MORPHOLOGY AND MICROSTRUCTURE OF PULSE ELECTRODEPOSITED ZINC IRON BINARY-ALLOYS

Zinc-iron electrodeposited sheet steels have been widely adopted for automobile bodies for their improvements in the corrosion resistance and paintability. In princiles, these properties depend on the crystal structure, morphology and microstructure of deposits. The deposits with various pulse current-off time have been electrodeposited from sulfate bath and examined by scanning microscopy and X-ray diffraction. All the deposits consist of the η- and Γ-phases, and the deposit morphology consists of hexagonal columnar crystals and Γ-phase granular crystals. These hexagonal columnar crystals consist of the η-phase plates and fine granular Γ-phase dispersively precipitate within the grain and grain boundary of these η-phase plates. For the 1.0 ms pulse current-off time deposit, the granular crystals form only on the (00-1)η of hexagonal columnar crystals. For the deposit more than 1.0 ms, these granular crystals form both on the (00.1)η and {10.0}η of hexagonal columnar crystals. The amount of granular crystals increases as the increase of off time. Also the deposit cross-sectional observation reveals the increase of white microstructures whose zinc contents are less than dark microstructures. The X-ray diffraction shows the decrease of diffraction intensity and number of diffraction lines of η-phase, and the increase of those of Γ-phase. © 1990, The Iron and Steel Institute of Japan. All rights reserved.