Abstract
The corrosion resistance of the composite coatings of thermal sprayed Zn, Zn-Al alloys and Al, with a simplified painting of the polyurethane resin, exposed to the atmosphere for 12 years in Sapporo and Tokyo was evaluated by the electric insulation test, the SEM observation and the EPMA. In spite of losing the electric insulation already, the simplified painting showed an excellent resistivity comparing to a conventional multi-layer painting. The diffusion of the iron through the sprayed Zn was larger than that through the sprayed Al, while the amounts of chloride and sulfur penetrating through the painting on the sprayed Al was larger than those on the sprayed Zn. This suggests that the thermal sprayed Zn layer has a tendency of the cation selective permeability. The protection at the scratched portion on the composite film seemed to be obtained by the cathodic protection in Zn, and the plug effect with the oxide in Al. Corrosivity of the atmosphere caused by chloride and sulfur was larger at Sapporo than at Tokyo. The fact suggests that the influence of the airborne salinity and the pollution substances is severe at the coast of Japan Sea, especially in a long period of the snow falling season.
