Confocal Laser Scanning Microscopy as a Tool for In Situ Monitoring of Corrosion Underneath Organic Coatings

Schneider, Oliver; Ilevbare, G. O.; Scully, John R.; Kelly, Robert G.

doi:10.1149/1.1413703

Cited by 17 publications

(12 citation statements)

References 9 publications

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“…The z-step height was 0.6 m. The samples were connected to a specially constructed flat electrochemical cell made from polymethylacrylate and fastened onto the CLSM stage. 37 The cell al-lowed for immersion of the objective lens into the electrolyte and for its approach to the sample surface. One sample was immersed in 0.5 M NaCl, one in 0.5 M NaCl + 0.0032 M HCl ͑pH 2.5͒, and two in 0.1 M Na 2 SO 4 ͑pH 3.5 or pH 3.0, adjusted with H 2 SO 4 ͒.…”

Section: Methodsmentioning

confidence: 99%

“…CLSM has been applied to the study of bare-aluminum-alloy corrosion, 8,15,17,33,34 the anodization of AA5052-H32, 35,36 and was also shown to be capable of monitoring the corroding alloy surface underneath a transparent organic coating. 37,38 In the first part of this series we focused on the role of localized corrosion of intermetallic particles and of metastable pitting on the bare alloys, 15 whereas the second part dealt with trench formation at these particles. 17 In this study, the blister formation on coated AA2024-T3 was monitored with in situ CLSM in four different electrolyte environments: 0.5 M NaCl, 0.5 M NaCl + 0.0032 M HCl ͑pH 2.5͒, and 0.1 M Na 2 SO 4 + 0.005 M NaCl ͑pH 3.5 and 3.0, adjusted with H 2 SO 4 ͒.…”

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confidence: 99%

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In Situ Confocal Laser Scanning Microscopy of AA2024-T3 Corrosion Metrology

Schneider

Ilevbare

Kelly

et al. 2007

J. Electrochem. Soc.

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Epoxy-coated AA2024-T3 samples were exposed to solutions of specific chloride concentration and pH. Underfilm corrosion processes were monitored in situ with confocal laser scanning microscopy. In near-neutral solutions, pitting at both intermetallic compounds and within the alloy matrix was observed during coating blister formation and growth. Evidence for anodic undermining/corrosion product wedging was obtained. In addition, general corrosion of the matrix led to a strong roughening of the surface. In acidic NaCl solutions, localized corrosion was observed at the original blister site. Thereafter, general attack on the Al-matrix near the original blister was more important than intermetallic particle corrosion. In acidic sulfate solutions, the coating started to fail at many locations on the sample at the same time due to attack of the coating and loss of adhesion at the interface. This more global failure is in agreement with electrochemical impedance measurements and the observation of numerous blisters on large-area panels.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

In Situ Confocal Laser Scanning Microscopy of AA2024-T3 Corrosion Metrology

Schneider

Ilevbare

Kelly

et al. 2007

J. Electrochem. Soc.

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“…In the materials science field the technique has mainly been used to investigate wear and in the context of surfaces. A few studies have been made using CLSM in the corrosion science field (33)(34)(35)(36). The technique is better described in the literature (37).…”

Section: Fourier Transform Infrared Spectroscopy (Ftir)mentioning

confidence: 99%

Atmospheric Corrosion of Magnesium Alloys: Influence of Temperature, Relative Humidity, and Chloride Deposition

LeBozec¹,

Jönsson²,

Thierry³

2004

CORROSION

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The low density and high specific strength of magnesium alloys have created a great deal of interest in the use of these alloys in the automotive and aerospace industries and in portable electronics. All of these industries deal with applications in which weight is extremely important. However, an obstacle to overcome when using magnesium alloys in engineering applications are their unsatisfactory corrosion properties. This thesis is devoted to the atmospheric corrosion of the two magnesium alloys AZ91D and AM50, in particular the ways the microstructure and exposure parameters of these alloys influence their corrosion behaviour. The work includes both laboratory and field studies. The results obtained show that the microstructure is of vital importance for the corrosion behaviour under atmospheric conditions. The microstructure of magnesium-aluminium alloys contains different intermetallic phases, e.g. Al 8 Mn 5 and β-Mg 17 Al 12. The local nobility of these intermetallic phases was measured on a submicron level in an atmospheric environment. It was shown that particles of the Al-Mn type exhibit the highest Volta potential among the microstructure constituents of the AZ91D magnesium alloy. Further, it was shown that the Volta potential was highly dependent on the aluminium content of the magnesiumaluminium phases in the surface layer. When thin electrolyte layers are present, CO 2 diffuses readily to the surface forming magnesium carbonate, hydromagnesite. The CO 2 lowers the pH in areas on the surface that are alkaline due to the cathodic reaction. This stabilises the aluminium-containing surface film, the result being increased corrosion protection of phases rich in aluminium. Both in the laboratory and under field conditions the corrosion attack was initiated in large α-phase grains, which is explained by the lower aluminium content in these grains. The thin electrolyte film, which is formed under atmospheric conditions, decreases the possibility of galvanic coupling of alloy constituents located at larger distances from each other. Thus the cathodic process is in most cases located in the eutectic α-/β phase close to the α-phases, instead of in intermetallic Al-Mn particles, even though the driving force for the initiation of the corrosion attack in Al-Mn particles should be high, due to their high nobility. .

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“…A few studies have been made using CLSM in the corrosion science field. [8][9][10][11] The advantages of CLSM, compared to other profilemetry measurement techniques, are the short measurement times and the high magnification. High magnification can be achieved due to the short wavelength of the blue laser.…”

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The Initial Steps of Atmospheric Corrosion on Magnesium Alloy AZ91D

Jönsson¹,

Persson²,

Gubner³

2007

J. Electrochem. Soc.

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Magnesium, with its low density, is a very interesting metal in applications in which weight is important. In this work the initiation of corrosion attacks on magnesium alloy AZ91D has been investigated under atmospheric conditions, using confocal laser scanning microscopy and SKPFM. The corrosion attack starts in the ␣ phase in larger grains and is under atmospheric conditions initiated at the boundary between the ␣ phase and the eutectic ␣-/␤ phase. The SKPFM measurement shows that a high Volta potential difference exists between the larger grains and the surrounding eutectic ␣-/␤ phase and the ␤ phase. A microgalvanic element is formed in the thin adlayer on the surface, with anodic Mg dissolution in the ␣ phase and the cathodic reaction primarily in the eutectic ␣-/␤ phase. The initiation in the larger grains could be explained by the smaller aluminum content in the larger grains due to the solidification process. Even though intermetallic Al-Mn particles show a high Volta potential difference with the connecting ␣ phase, they are not involved in the initiation of the corrosion. This is explained by the position within the microstructure of Al-Mn particles embedded in the ␤ phase and located away from the ␣ phase.Magnesium alloys have low density and high specific strength, and these properties have created a great deal of interest in the use of these alloys in the motor and aerospace industries and in portable electronics. All of these industrial areas deal with applications in which weight is important. However, a big problem with magnesium alloys is their unsatisfactory corrosion properties. Understanding the corrosion properties of these alloys is vital if they are to become suitable alternatives for lightweight automotive components.In recent years, significant improvements have been made in achieving better corrosion resistance, particularly by reducing the contents of impurities such as Fe, Cu, and Ni. Intermetallic phases, a result of the casting process, play an important role in the corrosion process. The role of these intermetallic phases has been addressed in a number of article. 1-6 However, despite the fact that magnesium alloys as structural materials are mostly used in atmospheric environments, the interpretation of the effect of microconstituents is almost exclusively based on electrochemical data obtained from measurement in solutions. The corrosion processes in aqueous solutions are different from those occurring in an atmospheric environment.In an earlier work 7 the authors investigated the local nobility of the different intermetallic phases in the AZ91D alloy with the help of scanning Kelvin probe force microscopy ͑SKPFM͒. The results showed that under laboratory air conditions both the Al 8 Mn 5 and the ␤-Mg 17 Al 12 phases of the AZ91D alloy had a Volta potential which was, respectively, approximately 400 and 200 mV more noble than that of the ␣-magnesium phase. In the present work the influence of these intermetallic phases on the initial atmospheric corrosion process has been investi...

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Confocal Laser Scanning Microscopy as a Tool for In Situ Monitoring of Corrosion Underneath Organic Coatings

Cited by 17 publications

References 9 publications

In Situ Confocal Laser Scanning Microscopy of AA2024-T3 Corrosion Metrology

In Situ Confocal Laser Scanning Microscopy of AA2024-T3 Corrosion Metrology

Atmospheric Corrosion of Magnesium Alloys: Influence of Temperature, Relative Humidity, and Chloride Deposition

The Initial Steps of Atmospheric Corrosion on Magnesium Alloy AZ91D

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