Scratch and wear resistance of nano-silica-modified silicate conversion coating on aluminium

The silicate conversion coating was modified with nano-silica and applied on the surface of AA2024 by dip-coating technique. The mechanical properties of produced modified silicate layer were investigated by the pencil scratch hardness, cross-cut and abrasion resistance tests. The characterisation of coated surface before and after the tests was studied with optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and atomic force microscopy. Addition of nano-silica to the silicate coating caused an enhancement in the SiO₂:K₂O ratio. The results showed that the homogeneity of coating surfaces increased in the presence of nano-silica. The wear and scratch resistance of the modified silicate layer improved against the sliding conditions. In addition, the adhesion of coating layer to the substrate metal increased.