Influence of Surface Post-Processing on Crystal Refinement and Characteristics of Hopeite Coating by Phosphating

Hopeite (Zn3(PO4)2·4H2O) conversion coating was prepared on pure titanium using mild phosphate chemical conversion technology. In this investigation the effect of post-processing after phosphating was focused on coating microstructure, chemical composition, adherence and corrosion resistance. Different sequential order of drying and rinsing of the coated samples were carried out. The results demonstrated that the priority shift of rinsing or drying did not change the hopeite phase of the conversion coating, but played a significant role in the crystal size and coating microstructure. Compared with the traditional preparation of the coating, a more compact and uniform coating with finer crystals grains (3–5 μm) was obtained by the unconventional post-treatment of drying before rinsing, along with a higher bonding strength and corrosion resistance.