Towards development of anticorrosive CaCO3-coated passive layer on Mg alloy with ultrasound-assisted electrodeposition

An anticorrosive CaCO3-coated Mg(Al)O passive layer was obtained via the ultrasound-assisted electrodeposition on AZ41 Mg alloy for concrete formwork. Corrosion rate of the CaCO3/Mg(Al)O coated AZ41 Mg alloy was lower than 0.005 mmy-1 in Portland cement (PC) system containing 0.6 M NaCl. Ultrasound plays a dual-role in forming a dense Mg(Al)O passivation film and densifying the outer CaCO3 layer. Furthermore, re-passivation instead of corrosion was observed during the embedment, attributed to the double-layer structure effectively increasing the critical chloride ion concentration for corrosion. Formation and anticorrosion mechanism as well as the role of the passivation film in anticorrosion are discussed.