A combined coating strategy based on atomic layer deposition for enhancement of corrosion resistance of AZ31 magnesium alloy

Abstract

Rapid corrosion restricts the wide application of Mg and Mg-based alloys. In this work, a combined surface strategy was employed to modify the surface of AZ31 Mg Alloy. An atomic layer deposition (ALD) technique was utilized to prepare ZrO 2 nanofilm on Mg substrate. During this course, the film thickness could be precisely controlled by adjusting the ALD cycles with a deposition rate of 0.117 nm/cycle. The subsequent PLGA grafting on ZrO 2 nanofilm was carried out by a spin-coating process to further enhance the corrosion resistance. The nanoscratch tests showed that this hybrid coating had good bonding strength with substrate and similar Young's modulus to natural bone. In vitro corrosion tests demonstrated that a thicker ZrO 2 nanofilm on the surface could reduce the corrosion rate of Mg substrate when compared to a thinner coating. When increasing ZrO 2 deposition cycles from 25 to 100, the corrosion resistance could be significantly increased by two or three orders of magnitude. Hydrogen evolution tests revealed the synergetic effects of both galvanic corrosion and local acidic action could accelerate the corrosion of the AZ31 modified with the PLGA/ZrO 2 coating once the ZrO 2 nanofilm was damaged. Therefore, by changing the ALD cycles, the corrosion resistance of both ZrO 2 thin film and ZrO 2 /PLGA hybrid coatings can be adjusted. This work provides an effective combined surface strategy that can be employed to adjust the corrosion resistance of Mg-based alloys for biomedical applications.