Trivalent Chromium Process Research Articles

Effect of Alkaline Etching on Formation Behavior and Corrosion Resistance of a Cr-Zr-Ti TCP Conversion Coating on AA2024 Aluminum Alloy

Abstract Trivalent chromium process conversion coating is considered to be the ideal alternative to traditional chromate conversion coating due to its high corrosion resistance and low toxicity. However, achieving a high corrosion resistance trivalent chromium conversion coating on 2xxx aluminum alloys has been a great challenge. Herein, based on a newly developed trivalent chromium conversion solution (CN patent, ZL 202210804263.2), the effect of alkaline etching on the formation behavior and corrosion resistance of the coating on AA2024-T351 aluminum alloy was investigated. It was found that under the same conditions, the mechanically polished sample and the sample alkaline etched for 30 s showed the highest corrosion resistance. When the alkaline etching time was too short or too long, the corrosion resistance of the coating deteriorated. This is ascribed to changes in the surface microstructure of the alloy during alkaline etching, i.e., reduced number of intermetallic particles and formation of a copper enrichment layer. Reducing the number of intermetallic particles on the alloy surface is beneficial for uniform growth of the coating. However, the copper enrichment layer participated in formation of the coating, resulting in doping of copper species in the coating, which is detrimental to the corrosion resistance of the coating.

Preparation and characterisation of black conversion coating of Cr(NO3)3–CoCl2–NiCl2 of Zn–Ni alloy electroplated on 2024 aluminium alloy surface

AbstractTo meet the application requirements of electronic connectors, a trivalent chromium process (TCP) conversion coating was prepared on the Zn–Ni alloy plating of 2024 aluminium alloy. The composition of the TCP solution was as follows: 45 g/L Cr(NO3)3, 14 g/L CoCl2, 1.3 g/L NiCl2, 10 g/L citric acid, 10 g/L succinic acid and 1 g/L sodium dodecyl sulphate. The properties of TCP were characterised by a range of techniques, including macroscopic observations, scanning electron microscope, energy‐dispersive X‐ray spectrometer, three‐dimensional (3D) morphometry, electrochemical impedance spectroscopy, polarisation curves and conductivity tests. The TCP prepared in this experiment exhibits a uniform black colour and bright appearance, predominantly composed of Zn, Ni, O, Cr and Co. The TCP enhances the impedance of Zn–Ni alloys, reduces the corrosion current to 1.99 × 10−5 A/cm2 and maintains a flatter surface 3D morphology and less surface roughness following electrochemical testing. It has better corrosion resistance. Following the preparation of the TCP on a suitably sized shell sample, the shell resistance was 1.2 mVDC with good electrical conductivity, which meets the requirements for electrical connector applications.

Inhibiting Metal Galvanic and Carbon Corrosion in Aluminum Alloy-Carbon Fiber Reinforced Composite Joints by Spontaneous Deposition of Diazonium Adlayers on Exposed Carbon Fibers

The spontaneous formation of a diazonium molecular adlayer on the exposed fibers of a carbon fiber reinforced polymer (CFRP) composite was investigated as a surface treatment. The purpose of the surface treatment is to reduce the extent of galvanic corrosion on a trivalent chromium process (TCP) conversion-coated aluminum alloy when the two materials are mechanically joined as is common in aircraft structures. The adlayer functions to reduce the rate of dissolved oxygen reduction on the more noble carbon thereby reducing the rate of galvanic corrosion on the more active metal alloy. The formation of the adlayer (4-nitrophenyl (NP), 4-nitroazobenzene (NAB), or 2-fluorene diazonium tetrafluoroborate (FL)) was achieved by immersing the CFRP composite specimen in a solution of 5 mM diazonium salt dissolved in acetonitrile for a specified time (1–24 h) under open circuit conditions (so-called spontaneous deposition). Cyclic voltammetry (CFRP composite) and rotating disk voltammetry (glassy carbon) were used to investigate the oxygen reduction reaction kinetics in naturally aerated 0.5 M Na2SO4 (pH 5–6). The oxygen reduction reaction current was suppressed by greater than 90% by the NP and NAB adlayers and 80% by the FL adlayer. The surface treatment (24 h immersion) with NAB significantly reduced the galvanic corrosion damage on TCP conversion-coated aluminum alloy during a 14-day continuous neutral salt spray (NSS) exposure. The mass loss (mg/cm2) and corrosion intensity (g/m2y) were reduced by over 10×. The spontaneously formed NAB adlayers are stable during the salt-spray exposure and provide better inhibition of galvanic corrosion on the aluminum alloy and resistance to carbon corrosion than do NAB adlayers formed by an electrochemically assisted process reported on previously.

Influence of trivalent chromium process (TCP) concentration on the anti-corrosion protection of 2024-T3 aluminium alloy

ABSTRACT In the present work, the surface of 2024-T3 aluminium alloys was coated with different concentrations (25, 35, and 50 wt.%) of the trivalent chromium process (TCP), and they were evaluated by comparing them to hexavalent chromium coatings (HCC). The findings show that TCP coating had a porous surface regardless of the concentration of TCP coating while the HCC exhibited a cracked pattern. The TCP coating increased the surface roughness as well as the wettability compared to HCC. The immersion test in 3.5 wt. % NaCl solution revealed that the open circuit potential (Eocp) of coated samples was more positive than that of the uncoated sample. However, the HCC coating was slightly more anodic after half of the immersion. The potentiodynamic test confirmed the formation of a passive region for all samples. Furthermore, the corrosion potential (Ecorr) and the critical pitting potential (Epit) were more positive for the lowest concentration coating. The polarisation resistance of the samples suggested that the HCC coating was superior to TCP coatings. In general, the low concentration of TCP coating improved the corrosion protection of 2024-T3 but not better than HCC coating due, probably, to the porous surface morphology.

The Electrochemical Behavior of As-Prepared Aluminum Alloy A360 Produced by Selective Laser Melting Fabrication with and without a Trivalent Chromium Process Conversion Coating

We report herein on the electrochemical behavior and corrosion resistance of as-prepared aluminum alloy, A360 (AlSi10Mg), fabricated by additive manufacturing, with and without a trivalent chromium process conversion coating. Selective laser melting was the 3D printing process used for the alloy build. The corrosion suppression provided by the coating system was assessed through electrochemical measurements and accelerated degradation testing during a 14-day continuous neutral salt-spray exposure. The results indicate that the conversion coating can be formed by solution pretreating (degreasing and deoxidation) the alloy (X-Z plane perpendicular to the build plane) with its native surface roughness (as-prepared) followed by immersion for 10, 15 or 20 min in the coating bath. All three immersion times provide an equivalent level of corrosion protection to the alloy. The conversion coating suppresses both anodic and cathodic currents, increases the polarization resistance, and provides both anodic and cathodic corrosion protection to the as-prepared alloy. The conversion-coated specimens exhibit good stand-alone corrosion resistance during a 14-day neutral salt-spray exposure with corrosion intensity values (g/m2-year) ∼10x lower than values for the uncoated, as-prepared alloy specimens.

Inhibiting the Oxygen Reduction Reaction Kinetics on Carbon Fiber Epoxy Composites Through Diazonium Surface Modification-Impacts on the Galvanic Corrosion of Coupled Aluminum Alloys

We report on the chemical modification of carbon fiber reinforced polymer (CFRP) composites by the electrochemical reduction of 4-nitrophenyl (NP) and 4-nitroazobenzene (NAB) diazonium salts. The electrochemically assisted modification of the exposed carbon fibers was accomplished using cyclic voltammetry from 0.6 to −0.5 V (vs Ag QRE) for 25 cycles in deaerated acetonitrile containing 0.1 M tetrabutylammonium tetrafluoroborate (NBu4BF4) and 5 mM aryldiazonium salt. Raman spectra of the modified composites confirmed the formation of stable 4-NP and 4-NAB adlayers. The influence of diazonium surface pretreatment on the oxygen reduction reaction (ORR) kinetics was assessed by measuring the voltametric curves for dissolved oxygen reduction on unmodified and chemically modified composites in naturally aerated 0.5 M Na2SO4. The adlayers are believed to reduce the kinetically controlled current for the ORR by blocking reactive surface sites for O2 chemisorption. Results show the adlayers are stable during a 7-day continuous neutral salt spray (NSS) exposure and the extent of galvanic corrosion on trivalent chromium process (TCP) conversion-coated aluminum alloys is significantly reduced when joined with a surface treated composite. The extent of carbon corrosion and microstructural degradation of carbon fibers is also reduced by the organic adlayers.

Surface Modifications Induced by Pretreatments and Effects on The Chemical Structure of TCP Conversion Coating on Al-Cu-Li Alloy (AA2050)

Trivalent Chromium Process (TCP) was developed as a promising conversion process aiming at enhancement of corrosion properties and adhesion of aluminium alloys. The alkaline etching and acid pickling are usually applied as surface pretreatments on aluminium alloys before TCP deposition in order to optimize their properties. In this work, the surface modifications of an Al-Cu-Li alloy (AA2050-T8) at different stages of pretreatment (alkaline degreasing and acid pickling) and subsequent TCP are investigated by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy. The pretreatments leading to significant enrichments in Cu and less marked in Ag, show also a strong influence on the subsequent formation of TCP in comparison to the non-pretreated, polished AA2050-T8 alloy. A slight decrease in Li content is observed in the oxide layer after pretreatment and no Li is present in the outer TCP layer. A thicker TCP conversion coating (outer oxide) with less cracks is formed on the pretreated alloy surface than on the polished one. Moreover, a Cu enrichment is evidenced in the TCP layer of the pretreated sample, which results in enhanced cathodic activity of pretreated sample with reference to polished sample as demonstrated by linear sweep voltammetry.

Influence of ageing on the corrosion behaviour of 2024 aluminium alloy coated with a trivalent chromium conversion layer

Time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to study the influence of ageing of 2024 aluminium alloy at 190 °C on subsequent degreasing and deoxidation behaviour. After degreasing and deoxidation of the aged alloy, an increase in the surface Cu coverage and a surface roughening were observed as compared to a non-aged alloy. The Cu surface enrichment affected the growth mechanisms of the trivalent chromium process (TCP) coating. The TCP coating formed on an aged sample was thicker, but more defective leading to the decrease of its anticorrosion properties, as compared to a non-aged sample.

Microstructure and Electrochemistry of Al-Rich Primer

Al-rich primer (AlRP) is designed to be anodic relative to high strength Al alloys, so that it drives the mixed potential of Al alloy substrates (e.g. AA2024) into the cathodic region below the breakdown potentials of the Al alloys, preventing localized corrosion. The Al-rich primer (AlRP) under study is composed of spherical Al-Zn-In pigments in an epoxy binder. The 2D and 3D microstructure of the AlRP was studied using a combination of X-ray microscopy, plasma focus ion beam/scanning electron microscopy, and transmission electron microscopy techniques. The primer contained Al-Zn-In particles with various sizes ranging from tens of nanometers to microns, epoxy binder and a significant volume of voids. Potentiodynamic polarization testing was performed to measure the electrochemistry of the Al-Zn-In bulk alloy under neat primer in NaCl solution to simulate the environment which Al-Zn-In pigments are exposed to in the real primer. The bulk alloy under neat primer exhibited higher breakdown potential than the bare bulk alloy exposed to NaCl solution. The polarization curves of the bulk alloy under neat primer provide more accurate boundary conditions for modeling of the galvanic interaction between the AlRP and an alloy substrate. Galvanic corrosion between an AA2024 sample and Al-Zn-In bulk alloy was also studied using a zero resistance ammeter. A trivalent chromium process treatment on galvanic couples can protect AA2024 substrate from cathodic corrosion.Acknowledgements: this project is funded by the Office of Naval Research through the Small Business Innovation Research (SBIR) program. We thank Naval Air Systems Command (NAVAIR) for providing Al-rich primer samples. We acknowledge Dr. Mansoureh Norouzi Rad at Zeiss for 3D microstructure reconstruction on Al-rich primer using X-ray microscope, and Thermo Fisher Scientific for 3D microstructure reconstruction on Al-rich primer using Helios Plasma FIB/SEM. We appreciate Dr. Babu Viswanathan at OSU for STEM characterization, and Swagelok Center for Surface Analysis of Materials (SCSAM) at Case Western Reserve University for Ar ion polishing.

Characterization and electrochemical assessment of Al-Zn-In alloy with trivalent chromium process coating

To reduce self-corrosion of Al-Zn-In pigments in an Al-rich primer, trivalent chromium process (TCP) was applied to the pigments before mixing in the epoxy binder. The formation of TCP and its effects on both the Al-Zn-In bulk alloy and pigment particles were investigated in this study. The TCP layer on the Al-Zn-In alloy has a bilayer structure similar to TCP layers formed on other alloys. The corrosion rate of bulk Al-Zn-In alloy is reduced by the TCP treatment. The TCP layer likely blocks the access of Cl− to the Al-Zn-In alloy, which reduces corrosion attack initiation.

Crystalline chromium electroplating with high current efficiency using chloride hydrate melt-based trivalent chromium baths

Chromium (Cr) plating using trivalent chromium has been investigated as a replacement for the highly-toxic hexavalent chromium bath. Herein, we report novel chromium plating baths using hydrate-melts. Hydrate-melts have been investigated in recent years as an electrolyte for aqueous Li-ion batteries with a wide electrochemical window, and can be used as an electroplating bath in which the reduction of protons, i.e., bath decomposition, is suppressed. By using a hydrate-melt for electroplating with trivalent chromium, the increase of local pH during electrolysis is suppressed and generation of the electrochemically-inert oligomer of chromium hydroxide can be avoided. Crystalline chromium electrodeposits were successfully obtained from the hydrate-melt-based aqueous baths, which had not been possible with the conventional trivalent chromium process requiring organic coordination agents. Moreover, a current efficiency greater than 80% was achieved. The hydrate-melt-based aqueous bath, with low material cost, is a promising candidate for industrial trivalent chromium plating.

Comparative analysis of the anticorrosive properties of trivalent chromium conversion coatings formed on 2024-T3 and 2024-T351 aluminium alloys

The anticorrosive properties of the trivalent chromium process (TCP) coatings were studied for a 2024 aluminium alloy (AA2024) in both T3 and T351 metallurgical states. Better corrosion resistance was measured for the TCP coated AA2024-T3 compared to AA2024-T351, which was clearly related to the surface copper coverage measured after the pre-treatments for the different samples. The differences were explained considering the reactivity of both the S-phase coarse intermetallics (IMCs) and intergranular Cu-rich precipitates during deoxidation. Large S-phase IMCs and numerous intergranular Cu-rich precipitates constituted critical metallurgical parameters for the anticorrosive properties of the TCP coatings.

Investigation of the Trivalent Chromium Process Conversion Coating as a Sealant for Anodized AA2024-T3

The sealing of an anodic coating on AA2024-T3 with a trivalent chromium process coating (TCP-HF) was investigated. Specimens were anodized in 9.8 wt% H2SO4 at 15 V DC (23 min) producing an oxide coating weight of ca. 1200 mg ft−2 and a thickness of ca. 5 μm. Elemental analysis revealed the sealant forms across the outer oxide layer and within the pores up to a depth at least approaching 1 μm. Anodic and cathodic currents in potentiodynamic polarization curves were suppressed by 5–10× and low frequency impedance (Z0.01 Hz) values were 5× higher for anodized specimens sealed with TCP (∼5 × 106 ohm-cm2), as compared to the unsealed anodized controls. During continuous exposure to 3.5 wt% NaCl, Z0.01 Hz values remained unchanged and greater than 106 ohm-cm2 after 5 days for the TCP-sealed specimen and decreased by 10× for the unsealed anodized control after just three days. A 14-day (336 h) neutral salt-spray exposure produced no significant pitting, discoloration or major coating detachment on anodized specimens sealed with TCP. Overall, the results indicate that the TCP sealant increases the barrier properties of the anodic coating and functions to provide anodic and cathodic corrosion protection.

Transmission Line Modeling of Al-Rich Primer on AA2024-T3

Al-rich primer (AlRP) has been investigated as an alternative to hexavalent chromate based coating systems. The AlRPs used in this study are composed of an epoxy matrix and active Al–Zn–In pigment particles. The surface treatment on the Al–Zn–In pigment particles was the only difference between two AlRPs studied. The pigment particles in one of the AlRPs were treated with trivalent chromium process (TCP), and particles in the other AlRP were not. Overall, the performance of AlRP with TCP-treated pigments was better than the one with bare Al–Zn–In pigments. Electrochemical impedance spectroscopy (EIS) was used to monitor the change of two AlRPs immersed in 0.1 M NaCl solution up to 16,000 h. The evolution of Bode plots was separated into two or three periods of different behavior and the EIS spectra were interpreted using an equivalent electrical circuit using a modified transmission line. The water uptake of the coatings was obtained by extracting coating capacitance in the high frequency range. The AlRPs were saturated with water within 24 h of immersion. Several transmission line parameters of each AlRP were extracted and compared. The ionic resistance through the porous coating and the interfacial resistance between Al pigment particles and the pore electrolyte match well with the open circuit potential evolution.

The Effect of Trivalent Chromium Process on Al-Zn-In Pigments in Epoxy Primer on the Corrosion Protection of AA2024-T3

Active metal pigments in metal-rich coatings are oxidized preferentially and provide sacrificial protection to more-noble metallic substrates. Al-rich primer (AlRP), which contains pigment particles made from an active aluminum alloy (Al-5Zn-0.02In), uses this mechanism to provide a chromate-free epoxy primer system. To address the high self-corrosion rate of active aluminum pigments, the active aluminum pigment particles are pretreated using trivalent chromium process (TCP). In this study, the effects of different TCP treatment times were evaluated, and coating protection properties were studied. Potentiodynamic polarization tests were performed in aerated 0.1 M NaCl solution for a TCP-treated bulk active aluminum alloy and for AA2024-T3. The potentiodynamic polarization curves show that the corrosion potential of the bulk active aluminum alloy is about 500 mV lower than that of AA2024-T3. Therefore, bulk active aluminum alloy is a candidate alloy for cathodic protection of AA2024-T3. In addition, the TCP treatment reduces the corrosion rate of the bulk active aluminum alloy by one order of magnitude. AlRP-coated AA2024-T3 panel samples were scribed and exposed in corrosion chambers, and the cross section of each coating was evaluated by scanning electron microscopy and energy dispersive x-ray spectroscopy mapping. The accelerated corrosion exposure results show that AlRP coatings containing TCP-treated particles provided better protection to the scribe than the one with bare pigment particles. The adhesion of the AlRPs based on pull-off adhesion tests was similar regardless of the TCP treatment time of the pigments, but the adhesion of AlRP was reduced in comparison to a neat epoxy coating.

The Effect of Surface Treatment on the Performance of a Trivalent Chromium Process (TCP) Pretreatment on AA7075 Aerospace Alloys for the Protection Against Filiform Corrosion

The performance of a trivalent chromium process (TCP) pretreatment conversion coating, applied to AA7075 aerospace aluminum alloys, for its ability to improve the filiform corrosion (FFC) of a polyvinyl-butyral coating, was studied as a function of surface treatment. Data from atmospheric FFC and full-immersion corrosion experiments are compared with surface characterization data to gain an understanding of the FFC kinetics on this alloy and mechanism by which the TCP coating provides inhibition. Specimens were prepared with three different surface treatments and studied with and without a TCP pretreatment conversion coating. A biphasic layer incorporating a zirconium-chromium mixed oxide outer layer and a fluoroaluminate interfacial layer was observed on all pretreated specimens. Enhanced corrosion protection by the TCP coating was observed when an acid pickle surface treatment was applied and the FFC filament propagation was stifled with an efficiency of 86%. A zirconium-rich outer oxide layer of approximately 22 nm, more than double the thickness of that measured for the other surface-treatments, is reported. Such layers are reported to be sufficiently dense so as to block ion transport from solution to the alloy surface. This acid pickle surface treatment is shown to effectively reduce the thickness of the native oxide layer and remove intermetallic particles from the surface enabling the formation of a more homogeneous TCP layer. Furthermore, Cu replating resulting from an acidic deoxidation step is shown to have no discernable effect on FFC.

Chromate-free chemical conversion coatings for aluminum alloys

AbstractCorrosion of metallic components represents a major issue in the aeronautical sector, giving rise to safety concerns and significant financial damages. Conversion coatings (CC) based on hexavalent chromium provide exceptional corrosion protection at relatively low cost. However, environmental issues and health concerns raised a growing interest in the development of alternative technologies. These must not only be cost effective and environmentally friendly but also provide corrosion resistance and adhesion performance comparable to Cr6+-based CCs. Simultaneously fulfilling all of these criteria is a difficult challenge, and an industrial application has so far only been achieved by a small number of systems. This review critically summarizes the recent scientific literature and patents for chromate-free CCs on aluminum alloys and tries to assess their potential regarding the highly demanding aerospace requirements. The bath composition and coating characteristics of the trivalent chromium process, rare earth chemical conversion coatings, transition metal oxyanion additives, Zr/Ti-based chemical conversion coatings, sol-gel coatings, and smart coatings providing stimulus-related inhibitor release are discussed. The advantages and disadvantages of the alternative technologies with regard to their practical implementation are debated, as the aeronautics industry is confronted with the necessity to move away from chromates in the near term.

Influence of post-treatment time of trivalent chromium protection coating on aluminium alloy 2024-T3 on improved corrosion resistance

Low corrosion protection performances of Trivalent Chromium Process (TCP) coatings with reference to Chromium Conversion Coatings (CCC) deposited on aluminium alloys can be overcome by application of post-treatment processes. This work shows the effect of post-treatment bath (containing hydrogen peroxide and lanthanum salt) on the chemical composition, structure and the corrosion performances of TCP coating deposited on AA 2024-T3 aluminium alloy. Different times of post-treatment bath were applied on the TCP coating and the samples were analyzed by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Glow Discharge-Optical Emission Spectrometry (GD-OES). The ToF-SIMS and GD-OES depth profiles show that the post-treatment time has no influence on the thickness of the TCP coating and on its bi-layered structure. It is composed of an outer layer, rich in zirconium and chromium oxides and an inner layer rich in aluminium oxides and oxy-fluorides. 3D ToF-SIMS images reveal an enrichment of Cr and Zr-like species over the surface of intermetallic particles with reference to alloy matrix, whereas a homogenous distribution of La is observed. The analysis of in-depth distribution shows that La is present principally in the outer part of the TCP coating. The La concentration increases with increasing post-treatment time. The effect of post-treatment time on protection was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV) in a 0.001 M NaCl + 0.1 M Na2SO4 electrolyte. The increased post-treatment time enhances the cathodic inhibition against oxygen reduction. The post-treatment provides improved coating homogeneity and sealing properties.

Trivalent Chromium Conversion Coating Formed on Hot Dip Zn-55Al-1.6Si Coated Steel

Trivalent Chromium Process (TCP) coating on hot dip Zn-55Al-1.6Si coated steel was investigated by XPS, SEM and EDS. The XPS revealed that aluminium oxides enriched the conversion coating surface. SEM and EDS analyses indicated that composition and microstructure of the conversion coating were not uniform on the dendrite and inter-dendrite regions within the Zn-Al alloy coating, and a small amount of spherical precipitation with the same composition as the conversion coating was detected in the zinc-rich inter-dendrite region. The optimal forming parameters of dilute passivator determined by salt spray test and orthogonal test is: 40°C, 50 vol.% and 3 min. In addition, the salt spray corrosion resistance of the optimal conversion coatings can reach 192 h, and the optimal TCP coating can reduce the cathodic corrosion current density in 0.05 M NaCl solution by an order of magnitude due to the electrochemical polarization measurements.

Evaluation of a Trivalent Chromium Process (TCP) Conversion Coating on AA2024-T3 That Requires No Surface Pretreatment

We report on the study of a new commercial trivalent chromium process (TCP) conversion coating, TCP-1, that requires no deoxidation or etching surface preparation of the aluminum alloy for optimum performance. The corrosion resistance provided by TCP-1 and a comparable conversion coating, TCP-2, both formed by immersion on AA2024-T3, were evaluated using scanning electron microscopy and energy dispersive X-ray analysis, digital microscopy, XPS depth profiling, electrochemical impedance spectroscopy and potentiodynamic polarization techniques. Accelerated degradation testing was also performed to determine how the laboratory electrochemical data correlate with the coating's corrosion protection during neutral salt-spray exposure and full-immersion testing. The results indicate that TCP-1 produces a protective coating on the metal that minimizes corrosion to an equivalent degree as TCP-2; a conversion coating that requires a conventional deoxidation step prior to application. Electrochemical data revealed that both TCP coatings increase the polarization resistance by ∼100x and suppress anodic and cathodic currents by ∼10–100x, as compared to the uncoated alloy. Specimens coated with either TCP coating exhibited little degradation, discoloration or corrosion during a 14-day neutral salt-spray (ASTM B117) exposure and a 14-day full immersion in 3.5 wt.% NaCl at 55°C. In summary, the stand-alone corrosion protection provided by TCP-1 to this alloy is as good as the protection provided by a standard TCP coating.