Phosphorylated PVA coatings for corrosion protection of Mg AZ31 alloy

In this paper, the influence of different amounts of phosphoric acid on the protective properties of phosphorylated PVA (PPVA) coatings on a Mg AZ31 alloy is investigated. PPVA coatings and free-standing films were prepared by dip-coating and casting, respectively, and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and swelling assays. The anticorrosion properties of the coatings were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization, both in 3.5 wt% NaCl solution. The results show that | Z | values increase with the amount of H 3 PO 4 , reaching values on the order of 10 5 Ω cm 2 for the coating with the highest amount of H 3 PO 4 (0.100 PPVA). Additionally, this sample shows the lowest swelling degree (around 80%). Polarization tests demonstrate that all coatings significantly decrease j corr (from 4.8 μA cm −2 to values around 0.3 μA cm −2 ) by means of a cathodic inhibition. These results make of PPVA coatings interesting water-based alternatives to polysaccharide coatings.