Abstract
Investigated was corrosion behavior of Zn and Zn-Fe alloy electroplated steel sheets under paint film in atmospheric exposure test and modified Volvo test (atmospheric exposure test with 5mass%NaCl solution sprinkling). 1) Creepage width of paint film remained small in the range below 14mass% Fe, and increased with Fe content in deposit in the range above 20mass%Fe in atmospheric exposure test, though it exhibited minimum value at 15mass%Fe in modified Volvo test. 2) The creepage width in both outdoor exposure test and modified Volvo test showed correspondence to corrosion current density of unpainted specimens exposed to each test in the range below 30mass%Fe, indicating that corrosion under paint film is predominantly determined by corrosion rate of the deposit with corrosion products formed in corrosion test. 3) It was considered that wedge effect of iron rust resulting from volume expansion additionally affected the corrosion in the range above 30 mass%Fe. 4) Furthermore, corrosion reaction under paint film was discussed on the basis of EPMA analysis.
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