Zn-Al-Mg 합금도금강판의 도금 층 냉각속도 제어에 따른 미세조직 및 부식거동 분석
Effects of Cooling Rates of Coating Layer on Microstructures and Corrosion Behaviors of Zn-Al-Mg Alloy Coated Steel Sheets
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To understand effects of cooling rates of coating layer on microstructures and corrosion behaviors of hotdip alloy coated steel sheets (Zn-5%Al-2%Mg) in a neutral aqueous condition with chloride ion, a range of experimental and analytical methods were used in this study. Results showed that a faster cooling rate during solidification decreased the fraction of primary Zn, and increased the fraction of Zn-Al phase. In addition, interlamellar spacing became refined under a faster cooling rate. These modifications of the coating structure had higher open circuit potentials (OCP) with smaller anodic and cathodic current densities in the electrochemical potentiodynamic polarization. Surface analyses after a salt spray test showed that the increase in the Zn-Al phase in the coating formed under a faster cooling rate might have contributed to the formation of simonkolleite (Zn5(OH)8Cl2·H2O) and hydrotalcite (ZnAl2(OH)6Cl2·H2O) with a protective nature on the corroded outer surface, thus delaying the formation of red rust.
Abstract
To understand effects of cooling rates of coating layer on microstructures and corrosion behaviors of hotdip alloy coated steel sheets (Zn-5%Al-2%Mg) in a neutral aqueous condition with chloride ion, a range of experimental and analytical methods were used in this study. Results showed that a faster cooling rate during solidification decreased the fraction of primary Zn, and increased the fraction of Zn-Al phase. In addition, interlamellar spacing became refined under a faster cooling rate. These modifications of the coating structure had higher open circuit potentials (OCP) with smaller anodic and cathodic current densities in the electrochemical potentiodynamic polarization. Surface analyses after a salt spray test showed that the increase in the Zn-Al phase in the coating formed under a faster cooling rate might have contributed to the formation of simonkolleite (Zn5(OH)8Cl2·H2O) and hydrotalcite (ZnAl2(OH)6Cl2·H2O) with a protective nature on the corroded outer surface, thus delaying the formation of red rust.
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