Improving the electrochemical corrosion resistance of a high-Ca heat-resistant magnesium alloy by enhancing the barrier effect of the cathodic phase skeleton

Abstract

Mg-Al-Ca-based alloys are highly susceptible to electrochemical corrosion due to the micro-galvanic corrosion induced by the large potential gap between the cathodic second phase and the anodic α-Mg matrix. This study reports a new strategy of improving their corrosion resistance by enhancing the barrier effect of the cathodic phase skeleton based on a Mg-5Al-3Ca-xZn alloy. The results indicate that the supersaturation of Zn in the C36-(Mg,Al)₂Ca phase skeleton, combined with the further formation of Ca₂Mg₆Zn₃ through a peritectic reaction, significantly increases the potential difference between the second-phase skeleton and the matrix, however, the corrosion rate of the alloy in the 3.5 wt.% NaCl solution anomalously decreases accordingly. It suggests that the corrosion kinetics of this alloy are governed by the barrier effect of the continuous cathode phase skeleton, outweighing the micro-galvanic effect that dominates the corrosion process for most magnesium alloys. A new understanding of the barrier effect of the cathodic phase based on the local pH variation is proposed. This study offers a new perspective for the development of high-Ca magnesium alloys that exhibit superior electrochemical corrosion resistance.