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

Abstract

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.