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The growing interest in finding the best way to strengthen Mg alloys has recently focused on the development of Mg-Y-Zn alloys with long-period stacking ordered (LPSO) structures [1]. The microstructure of Mg-Y-Zn containing LPSO structures formed during plastic deformation was found to be beneficial in terms of mechanical properties [2]. The goal of this work is to investigate the role of strengthening phases with novel long period stacking-ordered (LPSO) structures in the corrosion resistance of Mg-Y-Zn alloys. Two Mg-based alloys are investigated: WZ42 containing 3.5 wt.% Y and 1.6 wt.% Zn and WZ104 with a chemical composition of 10 wt.% Y and 3.7 wt.% Zn. Once the predominant corrosion mechanism is known, in further perspective, this would lead to the possibility of a successful application, especially the application that satisfied the targeted function of Mg-Y-Zn alloys mainly for implants regarding diseases of the musculoskeletal system.
To achieve the goal of research, optical microscopy observations of the microstructure of the investigated alloys were performed followed by more detailed scanning electron microscopy (SEM) observations along with energy dispersive spectroscopy (EDX) analysis of the chemical composition. After the prevalent features of the microstructure were determined, their impact on corrosion behavior was investigated. Corrosion tests were performed in a naturally aerated phosphate buffered saline solution (PBS) at 37 ° C. Parameters describing corrosion resistance were obtained using electrochemical testing consisting of open-circuit potentials (OCP), electrochemical impedance spectroscopy (EIS), and the potentiodynamic polarization measurements. Immersion tests with subsequent SEM observations enabled us to describe corrosion mechanisms that occurred on the surface of alloys.
As demonstrated, the dominant morphology of the LPSO phases in WZ42 is block-like, while in WZ104 the thin platelet LPSO phase prevails. Randomly distributed LPSO structures are observed in both alloys. WZ42 contains a smaller volume fraction of LPSO phases than WZ104. The results of the electrochemical tests showed that WZ42 is more corrosion resistant than WZ104. Immersion tests with subsequent SEM observations revealed that the corrosion damage occurred mostly in the close proximity of the LPSO phases. The more LPSO phases formed in the alloy the higher number of areas, where the corrosion is initiated.
[1] A. Yokota, M. Matsushita, N. Geshi, D. Yamasaki, T. Shinmei, M. Yamasaki, Y. Kawamura, Formation Process of Long-Period Stacking-Ordered Structures in Mg97Zn1Y2 Alloy Comprising HCP and Cubic Phases Fabricated by High-Pressure High-Temperature Annealing, Metals. 11 (2021) 1031.
[2] D. Drozdenko, G. Farkas, P. Šimko, K. Fekete, J. Čapek, G. Garcés, D. Ma, K. An, K. Máthis, Influence of Volume Fraction of Long-Period Stacking Ordered Structure Phase on the Deformation Processes during Cyclic Deformation of Mg-Y-Zn Alloys, Crystals. 11 (2020) 11.
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