Abstract
By micro-arc oxidation (MAO) process in a silicate electrolyte, the oxide coatings were successfully formed on a coarse-grained casting AZ91D Mg alloy and an ultra-fine grained (UFG) one fabricated by equal-channel-angular-pressing (ECAP). The effect of substrate microstructure on morphologies and corrosion resistance of the MAO coatings on AZ91D alloys were investigated by scanning electron microscopy observation, immersion tests and electrochemical impedance spectrum (EIS) measurements. In comparison, the MAO coating on the UFG Mg alloy has lower corrosion rate and larger Rf value. Three factors enhance the corrosion resistance. The first is the MAO coating with uniform size and distribution of micro-pores due to homogenous micro-arc discharge. Secondly, the number of open holes decreases due to the finer β-phase after ECAP process. The most important one is the higher compactness and thickness of the coating on the UFG Mg alloy. It implies that the MAO coatings have a great potential in surface protection of UFG Mg alloys.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
