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Mechanistic studies of localized corrosion of Al alloys by high resolution in-situ and ex-situ probing techniques
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.
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 [en]
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: urn:nbn:se:kth:diva-4588ISBN: 978-91-7178-817-7 (print)OAI: oai:DiVA.org:kth-4588DiVA: diva2:13004
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
List of papers
1. In-situ investigation of localized corrosion of aluminum alloys in chloride solution using integrated EC-AFM/SECM technique
Open this publication in new window or tab >>In-situ investigation of localized corrosion of aluminum alloys in chloride solution using integrated EC-AFM/SECM technique
2005 (English)In: Electrochemical and solid-state letters, ISSN 1099-0062, Vol. 8, no 6, B21-B24 p.Article in journal (Refereed) Published
Abstract [en]

Scanning electrochemical microscopy (SECM) has been integrated with electrochemical atomic force microscopy (EC-AFM), and applied for in situ studies of localized corrosion of Al alloys in NaCl solution. The instrument utilizes a dual mode probe, which functions both as a normal cantilever and as an ultramicroelectrode. The I-/I3- redox mediator was used for mapping of local electrochemical current. Concurrent topography and electrochemical activity maps have been obtained on the same surface area with micrometer lateral resolution. Preliminary results show ongoing localized dissolution related to intermetallic particles in the Al alloys, which may occur well below the breakdown potential.

Keyword
Aluminum alloys; Atomic force microscopy; Intermetallics; Microstructure; Scanning electron microscopy; Sodium chloride
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7852 (URN)10.1149/1.1911900 (DOI)000229056000020 ()2-s2.0-20844438052 (Scopus ID)
Note
QC 20100702Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-19Bibliographically approved
2. Probing of local dissolution of Al-alloys in chloride solutions by AFM and SECM
Open this publication in new window or tab >>Probing of local dissolution of Al-alloys in chloride solutions by AFM and SECM
2006 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, 5499-5503 p.Article in journal (Refereed) Published
Abstract [en]

Local dissolution of Al alloys was probed in situ in chloride solutions by using atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM). Preferential dissolution in the boundary region between some intermetallic particles (IMPs) and alloy matrix, and trench formation around large IMPs during free immersion and under electrochemical anodic polarization were observed, which indicate different dissolution behavior associated to different types of IMPs. Moreover, by using an integrated AFM/SECM system with a dual mode cantilever/microelectrode probe, simultaneous probing of electrochemical active sites and topographic changes over the same area was performed with submicron resolution. This allowed the ongoing localized corrosion processes related to the IMP to be revealed.

Keyword
localized corrosion; Al alloys; intermetallic particles; EC-AFM and SECM
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7853 (URN)10.1016/j.apsusc.2005.12.023 (DOI)000238623300063 ()2-s2.0-33744547851 (Scopus ID)
Note
QC 20100705. Conference: 8th International Conference on Atomically Controlled Surfaces, Interfaces, and Nanostructures/13th International Congress on Thin Films. Stockholm, SWEDEN. JUN 20-23, 2005. Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-19Bibliographically approved
3. Integrated AFM and SECM for in situ studies of localized corrosion of Al alloys
Open this publication in new window or tab >>Integrated AFM and SECM for in situ studies of localized corrosion of Al alloys
2007 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 0019-4686, Vol. 52, no 27, 7697-7705 p.Article in journal (Refereed) Published
Abstract [en]

Rolled 3xxx series Al alloys, e.g., EN AW-3003, are generally used as fin or tube material in heat exchangers for automobiles. With reducing fin thickness, maintaining fin material integrity is of increasing importance. This study aimed at exploring the differences in intrinsic corrosion properties between EN AW-3003 and a newly developed Al–Mn–Si–Zr fin alloy using state-of-the-art local probing techniques. Volta potential mapping of both alloys by scanning Kelvin probe force microscopy (SKPFM) indicates a cathodic behaviour of constituent intermetallic particles (>0.5 μm) relative to the alloy matrix. Compared to EN AW-3003, the Al–Mn–Si–Zr alloy has a smaller number of particles with large Volta potential difference relative to the matrix. In situ atomic force microscopy (AFM) measurements in slightly corrosive solutions showed extensive localized dissolution and deposition of corrosion products on EN AW-3003, and only a small number of corroding sites and “tunnel-like” pits on Al–Mn–Si–Zr. Probing the ongoing localized corrosion process by integrated AFM and scanning electrochemical microscopy (SECM) revealed more extensive local electrochemical activity on EN AW-3003 than on Al–Mn–Si–Zr. In all, the lower corrosion activity and smaller tunnel-like pits resulted in lower material loss of the Al–Mn–Si–Zr alloy, a beneficial property when striving towards thinner fin material.

Keyword
Al alloy; Localized corrosion; SKPFM; In situ AFM; Integrated in situ AFM/SECM
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7854 (URN)10.1016/j.electacta.2006.12.073 (DOI)000249857800026 ()2-s2.0-34547862411 (Scopus ID)
Note
QC 20100705. ELECTROCHEMICAL METHODS IN CORROSION RESEARCH Selection of papers from the 9th International Symposium (EMCR 2006) 18-23 June 2006, Dourdan, France Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-19Bibliographically approved
4. AFM-based SECM for insitu investigation of localized corrosion: Part I: Instrumental set-up and SECM simulation
Open this publication in new window or tab >>AFM-based SECM for insitu investigation of localized corrosion: Part I: Instrumental set-up and SECM simulation
Show others...
(English)In: Journal of the Electrochemical Society, ISSN 0013-4651Article in journal (Other academic) Submitted
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7855 (URN)
Note
QS 20120326Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-26Bibliographically approved
5. AFMbased SECM for in-situ investigation of localized corrosion: Part II: Characterization, calibration and verification
Open this publication in new window or tab >>AFMbased SECM for in-situ investigation of localized corrosion: Part II: Characterization, calibration and verification
Show others...
(English)In: Journal of the Electrochemical Society, ISSN 0013-4651Article in journal (Other academic) Submitted
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7856 (URN)
Note
QS 20120326Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-03-26Bibliographically approved
6. Multianalytical and in situ studies of localized corrosion of EN AW-3003 alloy: influence of intermetallic particles
Open this publication in new window or tab >>Multianalytical and in situ studies of localized corrosion of EN AW-3003 alloy: influence of intermetallic particles
2008 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 155, no 4, C138-146 p.Article in journal (Refereed) Published
Abstract [en]

The influence of intermetallic particles (IMPs) on the localized corrosion behavior of an EN AW-3003 alloy was investigated in situ by conventional electrochemical measurements and high-resolution local probing techniques in chloride solutions with and without acetic acid. The open-circuit potential (OCP) fluctuations indicate local activities on the surface, and electrochemical impedance spectroscopy measurements suggest active dissolution in acidic solutions but a passivelike behavior in near-neutral solutions. Integrated atomic force microscopy/scanning electrochemical microscopy (AFM/SECM) was used to investigate the localized activities on the surface in a diluted chloride solution. The concurrent AFM and SECM images reveal cathodic activity of the IMPs and enhanced anodic current due to localized dissolution adjacent to some large IMPs upon anodic polarization. Moreover, in situ AFM imaging at OCP in solutions containing acetic acid show localized dissolution around the IMPs, leading to formation of deposits of ringlike corrosion products. The in situ observations reveal the microgalvanic effect of the IMPs, and the large IMPs are more prone to initiate localized corrosion compared to submicrometer dispersoids. Infrared absorption spectroscopy measurements after the exposure and thermodynamic calculations suggest the formation of mixtures of aluminum oxihydroxide and acetate on the surface in the presence of acetic acid.

Keyword
Acetic acid; Anodic polarization; Atomic force microscopy; Corrosion; Electrochemical impedance spectroscopy; Intermetallics
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7857 (URN)10.1149/1.2834454 (DOI)000253761700029 ()2-s2.0-40549117926 (Scopus ID)
Note
QC 20100705Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2012-02-14Bibliographically approved
7. The role of intermetallic particles in localized corrosion of an aluminum alloy studied by SKPFM and integrated AFM/SECM
Open this publication in new window or tab >>The role of intermetallic particles in localized corrosion of an aluminum alloy studied by SKPFM and integrated AFM/SECM
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.

Keyword
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:nbn:se:kth:diva-7858 (URN)10.1149/1.2883737 (DOI)000254779700024 ()2-s2.0-41849083105 (Scopus ID)
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

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Citation style
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  • fi-FI
  • nn-NO
  • nn-NB
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Output format
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