Modulating tribological properties and degradation rate in Hank's solution of Zn–Mn alloys electrodeposited on Mg with variable Mn content

Zn-Mn alloy coatings with small amounts of Mn (Zn-0.19 wt.% Mn, Zn-0.21 wt.% Mn, Zn-0.26 wt.% Mn and Zn-0.34 wt.% Mn) were formed by electrodeposition, onto pre-treated Mg substrates (Mgt) covered with a Zn film (Zn/Mgt). The chemical composition in depth profiles, morphological and structural characteristics of the Zn-Mn coatings on Zn/Mgt (labeled as Zn-Mn/(Zn/Mgt)) were analyzed using Glow Discharge Optical Emission Spectroscopy (GD-OES), Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). When the manganese content was greater than 0.19 wt.%, the results reveal the formation of two Zn-Mn phases: η-ZnMn and ζ-MnZn13; while the formation of the ζ-MnZn13 phase was favored by increasing the Mn content in the alloy. On the other hand, microhardness, wear resistance, and coefficient of friction significantly increase when coating Zn/Mgt substrate with the Zn-Mn alloy. The corrosion performance of this alloy was evaluated by potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The degradation rate in Hank's solutions of the pristine Mg substrate (0.29 mm yr-1) decreases due to the Zn-Mn coating. Furthermore, the degradation rate of Zn-Mn was further decreased from 0.051 to 0.022 mm yr-1, by varying the amount of Mn in the Zn-Mn alloy from 0.19 to 0.26 wt.% Mn, respectively. However, the rate of degradation increases up to 0.064 mm yr-1 at higher Mn content, Zn-0.34 wt.% Mn. Therefore, the microhardness, wear volume, and degradation rate of Zn-Mn/(Zn/Mg) in Hank's solution can be modulated by varying the Mn composition in the alloy.