The Anodic Role of Ni-Containing LPSO Phases During the Microgalvanic Corrosion of Mg 98 Gd 1.5 Ni 0.5 Alloy
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JMEPEG (2019) 28:2451–2458 https://doi.org/10.1007/s11665-019-04018-x
The Anodic Role of Ni-Containing LPSO Phases During the Microgalvanic Corrosion of Mg98Gd1.5Ni0.5 Alloy Zhenhua Han, Kai Zhang, Jun Yang, Ran Wei, Yixin Liu, and Changjun Zhang (Submitted June 12, 2018; in revised form February 6, 2019; published online April 9, 2019) In the present study, the corrosion characteristics of cast Mg98Gd1.5Ni0.5 alloy with Ni-containing longperiod stacking ordered (LPSO) structures were investigated. The results reveal that the Ni-containing LPSO phases were more active than the Mg matrix and preferentially eroded during the immersion process. This behavior indicates that the Ni-containing LPSO phases could have acted as microanodes, in contrast to the cathodic role of the Ni-free LPSO phases in other Mg alloys. Furthermore, the potential difference of approximately 600 mV between the phases accelerated the dissolution rate of the LPSO phase. Corrosion of the Mg matrix also occurred due to the inhomogeneous microstructure of the matrix. The synergetic corrosion between the Ni-containing LPSO phases and the enrichment of Cl2 in the thick corrosion product films dominated the propagation of corrosion, which substantially deteriorated the corrosion resistance and accelerated the corrosion process of the Mg98Gd1.5Ni0.5 alloy. Keywords
corrosion resistance, long-period stacking ordered structures, Mg alloy, microstructure
1. Introduction The corrosion behavior of Mg alloys with a long-period stacking ordered (LPSO) phase has been widely studied (Ref 15). The LPSO phase can act as a microcathode during the microgalvanic corrosion of Mg alloys because the phase is electrochemically nobler than the Mg matrix. For example, Li et al. (Ref 2) revealed that the LPSO phase exhibited a higher electropotential than that of the Mg matrix by Scanning Kelvin Probe Force Microscopy (SKPFM) tests of Mg-Zn-Y alloy, which provided direct evidence of the cathodic role of LPSO phases during microgalvanic corrosion. The volume fraction and distribution of LPSO phases have a dual effect on the corrosion properties of Mg alloys. Zhang et al. (Ref 3) suggested that discrete and small amounts of LPSO phases would accelerate the corrosion process of the Mg matrix, while LPSO phases with large-scale and continuous networks would enhance the corrosion resistance of Mg alloys. The corrosion behavior of Mg alloys is also closely related to the orientation of the LPSO phase. The corrosion rate of longitudinal sections of extruded Mg97Y2Zn1 alloy was higher than that of transversal sections, which was attributed to the barrier effect of LPSO phase arrangements on the surface of the longitudinal samples (Ref 4). Furthermore, controlling the cooling rate during
Zhenhua Han, School of Material Science and Engineering, XiÕan University of Technology, XiÕan 710048, China; Kai Zhang, Yixin Liu, and Changjun Zhang, School of Material Science and Engineering, ChangÕan University, XiÕan 710048, China; Jun Yang, Changqing Downhole Technology Company, Chuanqing
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