Sputter-Deposited Mg-Zr Alloys – Surface Characteristics and Electrochemical Behavior in Borate Solutions

Abstract

Abstract The effect of zirconium on the electrochemical kinetics and surface characteristics of Mg-(6 – 81 at %) Zr alloys was investigated by different electrochemical techniques. The sputter-deposited alloy is subjected to X-ray photo-electron spectroscopic analyses. Alloys with ≥ 29 at % Zr were spontaneously passivated. The passive film resistance is much higher than that formed on Mg metal. The high resistance of the passive film was attributed to a continuous connected network of a double oxy-hydroxide composed mainly of Zr4+ and a small amount of Mg2+. XPS measurements revealed a dynamic nature of the passive film, where concentration gradient of Zr4+, Mg2+, OH – and O2– species was recorded throughout a few nanometers depth. An optimum Zr content is required to promote the formation of stable oxy-hydroxide film. Alloys with Zr content ≥ 29 at % attains critical oxide film composition with Zr4+ ≥ 0.69 cation fractions and thickness in the range of 3.2 ∼ 4.5 nm.