Corrosion Resistant Magnesium Alloys

Lunder, Otto; Videm, Marianne; Nisancioḡl̄ū, Kemal

doi:10.4271/950428

Cited by 16 publications

(13 citation statements)

References 11 publications

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“…However, it is also accepted that the b-phase is a corrosion barrier and its presence in an AZ alloy is beneficial to the corrosion resistance of a magnesium alloy, [45,47,58,59,62,64] i.e., the presence of (phase in the magnesium alloy can effectively enhance its corrosion resistance. [27,50,53,67] For example, diecast Table 2.…”

Section: Reviewsmentioning

confidence: 99%

Recent Progress in Corrosion and Protection of Magnesium Alloys

2005

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Magnesium alloys are advanced light structural and functional materials being increasingly used in the automotive, aerospace, electronic, and energy industries. However, their corrosion performance at the current stage of development is still not good enough for increasingly diverse practical applications. The Cooperative Research Centre for Cast Metals Manufacturing (CAST) in Australia is one of the most active research organizations in the world established to cope with the problems associated with the development and application of advanced light metals. Corrosion and prevention of magnesium and its alloys is an important part of CAST's research program. This paper presents a brief summary of recent research achievements by CAST and relevant research work in this area in the world. This overview covers “anodic hydrogen evolution”, estimation of corrosion rate, corrosion of aluminum‐ and non‐aluminum‐containing magnesium alloys, influences of composition and microstructure on corrosion, corrosion of a die‐cast magnesium alloy, galvanic corrosion, coolant corrosion, and an aluminum‐alloyed coating. The aim of this overview is to deepen the current understanding of corrosion and protection of magnesium and its alloys and to provide a base for future research work in this field.

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Section: Reviewsmentioning

confidence: 99%

Recent Progress in Corrosion and Protection of Magnesium Alloys

2005

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“…However, it seems that a threshold of 4% Al in the alloy is required. Precipitation of the more corrosionresistant Mg 17 Al 12 (β-phase), which acts as a corrosion barrier, has also been claimed to improve corrosion [13]. Furthermore, it was reported that the corrosion potential of β-phase in 5% NaCl saturated solution with Mg(OH) 2 was approximately 490 and 420 mV more cathodic to pure Mg and AZ91 alloy, respectively [13].…”

Section: Introductionmentioning

confidence: 99%

“…AZ91 alloy has a two-phase microstructure typically consisting of a matrix of α-Mg grains with an intermetallic β-phase (Mg 17 Al 12 ) along the grain boundaries [16]. The physical significance of aluminum as the alloying element is largely related to an increased passivity of the oxide film formed on the surface [17]. However, it seems that a threshold of 4% Al in the alloy is required.…”

Section: Introductionmentioning

confidence: 99%

Corrosion Behaviour of AZ and ZA Magnesium Alloys in Alkaline Chloride Media

Öteyaka

Ghali

Tremblay

2012

International Journal of Corrosion

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Corrosion behaviour of AZ and ZA magnesium alloys in untreated, aerated, and deaerated chloride media was investigated. The influence of impurity, alloying element, and oxygen on corrosion potential, rate, and pitting was examined in alkaline media saturated with Mg(OH) 2 at pH 9 and 25• C. After 8 h immersion, slightly less active corrosion potentials were generally observed in deaerated than oxygen containing solutions. AZ91D and ZA104 alloys recorded much lower corrosion rates in deaerated medium as compared to AZ91E, ZAC 10403 (0.3Ca), and ZACS1040305 (0.3Ca+ 0.5Sr). Generally, ZAC alloy showed the highest corrosion rate, followed by ZACS alloy, and both showed a constant value in the three media with or without oxygen. The effect of oxygen is then dependent on the alloy properties and is not a simple acceleration of the cathodic reaction but could cause also inhibition and/or passivation. Pit depth and distribution were influenced by alloy composition. The pits were found deeper and more localized on AZ and more uniformly dispersed on ZA alloy surfaces.

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“…All the intermetallic particles are cathodic to a-Mg in a corrosive environment. [38][39][40] As mentioned in the first paragraph of this section, the corrosion resistance of the diecast Mg alloy was strongly related to the interdendritic phases in die chill skin. Thus, as will be discussed in the following paragraphs, the TEM experiments to elucidate the microstructures of the Al-rich a phase were essential to determining the link between the microstructure (Figures 2, 3, 4, 9, and 10) and corrosion performance (Figures 6 through 8).…”

Section: Discussionmentioning

confidence: 94%

“…The b particles and Al-Mn particles are cathodic to a-Mg. [38][39][40] Based on the electron microscopic observations herein, Figure 13 presents schematic cross sections of the microstructure at the diecast surface and the corrosion caused by the galvanic effect. The primary a grains, primary b, and the Al-rich a eutectic phase presented in Figure 13 are greatly magnified.…”

Section: Discussionmentioning

confidence: 99%

Characterization and Improvement in the Corrosion Performance of a Hot-Chamber Diecast Mg Alloy Thin Plate by the Removal of Interdendritic Phases at the Die Chill Layer

Uan

2008

Metall Mater Trans A

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This work presents results concerning the effect of the die chill layer on the corrosion performance of a hot-chamber diecast AZ91D thin plate, with particular attention to the role of interdendritic phases (primary b (Al 17 Mg 12 ) and surrounding a phase). The primary b phase in the die chill layer was removed by Ar + etching, but the other main constituent phases remained on the surface of the sample. Although previous researchers have attributed intense galvanic corrosion to the cathodic phase (primary b), this work demonstrates that the removal of the primary b phase from the diecast sample surface did not improve the corrosion performance of the sample. Transmission electron microscope (TEM) examinations were performed, to elucidate the microstructure near the die chill surface, especially focusing on the a-Mg phase that surrounds the primary b phase. The surrounding a-Mg phase (known as ''Al-rich a'' or eutectic a) actually did not contain a high concentration of aluminum solid solution. Instead, the Al-rich a was composed of fine Al 12 Mg 17 b particles and Al-Mn-like particles (smaller than 0.5 lm) that were distributed in a low-Al-containing Mg matrix (~4 wt pct Al). Such fine cathodic particles seem to participate strongly in the corrosion. Removing the primary b phase alone did not increase the corrosion resistance of the material, because many of the cathodic fine particles remained in the Al-rich a phase region. This work studied an HF-H 2 SO 4 /CaCO 3 etching method for removing interdendritic phases (both the Al-rich a and the primary b) from the surface chill layer of the diecast thin plate. Therefore, testing in 5 wt pct chloride solution demonstrated that the I corr of the HF-H 2 SO 4 /CaCO 3 -treated specimen was 3 to~16 lA/cm 2 , which was significantly lower than the I corr~1 600 lA/cm 2 of the as-diecast Mg sample.

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Corrosion Resistant Magnesium Alloys

Cited by 16 publications

References 11 publications

Recent Progress in Corrosion and Protection of Magnesium Alloys

Recent Progress in Corrosion and Protection of Magnesium Alloys

Corrosion Behaviour of AZ and ZA Magnesium Alloys in Alkaline Chloride Media

Characterization and Improvement in the Corrosion Performance of a Hot-Chamber Diecast Mg Alloy Thin Plate by the Removal of Interdendritic Phases at the Die Chill Layer

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