Morphological and microstructural evolutions of manganese phosphate coating formed in Ni²⁺ ion containing electrolyte

The effect of Ni²⁺ ion in a phosphating solution on the formation of phosphate compound on steel surface is studied. Experimental results indicate that Ni²⁺ promotes the nucleation of the formation of phosphate compound. The number of nucleation sites increases and the particle size decreases as the Ni²⁺ ion concentration in the phosphating solution increases. The presence of Ni²⁺ ions in the coating solution strongly influences the surface morphology and the distributions of Ni, Cr, Mo and V in the phosphate layer. The manganese phosphate coating is a two layered structure which consists of an iron rich inner layer and a Mn rich outer layer. The reduced Ni strips that are located near the centre of the phosphate compound mark the initial substrate surface before phosphating.