Behavior of compounds on the corrosion of ZK61-xCe magnesium alloys

Abstract The corrosion kinetics and the influence of Ce content on the corrosion performance of ZK61-xCe (x = 0, 0.5, 1.0, 1.5, wt%) magnesium alloys in NaCl (0.1 mol l −1 ) solution were investigated using hydrogen evolution tests combined with observations of corrosion morphology. The role of compound on the corrosion of the alloy was analyzed based on changes in the microstructure, electrode potentials of compounds and matrix, and electrochemical properties of the corrosion product film. The results show that the corrosion rate of the experimental alloy is faster in the first 3 h, then the corrosion rate is gradually reduced, and the corrosion process fits the power-exponential dynamics equation. The corrosion rate constants k and exponential n in the corrosion kinetic equations first decrease and then increase with the increase of Ce content, with the Ce content is 0.5wt%, the alloy has the slowest corrosion rate and the best corrosion resistance. The corrosion rate of the alloy is controlled by the micro-galvanic corrosion. After adding Ce to the ZK61 alloy, the MgZn 2 in the alloy is converted to (Mg, Zn) 12 Ce with more negative electrode potential, and the electrode potential decreases from −0.811 V to −1.002 V. The electrode potential of the α -Mg matrix in the alloy is about −1.451 V, and the potential difference between the compounds and the α -Mg matrix decreases, the corrosion driving force of micro-galvanic corrosion decreases, and the corrosion resistance increases. With the increase of Ce content, the amount of (Mg, Zn) 12 Ce compounds increases, resulting in an increased number of micro-galvanic couples, increased migration charge density, and decreased corrosion resistance. As the corrosion proceeds, the number of (Mg, Zn) 12 Ce exposed on the surface of the substrate increases, blocking the contact between the substrate and the corrosion medium, himpeded lateral corrosion propagation and longitudinal corrosion extension of the α -Mg matrix.