Effect of tantalum film on corrosion behaviour of AA6061 aluminium alloy in hydrochloric acid- and chloride-containing solutions

ABSTRACT

The present work is concerned with the corrosion resistance of AA6061 aluminium alloys with tantalum films in hydrochloric acid- and chloride-containing solutions. The tantalum films were produced by magnetron sputtering at different sputtering times (50 and 120 min). The films’ morphologies were observed by metallographic microscope and scanning electron microscope with energy dispersion spectrum. It is shown in this paper that with longer sputtering time, the film’s thickness increased, but it became less dense. The corrosion behaviour was characterised by potentiodynamic polarisation, scanning electrochemical microscopy analysis and an immersion experiment. These investigations revealed that the corrosion resistance of AA6061 aluminium alloy in chloride ions medium and hydrochloric acid was significantly improved after deposition of a tantalum film. Specifically, samples deposited for 50 min exhibited the best corrosion resistance in hydrochloric acid, while samples deposited for 120 min showed best corrosion resistance in sodium chloride solution.     

Electrochemical impedance measurements on Ni–P coated magnesium alloy,chromated magnesium alloy,and anodised aluminium alloys in aqueous salt solutions

Abstract

Both electroless nickel coated and chromated surfaces of magnesium alloy AZ 31 and hydrothermally sealed anodised surfaces of unalloyed aluminium Al-2S and aluminium alloy 6061 have been prepared and the corrosion behaviour of these surfaces in aqueous K Cl and K₂SO₄ solutions has been studied using electrochemical impedance spectroscopy (EIS). The effect of the concentration of hypophosphite in the plating bath used for electroless plating on the Ni-P layers formed and their corrosion behaviour has also been studied. The EIS studies have shown that the diffusion of ionic species is less for yellow chromated surfaces of magnesium alloy than for black chromated ones. In the case of anodised aluminium surfaces, impedance values are much higher in KCl than in K₂SO₄ solutions. The effect of anodising time on pore resistance R _po and barrier capacitance C_b has also been studied. Data from EIS indicate that the pore resistance of aluminium alloys A1-2S and AA 6061 attains a saturation value after anodisation for ~45 min.     

Effect of the reinforced boron carbide particulate content of AA6061 alloy on formation of the passive film in seawater

The effect of boron carbide (B₄C) reinforcement on the corrosion of AA6061 alloy was studied by investigating passive films formed in seawater. The higher passive current and its potential-dependence for these composites indicated formation of porous passive film. Electrochemical impedance spectroscopy (EIS) graph suggests that the alloy surface is partly or totally active. The formed passive film is n-type semiconductor junction in nature. The difference between corrosion potential (E_corr) and potential at zero charge (PZC) suggests that the chloride ions responsible for film breakdown exist within the passive film. A suitable mechanism is proposed for the passive film breakdown.     

A novel phosphate conversion film on Mg-8.8Li alloy

The super light Mg-Li alloys exhibit excellent formability due to the addition of lithium, but the corrosion resistance is deteriorated. A novel conversion film is developed to improve the corrosion resistance. The surface morphology of conversion film was observed using scanning electron microscopy (SEM). The chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion behaviors of Mg-8.8Li alloy and conversion film were investigated with electrochemical and immersion tests. The experimental results indicated that the Mg-8.8Li alloys with and without the protection of conversion film can both be used in NaOH solution safely. But the Mg-8.8Li substrate was susceptible to corrode in NaCl and Na₂SO₄ solutions, and the conversion film can prevent them from corroding. Compared with the NaCl solution, the Na₂SO₄ solution was a strong corrosive medium to the conversion film.     

Microstructure and some properties of aluminium alloy AA6061 reinforced in situ formed zirconium diboride particulate stir cast composite

The objective of this work is to fabricate aluminium alloy AA6061 reinforced with ZrB₂ particles (10 wt-%) by the in situ reaction of K₂ZrF₆ and KBF₄ salts with molten aluminium. The microstructure, tensile strength, wear resistance and corrosion rate of the fabricated composite were compared with those of matrix alloy. The in situ formed ZrB₂ particles were uniformly dispersed in the aluminium matrix predominantly concentrated in inter granular regions and refined the microstructure of the matrix alloy. The incorporation of in situ formed ZrB₂ particles into the aluminium matrix improved tensile strength and wear resistance but reduced ductility and corrosion resistance.     

Improving corrosion resistance of pure Al through ECAP

Abstract

Significant grain refinement and corrosion resistance improvement were achieved in industrial pure Al through equal channel angular pressing (ECAP). The effect of microstructure change on its corrosion resistance was investigated by optical/electron microscopy observation, constant immersion tests, polarisation tests and electrochemical impedance spectroscopy (EIS) in aqueous NaCl solution. The ultrafine grained (UFG) bulk pure Al (with grain sizes of 300–500 nm) has a higher pitting potential E_pit, a lower corrosion current density I_corr in polarisation tests and an increased polarisation resistance R_p from EIS plots, along with reduced corrosion damage in immersion tests, compared with the as cast material. It was found that the improved corrosion resistance resulted from the uniform distribution of fine Si containing impurities and the formation of a denser oxide film. The ECAPed samples with smaller Si containing impurities have lower microgalvanic currents and reduced susceptibilities of pitting corrosion, which is consistent with the classical ‘small cathode, large anode’ mechanism. The strain induced crystalline defects, for example, high angle grain boundaries and dislocations, appear to provide more nucleation sites for the formation of a denser and thicker oxide film, thus enhancing its corrosion resistance.     

Microstructure and corrosion behaviour of ferritic steel–Zr-based metal waste form alloys in simulated ground water

ABSTRACT

The microstructure and corrosion behaviour of the metal waste form (MWF) alloys based on ferritic steel with Zr content in the range of 3–15?wt-% were investigated. The MWF alloys are composed of α-Fe and Fe-Zr phases and with the increase of Zr content, α-Fe phase gradually decreases and the relative content of Fe–Zr intermetallic phase also increases. TEM and XRD confirmed the presence of Fe₂Zr and Fe₂₃Zr₆ intermetallics. Potentiodynamic polarisation curves showed The MWF alloys exhibited passivation behaviour in the simulated Kalpakkam (KGW) and Rajasthan ground water (RGW) media. Electrochemical impedance spectra revealed improved passive film stability in RGW than in KGW which is related to the formation of more stable adherent insoluble passive film in RGW. Higher Zr containing MWF alloy exhibited higher corrosion resistance than lower Zr containing MWF alloys. The relative content of Fe–Zr intermetallics is attributed for the corrosion resistance of The MWF alloys.     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

Effect of Reinforcement Coating on the Oxidation Behavior of AA6061/SiC/20p Composite

The oxidation behavior of SiO₂-active coatings on SiC reinforcement particles of an aluminium-matrix composite, AA6061/SiC/20p, was studied. In order to improve the processing behavior of the composites the SiC particles were coated prior to composite manufacture by a casting procedure, using the sol–gel technique. The oxidation resistance of the composites was analyzed to determine the influence of the manufacturing varibles. Gravimetric tests were used to evaluate the oxidation kinetics at 500°C. The nature of the corrosion products before and after accelerated testing was analyzed by Scanning-Electron Microscopy (SEM), EDX and low-angle X-ray Diffraction (XRD), to determine the influence of the oxidation environment on microstructural changes. Corrosion damage to the AA6061/SiC/20p composite was dependent on the manufacturing process and increased with the manufacturing temperature. Three corrosion products were detected –Al₂O₃, MgO and MgAl₂O₄. The corrosion resistance decreased slightly when the SiO₂ coating was used, and the matrix/SiC interfaces acted as preferential nucleation sites, but the intensity of the oxidation process was low. The use of active coatings on reinforcement particles is justified by the improvement in their wettability by molten aluminum, in spite of some slight loss of oxidation resistance     

Nanomechanics of Mg-Al intermetallic compounds

Cold spraying of pure Al powder on a pure Mg substrate together with subsequent post-spray annealing treatment produced Mg₁₇Al₁₂ (β-phase) and Mg₂Al₃ (γ-phase) intermetallic layers on the surface of the substrate. These layers showed significantly better nanomechanical properties, including the reduced elastic modulus and nanohardness, which were determined using nanoindentation, than commercial purity Mg and AZ91 alloys. Combined with their improved corrosion resistance, it is believed that both the γ-phase and the β-phase layers can provide effective protection of Mg alloys from wear and corrosion. The effect of post-spray annealing process on the formation of thick, uniform and dense intermetallic layers on pure Mg substrate was also investigated.     

纯Sn焊料表面高温氧化膜的腐蚀演化行为（英文）

对150℃高温时效条件下纯锡焊料表面氧化膜形貌、组成、厚度及耐蚀性的演化行为进行研究。结果表明,高温时效加速焊料表面原有自然氧化膜层中的Sn(OH)₄向SnO₂转变,同时加速新鲜Sn基体的氧化,从而使纯Sn焊料表面氧化膜厚度和粗糙度随时效时间的延长逐渐增加。然而,表面氧化膜层的耐蚀性随时效时间的延长呈先增强而后减弱的趋势。此外,还对纯Sn焊料表面氧化膜层的成膜机制及膜层演化机制进行讨论。     

Effect of Al2O3 reinforcement and precipitates on corrosion behaviour of 2618 and 6061 aluminium MMCs

ABSTRACT

The corrosion resistance features of two different Metal Matrix Composites based on 6061 and 2618 aluminium alloys reinforced by 20% Al₂O₃ particles by stir casting process, were studied in 3.5% NaCl and compared. The composites and their respective base alloys were characterised in terms of microstructure by optical and scanning electron microscopy and in terms of corrosion resistance by polarisation curves and electrochemical impedance. Results show how the presence of Al₂O₃ has different effects depending on matrix composition. In 6061 MMC, Al₂O₃ promotes the formation of Mg₂Si which has a cathodic behaviour altering the pitting susceptibility of the composite. In 2618 MMC, the high content of Cu induces a strong uniform attack. The subsequent increase in the Open Circuit Potential caused a pitting attack.     

Corrosion protection of molybdate doped polypyrrole film prepared in succinic acid solution

ABSTRACT

Polypyrrole (PPy) was prepared on the mild steel substrate by electrochemical polymerisation in the solution containing pyrrole monomer and succinic acid. The mild steel surface could be passivated before and during electropolymerisation by molybdate. The morphology and structure of the PPy film were studied with SEM. The typical cauliflower structure of PPy was observed. Raman and IR spectroscopy showed that the obtained PPy was in an oxidised state. The thermal stability of PPy was investigated by the thermal gravimetric analysis, showing that PPy was stable at higher than 480°C. The electrochemical property of the PPy film was performed by open circuit potential, polarisation curves (I/E), and electrochemical impedance spectroscopy. The corrosion behaviour of mild steel (CT3) with PPy film in solution NaCl 3% was studied.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Evaluation of corrosion behavior of Al-Mg-Li alloys in seawater

Weldalite 050, a high-strength Al-Mg-Li alloy, was evaluated for its corrosion resistance in deaerated and air saturated Arabian Gulf water to determine its suitability for marine applications. Weight loss and electrochemical studies showed that the alloy had minimum corrosion rates of 1.82 and 4.82 mpy (mils per year), respectively, in deaerated and air saturated Arabian Gulf water with very high total dissolved solids (TDS) content. Weldalite 050 exhibited good resistance to corrosion at velocities up to 3.9 m/s. The formation of Al₂MgLi, Al-Li, Al₁₂Mg₁₇, and Al-Li precipitates has a pronounced effect on its corrosion resistance. The corrosion resistance of Weldalite 050 compares favorably with that of alloys 5052 and 5054, wrought alloys 6061 and 6013, and silicon carbide (SiC) reinforced alloys 6061 and 6013.     

Corrosion-resistant alloy testing and selection for oil and gas production

ABSTRACT

Corrosion-resistant alloys (CRAs) are employed in severe oil and gas production environments that operate at high pressures and temperatures and contain chlorides, CO₂, and H₂S. They exhibit high resistance to uniform corrosion in these environments due to their passivity. However, they can suffer from different forms of environmentally assisted cracking (EAC), depending on the environmental and metallurgical conditions. This paper reviews the recent literature of EAC in CRAs and presents an overall framework for evaluating the SCC based on electrochemical modelling of corrosion and repassivation potentials for localised corrosion. The modelling is supported by experimental data on crack growth as a function of environmental variables, alloy content, and potential.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

不锈钢表面Cr-Pd合金电沉积及镀层在强还原性介质中的耐蚀性

通过选择络合剂、缓冲剂及采用方波脉冲电流和优化电镀工艺, 在酸性镀液中实现了Cr-Pd共镀, 并在不锈钢表面制备出均匀致密且与基体结合良好的Cr-Pd合金镀层. 通过改变镀液中铬盐和钯盐的相对含量, 可以大范围改变镀层成分. Cr-Pd合金镀层可显著提高不锈钢在高温还原性腐蚀介质中的耐蚀性, 在沸腾的20%(质量分数)H₂SO₄溶液中, Cr-Pd合金镀层使316L不锈钢的腐蚀速率降低了4个数量级以上. 镀层中的Cr和Pd对致钝具有协同促进作用, 当镀层中含有2.5%Pd(质量分数)时即具有明显的促进钝化效果, 含33.3%Pd镀层对不锈钢的保护效果与纯Pd镀层相当.     

Mass transport control of localised corrosion processes: in situ local probing and modelling

ABSTRACT

In this paper, the importance of mass transport in localised corrosion process is demonstrated using two examples describing the corrosion behaviour of two types of cut-edge electrodes regarding, (i) the sacrificial dissolution of a sacrificial Zn coating on steel (galvanised steel) and (ii) the release of inhibitors from a primer on an aluminium alloy (AA2024). In the two cases, in situ pH imaging with an ion-selective microprobe is used to confirm, (i) the role of corrosion products on the galvanic current profiles and (ii) the competition between the inhibition and the triggering of the local corrosion activity around intermetallic particles. It is illustrated how the experimental results can be supported by a 2D mass transport modelling.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Effectiveness of pretreatment method to hinder rebar corrosion in concrete

Abstract

This paper aims to evaluate the ability of phosphate pretreatments applied on steel rebars to hinder the corrosion reinforcements using synthetic pore electrolyte and mortar contaminated by chloride ions. The electrochemical behaviour of the pretreated substrate was assessed by corrosion potential, polarisation resistance and electrochemical impedance spectroscopy measurements. The results have demonstrated that the treatment of the rebar by immersion in the Na₃PO₄ (0·5M) solution favours the formation of a passive layer on the steel rebar surface, which increases the resistance to corrosion initiation up to 0·3M Cl^– instead of 0·1M Cl^– without treatment. The pretreatment also provides enhancement of corrosion protection of the steel rebar in mortar. The evolution of the impedance spectra in function of chloride concentration is in a fairly good agreement with the results obtained from R_P measurements.     

Comparison of corrosion scales formed on KO8OSS and N8O steels in CO2/H2S environment

Abstract

Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied to analyse the microstructure and composition of the corrosion scale formed on KO80SS and N80 tubes with carbon dioxide (CO₂) and hydrogen sulphide (SO₂). The corrosion scales of both KO80SS and N80 tubes were of the double layer structure, and not only uniform corrosion but also localised corrosion was observed. The crystal of the surface layer is laminar. The main phase in the outer layer is calcium carbonate (CaCO₃), and the inner scale consisted of iron carbonate (FeCO₃) for KO80SS steel and FeS_0·9 with a little amount of FeCO₃ for N80 steel respectively. Additionally, the electrochemical techniques were used to investigate the characteristics of the corrosion scales. The results indicated that the polarisation resistance R_p of KO80SS steel film was nobler than that of N80 steel film. Finally, the corrosion current I_corr of KO80SS steels was lower than that of N80 steels. Corrosion scale of KO80SS tube steels is more protective to the matrix than that of N80 tube steels.     

Electrochemical evaluations of zinc-rich epoxy primers modified with polyaniline and exfoliated polyaniline graphite nanocomposite

ABSTRACT

Polyaniline (Pani) and exfoliated polyaniline graphite (EPaniG) nanocomposites were used to modify the protective properties of an epoxy zinc-rich primer (ZRP). The corrosion resistance properties of primers were evaluated in 3.5% sodium chloride solution for a period of 120 days via electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS). EN data were analysed via Wavelet and Hilbert spectra analysis to evaluate the protection mechanism of different ZRP coatings during immersion. Coating resistance and charge transfer resistance of the primers were evaluated by EIS measurements. Results showed good compatibility between |Z|_0.01Hz from EIS measurements and mean noise resistance which results from EN data and these evaluations allowed the examination of coating performances during immersion. Free corrosion potential (E_corr) measurements and salt spray test revealed that both the cathodic protection and barrier properties of the ZRP primer were improved after addition of EPaniG nanocomposite to the ZRP sample.