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.