Protection of Aluminium Alloys against Stress Corrosion Cracking in Saline Water by Properly Oriented Anodic Coatings: IV. Influence of the temperature of the anodising bath

Skoulikidis, Th.; Spathis, P.

doi:10.1179/000705982798274516

Cited by 6 publications

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“…The influence of the oxide thickness on the SCC behaviour of the anodized Al‐alloy is explained by the change of the protective properties of oxides with thickness, being more protective against corrosion, but less resistant against mechanical stress, than is bare aluminium (Skoulikidis and Spathis, 1982; Skoulikidis and Karageorgos, 1980; Skoulikidis and Colios, 1987). Thus, a maximum of the protective properties at an oxide thickness of 10 μ m was observed, where subsequently the time to failure decreases for thicker coatings, the differences being greater for the higher concentrations of sulphate ions.…”

Section: Discussionmentioning

confidence: 99%

“…It has been shown that, during anodizing, a porous Al 2 O 3 film with a cellular structure up to a thickness of 36 mm is formed, with cells oriented parallel to the direction of gravity as a result of the rapid evolution of oxygen in the opposite direction. It was found that the protective properties of oxides change with thickness and structure, being better against corrosion than aluminium, but worse against mechanical stress (Skoulikidis and Spathis, 1982;Skoulikidis and Karageorgos, 1980;Skoulikidis and Colios, 1987 In most cases of studies of SCC in saline water, a 3.5 per cent NaCl solution is used as the corrosive environment. However, a typical composition of seawater also contains various other ions, such as K þ , Mg 2þ , Ca 2þ , Br 2 and mainly SO 22 4 .…”

Section: Introductionmentioning

confidence: 98%

“…The oxide thickness usually employed in natural conditions is 10‐15 μ m and for marine environments 20‐25 μ m. It has been shown that, during anodizing, a porous Al 2 O 3 film with a cellular structure up to a thickness of 36 μ m is formed, with cells oriented parallel to the direction of gravity as a result of the rapid evolution of oxygen in the opposite direction. It was found that the protective properties of oxides change with thickness and structure, being better against corrosion than aluminium, but worse against mechanical stress (Skoulikidis and Spathis, 1982; Skoulikidis and Karageorgos, 1980; Skoulikidis and Colios, 1987; Mert et al , 2011).…”

Section: Introductionmentioning

confidence: 99%

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Influence of seawater composition on SCC behavior of anodized 1050 Al‐alloy

Spathis

Papastergiadis

2013

Anti-Corrosion Methods and Materials

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Purpose -The purpose of this paper is to study the stress corrosion cracking (SCC) behaviour of anodized 1050 Al-alloy in marine environments at different concentrations of sulphate ions. Design/methodology/approach -The SCC experiments were performed by measuring the time to failure in 3.5% NaCl solution, or in the presence of three different concentrations of sulphate ions under conditions of applied anodic current. For the interpretation of the results, changes in potential during SCC tests and optical microscope micrographs of stress corrosion tested specimens at various periods of time, were obtained. Findings -The influence of seawater composition on the SCC behaviour of the anodized 1050 Al-alloy depends on the concentration of sulphate ions, the oxide thickness and the stress level. At the higher stress levels and low concentrations of sulphate ions, increased times to failure were observed. These results were attributed to the inhibitory action of sulphate ions. At a low stress level and higher concentration of sulphate ions, the increased times of exposure and the more intensive corrosive environment led to partial destruction of the anodic coatings and a decrease in the time to failure. Better protective properties were observed at an oxide thickness of 10 mm. The thicker oxides did not protect so well because they were more brittle, cracking under strain and allowing corrosive species to reach the metal surface.Research limitations/implications -The hypothesised mechanism of the effect of seawater composition on the SCC behaviour of anodized Al-alloys depended on the concentration of sulphate ions and the stress level remains yet to be confirmed. Practical implications -The selection of suitable anodic coatings for the protection of aluminium alloys against stress corrosion cracking depends on the composition of the marine environment. Originality/value -The paper provides information regarding the influence of sulphate ions on the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Influence of seawater composition on SCC behavior of anodized 1050 Al‐alloy

Spathis

Papastergiadis

2013

Anti-Corrosion Methods and Materials

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“…The orientation of the coatings was controlled by positioning the specimens with their axes horizontal (HA) or vertical (VA) in the acid bath. According to previous experience (Skoulikidis and Spathis, 1982), this produces coatings with grains oriented perpendicular or parallel to the stressing direction, respectively. Thicknesses of 5, 15 and 25 mm, were produced with various current densities and anodising times ( Table I).…”

Section: Experimental Methodsmentioning

confidence: 95%

“…The behaviour of anodised aluminium alloys depends on the conditions of anodising: the anodising bath, type of coating, oxide thickness and structure, current density and the temperature of anodising. Also, among the various acid and salt solutions used as anodising baths, porous layers are formed in those with a low pH, whereas barrier layers are produced with a neutral pH and a solution of 15-20 per cent H 2 SO 4 is the most commonly used (Skoulikidis and Karageorgos, 1980;Skoulikidis and Spathis, 1982;Skoulikidis and Colios, 1987).…”

Section: Introductionmentioning

confidence: 98%

Influence of anodic coatings on stress corrosion behaviour of 7017 aluminium alloy

Spathis

2013

Anti-Corrosion Methods and Materials

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Purpose -The purpose of this work was to study the cracking susceptibility of a 7017 aluminium alloy, after anodising under various conditions. Design/methodology/approach -Slow strain tests in dry air, laboratory air and sodium chloride solution were employed. Anodic oxide films were produced with various applied current densities and thicknesses, in horizontal or vertical orientation of the coatings, at the free corrosion potential and also at various anodic or cathodic potentials. For the interpretation of the results, a metallographic study of the specimens before and after straining to failure was carried out using a scanning electron microscope. Findings -The behaviour of anodic coatings was found to depend very much on the anodising conditions. The coatings reduced the ductility of the alloy in dry air but can actually increase the ductility in laboratory air and in 3.5 per cent sodium chloride solution. In most cases, the ductility of coated specimens was greater in 3.5 per cent NaCl solution than in dry air, possibly due to crack blunting by the aggressive environment. Anodic coatings moved the free corrosion potential of the alloy in the noble direction and both the anodised and the bare alloy generally suffered a reduction in ductility at potentials anodic or cathodic to the free corrosion potential, the fall being more rapid for the anodised alloy.Research limitations/implications -The mechanism causing the increased ductility of coated specimens in 3.5 per cent NaCl solution than in dry air remains yet to be confirmed. Practical implications -The selection of suitable anodic coatings for the protection of aluminium alloys against stress corrosion cracking depends on the anodising conditions. Originality/value -The paper provides information regarding the influence of anodising conditions on the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

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