The texture-surface morphology relationship in zinc-iron electrolytic coatings

A combination of X-ray texture measurements and atomic force microscopy topographical analysis was used to characterize the growth surface of Zn-Fe alloys electrolytically deposited on cold rolled steel substrates. Deposits, which initially exhibited a morphology of approximately 20 nm thick platelets inclined 10 degrees-20 degrees to the substrate surface, subsequently evolved either into triangular pyramids or hexagonal columnar crystals depending on the presence of Sn2+ ions in the sulphate electrolyte. The morphology of the triangular pyramids, formed in the absence of Sn2+ ions, had (10.0) and (00.1) planes of eta (hcp) phase tilted to the substrate surface. For the morphology of hexagonal columnar crystals, formed in the presence of Sn2+ ions, the (00.1) basal planes of eta phase were aligned parallel to the substrate surface. The macro and nano-size steps of growth were identified on both morphologies in order to locate the active growth front. It is concluded that the lateral growth on the same (00.1) basal planes of eta phase led to the formation of essentially different morphologies and textures of the Zn-Fe deposits. (C) 1998 Chapman & Hall.