パルス電着したZn-Ni合金めっき鋼板の構造と耐食性

概要

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Zn-Ni alloys were electrodeposited onto steel sheets from a sulfate bath containing zinc cation and nickel cation at duty cycles of 100, 90, 70, 50 and 20%. The Ni content of the deposits increased and cathodic current efficiency decreased with a decreasing in duty cycle. The surface morphology changed from granular to smooth and crystal structure changed from a mixture of Zn and Zn-Ni alloy phase to Zn-Ni alloy single phase with a decreasing in duty cycle. It was thought that these changes were attributed to the selective dissolution of zinc from deposits during offtimes and to the decrease in the thickness of the diffusion layer caused by galvanostatic pulse condition. Although internal plating stress increased with a decreasing in duty cycle, they reached a constant level after anodic dissolution in NaCl solution due to the occurrence of microcracks in the deposits. Corrosion protection properties increased with decreases in the duty cycle.
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