Polypyrrole/zinc bilayer coating on ZK60 magnesium alloy for enhanced corrosion protection in Hank's solution.

A polypyrrole/zinc (PPy/Zn) bilayer coating is prepared to significantly improve the corrosion resistance of ZK60 magnesium alloy in 37 °C Hank's solution to meet the requirements for biodegradable metals. The zinc coating composed of dense and uniform flake-like zinc crystals displays good abrasion resistance and adhesion strength, acting as a vital intermediate layer for growing the PPy film doping with tartrate anions (TA−). The prepared PPy/TA films (10, 20 and 28 μm) on the Zn coating are compact and have high stability in Hank's solution. The electrochemical and hydrogen evolution tests for PPy/Zn/ZK60 specimens show that the PPy/TA film's stability determines the protective performance of PPy/Zn coating in a long immersion period. The PPy(20 μm)/Zn coating has the longest protection time (40 ± 4 days), and too thick PPy film (28 μm) damages its structure to accelerate breakage, developing local corrosion quickly on ZK60. The corrosion mechanism involved is discussed. PPy/Zn bi-layered coating prepared on ZK60 magnesium alloy significantly improves its corrosion resistance in Hank's solution. The compact PPy film on the Zn coating is stable under chemical and electrochemical attacks, preventing the entrance of corrosion media to prolong its protection time. After PPy is broken, a local corrosion area develops quickly on ZK60. [Display omitted] • PPy/Zn bi-layered coating is prepared on ZK60 for biodegradable applications. • Zn coating acts as a vital intermediate layer for growing high-stability PPy. • PPy doping with tartrate anions (PPy/TA) has high stability in Hank's solution. • PPy/TA film's stability determines the protective performance of PPy/Zn coating. • Too thick PPy/TA film may damage its structure to accelerate its breakage. [ABSTRACT FROM AUTHOR]