Effect of trace inorganic additives on the morphology and crystal orientation of Zn electrodeposited on the steel from sulfate electrolyte

The effects of trace inorganic additives on the morphology and crystal orientation of electrodeposited Zn have been investigated by using a polycrystal commercial low carbon Al-killed steel sheet as a base material and the sulfate bath with inorganic compounds of 4.8×10^-6 to approximately 4.1×10^-2 mol/l to bath. The current density, flow rate and bath temperature are 50 A/dm². 1.2 m/s and 60 °C, respectively. The inorganic additives can be classified into 3 groups by the effects on the morphology and crystal orientation of electrodeposited Zn. When the inorganic compounds of Fe, Ni, Co, Al, Mg and Mn (Group I) are added to the bath, the relative intensity of (0002)Zn and Zn crystal size do not change because Group I additives do not offend the heteroepitaxial growth of Zn and the overpotential for Zn deposition. When the inorganic compounds of Cr, W, Mo and Zr (Group II) are added to the bath, the relative intensity of (0002)Zn increases because Group II additives do not change the heteroepitaxial growth of Zn but decreases the overpotential for Zn deposition. When the inorganic compounds of Cu, Pb, Cd, In, Sn, Ge, Sb and Ag (Group III) are added to the bath, the relative intensity of (0002)Zn increases and Zn crystal size becomes small because these additives co-deposit with Zn and prevent the heteroepitaxial growth of Zn.