Corrosion Inhibition of Combined Inhibitor on AZ91D Magnesium Alloy in Ethylene Glycol Coolant

Electrochemical methods, surface morphology observation and corrosion product analysis were used to inverstigate the inhibition of combined inhibitors compound by dibasic sodium phosphate (DSP) and gluconate sodium (GS) on AZ91D magnesium alloy in 50% (volume) ethylene glycol coolant. The results show that DSP is a mixed type corrosion inhibitor for AZ91D magnesium alloy in 50% ethylene glycol coolant. GS has no corrosion inhibition. There exists synergistic effect between DSP and GS, it is a combined inhibitor with mainly controling the anodic process.. It tended to be a stable inhibition ratio as the mass concentration ratio of DSP to GS was 4:1 i.e., combined inhibitior E. With the increase of the content of combined inhibitor E, inhibition efficiency increased, when 2.5 g/L was added, the inhibition efficiency reached above 90%. The corrosion effect of the mixed inhibitor for AZ91D was to form MgHPO₄, which may form a complex on the AZ91D surface due to the action of GS, and then depressed the corrosion of AZ91D in ethylene glycol coolant.