A Novel Sealant Containing Calcium Sulfoaluminate Nanoparticles on Micro-Arc Oxidation Coating and Its Sealing Mechanism.

Although micro-arc oxidation (MAO) coatings are widely used due to their corrosion and wear resistance, their inherent micro-pore defects seriously affect their service life. The conventional sealing materials to these defects often fail to bond well with the pore wall due to volume shrinkage during curing, resulting in a service life that still does not meet expectations. Here, a novel pore-sealant is prepared to overcome the issue by adding nano calcium sulfoaluminate (CAS) expansive fillers. The modified CAS particles were compounded with glycidyl methacrylate (CAS sealant) and were driven to seal the micro-pores of MAO coatings by negative pressure. Results indicate that the surface porosity of the MAO coating decreased almost to zero after sealing treatment with the CAS sealant. Its low-frequency impedance |Z|0.01Hz remained at 108 Ω·cm2 after 672 h of immersion, which is three orders of magnitude higher than that achieved by traditional sealing methods. The mechanism is that the interface defects at fillers/pore walls are filled by the sealant volume expansion due to CAS water absorption, which significantly inhibits the rate of corrosion medium penetration into the coating.