It seems that PVA may promote the nucleation of the phosphate conversion coating. It has many OH groups which highly tend to be adsorbed on the anodic sits of the metal surface restricting the steel dissolution rate. Also, PVA may form PVA-Zn2+complexes on the steel surface in the phosphate solution. PVA-Zn2+complex may be converted into PVA-Fe2+complex on the anodic sites of the metal surface by releasing Zn2+ions according to Eq.