Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy

• Scanning electrochemical microscopy is used to characterise Pr conversion coatings.
• H2 evolution was detected in generation/collection mode using H2 electro-oxidation.
• Passive domains and ionic accumulation were displayed in AC mode.
• H2 evolution occurred mainly at surface domains with less insulating properties.

Surface passivation of AZNd Mg alloy with Pr(NO3)3 is studied using scanning electrochemical microscopy (SECM) in surface generation/tip collection (SG/TC) and AC modes. Corrosion protection afforded by the Pr treatment and the degradation mechanism in a simulated biological environment was examined on a local scale and compared with non-treated AZNd. SG/TC mode results revealed a drastic decrease in H2 evolution due to the Pr treatment. Mapping the local insulating characteristics using AC–SECM showed higher conductivity of the surface where H2 evolution was most favorable.