Low‐voltage anodizing of AZ91 magnesium alloy: surface morphology and corrosion behaviour assessed by impedance analysis

Abstract

Magnesium alloys, particularly AZ91, have emerged as promising candidates for biomedical implants due to their low density, biocompatibility, and mechanical properties resembling natural bone. However, their high chemical reactivity and poor corrosion resistance in physiological environments remain major limitations. This study investigates the effect of low‐voltage anodizing on the surface morphology, porosity, corrosion resistance, and hardness of AZ91 alloy using a phosphate‐based electrolyte composed of 0.2 M K 3 PO 4 and 0.6 M K 2 HPO 4 . A series of anodizing treatments were conducted at voltages ranging from 0.5 V to 1.5 V and durations of 10 min, 20 min, and 30 min. Surface characterization via scanning electron microscopy (SEM) and porosity analysis revealed that the optimal condition—1.5 V for 20 minutes — produced the most compact and uniform oxide layer with minimal porosity. Electrochemical impedance spectroscopy confirmed enhanced corrosion resistance under these conditions, while hardness testing demonstrated significant improvement in surface hardness. These findings suggest that low‐voltage anodizing is a viable strategy for improving the durability and performance of AZ91 magnesium alloy toward potential biodegradable applications.