The relationship between the morphology of Zn-Co electrodeposits and mechanism in an acidic sulfate bath is studied.he substrates were electropolished, cold rolled low carbon steel sheets. The specimens were galvanostaticly electrodeposited at current densities of 10, 100 and 200 mA.cm -2 . At 10mA.cm -2 Nuquest plot shows three time constants. A high-frequency capacitive loop due to charge transfer resistance of deposition, an inductive loop at lower frequencies and the inductive loop atmedium frequencies is probably resulted from two-step discharge of Zn 2+ via Zn + ad species. In this state ridge morphology is observed. Increasing the current density to 100mA.cm -2 promotes a mixed morphology of ridges and platelets. In Nyquest plot corresponding to the deposition, induction and capacitive loops at medium and low frequencies have become very small. At 200mA.cm -2 a needle like morphology is obtained because of random arrangement of thin-platelets at every direction. X-ray pattern of this coating is confirmed this. A high concentration of Co 2+ at the vicinity of cathode and encourage, coagulation of the zinc hydroxide layer to promote random growth. The zinc hydroxide coagulation also created low frequency data on Nyquest plot.
