Corrosion resistance of a nano-Mg modified silane conversion coating with cathodic protection on magnesium alloy AZ91D

Abstract

In order to give the capability of cathodic protection to silane conversion coating (SCC), nano-Mg particles was used to modify SCC, and a nano-Mg modified SCC (nano-Mg@SCC) was prepared on magnesium alloy (MA) AZ91D. The microstructure and anti-corrosion of nano-Mg@SCC were characterized. Both Si-O-Mg and Si-O-Si bonds were mainly responsible for constructing the nano-Mg@SCC/AZ91D system: the former bond acted at the interfaces between nano-Mg particles and SCC as well as between nano-Mg@SCC and AZ91D substrate, and the latter bond acted in the interior of nano-Mg@SCC. The corrosion current density (ic) and the coating resistance (Rc) for the nano-Mg@SCC coated AZ91D were respectively lower and higher than those for the single-SCC coated AZ91D; at the same time, both stable open circuit potential (OCP) and corrosion potential (Ec) of nano-Mg@SCC coated AZ91D were more negative than those of bare AZ91D. The nano-Mg@SCC retained the original capability of physical barrier and possessed the new capability of cathodic protection, so nano-Mg@SCC provided better corrosion resistance to AZ91D substrate than single-SCC did.