Development and analysis of frits for enamelling AA2024, AA6082 and AA7075 aluminium alloys

This study reports the development of frits with different composition, time, and firing temperature for mitigating the corrosion of AA2024, AA6082, and AA7075 aluminium alloys in chloride-containing solutions. The melting points of the frits were determined using a heating microscope, while the thermal expansion was measured using dilatometry. Several frits were prepared, of which seven were coated on AA2024, AA6082 and AA7075 aluminium alloys. The corrosion resistance of the coated samples was tested in 5 wt% NaCl solution at 25°C using potentiodynamic curve measurements. The corrosion resistance of the coated samples increased compared with the respective uncoated aluminium alloys. The composition and in-depth homogeneity of the best-performing coated samples were confirmed using a gas cluster ion beam sputtering source associated with X-ray photoelectron spectroscopy analysis. Furthermore, O₂⁺ sputtering was performed in association with time-of-flight secondary ion mass spectrometry to describe the three-dimensional composition of the frits.     

Anticorrosive properties with catalytic behaviour of primer PANI film and top PPy coating synthesised in presence of novel norephedrine based amino alcohol compound

Polyaniline film as primer coating was deposited on stainless steel (SS) in aniline containing aqueous oxalic acid solution, and subsequent synthesis of top PPy film with 2-((5-ethylthiophen-2-yl) methylamino)-1-phenylpropan-1-ol (AAN) compound of different concentrations was achieved in acetonitrile-LiClO₄ successfully. The corrosion performances of coated and uncoated electrodes in 3·5%NaCl solution were evaluated with the help of AC impedance spectroscopy, anodic polarisation plots and open circuit potential time curves. The protective effect of bilayer coatings with AAN compound on SS electrode grew in parallel with extended exposure time. The regular increase in the charge transfer resistance of SS/PANI/PPy-AAN17 electrode was attributed to allowing the limited ion diffusion of top PPy coating with AAN17 compound. The high 21764 Ω s^?1/2 value of the Warburg coefficient showed that PPy-AAN17 film on the SS/PANI coating led to the formation of protective oxide layers due to the catalytic behaviour of PANI film.     

“Stopping off” Materials for Use in the Electro-Deposition of Nickel

The results are presented of a quantitative study of the phosphoric acid anodizing of high purity aluminium. The effects of electrolyte concentration, temperature, anodizing time, current density and air agitation on the coating weight, metal loss, coating ratio and density of the anodic coating were investigated.

The use of phosphoric acid anodic coatings as a base for electrodeposition is discussed with particular reference to plating in a copper pyrophosphate solution and the growth of copper deposits in the anodic film. Tests on chromium/nickel/copper electrodeposits on 38 aluminium alloy are briefly described.     

A study of Corrosion Protection of Aluminum Metal by Tetraethoxysilane Plasma Polymerized Coatings -Influence of Aluminum Surface Pretreatments-

PLASMA polymerization refers to the vacuumdeposition and polymerization process that is caused byreactive species created in a plasma state and also at thesurface exposed to the plasma state.It has manyadvantages for coating or film application[1].Specialadvantages of plasma polymerized(PP)films are asfollows:a thin film of thickness of a few tens ofnanometers to a micrometer can be easily achieved;such films are highly cross-linked and pinhole-free,andhave outstanding barrier characteristic…     

Surface characterization and immersion tests of TiNi alloy coated with Ta

The surface chemical composition and chemical state of Ti–50.6 at.% Ni alloy samples coated with tantalum by an arc ion plating method were investigated by X-ray photoelectron spectroscopy (XPS). The results of XPS survey and high resolution spectra show that a thin oxide film with Ta₂O₅ in the outmost layer and tantalum suboxides in the inner layer are formed on the tantalum coating as a result of natural passivation of Ta in the atmosphere. The Ni ion release with time from uncoated and coated samples immersed in 0.9%NaCl solution was also investigated by atomic absorption spectrometry (AAS). Compared to the coated samples, the uncoated samples show a higher release rate that decreases slightly with time. The degree of dissolution for the coated sample is reduced from 0.28 to 0.74 μg/cm² after 49 days, implying the coating has a beneficial effect on the inhabitation of Ni ion release from the TiNi substrate. The atomic force microscope (AFM) images and section analysis show that the root mean square (RMS) roughness increases from 10.349 to 65.587 nm, and the maximum roughness (R_max) increases from 36.027 to 278.22 nm, confirming that immersion in the NaCl solution results in roughening of the coating surface.     

Korrosionsprozesse durch und unter organischen Überzügen

Corrosion proceses through and under organic coatings Areas of metal covered with a sound protective organic coating can serve as cathode to corrosion process occuring at areas of metal exposure. Corrosion currents are carried through the organic coating by ion transport. Factors favouring ion transport result in less resistant coatings. Increase in coating thickness sharply increase the resistance to corrosion currents. Breakdown of the protective system is associated with some form of coating detachment. Of particular concern is an underfilm corrosion process which proceeds from a point of origin and in which the surface metal at the periphery of the growing, detached spot serves as anode. Such corrosion is stimulated by reduction processes taking place directly through the organic coating or at other exposed metals. For tinplate food cans, the tin coating constitutes a permanent anodic surface phase, and the anodic untermining process consists of dissolution of tin from between the steel and the organic coating. For organic- coated aluminium there is no permanent anodic surface phase. The metal at the extremity of the crevice between the organic coating and the aluminium becomes anodic just as does the base of a pit in aluminium. Anodic untermining corrosion, however, occurs preferentially to pitting.     

Anodic behaviour of a model second phase: Al-20at.%Mg-20at.%Cu

The anodic behaviour of sputtering-deposited Al-20at.%Mg-20at.%Cu alloy is investigated during anodizing and potentiodynamic polarization treatments using transmission electron microscopy, X-ray photoelectron spectroscopy and medium energy ion scattering. The composition of the alloy is close to that of the S-phase in 2024 aluminium alloy. The anodizing behaviour in both 0.1 M ammonium pentaborate and 0.1 M sodium hydroxide electrolytes follows the behaviour of more dilute, solid-solution, aluminium alloys, with enrichment of copper developing in the alloy during the growth of an alumina-based initial oxide containing incorporated magnesium species. Oxygen gas is generated following sufficient enrichment of copper for its oxidation to proceed and hence, for copper species to enter the oxide film. The generation of oxygen gas causes extensive damage to the film, which limits the voltage to relatively low values. Potentiodynamic polarization in 0.1 M sodium hydroxide electrolyte revealed mainly passive behaviour following an initial period of corrosion during which the passive film is developed. In this initial period, copper enriches in the alloy, beneath an oxide film containing aluminium and magnesium species. The magnesium species migrate faster through the film than the aluminium species and form a surface layer of MgO/Mg(OH)₂, which protects against losses of aluminium species to solution and permits the establishment of the passive film. The steady open-circuit potential of the passivated alloy in the hydroxide solution is about −550 mV (SCE), compared with about −1940 mV (SCE) for aluminium.     

In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions

The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times (t < 1000 s) only in chloride solutions. In situ measurements of current density and pH distributions over cut-edge coated steels immersed in chloride solutions revealed a quasi-steady state current between the coating and the steel substrate, resulting from local (pitting like) dissolution of the aluminium–silicon-based alloy coating. In sulphate solutions, the coating is not at all sacrificial and remains passive.     

Protection behaviour of surface films formed on AZ91D magnesium alloy in nitrogen/1,1,1,2-tetrafluoroethane atmospheres

Protective surface coatings on an AZ91D magnesium alloy were formed in an atmosphere mixture of nitrogen and 1,1,1,2-tetrafluoroethane (HFC-134a). The surface composition and microstructure were characterized using X-ray diffraction analysis and scanning electron microscopy, respectively. The cross-section morphologies of the coatings show that an increase in conversion time results in an increase in the continuity and compactness of the coating generated on the surface of the AZ91D alloy. The corrosion resistance tests performed by immersion into 3.5% NaCl solutions were investigated by electrochemical measurements. The results showed that the coated samples had higher corrosion resistance than the uncoated alloy. On the other hand, the corrosion density of the coated samples decreased by increasing the conversion time by about two orders of magnitude, compared with the un-coated samples. This behaviour is attributed to the formation of a protective surface film constituted mainly for MgF2, together with other phases. The nature of these phases depends on the process conditions.     

Polypyrrole electrodeposited on copper from an aqueous phosphate solution: Corrosion protection properties

Highly adherent and homogenous polypyrrole films were electrodeposited at copper from a dihydrogen phosphate solution. The polypyrrole films were electrosynthesized in the overoxidized state by cycling the copper electrode from -0.4 to 1.8 V (SCE) in a pyrrole-containing phosphate solution. The growth of the polypyrrole films was facilitated by the initial oxidation of the copper electrode in the phosphate solution to generate a mixed copper-phosphate, copper oxide or hydroxide layer. This layer was sufficiently protective to inhibit further dissolution of the copper electrode and sufficiently conductive to enable the electropolymerization of pyrrole at the interface, and the generation of an adherent polypyrrole film.Potentiodynamic polarization measurements, Tafel analyses and open-circuit potential data revealed that the polypyrrole coating effectively protects the copper substrate from corrosion in a chloride solution. However, the corrosion protection properties were reduced with longer immersion times.     

Inhibition of copper corrosion by coatings of alkyl esters of carboxybenzotriazole

The inhibitive effect of coatings formed dipping copper in solutions of alkyl esters (methyl, butyl, hexyl and octyl) of carboxybenzotriazole was studied by potentiodynamic polarisation, electrical impedance spectroscopy, coulometry and surface enhanced Raman scattering (SERS) spectroscopy. The inhibition efficiency of the dry film depends on type of solvent used in the coating solution, temperature and period of immersion. Pretreatment by immersing copper in hot (70 °C) aqueous solution (1×10⁻⁴ M) for approximately 2-3 h gave a film with the highest degree of corrosion protection. Higher temperatures or longer time of immersion reduce the protectiveness of the film. Copper coated using either alcohol or acetone as solvent was less well protected than when dipped in aqueous solution. Impedance spectra showed that the film formed by pretreatment in aqueous solution of inhibitors can be stable in acidic sulphate corrodent (pH∼0) for up to 3 days before breaking down. In near-neutral sulphate solution (pH∼8) the film can be stable for up to 10 days. In both acidic and neutral sulphate solution, the inhibition efficiencies of the protective film increased with the length of the alkyl ester chain in the order: methyl < butyl < hexyl < octyl. This is different to the behaviour of copper in a near-neutral aqueous corrodent containing dissolved inhibitor. The ester films also exhibit anti-tarnishing properties in a sulphidising environment with inhibition efficiencies increasing as the alkyl chain is made longer. Again the films formed by pretreatment in aqueous solution have superior anti-corrosion properties compared to those formed by pretreatment in either alcohol or acetone solution. SERS measurements indicate that the azole ring is close to the copper surface with chemisorption through azole nitrogen. It is also suggested that the hydrocarbon chain of the ester is physically adsorbed on the copper.     

Comparison of testing solutions on the protection of Al-alloys using a Mg-rich primer

Magnesium-rich coatings present a new and challenging field of development for the corrosion protection of aluminium structures. These coatings are capable of sacrificial protection, but assessment of their efficiency and durability can be strongly affected by the testing environment. In this work two solutions commonly used in our studies are compared: 0.1% NaCl and dilute Harrison solution (DHS). The corrosion behaviour of two aluminium alloys coated with a magnesium-rich coating, of pure magnesium and of the bare aluminium substrates was assessed in the two solutions using electrochemical techniques. The corrosion rate of pure magnesium was higher in DHS, although the dissolution rate of the magnesium embedded in the polymer matrix was not significantly affected. The impedance spectra of the scribed samples resembled that of the bare substrates in NaCl solution but not in DHS.     

Poly(N-methyl pyrrole) and its copolymer with pyrrole for mild steel protection

In this study, it was aimed to overcome disadvantages of polypyrrole films like water up taking and resulting low stability, via copolymerization of pyrrole and N-methyl pyrrole and preparing their bilayer films. Poly(N-methyl pyrrole) coating was synthesized electrochemically on mild steel and its corrosion performance has been investigated in 3.5% NaCl aqueous solution, by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential-time relation. This coating was found to have lower protection efficiency than single poly(pyrrole) coating. This case was related to weak adsorption behavior of poly(N-methyl pyrrole) film on mild steel. On the other hand, when this film was applied as a top coat on polypyrrole coated sample; the obtained coating system hindered the attack of corrosive environment and protected mild steel efficiently. The underlying poly(pyrrole) film was strongly adherent and the top poly(N-methyl pyrrole) coat improved barrier property by decreasing permeability and water mobility. Poly(pyrrole-co-N-methyl pyrrole) has also been synthesized from aqueous oxalic acid solutions containing various ratios of these two monomers. The copolymerization rate and protective behavior of copolymer were strongly affected by the monomer concentration ratio. The ratio of 1:3 (N-methyl pyrrole/pyrrole) gave the most protective copolymer coating and it exhibited better barrier property than single PPy. This was related to introduction of -CH₃ group which creates hydrophobic effect, when compared to -NH group of pyrrole unit. However, the solution with the ratio of 1:1 yielded a coating which had lower protection efficiency than single poly(pyrrole) film. This behavior was attributed to significant decrease in adsorption strength as the ratio of n-methyl pyrrole increased.     

覆铝钢板搪瓷保护层耐蚀性研究

研究了涂层化学组成与覆铝钢板表面搪瓷涂层的耐蚀性能之间关系。结果表明,当涂层受Ｈ＾＋侵蚀时,均匀分布在涂层中的ＴｉＯ２晶体可以阻止Ｈ＾＋通过硅酸盐骨架中网穴对搪瓷涂层的腐蚀;当受ＯＨ＾－作用时,组成中的ＺｒＯ２首先与ＯＨ＾－生成Ｚｒ（ＯＨ）４,进一步与涂层表面的硅醇结合形成保护膜,阻止ＯＨ＾－的腐蚀。     

A study of conversion coating development on aluminium in chromate/fluoride solutions using secondary ion mass spectrometry

A Cameca Ion Analyzer has been used to examine aluminium surfaces, covered by 73 nm thick barrier type anodic films, after natural immersion for 1–15 min in a chromate/fluoride conversion coating solution at 293 K. The conversion coating produced is essentially amorphous chromium-containing material, probably largely hydrated chromic oxide, but contains a cellular-type structure with aluminium and fluoride, probably as complex oxyfluoride, concentrated in the inter-cellular regions. The major role of the F^? ion is to remove the initial oxide film, maintain the surface active and permit nucleation and lateral growth of the conversion coating over it. The F^? ion is more aggressive towards anodic and other alumina than CrO₄^2? and PO₄^3? ions, without appearing to enter the anodic film material per se, but is also more aggressive towards the aluminium substrate than C1^? ion, acting initially at flaws and undermining the film.     

Emeraldine base as corrosion protective layer on aluminium alloy AA5182, effect of the surface microstructure

AA5182 aluminium alloy cold rolled samples were coated by thin films of emeraldine base (EB) obtained from a 5% solution in N-methylpyrrolidinone. Accelerated corrosion tests prove this coating very effective for corrosion protection of aluminium alloys in neutral environment. This study underlines the prominent role of surface cathodic intermetallic particles in pit initiation and coating break down in enhanced corrosion conditions and suggest that, beside the EB barrier properties, the enhanced corrosion resistance observed on the EB coated samples could partly arise from two other mains factors:

•

a weak redox activity of the polymer which passivate the metal,

•

a proton involving self-healing process taking place at the polymer-metal interface, which contributes to delay local acidification in first steps of corrosion on EB coated aluminium surfaces.

     

离子束增强沉积纳米金属薄膜的摩擦特性

在原子力显微镜上对采用离子束增强沉积方法制备的4种纳米金属薄膜的摩擦特性进行了研究,分析了载荷和滑动速度对金属薄膜摩擦特性的影响,并对4种纳米金属薄膜的特性进行了比较.结果表明:铜薄膜的摩擦力随着滑动速度的增加而基本保持不变,镍薄膜的摩擦力随着滑动速度的增加而略有增加,钛薄膜的摩擦力随着滑动速度的增加而显著增加,而铝薄膜的摩擦力随着滑动速度的增加而减小;4种纳米薄膜的摩擦力均随着载荷的增大而增大,并且都存在一个载荷值,超过这个值,接触刚度增大,摩擦力急剧增加;4种薄膜中,铜薄膜的摩擦力最小,铝薄膜在载荷较大时的摩擦力最大;4种纳米金属薄膜摩擦特性的差异与薄膜的结构、形貌特征有关.     

Electrochemical synthesis of novel conductive polymer and corrosion protection properties on aluminium

Abstract

In this study, the new original copolymer film of pyrrole and 2-amino-4-methyl-pyridine has been electrochemically synthesised on 7075 aluminium alloy. The synthesis was achieved in aqueous oxalic acid containing 1∶1 monomer feed ratio. The characteristics of copolymer film were compared with polypyrrole film on Al under the same conditions. The characterisation of synthesised polymers was realised with the help of scanning electron microscopy. Fourier transform infrared spectroscopy and gel permeation chromatography techniques. The conductivity values of films were measured with four-probe technique. The stability of copolymer film as a coating material has also been investigated in 3·5% NaCl solution. The quantum theoretical calculations have been employed, and some parameters (dipole moment, energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital) were determined. The calculated quantum parameters revealed correlation with experimental data. Under such severe conditions, the copolymer film exhibits protective coating behaviour on Al. This original, highly stable and conductive copolymer film can find wide application area for various purposes (anticorrosive, electrocatalytic, etc.).     

高能离子刻蚀前处理对AlTiSiN涂层切削性能的影响

目的提高AlTiSiN涂层与刀具基材的结合强度,降低涂层表面的粗糙度,减少切削过程中涂层的剥落,改善涂层刀具的切削寿命。方法采用离子源增强的多弧离子镀设备刻蚀清理基体材料,并制备AlTiSiN涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、粗糙度仪、划痕仪和铣削实验探讨涂层沉积前不同Ar离子刻蚀清洗工艺对AlTiSiN涂层结构、膜基结合力和涂层表面形貌的的影响,探究不同刻蚀清洗工艺对涂层刀具切削机理和切削性能的影响。结果 AlTiSiN涂层的相结构主要由(Al,Ti)N固溶体相组成,涂层沿着基体呈现柱状生长。随着高能Ar离子刻蚀电流由40 A增加至100 A,涂层的表面粗糙度降低,Ra值由140 nm降至69 nm,Sq值由226 nm降至117 nm;涂层与基体之间的结合强度增加,Lc2由41 N增加至52 N;切削加工DC53模具钢结果显示,当清洗电流增加至100 A,涂层的剥落几率降低,涂层刀具的切削寿命增加,由11 m增加至23 m。结论高能离子刻蚀前处理过程可有效增加涂层与基体之间的结合强度,降低涂层表面粗糙度,进而提高涂层刀具的切削寿命。刻蚀清洗所用电流强度越大,清洗效果越好,刀具涂层切削性能提高越明显。     

Corrosion and Cavitation Erosion Behaviours of Cast Nickel Aluminium Bronze in 3.5% NaCl Solution with Different Sulphide Concentrations

The effect of sulphide(Na_2S) concentration(SC) on the corrosion and cavitation erosion behaviours of a cast nickel aluminium bronze(NAB) in 3.5% NaCl solution is investigated in this study.The results show that when the SC exceeds 50 ppm,the hydrogen evolution reaction dominates the cathodic process,and a limiting current region appears in the anodic branch of the polarisation curve due to the formation of a copper sulphide film,which is a diffusion-controlled process.After longterm immersion,the increased mass loss rate of NAB with the sulphide additions of 20 and 50 ppm is attributed to the less protective films,which contains a mixture of copper oxides and sulphides.Moreover,NAB undergoes severe localised corrosion(selective phase corrosion,SPC) at the β' phases and eutectoid microstructure α+κ_Ⅲ.By comparison,NAB undergoes general corrosion and a copper sulphide film is formed in 100 and 200 ppm sulphide solutions.Cavitation erosion greatly increases the corrosion rate of NAB in all solutions and causes a negative potential shift in 3.5% NaCl solution due to the film destruction.However,a positive potential shift occurs in the solutions with SC higher than 50 ppm due to the accelerated mass transfer of the cathodic process.The cavitation erosion mass loss rate of NAB increases with the increase of SC.The occurrence of severe SPC decreases the phase boundary cohesion and causes brittle fracture under the cavitation impact.The corrosion-enhanced erosion is the most predominant factor for the cavitation erosion damage when the SC exceeds 50 ppm.