Corrosion behaviour of zinc deposits obtained under pulse current electrodeposition: Effects of coumarin as additive

The corrosion behaviour of zinc deposits obtained under pulsed current electrodeposition from an acidic chloride bath in the presence and absence of coumarin has been investigated. The effects of pulse peak current density (Jp) on the morphology of zinc deposits were studied by scanning electron microscopy. An increase in Jp from 40 to 280 A dm−2 yields deposits with a finer grain size. The refinement of the grain size was more considerable in the presence of coumarin (Jp = 280 A dm−2). The preferred orientation of zinc deposits was studied by X-ray diffraction. At Jp = 40 A dm−2, the preferred orientation of zinc deposits was (1 0 3) and changed to (0 0 2) at Jp = 80 A dm−2. An increase in Jp to 280 A dm−2 did not change the preferred crystallographic orientations except for an increase in the peak intensity of the (0 0 2) plane. In the presence of coumarin, the preferred crystallographic orientations changed at Jp = 280 A dm−2 from the (0 0 2) plane to the (1 0 3) plane. The corrosion behaviour was investigated in an aerated 3.5% NaCl solution; the anodic polarization and electrochemical impedance spectroscopy curves were performed. The corrosion resistance of zinc deposits was improved by increasing the pulse peak current density (Jp); whereas, the presence of coumarin did not improve the corrosion resistance.