The corrosion inhibition mechanism of Ca(H2PO4)2 on AZ91D magnesium alloy in 3.5 wt% NaCl solution

Abstract

In this work, Ca(H₂PO₄)₂ was used as a green corrosion inhibitor for AZ91D magnesium alloy in 3.5 wt% NaCl solution. The corrosion inhibition behavior and mechanism were analyzed using electrochemical tests, high-definition video measuring microscopy, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The electrochemical testing results showed that the optimal corrosion inhibition concentration of Ca(H₂PO₄)₂ was 0.6 g L⁻¹, and the highest corrosion inhibition efficiency was 89.29% after 48 h immersion in the corrosive medium. Optical microscopy and SEM images showed that an obvious protective film formed on the Mg alloy surface in solution inhibited with Ca(H₂PO₄)₂. EDS and XRD results showed that the protective layer was composed of Mg(OH)₂ + MgHPO₄ + Ca₃PO₄, and MgHPO₄ played a major role. The precipitation mechanism of Ca(H₂PO₄)₂ as a corrosion inhibitor was proposed.