Sputter-deposited Mg–Al–Zn–Cr alloys – Electrochemical characterization of single films and multilayer protection of AZ31 magnesium alloy

•We propose a concept of Mg protection by alloys with resistant metals.•High passivity of Mg–Al–Zn–Cr alloys is achieved when Cr concentration is over 30%.•Effective protection of AZ31 is achieved by annealed multilayer Mg–Cr structures.

Mg–Al–Zn–Cr alloy films were deposited on glass and AZ31 substrates by dc magnetron sputtering in a wide range of Cr concentrations. Distinctive passive regions and breakdown potentials identified high passivity when Cr concentrations were over 30 at.%. Both single and multilayer structures did not show any protective effect on the AZ31 magnesium alloy. SEM revealed a distinctive corrosion activity along the AZ31–alloy interface leading to delaminating of the alloy film. A high protection performance of AZ31 was achieved when applying annealed multilayer structures. The research proposes a concept of magnesium protection by Mg alloys with resistant metals, which do not form intermetallic compounds with Mg.