Improvement in corrosion characteristics of AZ31 Mg alloy by square pulse anodizing between transpassive and active regions

► Anodization of AZ31 Mg alloy with the square pulses between transpassive (10 VAg/AgCl) and active (−1.35 VAg/AgCl) regions. ► Anodic film formed at duty ratio of 91 for 600 s afford the highest corrosion resistance in 0.1 M NaCl solution. ► Pore density decreased approximately 11-fold than that obtained with a constant potential.