Enhancing the anti-corrosion performance and biocompatibility of AZ91D Mg alloy by applying roughness pretreatment and coating with in-situ Mg(OH)2/Mg-Al LDH

Corrosion-resistant and biocompatible films were fabricated on AZ91D Mg alloy substrates by varying their roughness levels using metallographic preparation and subsequent hydrothermal procedures. The coated films comprised a mixed structure of Mg(OH)2 and Mg-Al layered double hydroxides (LDH) and exhibited excellent compactness. Coating film thickness increased with decreasing surface roughness. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. Metallographic pretreatment influenced the chemical activity of the Mg alloy surface and helped modulate the dissolution rate of the Mg17Al12 phase during the hydrothermal procedure. With decreasing roughness of the Mg substrate, the Al3+ concentration gradually increased, accelerating the in-situ formation of the Mg(OH)2/LDH composite coating and improving its crystallinity. A thick and dense Mg(OH)2/LDH coating was synthesized on the Mg substrate with the least roughness, substantially improving the corrosion resistance of the AZ91D alloy. The lowest corrosion current density ((5.73 ± 2.75) × 10−8 A·cm−2) was achieved, which was approximately three orders of magnitude less than that of bare AZ91D. Moreover, the coating demonstrated biocompatibility with no evident cytotoxicity, cellular damage, and hemolytic phenomena. This study provides an effective method for preparing coatings on Mg alloy surfaces with excellent corrosion resistance and biocompatibility.