Effect of electrolysis conditions on the morphology and crystal orientation of zinc electrodeposit

The effect of electrolysis condition on the morphology and crystal orientation 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 current density of 50-200A/dm², flow rate of 1-2m/s and bath temperature of 50-70°C. Under the conditions where overvoltage of electrodeposit is high, such as high current density, low flow rate and low temperature, heteroepitaxy of steel/zinc decreases, so that zinc crystals become fine and random in size and growth direction. Under the high overvoltage conditions, orientation indexes of (0002) Zn and (101̄3) Zn decrease but those of (101̄1) Zn and (101̄0) Zn increase. When zinc electrodeposits grow heteroepitaxially, (0002) Zn and (101̄3) Zn planes are preferred. From these results, zinc electrodeposits are thought to progress as follows : At initial stage of plating, zinc electrodeposits grow heteroepitaxially at preferred orientations of (0002) Zn and (101̄3) Zn. Then, random growth of zinc begins partly on the (0002) Zn and (10̄1̄0) Zn and finally random growth of (101̄1) Zn and (101̄0) Zn occurs partly on the (0002) Zn and (101̄3) Zn.