| The corrosion property and formability of a steel treated with Zn powder containing paint were studied. Two kinds of substrates, hot rolled steel and Dacro treated steel, were painted with Zn powder containing paint in the various range of Zn powder contents, 60∼87 vol.%. In order to examine the corrosion property and formability, salt spray test, electrochemical polarization test and bend test were carried out. In the case of hot rolled steel plate, good corrosion resistance was obtained above 82 vol.% of Zn powder content. But the formability became severely worse above 82 vol.% of Zn powder content. Therefore, when Zn powder containing paint is used to treat steel surface, it can be applied to the parts that do not require subsequent forming process. In the case of Dacro treated steel, a Dacro layer was degraded by Zn powder containing paint layer. This phenomenon was caused by the increase in OH^- ion concentration produced by cathodic reaction at the steel surface. In fact, the corrosion potential of the Dacro treated layer increased in a 3% NaOH solution and the Dacro layer was completely dissolved by immersion in a 3% NaOH solution. When the Dacro treated plate was coated with a paint without Zn powder, the corrosion resistance was found to improve significantly and the formability was also very good. |
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