Synergistic corrosion inhibition of sodium phosphate and sodium dodecyl sulphate on magnesium alloy AZ91 in 3.5 wt% NaCl solution

A high-efficiency inhibitor is urgently needed for magnesium alloys to mitigate their corrosion in service. Herein, we prepared a compound inhibitor consisting of sodium phosphate (Na 3 PO 4 ) and sodium dodecyl sulphate (SDS) that can provide long-term protection for magnesium alloys. The synergy between Na 3 PO 4 and SDS on corrosion inhibition of magnesium alloy AZ91 was investigated with electrochemical measurements and surface characterisation . The inhibitive efficiency of 95.18% and synergistic coefficient of 1.2 are achieved at a formula of 10 mM Na 3 PO 4 + 5 mM SDS within 2-hour immersion. The efficiency is enhanced to 99.70% after 120 h. Na 3 PO 4 plays the dominant role of anodic inhibition by forming a precipitation film on the matrix phase α-Mg, while SDS, as a subsidiary, is preferentially adsorbed on the secondary phase β-Mg 17 Al 12 and vicinity, inhibiting cathodic reductions. The above results are promising to be applied in the development of high-efficiency compound inhibitors for magnesium alloys.