The effect of chromic sulfate concentration and immersion time on the structures and anticorrosive performance of the Cr(III) conversion coatings on aluminum alloys

Chen, Weikun; Bai, Ching-Yuan; Liu, Chung-Ming; Lin, Chao-Sung; Ger, Ming-Der

doi:10.1016/j.apsusc.2010.03.003

Cited by 57 publications

(25 citation statements)

References 18 publications

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“…22 Corrosion resistance provided by TCP conversion layers is widely discussed in the literature. 10,11,15,18,19 The TCP can potentially replace existing chromate conversion coatings, even if their corrosion resistance is inferior.…”

mentioning

confidence: 99%

“…10,11,15,18,19 The TCP can potentially replace existing chromate conversion coatings, even if their corrosion resistance is inferior. 19 Li et al 10,15 have shown that TCP coatings provide both anodic and cathodic protection by blocking physically Al-rich sites and copper-containing intermetallic particles. They also concluded that TCP offers a better corrosion protection to AA6061 and AA7075 than to the AA2024 aluminum alloys.…”

mentioning

confidence: 99%

“…10,11,[17][18][19][20] Although TCP has been designed to contain chromium only at a + 3 oxidation state, some authors pointed out the presence of hexavalent chromium 10,12,18,21,22 while others indicate that only trivalent chromium was found.…”

mentioning

confidence: 99%

“…11,12,18 TCP conversion coatings are amorphous, 14,18 and have a two-layer structure as described by a majority of authors, with an outer part containing zirconium, chromium, oxygen and fluorine and an inner layer composed of aluminum, fluorine and oxygen. 10,11,[17][18][19][20] Although TCP has been designed to contain chromium only at a + 3 oxidation state, some authors pointed out the presence of hexavalent chromium 10,12,18,21,22 while others indicate that only trivalent chromium was found. 11,23 Hexavalent chromium has been detected on TCP formed on pure aluminum after one hour of drying in air by Qi et al 18 Li et al demonstrated that hexavalent chromium was locally present in TCP coating above intermetallic particles of AA-2024 after * Electrochemical Society Fellow.…”

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confidence: 99%

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Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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The effects of post-treatment applied on Trivalent Chromium Protection (TCP) coatings deposited on aluminum alloy 2024-T3 was studied by electrochemical and surface analytical techniques: X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The aim of the post-treatment was to improve the corrosion resistance of the TCP coating. To understand the influence of the post-treatment, using a bath containing H 2 O 2 and a lanthanum salt as an inhibitor, our approach was to study the effect of these two components separately. It was found that the improved corrosion protection provided by the post-treated TCP was related to a synergetic effect of the two components. XPS and ToF-SIMS analyses showed that (i) the thickness of the TCP coating is not modified by the post-treatment, (ii) lanthanum is present on the surface and in the bulk of the TCP and (iii) is found in very small amount only on the extreme surface. The total concentration of Cr(VI) (oxide/hydroxide) was estimated to be below 0.1 wt% in the post-treated TCP layer. It was concluded that lanthanum plays a significant role in improving the coating density and homogeneity and has a beneficial effect on the TCP coating cracking as observed by Scanning Electron Aluminum alloys are used for aerospace applications for their low weight and good mechanical properties.1-3 To improve the corrosion properties of aluminum alloys and to provide good paint adhesion, the first layer of coating applied on the aluminum alloy surface used to be a chromate conversion coating (CCC).4-6 However, hexavalent chromium used in the CCC coatings is highly toxic, 4,7 its use is very much restricted in Europe 8 and the United States 9 and will be forbidden by 2024 by the European Community with respect to the Registration, Evaluation, Authorization and Restriction of Chemicals (REACh).8 Therefore, new conversion coatings have been developed, and one of the most promising solutions is the Trivalent Chromium Protection coating called also as the Trivalent Chrome Process (TCP).10-14 TCP conversion coatings are formed by immersion in a solution containing Zr 4+ , Cr 3+ and F − ions, at a pH between 3.8 and 4.0. As it has already been widely discussed, the coating formation mechanism occurs by multiple chemical steps. 10,11,13,[15][16][17] The initial step involves dissolution of the aluminum oxide layer by fluorides. The removal of the oxide layer exposes the metal surface where cathodic reactions take place. Oxygen reduction reaction, and possibly hydrogen discharge, which counterbalance aluminum oxidation, consume protons and causes a pH increase at the interface between the metallic substrate and the solution, as measured by Li et al. 15 The high pH favors the precipitation of ions present in the solution, forming a hydrated layer of zirconium and chromium oxide. The thickness of the TCP layer is usually of the order of 100 nm, depending on the nature of the aluminum alloy, the concentration of the solution and the immersion time.11,12,18 ...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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“…33 To study this correlation, Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the corrosion resistance of the samples treated with different cerium concentrations. From Fig.…”

Section: Effect Of Cerium Concentrationmentioning

confidence: 99%

Preparation and Corrosion Behaviour of Cerium Based Sol-gel Composite Coatings on AA2024-T4 Aluminum Alloy

Peng

Chang

et al. 2016

Electrochemistry

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A serial of composite coatings produced by combination of cerium sol-gel coatings and cerium conversion layers has been developed in this work: (1) sol-gel coating sealed by conversion coating; (2) sol-gel coating sealed by lowdensity sol; (3) conversion coating thickened by sol-gel coating. For both sol-gel coatings and conversion coatings, cerium chloride heptahydrate (CeCl 3 ·7H 2 O) was used as cerium source. In order to evaluate the anti-corrosion properties of these composite coatings, Electrochemical Impedance Spectroscopy (EIS) and salt spray test (SST) were employed as the assessing method. Furthermore, the surface morphology of these composite coatings was characterized by SEM observation. The EIS and SST results thus obtained showed that the anti-corrosion properties of the composite coating (1) had been remarkably improved compared to the any single layer of sol-gel coating or conversion coating. Furthermore, the SEM observation revealed that the morphology of that composite coating was uniform and homogeneous, which may explicate the superior corrosion-resistant performance obtained by the composite coating (1). By contrast, other composite coatings including composite coating (2) and (3) were not as good as composite coating (1) in corrosion resistance, which could be attributed to cracks and heterogeneous microstructure existing on the surface of these composite coatings.

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Local Evolution of pH with Time Determined by Shear Force‐based Scanning Electrochemical Microscopy: Surface Reactivity of Anodized Aluminium

et al. 2016

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1IntroductionIn order to enhance the corrosion resistance of aluminium alloys [1] used in the aircraft industry,amulti-layer coatings ystem is formed on the metallic surface.T he first step generally consists in ana nodizing process performed in an acidic electrolyte such as sulphuric acid [2,3].T he resulting anodizedl ayer is constituted by an etwork of nanosized pores. Then this porous anodized layer is sealed in as olution containingc ompounds acting as corrosion inhibitors.C hromate is the most efficient one thanks to as pecific property of corrosion self-healing [4][5][6].H owever,d ue to its carcinogenic toxicity [7],c hromate should be banned from 2017 in the European Union.R ecently,n ew sealing solutions containing chromium(III) and zirconium(IV)s pecies have been developed and seem to be an interesting alternativet ou sual chromates [8][9][10].Nevertheless,t he efficiencyo ft he sealing processes mainly depends on the surface reactivity of the nanoporous oxide structureo nt he different anodized aluminium alloys.I nt his framework, the purpose of this work is to in-situ determine the time course of the pH change in the sealing solution, near the surface of the nanoporousa nodized structure formed on 7175 aluminium alloy.Scanninge lectrochemicalm icroscopy (SECM) was chosen here to monitor the pH at this interface using ap Hm icroelectrode.W hile SECM is historically based on monitoring the amperometric response of microelectrode [11],p otentiometric probes have rapidly been used for monitoring pH or metalc ation concentration at inter-faces [12][13][14] and applied to the analysis of metal surface treatment [15] and corrosion [14,[16][17][18][19][20]. In contrast to amperometric probes,m ost potentiometric probesc annot be positioned accurately in solution at ac ontrolled distance from the interface to be analyzed [ 21,22].I nt he present work, an additional difficulty is the positioning of the pH sensitive electrode with asufficient accuracy in air before the solutioni si ntroduced in the electrochemical cell. In this specific case, neither potentiometric nor amperometric response of microelectrode can be usedt op osition it near to the aluminium alloy surface.Shear force controlf or SECM (SF-SECM) is one of the technologies that has been proposedf or positioning am icroelectrode at ad efined distance from as ample independently from the electrochemical measurement [23][24][25].D etermination of local pH changes in shear forcebased SECM have been performede ither with iridium oxide based pH-sensor [17,20] or membrane-based ionselective electrodes [22].I nc orrosion studies,s hear force Abstract:S hear force-based scanning electrochemical microscopy is applied for pH monitoring during asealing reaction at the interface between anodized 7175 aluminium alloy and as olution containing Cr(III) and Zr(IV) species.p Hm easurement is carriedo ut with the electrode positioned near enough to the surface to be in the diffusion zone of the liquid/solid interface,i nt he reach of the surface-generated pH modulati...

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The effect of chromic sulfate concentration and immersion time on the structures and anticorrosive performance of the Cr(III) conversion coatings on aluminum alloys

Cited by 57 publications

References 18 publications

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Preparation and Corrosion Behaviour of Cerium Based Sol-gel Composite Coatings on AA2024-T4 Aluminum Alloy

Local Evolution of pH with Time Determined by Shear Force‐based Scanning Electrochemical Microscopy: Surface Reactivity of Anodized Aluminium

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