Effect of small amount of inorganic additives on the lightness and the gloss of electrogalvanized steel sheets

Zn was electrodeposited on a commercial steel sheet from the sulfate baths containing a small amount of inorganic additives. The lightness and the glo ss of deposited Zn were evaluated by the conventional techniques and the mo rphology was observed using an atomic force microscope. On the basis of the ir effect on the appearance of deposited Zn, the additives used were classi fied into following three groups: Fe, Ni, Co, Al, Mg and Mn (Group I), Cr, W, Mo and Zr (Group II) and Cu, Ph, Cd In, Sn, Ce, Sb and Ag (Group III). T he additives of group I hardly affected the morphology, crystal orientation and surface roughness of deposited Zn, and therefore they caused no change in the lightness and the gloss compared with the deposit from additive-fre e bath. Since the additives of group II enhanced the (0002) orientation ind ex of deposited Zn, the surface roughness decreased significantly. As a res ult, the lightness and the gloss of deposited Zn increased although the mor phology was scarcely affected by these additives. The additives of group II I caused a significant change in the morphology of deposited Zn and therefo re the surface roughness changed considerably depending on the additive con centration in the baths. With an increase in the additive concentration in the baths, the lightness and the gloss were generally decreased although th e addition of extremely small amount of Cd Ge, Sb and Ag compounds to the b aths increased the lightness and the gloss of deposited Zn.