Light Metals for the Cathodic Protection of Steel Structures

Mears, R. B.; Brown, Chad

doi:10.5006/0010-9312-1.3.113

Cited by 23 publications

(12 citation statements)

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“…However, magnesium is one of the materials which bear stain most easily because of its quite low potential region where metallic magnesium can exist in wet environment. 1,2) As protective coatings for magnesium alloys, conventional anodizations by HAE 3,4) and Dow17 [5][6][7] treatments have successfully been utilized, but these methods need harmful chemical agents such as chromium oxide (VI) and fluoride which have recently been restricted by RoHS (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment) and current trend for reducing environmental load. Another protection of magnesium alloys by anodization is performed using an electrolyte which consists of phosphate and ammonium salt.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Corrosion Protection of Anodized Magnesium Alloys

et al. 2008

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Corrosion resistance of anodized surfaces on high-purity magnesium (99.95 mass%), rolled sheets of ASTM AZ31B (Mg-2.9Al-0.85Zn) magnesium alloy and die-cast plates of ASTM AZ91D (Mg-9.1Al-0.75Zn) magnesium alloy has been studied. Anodization was conducted by environment-friendly electrolysis whose electrolyte consists of phosphate and ammonium salt. The anodized surface was covered with amorphous film, and showed only discoloration during salt spray test where formation of corrosion product (magnesium hydroxide) was well suppressed within 605 ks. Even when the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion was well suppressed by formation of new type of dense protective films for each substrate which consist of oxygen, magnesium, aluminum and phosphorus. Anodic polarization curves indicate that the anodized surfaces show sacrificial function due to the thermodynamically unstable state of phosphorus in the anodized layers and its resulting release of electrons. From the viewpoint of kinetics in corrosion on the anodzed surfaces, the curves show that the anodized layers dissolve quite slowly into the electrolyte compared with the case of the untreated substrates. The excellent corrosion protectivity obtained by the anodization is considered to be based on the formation of a dense protective film on the exposed area, as well as sacrificial function of the amorphous anodized layer.

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Section: Introductionmentioning

confidence: 99%

Mechanism of Corrosion Protection of Anodized Magnesium Alloys

et al. 2008

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“…Suppression of oscillation, shielding of electromagnetic wave and recyclability of the alloys are also advantages in electric and electronic products as well as in automotive applications. However, magnesium is one of the materials which bear stain most easily because of its quite low potential region where metallic magnesium can exist in wet environment 1,2) (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Corrosion Protection of AZ91D Magnesium Alloy by Anodization Using Phosphate Electrolyte

et al. 2007

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Mechanism of corrosion protection obtained by anodization for die-cast plates of ASTM AZ91D (Mg-9 mass%Al-0.7Zn) magnesium alloy has been studied. Anodization was conducted by conventional Dow17 which utilizes chromium oxide (VI), ammonium fluoride and phosphoric acid, and by environment-friendly Anomag whose electrolyte consists of phosphate and ammonium salt. The anodized surface obtained in Dow17 showed local corrosion in salt spray test (SST) after $500 ks to form corrosion products consisting of magnesium hydroxides. On the other hand, the surface anodized in Anomag was covered with amorphous film, showed only discoloring in SST and corrosion product was scarcely observed. When the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion product was formed on the trench in the case of Dow17, but corrosion was well suppressed by formation of new type of protective film in the case of Anomag. Anodic polarization curves indicate that the surface anodized in Dow17 is protected by passive substances through which electrolyte can easily reach the substrate, and that in Anomag show sacrificial function where the anodized layer dissolves quite slowly into the electrolyte prior to the substrate. The excellent corrosion protectivity obtained in Anomag is considered to be based on the formation of a new type of protective film as well as sacrificial function of the original amorphous anodized layer.

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“…Suppression of oscillation, shielding of electromagnetic wave, rigidity and recyclability of the alloys are also advantages in electric and electronic products as well as in automotive applications (Cole, 2003). However, magnesium is one of the materials which bear stain most easily because of its quite low potential region where metallic magnesium can exist in wet environment (Pourbaix, 1974;Mears & Brown, 1945) (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…1). As protective coatings for magnesium alloys, conventional anodizations by Dow17 and HAE (Evangelides, 1955;Company, 1956;1981;1998;Ono & Masuko, 2003) treatments have successfully been utilized, but these methods require harmful chemical agents such (Pourbaix, 1974;Mears & Brown, 1945) (circled area shows rest potential).…”

Section: Introductionmentioning

confidence: 99%