Alloys In NaCl Solution Research Articles

Corrosion electrochemical behaviors of silane coating coated magnesium alloy in NaCl solution containing cerium nitrate

AbstractSol–gel coatings cannot provide adequate corrosion protection for metal/alloys in the corrosive environments due to their high crack‐forming potential. This paper demonstrates the possibility to employ cerium nitrate as inhibitor to decrease the corrosion development of sol–gel‐based silane coating on the magnesium alloy in NaCl solution. Cerium nitrate was added into the NaCl solution where the silane coating coated magnesium alloy was immersed. Scanning electron microcopy (SEM) was used to examine surface morphology of the silane coating coated magnesium alloy immersed in NaCl solutions doped and undoped with cerium nitrate. The corrosion electrochemical behaviors were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The results showed that the introduction of cerium nitrate into NaCl solution could effectively inhibit the corrosion of the silane coating coated magnesium alloy. Moreover, the influence of concentration of cerium nitrate on the corrosion inhibition and the possible inhibiting mechanism were also discussed in detail.

CORROSION MECHANISM AND MODEL OF ANODIZED FILM ON AZ91D MAGNESIUM ALLOY

The corrosion behavior of anodized film on AZ91D magnesium alloy in 3.5% neutral NaCl solution was investigated by saline immersion test. The results show that new corrosion points seldom occur on the surface of the said anodized film during the immersion time in 3.5% NaCl neutral aqueous solution after the first macroscopic corrosion point appears on the anodized film, while the previous corrosion point extends vertically or horizontally and turns into a corrosion pit which is in form of "strip". Moreover, the corrosion occurs firstly on α phase rather than β phase, when the corrosion of anodized film reaches the Mg alloy substrate. The corrosion products of anodized film on AZ91D magnesium alloy in neutral immersion solution were analyzed by XRD. A possible corrosion reaction and model about the corrosion of anodized film on AZ91D magnesium alloy in NaCl solution based on the experimental results is proposed.

Role of second phase particles in pitting corrosion of 3003 Al alloy in NaCl solution

AbstractThe second phase particles in 3003 aluminum (Al) alloy were characterized by scanning electron microscope, energy‐dispersive X‐ray analysis and X‐ray diffraction techniques. The role of second phase particles in Al alloy pitting corrosion was investigated by cyclic polarization measurement, and scanning vibrating electrode technique. Results demonstrated that the second phase particles in 3003 Al alloy are mainly Alx(Fe,Mn) intermetallics, with an average diameter of about 5 µm. The enrichment of Mn in second phase particles forms a galvanic cell effect relative to the adjacent Al alloy substrate. The initiation of pitting corrosion of 3003 Al alloy is the local dissolution of Al substrate around the second phase particles. When a sufficient amount of Al is dissolved away, the second phase particles drop off from the Al substrate, forming large pitting cavities that are usually linked each other.

Studies on the Influence of Chloride Ion Concentration on the Corrosion Behavior of ZSMX Magnesium Alloy

The paper presented reveals the influence of chloride ion concentration on the corrosion and electrochemical behavior of new ZSMX wrought magnesium alloy in NaCl solution. The experimental techniques used include potentiodynamic polarization tests. The corrosion rate usually increased with the increase in chloride ion concentration. This result can be explained by the distribution of intermetalics.

Corrosion Resistance of Dental Ti-Ag Alloys in NaCl Solution

The purpose of this study was to evaluate the corrosion resistance of experimental dental Ti-Ag alloys in 0.9% NaCl solution. Open-circuit potential (OCP) measurement and elution tests of the alloys with 5–30% Ag were performed. The amounts of both Ti and Ag ions released from the alloys with Ag � 20% were below the detection limit. A very small amount of Ti ions was released from some of the 22.5% Ag specimens and some of the 25% Ag specimens. The time for the Ti-Ag alloys with 5–25% Ag to become the stable potential was earlier than that for titanium, and the OCP of the alloys was higher than that of titanium. These results indicated that the corrosion resistance of the alloys with 5– 25% Ag was equivalent to that of titanium. On the other hand, it was suggested that the precipitation of TiAg deteriorated the corrosion resistance of Ti-Ag alloys because TiAg dissolved preferentially in the NaCl solution. Ti-Ag alloys with 5–25% Ag can be used not only as dental restorative materials but also as dental implant materials. [doi:10.2320/matertrans.M2009355]

The corrosion behaviour of Al–Zn–In–Mg–Ti alloy in NaCl solution

The corrosion behaviour of Al–5Zn–0.02In–1Mg–0.05Ti (wt.%) alloy was investigated by EIS, SEM and EDX. The results show that there exist different corrosion stages of the alloy in 3.5% NaCl solution with increasing time. At the initial stages, pits predominates the corrosion around precipitates with a typical inductive loop at low frequencies in EIS. In the late corrosion, a relative uniform corrosion predominate the corrosion process controlled by the dissolution–precipitation of the In and Zn ions and characterized by the second capacitive loop at low frequencies in EIS. The mud structure appears on the corrosion surface of the alloy.

Cerium conversion coatings for AZ91D magnesium alloy in ethanol solution and its corrosion resistance

Golden-yellow-colored cerium conversion coatings on AZ91D magnesium alloy were obtained by immersion in ethanol solution and post-treated in 3.0 wt.% Na 3PO 4 aqueous solution. SEM revealed that the coatings deposited more heavily on α phase than on β phase. XPS results showed that the coatings consist of CeO 2, Ce 2O 3, CePO 4, Al 2O 3, Mg 3(PO 4) 2 and MgO. Corrosion tests indicated that the coatings with post-treatment significantly reduced the corrosion rate of AZ91D alloy in NaCl solution. The post-treatment is necessary for better corrosion resistance. The corrosion resistance of the coatings with post-treatment is superior to that of DOW No.1 coating.

Electrochemical corrosion study of Sn–3Ag–3Cu solder alloy in NaCl solution

The corrosion behaviour of Sn–3Ag–3Cu (at%) alloy was investigated in 0.1 M NaCl solution by potentiodynamic polarization and impedance spectroscopy measurements and compared with that of the Sn–3Ag–0.5Cu (at%) solder employed in the packaging of some microelectronic components and devices. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to characterize the samples prior to and after the electrochemical tests. Results showed that in NaCl solution the corrosion resistance of the Sn–3Ag–3Cu alloy was better than that of the Sn–3Ag–0.5Cu solder. The presence of tin oxychlorides or oxyhydroxychlorides was detected at the surface of both alloys investigated after the electrochemical tests. The better corrosion behaviour of the Sn–3Ag–3Cu alloy compared to the Sn–3Ag–0.5Cu solder can be ascribed to a more adherent and compact corrosion products layer.

Electrochemical discharge performance of Mg-Li based alloys in NaCl solution

Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in NaCl solution was investigated by means of potentiodynamic and chronoamperometric measurements. The surface morphology after discharge was examined using scanning electron microscopy. Utilization efficiency was estimated with a mass-loss method. The results indicated that Mg–Li–Al–Sn has a higher discharge current density but lower utilization efficiency than Mg–Li–Al–Sn–Ce. The typical utilization efficiency after continuous discharging at constant potential of −1.0 for 2 h is 65% and 70% for Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce, respectively. The utilization efficiency decreased with the increase of anodic potential. Both alloys have similar self-discharge rate in NaCl solution at open-circuit potential.

Corrosion characterization of Mg–8Li alloy in NaCl solution

The corrosion mechanism of Mg–8Li alloy in NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion resistance of Mg–8Li alloy in 0.1 M NaCl solution gradually deteriorated with increasing of immersion time expect for 2 h immersion, which was consistent with the SEM observation of corrosion morphology. Mg–8Li alloy exhibited filiform type of attack under significant anodic control of magnesium solution reaction. The cathodic reaction was driven by hydrogen evolution reaction. The presence of filiform corrosion also proved a resistant oxide film naturally formed on the surface of Mg–8Li alloy.

Novel approach using EIS to study flow accelerated pitting corrosion of AA5083-H321 aluminum–magnesium alloy in NaCl solution

EIS was utilized as a novel approach to study the role of mechanical and electrochemical processes in flow accelerated pitting corrosion behaviour of AA5083-H321 aluminum–magnesium alloy in 3.5% NaCl solution. This alloy is a suitable material for manufacturing of high speed boats, submarines, desalination systems etc. Impedance spectra were obtained during 24 h of exposure of the samples to the test solution at different rotation speeds. The surface and cross section of the samples were studied by scanning electron microscopy (SEM) and EDAX analysis. The results indicated that increasing the rotation speed causes the depth of pits to increase. By further increasing the rotation speed to 5 and 7 m s−1, the flow condition causes the passive layer inside the pits to breakdown. Simultaneously, the thickness of the passive layer on the areas other than the pits becomes thinner. Shear stresses at 10 m s−1 are so severe that the passive layer on the entire surface breaks down and leads to micropitting corrosion.

Corrosion behaviors of a γ-toughened Cr 13Ni 5Si 2/Cr 3Ni 5Si 2 multi-phase ternary metal silicide alloy in NaCl solution

Corrosion behaviors of a novel corrosion-resistant γ-toughened Cr 13Ni 5Si 2/Cr 3Ni 5Si 2 multi-phase ternary metal silicide alloy and properties of the passive film formed in NaCl solution were examined by anodic polarization, cyclic polarization and electrochemical impedance spectroscopy (EIS) experiments as well as X-ray photoelectron spectroscopy (XPS) and potentiostatic polarization measurements. Effects of immersion time and chloride ion concentration on corrosion behaviors of the alloy were also evaluated. Results indicated that the alloy exhibited excellent corrosion resistance in NaCl solution due to the spontaneous formation of a compact and protective passive film composed mainly of chromium (III) oxide as well as the high chemical stability and strong inter-atomic bonds inherent to Cr 13Ni 5Si 2 and Cr 3Ni 5Si 2 intermetallic phases. Moreover, corrosion resistance of the alloy was quite insensitive to the increase of chloride ion concentration and was improved noticeably with the increasing immersion time.

Electrochemical corrosion behavior of cast Mg–Al–RE–Mn Alloys in NaCl solution

The electrochemical corrosion behavior of Mg–6Al–0.4Mn and Mg–6Al–4RE–0.4Mn (RE = Mischmetal) alloys is investigated in 3.5% NaCl solution. The results of corrosion process, polarization behavior, and electrochemical impedance spectroscopy of the alloys reveal that Mg–6Al–4RE–0.4Mn exhibits enhanced corrosion resistance. The addition of RE stabilizes the solid solution and modifies the passive film through a finer microstructure.

Corrosion behavior of magnesium and its alloy in NaCl solution

The electrochemical behavior of cast Mg, AZ91, and cast AZ91 in 0.1 M NaCl solution is investigated by measuring open-circuit potential (OCP), steady-state current-potential, and electrochemical impedance spectra (EIS). The similar electrochemical impedance behavior is found of three corrosion electrodes. There are two capacitances in high-and medium-frequency domains and one inductive loop or component in low-frequency domain. From equivalent circuit simulation, cast AZ91 has the worst corrosion resistance. The EIS results are in good agreement with those obtained by OCP and polarization curves. Based on the Cao theory, a simple corrosion mechanism is put forward, supplying a possible explanation for low-frequency inductive behavior for Mg and its alloy in NaCl solution at OCP.

Corrosion and inhibition of Cu-Zn alloys in NaCl solution by using permanganate and phosphate anions

Corrosion and inhibition of Cu-Zn alloys in NaCl solution by using permanganate and phosphate anions

Corrosion mechanism associated with T1 and T2 precipitates of Al–Cu–Li alloys in NaCl solution

To clarify the corrosion mechanism associated with T1 and T2 precipitates in Al–Cu–Li alloys, the simulated bulk precipitates of T1 and T2 were fabricated through melting and casting, their electrochemical behaviors and coupling behaviors with α(Al) in NaCl solution were investigated. Meanwhile, simulated Al–Cu–Li alloys containing T1 and T2 particles, respectively, were prepared and their corrosion morphologies were observed. A corrosion conversion mechanism associated with the precipitates of T1 and T2 was advanced. The precipitates of T1 and T2 are anodic to the alloy base and corrosion occurs on their surface at the beginning. While, during their corrosion process, the preferential dissolution of Li and the enrichment of noble element Cu make their potential move to a positive direction. As a result, the corroded T1 and T2 precipitates become cathodic to the alloy base at a later stage, leading to the anodic dissolution and corrosion of the alloy base at their adjacent periphery. However, due to more amount of active element Li and much less amount of noble element Cu in the precipitate of T2, the electrode conversion of T2 from anode to cathode is more superficial than that of T1, and the corrosion mainly occurs in T2.

Preparation of anti-corrosion films by microarc oxidation on an Al–Si alloy

Thick ceramic films over 140 μm were prepared on Al–7% Si alloy by ac microarc oxidation in a silicate electrolyte. The film growth kinetics was determined by an eddy current technique and film growth features in different stages were discussed. The microstructure and composition profiles for different thick films were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Their phase components were determined by X-ray diffraction. The electrochemical corrosion behaviors of bare and coated alloys were evaluated using potentiodynamic polarization curves, and their corrosion morphologies were observed. In the initial stage of oxidation, the growth rate is slow with 0.48 μm/min due to the effect of Si element though the current density is rather high up to 33 A/dm 2. After the current density has decreased to a stable value of 11 A/dm 2, the film mainly grows towards the interior of alloy. The film with a three-layer structure consists of mullite, γ-Al 2O 3, α-Al 2O 3 and amorphous phases. By microarc discharge treatment, the corrosion current of the Al–Si alloy in NaCl solution was significantly reduced. However, a thicker film has to be fabricated in order to obtain high corrosion-resistant film of the Al–Si alloy. Microarc oxidation is an effective method to form an anti-corrosion protective film on Si-containing aluminum alloys.

Enhancing the corrosion resistance of magnesium alloy AZ91D in 3.5 per cent NaCl solution by cerate conversion coatings

PurposeTo develop new eco‐environmentally friendly surface treatments based on cerate compounds as alternatives to the process involving toxic chromates for the corrosion protection of magnesium alloys.Design/methodology/approachA treatment process in which a surface was alkaline‐etched prior to ceria treatment is proposed. The process involves cleaning, etching in potassium hydroxide followed by treatment in ceria conversion coatings. The effect of surface preparation prior to ceria treatment on the corrosion resistance of AZ91D in 3.5 per cent NaCl solution was measured using AC impedance spectroscopy and DC polarization techniques. Surface examination was performed by scanning electron microscopy, energy dispersive X‐ray.FindingsIt was shown that the ceria treatment can be used as a localized corrosion inhibitor for alloy AZ91D in NaCl solution. The level of inhibition strongly depended on the cerium concentration. Moreover, ceria treatments improved the pitting corrosion resistance due to the formation of protective oxide films which act as a barrier to oxygen diffusion to the metal surface. According to the EIS and polarization measurements, alkaline etching in KOH is more effective in reducing the pitting corrosion of AZ91D than was HCl. It was shown that surface treatment in alkaline solution (KOH) prior to ceria treatments played an important role in inhibiting the active surface sites, rejecting the chloride ions from the surface and forming uniformly distributed oxide film.Originality/valueCeria conversion coatings seem very promising as alternatives to toxic chromating for the corrosion protection of magnesium alloys in NaCl solution.

Corrosion behavior of rapidly solidified Mg–Zn–rare earth element alloys in NaCl solution

Rapidly solidified flaky powder metallurgy (RS FP/M) processing was applied for preparation of corrosion-resistant bulk Mg alloys with Zn and rare earth elements. The corrosion behavior of the melt spun Mg–Zn–La and Mg–Zn–Yb alloy ribbons in 1% NaCl solution was investigated in order to determine optimum composition of corrosion-resistant Mg alloys. The effect of heat-treatment on the corrosion behavior of RS Mg–Zn–La and Mg–Zn–Yb alloys also was studied. In the Mg–Zn–La alloys, as-quenched alloys showed good corrosion resistance in the NaCl solution, but heat-treatment led to degradation due to microstructure change, that is, reduction in dispersion of the Mg 17La 2-type intermetallic compound. In the Mg–Zn–Yb alloys, both as-quenched and heat-treated Mg 97.5Zn 0.5Yb 2 alloys exhibited low corrosion rates because fine distribution of Mg 2Yb-type intermetallic compound in α-Mg matrix was not largely changed by heat treatment.

Corrosion protection performance of nano‐particles thin‐films containing vanadium ions formed on aluminium alloys

PurposeThe paper seeks to find out new eco‐environmentally friendly surface treatments based on vanadate compounds as alternatives to the process involving toxic chromates for the corrosion protection of aluminium alloys.Design/methodology/approachA treatment process in which the surface was etched prior to vanadia treatment is being proposed. The process involves cleaning, etching in potassium hydroxide followed by treatment in vanadia prepared by sol‐gel method. The effect of surface preparation prior to vanadia treatment on the corrosion resistance of AA6061 T6 in 3.5 per cent NaCl solution was measured using AC impedance spectroscopy and DC polarization techniques. Surface examination was performed by scanning electron microscopy (SEM), energy dispersive X‐ray (EDS), X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).FindingsIt has been shown that the etching process prior to vanadia treatment enhanced formation of a uniformly distributed compact surface V‐rich Al‐oxide film of smooth appearance and inhibited the active surface sites and thereby preventing localized corrosion.Originality/valueVanadate conversion coatings seem very promising as alternatives to toxic chromating for the corrosion protection of aluminium alloys in NaCl solution.