Microstructure and anti-corrosion properties of supersonic plasma sprayed Al-coating with Nano-Ti polymer sealing on AZ91-Magnesium alloy

Abstract

Supersonic plasma spray was used to deposit Al-coating on AZ91-alloy. Nano-Ti polymer was then employed to seal the pores on the as-sprayed Al-coating. The microstructures and corrosion resistances of the as-obtained Al-coating and Al+nano-Ti polymer composite-coating were examined by field scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), micro computed tomography (micro-CT), potentiodynamic polarization, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and neutral salt spray testing (NSS). For comparative purposes, AZ91-alloy was used as reference and tested under the same conditions. The as-sprayed Al-coating exhibited excellent properties with porosity of 1.5 ± 0.58% and bonding strength of 30 ± 2.68 MPa. By comparison, the composite-coating depicted a porosity of only about 0.05 ± 0.01% and bonding strength of 10.05 ± 1.72 MPa. The long-term anti-corrosion properties of Al-coating and composite-coating were better than that of AZ91-alloy, and composite coating possessed better protective effect with its Ecorr and Icorr of about −0.807 V and 1.4137 × 10−8 A·cm−2, respectively. Meanwhile, composite-coating surface without the formation of blisters, pulverization or macro-defects even after 720 h of accelerated corrosion using neutral salt spray experiments. The Al-coating displayed slight pitting corrosion on its surface, much milder than of AZ91-alloy. The composite coating exhibited superior corrosion resistance by forming wrapped pathways of nano-Ti polymer coating and excellent passivation layer of dense Al-coating.

Keywords

• Al coating
• Post-sealing treatment
• Supersonic plasma spraying
• Anti-corrosion mechanism