Corrosion and corrosion fatigue performances of micro‐arc oxidation coating on AZ31B cast magnesium alloy

In this work, the corrosion performances of micro‐arc oxidation (MAO) coating on AZ31B cast alloy were examined. MAO coating synthesized at a low current density of 34 mA/cm 2 has a uniform and compact microstructure with very fine micro‐pores and few structural defects; thus, robust protection is provided for the AZ31B substrate in corrosive solutions. The long‐term corrosion and corrosion fatigue behaviors of the MAO coatings formed at the optimal current density for 5 and 10 min were characterized. The results show that the MAO coating formed for 10 min provides greater protection in a salt fog environment than the coating formed for 5 min does because it is thicker. The fatigue life and fracture analysis of bare, MAO‐coated and E‐paint MAO‐coated AZ31B indicate that the MAO coating reduces corrosion fatigue life by 55% due to the micro‐pores and micro‐cracks on its surface providing initiation sites under stress conditions and accelerating crack propagation. However, E‐paint MAO‐coated specimens show improved corrosion fatigue strength in 10 7 cycles at ∼60 and ∼50 MPa under the same conditions due to the sealing of the micro‐pores and micro‐cracks in the MAO coatings.