Corrosion resistance of D,L-Polylactic Acid Coated- AZ31 and Porous AZ31

Abstract

D,L-Polylactic acid (PDLLA) coatings were prepared on the surface of AZ31 and porous AZ31, respectively. Before PDLLA coating, MgO coating or a zinc phosphate conversion coating (ZnP) formed on magnesium alloy AZ31. The electrochemical and dynamic degradation tests were used to investigate the degradation behaviours of the PDLLA coated samples. The weight loss and pH over the tests were recorded to characterize the corrosion performance. The surface topography of all specimens after the dynamic degradation was tested, which undermined the corrosion resistance of the PDLLA-AZ31. The results indicated that the uniform and smooth polymer films with thicknesses of about 3 μm were successfully prepared on the compact and porous AZ31. The results showed that PDLLA-AZ31 had higher free corrosion potentials (E_corr) and lower corrosion currents (I_corr) in the simulated body fluid at 37 °C. In addition, the pore of porous AZ31 had important effects on the corrosion of magnesium alloys. A model was proposed to illustrate the interaction between the PDLLA coating and AZ31 substrate. The results also suggested that this reciprocity may also exist on the implanted magnesium stents coated with biodegradation, which is a potential obstacle for the further development of bone repair.