Electrochemical property and in vitro degradation of DCPD–PCL composite coating on the biodegradable Mg–Zn alloy

Abstract In this study, dicalcium phosphate dihydrate (DCPD) and polycaprolactone (PCL) were successively prepared on a Mg–Zn alloy to obtain a composite coating. Electrochemical measurement showed that the corrosion potential (Ecorr) of the DCPD–PCL coated alloy increased by 0.14 V compared to that of the DCPD coated alloy. The corrosion current (icorr) was about one third of the DCPD coated alloy. The real impedance (Zre) of the DCPD–PCL coated alloy was approximately 4 times as large as that of the DCPD coated one. The immersion test implied that the integrity of the DCPD–PCL composite coating kept better in the m-SBF after 260 h immersion than the DCPD coating. The less released hydrogen indicated that the degradation rate was reduced compared to the DCPD coated alloy. The degradation rate rapidly increased after 150 h for the DCPD coated alloy while 225 h for the DCPD–PCL coated case which meant the composite coating could retard the corrosion for a longer time. Therefore, the composite coating can protect the Mg alloy more efficiently.