Texture and Surface Morphology in Zinc Electrodeposits

Texture and surface morphology strongly affects zinc deposit properties, such as corrosion, wear, and forming. Therefore the trend is now toward controlling the texture and morphology of the deposit, which is controlled by nucleation and growth processes during eletrodeposition. In this lecture nucleation and growth of zinc electrodeposits in acid sulfate bath onto steel surface of a low carbon steel surface will be discussed. Zinc electrodeposit consists oftt-crystals stacked on each other in different ways to produce quite different texture and morphology depending upon the applied overvoltage and y-texture intensity ofsteel substrate. At low overpotentials, non-fiber pyramidal (11.5) and (11.6) is the predominant texture component while at high overpotentials, (00.2) fiber texture component is dominant. The morphological analysis of the coating surface indicates that the non-fiber texture component results from epitaxial growth. It is shown that the non-fiber pyramidal texture component results from the hetero-epitaxial growth ofzinc andits intensity increases with increasing the intensity of y-fiber texture in the steel substrate. Steel substrate with a low intensity of y-texture component cannot support epitaxial growth of'zinc, but by increasing the intensity ofthe y-texture in the steel substrate, epitaxial growth ofzinc occurs andbecomes intense. It was found that epitaxial growth ofzinc starts with tip shape nodule formation. Merging ofthe tips during further development of the coating creates continuous layers, which are laid over each other producing the so-called ''ridges morphology". On the other hand, the (00.2) fiber component starts only from 3D nucleation followed by lateral oriented growth to promote the plane having the lowest surface energy (i.e. (00.2» parallel to the steel substrate surface and results "platelet morphology".

Keywords:

Electrodeposition , Zinc. Coatings , Texture , epitaxial growth