The Role of Mg<sub>17</sub>Al<sub>12</sub>Phase in the Corrosion of Mg Alloy AZ91

Lunder, Otto; Lein, John Erik; Aune, Terje Kr.; Nisancioḡl̄ū, Kemal

doi:10.5006/1.3585029

Cited by 364 publications

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“…According to results obtained through Scanning Kelvin Probe Force Microscopy, the β-Mg 17 Al 12 and η-Al 8 Mn 5 phases act as local cathodes when coupled to the α-magnesium phase (matrix) under atmospheric conditions [17]. Moreover, strong dissolution of the matrix has also been detected around these particles [19,20]. Other studies [34,35] have confirmed that the α-phase is less noble than β-Mg 17 Al 12 .…”

Section: Introductionmentioning

confidence: 73%

“…Filiform corrosion has previously been observed in pure magnesium [13,[49][50][51][52][53][54][55][56] as well as Mg-Al [57,58], Mg-Y [50], Mg8Li [55], AM30 [59], AZ31 [60,61], AZ80 [60], AZ91D [13] and AZ91 [51] alloys after immersion in chloride-containing solutions. It has been found that the propagation of filaments occurs with voluminous gas evolution at the head while the body immediately behind it passivates [62]. Filiform corrosion has been observed in high purity magnesium of unpolarised and galvanostatically polarised specimen in aqueous sodium chloride electrolyte [52,56].…”

Section: Global and Local Electrochemical Behaviour Of Az91 In 01 M mentioning

confidence: 91%

“…On the other hand, β-Mg 17 Al 12 can, if present in the form of a continuous network, act as a corrosion barrier and hinder corrosion propagation in the matrix [24][25][26]. Lunder [19] showed that β-Mg 17 Al 12 could reduce the corrosion rate of AZ91 by forming a corrosion-resistant barrier through the precipitation of an Alrich coring structure along grain boundaries.…”

Section: Introductionmentioning

confidence: 99%

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The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

Kot

Krawiec

2015

J Solid State Electrochem

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The microstructure of as-cast AZ91 alloy is complex, with the presence of Mg 17 (Al, Zn) 12 precipitates surrounded by an eutectic phase, AlMn intermetallic particles and an α-Mg solid solution. In addition, the distribution of aluminium in the alloy was found to be heterogeneous. Under these conditions, a multiscale approach coupling global and local electrochemical measurements seems to be a promising method to study its corrosion behaviour. Results show that the multiscale approach can be used in 0.1 M NaCl. In this case, AZ91 is susceptible to pitting corrosion. By contrast, the multiscale approach is not valid for AZ91 in 0.1 M Na 2 SO 4 . At the global scale, filiform corrosion and pitting corrosion are observed in the matrix, whereas only pits initiate when using the microcapillary techniques. The obtained results show that the local electrochemical techniques have to be used carefully in some environments.

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Section: Introductionmentioning

confidence: 73%

Section: Global and Local Electrochemical Behaviour Of Az91 In 01 M mentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

Kot

Krawiec

2015

J Solid State Electrochem

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“…[25][26][27][28] Khaselev et al anodized magnesium alloys in alkaline electrolytes containing aluminate [29][30][31] . They found the formation of MgAl 2 O 4 spinel phase under continuous sparking.…”

Section: Introductionmentioning

confidence: 99%

Influence of Phosphate Concentration on Plasma Electrolytic Oxidation of AZ80 Magnesium Alloy in Alkaline Aluminate Solution

2010

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Plasma electrolytic oxidation of AZ80 magnesium alloy in alkaline aluminate electrolytes develops MgAl 2 O 4 -based highly crystalline oxide coatings with the morphology changing largely with phosphate concentration in electrolyte. The thickness of the coatings increases with phosphate concentration from 5 mm in phosphate-free electrolyte to $70 mm in the electrolyte containing 0.1 molÁdm À3 phosphate after anodizing for 900 s. The formation of the latter thick coating is associated with intense sparking during anodizing. The thick coatings formed in the electrolytes containing 0.075 and 0.1 molÁdm À3 phosphate are highly cracked. In contrast, the coating formed in the electrolyte containing 0.05 molÁdm À3 phosphate is relatively uniform, showing the highest corrosion protection in 0.5 molÁdm À3 NaCl solution. The coatings consist of two layers, comprising an outer thick layer with high concentration of aluminum and an inner thin magnesium-rich layer.

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“…The absence of the intermetallics, which eliminates the microgalvanic coupling between the intermetallic particles (IMPs) and the α-Mg matrix, and reduces the susceptibility of the welded joint to localized pitting corrosion. [8][9][10][11] Many industrial applications require joining of dissimilar alloys, and therefore it is essential to understand the influence of the welding process on the corrosion behavior of dissimilar joints. It is currently unknown whether the corrosion behavior of dissimilar welds is governed by the microstructural changes occurring during the welding operation (as observed in similar welds) and/or by the galvanic coupling of the alloys themselves.…”

mentioning

confidence: 99%

Corrosion Mechanisms in Dissimilar AZ31/AZ80 Friction Stir Welds

Savguira

North

Thorpe

2018

J. Electrochem. Soc.

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Corrosion of dissimilar friction stir welds (FSW) made in AZ31/AZ80 magnesium alloys was investigated using the scanning reference electrode technique (SRET), and microcapillary polarization technique, complemented by optical and SEM/EDX microscopy. The corrosion rate of the base metals along with the welded specimen was estimated by mass loss testing. The stir zone material in both alloys showed a higher corrosion potential than the base metal due to the partial dissolution of β-Mg 17 Al 12 and Al-Mn particles. The basic corrosion mechanism in dissimilar welds was determined to be different from that of a similar joint. The corrosion behavior of the dissimilar FSW joint was governed by the galvanic coupling of the two alloys, and not by the microstructural evolution occurring during the welding process. The corrosion behavior of the joint was governed by the galvanic coupling between the α-Mg matrix in AZ31 and the Al-rich intermetallics in AZ80. The welded specimens exhibited the highest corrosion rate, while AZ80 was the most corrosion resistant material. Magnesium alloys can be successfully joined by friction stir welding (FSW) to achieve excellent mechanical integrity in completed welds. 1,2 One challenge arising from the utilization of this joining method is an increased susceptibility to localized corrosion in the material immediately adjacent to the welded joint. 3-6 Previous microcapillary polarization and scanning reference electrode technique (SRET) studies have revealed that the stir zones in AZ31B spot and seam welds are more cathodic than the bulk material. [3][4][5][6] Due to the difference in electrochemical potentials, a macrogalvanic cell is formed causing pitting corrosion in the thermo-mechanically affected zone (TMAZ) and the heat affected zone (HAZ) regions, which are located between the noble stir zone and the active base metal. 5 The differences in the electrochemical behavior of different regions in completed joints have been related to their microstructural evolution that occurred during the welding operation. The stir zone microstructure comprised a dynamically recrystallized matrix which was nominally devoid of intermetallics. The increase in the corrosion potential of the stir zone has been attributed to the dissolution of β-Mg 17 Al 12 and Al-Mn particles via two mechanisms: 4,5 1. Dissolution of intermetallics, which increases the concentration of Al in the α-Mg matrix, resulting in a higher corrosion potential of this region, 7 and 2. The absence of the intermetallics, which eliminates the microgalvanic coupling between the intermetallic particles (IMPs) and the α-Mg matrix, and reduces the susceptibility of the welded joint to localized pitting corrosion. [8][9][10][11] Many industrial applications require joining of dissimilar alloys, and therefore it is essential to understand the influence of the welding process on the corrosion behavior of dissimilar joints. It is currently unknown whether the corrosion behavior of dissimilar welds is governed by the microstructural changes o...

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The Role of Mg₁₇Al₁₂Phase in the Corrosion of Mg Alloy AZ91

Cited by 364 publications

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The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

Influence of Phosphate Concentration on Plasma Electrolytic Oxidation of AZ80 Magnesium Alloy in Alkaline Aluminate Solution

Corrosion Mechanisms in Dissimilar AZ31/AZ80 Friction Stir Welds

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The Role of Mg17Al12Phase in the Corrosion of Mg Alloy AZ91

Cited by 364 publications

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The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

Influence of Phosphate Concentration on Plasma Electrolytic Oxidation of AZ80 Magnesium Alloy in Alkaline Aluminate Solution

Corrosion Mechanisms in Dissimilar AZ31/AZ80 Friction Stir Welds

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The Role of Mg₁₇Al₁₂Phase in the Corrosion of Mg Alloy AZ91