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The role of intermetallic particles in localized corrosion of an aluminum alloy studied by SKPFM and integrated AFM/SECM
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-4431-0671
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-9453-1333
Sapa Technology, Finspång.
2008 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 155, no 5, C211-218 p.Article in journal (Refereed) Published
Abstract [en]

Aluminum alloy EN AW-3003contains a certain amount of micrometer-sized constituent particles and alarge number of nanometer-sized dispersoids. The practical nobility of intermetallicparticles relative to an alloy matrix was evaluated ex situby scanning Kelvin probe force microscopy (SKPFM), and localized corrosioninitiation of the alloy exposed to chloride solutions was studiedin situ by integrated atomic force microscopy (AFM) and scanningelectrochemical microscopy (SECM). The SKPFM results show a higher Voltapotential for the constituent particles than the matrix, and alarger difference for larger particles. In some cases, the boundaryregion between the large constituents and the matrix exhibits aminimum Volta potential. In contrast, a small Volta potential differencewas measured for the particles less than 1  µm. The SECMmapping of the alloy surface in the solution provided evidenceof a cathodic action of some constituent particles and alocal anodic dissolution adjacent to them. Concurrent AFM and SECMimages indicate that only some of the constituents are proneto initiate localized corrosion. Moreover, in situ AFM observations confirmenhanced localized dissolution in the boundary regions, verifying the cathodiccharacter of the constituent particles and a microgalvanic effect onlocalized corrosion. The fine dispersoids of nanometer size seem tohave no effect on the corrosion initiation.

Place, publisher, year, edition, pages
2008. Vol. 155, no 5, C211-218 p.
Keyword [en]
PROBE FORCE MICROSCOPY; SCANNING KELVIN PROBE; IN-SITU; CHLORIDE SOLUTIONS; MANGANESE-SILICON; AL-ALLOYS; BEHAVIOR; AFM; AA2024-T3; SECM
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-7858DOI: 10.1149/1.2883737ISI: 000254779700024Scopus ID: 2-s2.0-41849083105OAI: oai:DiVA.org:kth-7858DiVA: diva2:13003
Note
QC 20100705. Uppdaterad från Submitted till Published i DiVA 20100705.Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-19Bibliographically approved
In thesis
1. Mechanistic studies of localized corrosion of Al alloys by high resolution in-situ and ex-situ probing techniques
Open this publication in new window or tab >>Mechanistic studies of localized corrosion of Al alloys by high resolution in-situ and ex-situ probing techniques
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

A multi-analytical approach based on in-situ and ex-situ local probing techniques was employed to investigate localized corrosion mechanisms of some aluminum alloys in chloride containing solutions, focusing on the influence of intermetallic particles (IMPs) in the alloys. In the EN AW-3003 alloy, SEM-EDS analysis revealed constituent and dispersoid IMPs. There are two types of constituent IMPs, with size ranging from 0.5 to several μm, and composition typically Al6(Fe,Mn) or Al12(Mn,Fe)3Si, respectively,having a Mn/Fe ratio of about 1:1. Fine dispersoids of 0.5 μm or less in size normally have the composition Al12Mn3Si1-2. Scanning Kelvin probe force microscopy (SKPFM measurements showed that the constituent IMPs have a higher Volta potential compared to the matrix, and the Volta potential difference increased with particle size, probably related to the composition of the IMPs. The SKPFM results also showed a Volta potential minimum in the boundary region adjacent to some larger IMPs.

The open-circuit potential and electrochemical impedance spectroscopy measurements indicated local electrochemical activities occurring on the surface, and active-like dissolution in the acidic solutions, but a passive-like behavior in the near-neutral solutions. Infrared reflection-absorption spectroscopy measurements after exposure and thermodynamic calculations suggested the formation of mixtures of aluminum oxyhydroxide and acetate on the surface in acetic acid solutions. The formation and fraction of dominant species of the corrosion products depend on the pH of the solution, and aluminum chloride compounds may form at very low pH.

Moreover, an integrated in-situ atomic force microscopy (AFM) and scanningelectrochemical microscopy (SECM) set-up was used to investigate the localized activities on the surface. With a dual mode probe, acting as both AFM tip and SECM microelectrode, concurrent topography and electrochemical current images were obtained on the same area of the surface. Numerical simulations of the SECM suggested a micrometer lateral resolution under favorable conditions and the ability to resolve μmsized active sites with a separation distance of about 3 μm or larger. The simulations were verified by SECM mapping of the aluminum alloys in the chloride solutions. The AFM/SECM measurements revealed enhanced cathodic activity on some larger IMPs and local anodic dissolution around larger IMPs. In-situ AFM monitoring confirmed preferential dissolution in the boundary region adjacent to some of these IMPs. The results elucidate the micro-galvanic effect and size effect of the IMPs during the initiation of localized corrosion of the Al alloys.

Furthermore, differences in corrosion properties between EN AW-3003 and a newly developed Al–Mn–Si–Zr alloy were studied with a similar approach. Compared to EN AW-3003, the new alloy had a smaller number of particles with a large Volta potential difference relative to the matrix. In slightly corrosive solutions extensive localized dissolution and deposition of corrosion products occurred on EN AW-3003, whereas only a small number of corroding sites and “tunnel-like” pits occurred on the Al–Mn–Si–Zr alloy. The lower corrosion activity and the smaller tunnel-like pits resulted in lower material loss of the Al–Mn–Si–Zr alloy, which is beneficial for applications using a thin material.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. viii, 100 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:82
Keyword
localized corrosion, pitting, aluminum alloy, intermetallic particle, Volta potential, cathodic activity, micro-galvanic effect, size dependence, SKPFM, in-situ AFM, integrated AFM/SECM, numerical simulation, micrometer resolution, EIS.
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4588 (URN)978-91-7178-817-7 (ISBN)
Public defence
2008-01-21, Lecture Hall F3, Building F, Lindstedtsvägen 26, KTH, 10:00
Opponent
Supervisors
Note
QC 20100702Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-20Bibliographically approved

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Pan, JinshanLeygraf, Christofer

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