The use of microcapillary techniques to study the corrosion resistance of AZ91 magnesium alloy at the microscale

Krawiec, H.; Staněk, Stanislav; Vignal, V.; Lelito, J.; Suchy, J. S.

doi:10.1016/j.corsci.2011.05.054

Cited by 60 publications

(52 citation statements)

References 39 publications

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“…Perchlorate based electrolyte have been successfully used for microcapillary polarization of AZ31 and AZ91. 4,14 It has been shown that the perchlorate (ClO 4 − ) anions tend to complex less with the surface metal atoms as compared to chloride anions (Cl − ). 15 As a result perchlorate ions are less corrosive than chloride anions but still cause localized pitting corrosion on magnesium alloys (in a similar fashion to Cl − ions).…”

Section: Resultsmentioning

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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Section: Resultsmentioning

confidence: 99%

Corrosion Mechanisms in Dissimilar AZ31/AZ80 Friction Stir Welds

Savguira

North

Thorpe

2018

J. Electrochem. Soc.

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“…The microstructure of AZ91 was already studied, and results are presented in [37]. In summary, AZ91 has a very complex microstructure composed of α-Mg solid solution (dendrites), β-Mg 17 (Al, Zn) 12 precipitates, AlMn intermetallic particles and a eutectic phase (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The metallic matrix underwent strong dissolution. Numerous pits are observed in the matrix, most of which are located in the centre of α-Mg dendrites where the aluminium content is low (less than 3 at.%, Table 1 and reference [37]). The average pit diameter is 20 μm, although a few of the pits are larger than this.…”

Section: -Mg Dendritementioning

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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“…Experiments at the microscale were performed using the electrochemical microcell technique [38][39][40][41][42][43] and capillaries with a diameter in the range of 20-100 µm. Local polarisation curves were plotted from -1000 mV vs. Ag/AgCl up to pitting potential at a potential scan rate of 1 mV s -1 .…”

Section: Electrochemical Measurementsmentioning

confidence: 99%