Effect of fluoride coating on in vitro dynamic degradation of Mg–Zn alloy

A compact and flat fluoride coating with some pores was prepared on a Mg–Zn alloy in order to control its degradation behavior. The electrochemical tests demonstrated that the real impedance (Zre) of the fluoride-coated Mg–Zn was approximately 10 times as large as that of the untreated alloy. The free corrosion potential (Ecorr), compared to that of the uncoated Mg–Zn alloy, increased 646 mV for the coated metal. The free corrosion current (Icorr) of the Mg–Zn specimen with the fluoride film was about one tenth of that of the uncoated one. The in vitro dynamic degradation tests showed that the average weight loss of the fluoride-coated Mg–Zn was lower than that of the untreated alloy in the initial 4 h of the tests, indicating the film could function as a barrier coating on Mg–Zn matrix. However, the coating cracked and peeled severely after 4 h dynamic tests, which implied that the fluoride coating could not endure the sustaining washing of the modified simulated body fluid.