Improved Corrosion Resistance in AZ61 Magnesium Alloys Induced by Impurity Reduction

doi:10.1007/s40195-019-00914-2

Abstract

Abstract:

The effect of impurity element Fe on corrosion behavior of AZ61 magnesium alloys in various states has been investigated by immersion test and hydrogen evolution measurements in 3.5% sodium chloride solution. The corrosion rate is found to relay on the impurity Fe concentration in the alloys and decreases with decreasing Fe content. When Fe content drops from 150 ppm to 10 ppm, the corresponding corrosion rates under as-cast and solution treatment conditions are reduced from 8.54 mm/a and 8.61 mm/a to 2.54 mm/a and 0.21 mm/a, respectively. The corrosion pattern of the AZ61 alloys is the localized corrosion, and the galvanic couples are formed among the impurity particles, second-phase particles and the matrix. The Fe impurity particles tend to act as main cathodic to form micro-galvanic cell with the α-Mg matrix, which is harmful for corrosion resistance of AZ61 alloy.

Key words: AZ61 magnesium alloy, Impurity Fe, Corrosion rate

Yan Dai, Xian-Hua Chen, Tao Yan, Ai-Tao Tang, Di Zhao, Zhu Luo, Chun-Quan Liu, Ren-Ju Cheng, Fu-Sheng Pan. Improved Corrosion Resistance in AZ61 Magnesium Alloys Induced by Impurity Reduction[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(2): 225-232.

Figures/Tables 10

Table 1 Chemical compositions of AZ61 alloys

Fig. 1 Phase amounts (mass fraction) calculated with the PANDAT software [43] for different cooling conditions for AZ61 alloy with 150 ppm Fe: a rapid solidification under Scheil condition; b equilibrium condition (bcc body-centered cubic)

Fig. 2 SEM micrographs of AZ61 alloys with different Fe contents in various states

Fig. 3 Microstructure of as-cast AZ61 alloy with 150 ppm Fe a and corresponding EDS chemical maps for Al b, Fe c, Mn d

Fig. 4 Corrosion behavior of AZ61 alloys with different Fe contents measured by weight loss for 36 h

Table 2 Corrosion resistance of magnesium alloys and aluminum alloy

Fig. 5 Corrosion behavior of AZ61 alloys measured in terms of hydrogen evolution: a as-cast, b solution treatment, c as-aging

Fig. 6 Macroscopic corrosion morphology of as-cast AZ61 samples

Fig. 7 a SEM image, b partially higher magnification image of corroded surfaces of as-cast AZ61 alloy with 150 ppm Fe, c and d represent EDS spectrums collected from points A and B, respectively

Fig. 8 Schematic presentation of galvanic corrosion of Mg alloy

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