2007 年 71 巻 4 号 p. 379-387
The defects of the hot-dip galvanized coating found in the course of actual operation were sampled for clarifying the defect formation mechanism. The composition of galvanized coating was 43.4 mass%Zn-55 mass%Al-1.6 mass%Si. In the initial stage and middle stage of operation, five defects were selected from many defects. Observations of optical microscope and SEM, analyses by μ-XRF and SEM-EDS were carried out for the surface and the cross section of those defects. The results were summarized and classified into three kinds of formation mechanism as follows:
(1) One is the defect occurred from the remained oxide film on the steel surface which was not reduced in the surface treatment process.
(2) Second is the defect occurred from the dross (Fe-Al-(Si) intermetallic compound) formed in the bath.
(3) Third is the defect occurred from the aggregation consisted of the dross (Fe-Al-(Si) intermetallic compound) and metal oxides (CaO, SiO2 and Fe2O3, and so on) existing as impurities.