Influence of low level iron impurities on the initial interaction of water vapour with polycrystalline magnesium surfaces

Splinter, S.J.; McIntyre, N. S.; Heide, P.A.W. van der; Do, T.

doi:10.1016/0039-6028(94)90266-6

Cited by 20 publications

(11 citation statements)

References 16 publications

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“…The inner oxide layer is a cellular-like hydrated layer as a result of the water molecule penetrating the outer oxide layer to react with the Mg substrate. The oxide film formed in aqueous solution shows a sheet outer oxide layer, which consists of Mg(OH) 2 and a small amount of MgO. The inner oxide layer is similar to the whole oxide film formed in the humid air.…”

Section: Introductionmentioning

confidence: 98%

“…The oxide film formed in the air is thin (20-50 nm) to display amorphous structure, which consists of MgO and Mg(OH) 2 . The oxide film formed in the humid air contained outer oxide layer and inner oxide layer.…”

Section: Introductionmentioning

confidence: 99%

“…There are some researches concerning the surface oxide film on pure Mg and Mg alloys [1][2][3][4]. The oxide film formed in the air is thin (20-50 nm) to display amorphous structure, which consists of MgO and Mg(OH) 2 .…”

Section: Introductionmentioning

confidence: 99%

“…Among plenty of alloying elements, the effects of Al on the characteristics of surface oxide film were investigated deeply [10,11]. For example, the oxide film on AZ91 Mg alloy consisting of MgO, Al 2 O 3 , Mg(OH) 2 and Al(OH) 3 displays a multiple layer structure of oxides of Mg/oxides of Mg and Al/substrate. The thickness of oxide film is several decade nanometers, and it decreases with the increase of Al concentration.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of surface oxide film on magnesium lithium alloy

Song

Shan

Chen

et al. 2009

Journal of Alloys and Compounds

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Investigation of surface oxide film on magnesium lithium alloy

Song

Shan

Chen

et al. 2009

Journal of Alloys and Compounds

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“…Pretreatment should prepare the surface in an optimal way for a subsequent coating system, in which adhesion and corrosion resistance are the most important properties. This is especially difficult for magnesium alloys since the formation of reaction layers on the pretreated surface starts immediately in ambient air [5][6][7][8][9]. It is therefore necessary to investigate the change of the 'clean' surface with time resulting in a possible improvement of the pretreatment and coating process by avoiding uncontrolled formation of reaction layers.…”

Section: Introductionmentioning

confidence: 99%

Investigations of the aqueous corrosion of pretreated magnesium alloys by means of electrochemical noise measurements

Bender

Holzhausen

Heyn

2012

Materials & Corrosion

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An important possibility to improve the corrosion behaviour of magnesium alloys is the application of protective coatings. The quality of such coatings depends mainly on the pretreatment and the exposure conditions after pretreatment. Since magnesium surfaces change much faster under atmospheric conditions than those of almost any other technical material, it is necessary to pay special attention to this particular feature. The activity of acidpickled surfaces of the magnesium alloys AZ31 and AZ91 in dependence on the exposure time and the humidity conditions was investigated with electrochemical noise (EN) measurements. In addition to pickling, plasma chemical vapour deposition processes open new possibilities for an economical, as well as ecologically quite safe, pretreatment. The results of EN investigations after acid pickling as well as specific plasma oxidation treatments of the two magnesium alloys after exposure to air with different humidities are presented.

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Elektrochemische Korrosionsuntersuchungen an der Magnesiumlegierung AZ91: Beschreibung kritischer Parameter und deren Einfluss auf die Angriffsmechanismen auf NRC‐Proben

Lips

Schmutz

Heer

et al. 2004

Materials & Corrosion

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Aufgrund des zunehmenden Einsatzes von Magnesiumlegierungen als Strukturwerkstoff in Leichtbauanwendungen erlangen deren Korrosionseigenschaften erhöhte Beachtung. In dieser Arbeit werden wichtige Parameter, die zur Korrosion der Magnesiumlegierungen führen, untersucht und diskutiert. Es wird gezeigt, dass der pH-Wert in einer Lösung bis zu Werten über 11 ansteigt, die in Kontakt mit Magnesium oder AZ91 steht. Die Lösungsmenge und der Oberflächenzustand des Metalles spielen dabei im Gegensatz zum Chloridgehalt eine wichtige Rolle. Elektrochemische Messungen machen klar, dass sich erst bei einem pH-Wert von 12 eine stabile Oberflächenschicht bildet. Aggressive Chloridionen können diese Hydroxidschicht lokal zerstören, woraufhin eine Repassivierung stattfinden kann. Bei pH 11 fehlt dem Oberflächenfilm die Stabilität und es kommt zur lokalen Auflösung, so dass die Chloridionen eine geringe Rolle in der Initiierung der Korrosion spielen. Um eine höhere Stabilität zu erreichen, können Inhibitoren eingesetzt werden. Chromat wird in die Hydroxidschicht eingebaut und verleiht ihr so die nötige Stabilität bei pH 11. NRC-Bauteile (New Rheocasting) zeichnen sich aus durch ausgezeichnete mechanische Eigenschaften, doch kommt es wegen der speziellen Phasenverteilung vermehrt zu einer galvanischen Kopplung, weswegen sich die Korrosionsanfälligkeit erhöht. Langsam abgekühlte AZ91 Proben unterscheiden sich im Gefüge von den NRC-Proben und zeigen auch ein anderes Verhalten in der Initiierungsphase der Korrosion.Investigation of the corrosion behaviour of magnesium alloys is of interest because of its growing industrial use for light weight structural applications. In this study, important parameters related to the corrosion of magnesium alloys are analysed and discussed. It will be shown that the pH of a solution increases when it is in contact with magnesium or the AZ91 alloy. The volume of solution in contact with the surface and the surface finish of the metal are important parameters in contrast to chloride content. Electrochemical measurements show that a stable hydroxide layer is not formed below a pH-value of 12. Aggressive chloride ions can then locally attack this layer followed by repassivation. At pH 11 the surface layer does not show stability and it comes to local dissolution. The chloride ions have little influence on corrosion initiation. Inhibitors can be used to obtain a higher stability of the hydroxide surface layer. Chromates are incorporated in the hydroxide surface layer and increase film stability at pH 11. As-cast NRC samples (New Rheocasting) exhibit excellent mechanical properties, however because of their special phase distribution galvanic coupling occurs and the corrosion susceptibility increases. The microstructure of slowly cooled AZ91 samples solidified closer to equilibrium differs from that of NRC samples and they show also different corrosion initiation behaviour.

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Influence of low level iron impurities on the initial interaction of water vapour with polycrystalline magnesium surfaces

Cited by 20 publications

References 16 publications

Investigation of surface oxide film on magnesium lithium alloy

Investigation of surface oxide film on magnesium lithium alloy

Investigations of the aqueous corrosion of pretreated magnesium alloys by means of electrochemical noise measurements

Elektrochemische Korrosionsuntersuchungen an der Magnesiumlegierung AZ91: Beschreibung kritischer Parameter und deren Einfluss auf die Angriffsmechanismen auf NRC‐Proben

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