Effect of Ni precoating and organic additives on the morphology of zinc electrodeposit

The effect of Ni precoating and organic additives on the morphology of zinc electrodeposit was investigated by using the polycrystal commercial low carbon Al-killed steel sheet as a base material and the sulfate bath under the Ni precoating weight of 10-200 mg/m² and adding organic compound of 5-1000 ppm to bath. (1) Without reference to plating conditions, zinc electrodeposits grow heteroepitaxially at preferred orientations of (0002), (101̄3) and (0004)Zn of which angle between Zn basal plane and the sheet surface plane is less than 45°, zinc electrodeposits grow randomly at preferred orientations of (101̄2), (101̄1) (101̄0) and (112̄0)Zn of which angle between Zn basal plane and the sheet surface plane is larger than 45°. (2) When surface condition of sheet is changed by Ni precoating, fine zinc electrodeposits grow randomly from initial stage of plating, so that surface of zinc electrodeposits is smooth. (3) When organic compound is added to bath, the morphology of zinc electrodeposit changes according to the amount of additive. When the amount of additive is small, the morphology of zinc is same as that under Ni precoating condition. When the amount of additive is large, Zn basal plane grows vertically to the sheet surface plane and surface of zinc electrodeposit is rough because of high overvoltage of electrodeposit.