acid at room temperature. The coatings were dried in an oven at three different temperatures: 60, 110 and 210°C. The surface of the chromate coatings was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) combined with energy‐dispersive spectrometry (EDS). The results show that the drying temperature significantly affects the morphology of the chromate coatings and consequently affects their corrosion behavior. The chromate coatings dried at 110°C had few cracks and the lowest corrosion current. The chromate coatings dried at 60°C showed passivity. The EIS results show that the chromate coatings dried at 60°C has the largest impedance in a neutral 3.5% NaCl solution. Drying at higher temperature (210°C) degrades the chromate coatings by widening the cracks and reducing soluble Cr(VI) in the chromate layer. The favorable drying temperature for the chromate coatings on the EG steel is between 60 and 110°C.     

AZ91D 镁合金 Mo-Mn 无铬转化膜的制备与耐蚀性

目的通过Mo-Mn无铬转化膜提高AZ91D镁合金的表面耐蚀性。方法采用正交实验法,研究不同浓度的NaMoO4和KMnO4以及温度对转化膜的影响。优选实验参数后,考察时间对转化膜的影响。利用SEM及EDS研究转化膜的微观形貌及成分变化,测试转化膜在3.5%NaCl溶液中的极化曲线和交流阻抗谱。结果当NaMoO4和KMnO4的质量浓度分别为10,6 g/L,pH=5,温度为50℃,转化时间为40 min时,转化膜颜色较为均匀,微观裂纹相对较少,自腐蚀电位比镁基体大约提高0.075 V,自腐蚀电流密度比镁基体降低近1个数量级。当Na Mo O4和KMnO4的质量浓度分别为20,8 g/L,pH=5,温度为50℃,转化时间为40 min时,转化膜颜色最为均匀,微观裂纹相对最少,自腐蚀电位比镁基体提高大约0.047 V,自腐蚀电流密度比镁基体降低2个数量级。交流阻抗谱图显示,后一种转化膜试样的极化电阻为1450.2Ω,而镁基体的极化电阻为806.4Ω。结论 Mo-Mn无铬转化膜可以显著提高AZ91D镁合金的表面耐蚀性。