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

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.