Direct, pulsed or periodically reversed current was applied to the electrodeposition of Ag-Zn alloys from cyanide baths. In the direct current plating, the electrodeposition behavior of each metal showed the regular type composition in which the deposition of less noble Zn proceed only in the limiting current region of noble Ag. In the pulsed or periodically reversed current plating the reasonable explanation of the trends of change in alloy composition was made by mainly considering the recovery of Ag concentration in the vicinity of the cathode on the basis of above deposition mechanism. In these periodical electrodeposition, the composition of alloys was determined by the average cathodic current density, and it was estimated that the replacement reaction of deposited Zn with Ag ions occurred at the off-time of pulsed current plating and the same amount of deposited Ag and Zn dissolved in the anodic current pulse period of periodically reversed current plating. Further, the effect of pulsed or periodically reversed current on the surface appearance of the alloys was discussed.

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Scanning electron microscopic studies were carried out in connection with the surface appearance of the Ag-Zn alloys electrodeposited from cyanide bath with various kinds of current forms. In the direct current plating, the needle-like deposits were obtained at lower current densities, which changed to granular in shape at higher current densities. In the pulsed current plating at on-time/off-time ratio of 0.25, the surface appearance of the alloys was similar to that obtained with direct current at the same alloy composition. Significant alteration of the current modulation in the pulsed plating resulted in a change in surface appearance, that is, the smoother deposit was obtained by increasing the pulse off-time. In the periodically reversed current plating at a given average cathodic current density, the rounded granular deposits were obtained, regardless of the pulse cycle and duty of anodic current pulse. The displacement reaction and a chemical or electrochemical dissolution of the deposited metals were estimated to bring about the changes in the surface appearance observed in these periodical electrodeposition by measuring the alloy composition, cathode current efficiency and the depositing potential of the alloys.

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Zinc-iron-group metal alloys were electrodeposited from sulfate solutions. In a wide range of plating conditions, the deposition behavior of each metal showed the main features of anomalous codeposition. Evaluation of the pH in the vicinity of cathode and of the surface film resistance revealed the following mechanism of anomalous codeposition in which electrochemically less-noble zinc is deposited preferentially. During anomalous codeposition of zinc with iron-group metal, the electrodeposition of zinc proceeds with preceding zinc hydroxide formation on the cathode, which results from a rise in pH in the vicinity of cathode. On the other hand, since the critical pH for iron-group metal hydroxide precipitation is not attained in the cathode layer, iron-group metal deposition occurs by the direct discharge of iron-group metal ions through the zinc hydroxide film, which makes the iron-group metal deposition difficult. Consequently, the superiority of iron-group metal over zinc in nobility is canceled out by the film resistance of zinc hydroxide, resulting in the preferential deposition of zinc in anomalous codeposition.

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Zinc-aluminum alloys are useful for super plasticity character, but surface finishing of these alloys are difficult for eutectoid structure. If surface composition could be changed to resemble pure aluminum or zinc structure, surface finishing becomes easy. Various composition (Zn/Al ratio is 70/30, 78/22, 85/15, 87/13) of zinc-aluminum alloys were treated with ion etching or arc discharge and change of surface structure was examined. By ion etching zinc component was removed from zincaluminum surface more easily than aluminum. Conversely aluminum was removed more easily by arc discharge on 70/30, 85/15 and 87/13 alloys, but the surface composition did not changed on eutectoid structure only. A similar behavior was observed on sprayed alloy films. These results infered as the momentary high overheating and melting of alloy surface.

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In the pulsed current electrolysis of both zinc chloride and zinc sulphate baths, changes in the morphology of zinc deposits, cathodic overpotential and differential capacity were studied as a function of pulse current density, on-time and off-time. High pulse current density and long off-time electrolysis increased the cathodic overpotentials and thus produced fine grained deposits. Increase in on-time, however, gave no effect on the grain size of the deposits and overpotential values. These results suggest that the crystallization process of zinc in the pulsed current electrolysis is influenced by the cathodic overpotentials during on-time and the initial stage of off-time.

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