288
Fundamentals of Corrosion
surface layer, as with pure zinc coatings. As a result, no thickness or weight
loss is observed, even after several years of exposure in atmospheric field
testing.
It is normally recommended that thermally sprayed coatings be sealed
to avoid initial rust stains, to improve appearance, and to facilitate maintenance painting. Sealing is designed to fill pores and give only a thin overall
coating, too thin to be directly measurable. Epoxy or acrylic resin systems,
having a low viscosity, are used as a sealer.
8.4.1.6 Zinc-Iron Alloy Coatings
As compared with pure zinc, the zinc-iron alloy coatings provide increased
corrosion resistance in acid atmospheres but slightly reduced corrosion resistance in alkaline atmospheres.
16
14
12
10
6
4
2
0
0
5
10
15
Galvanized
Galvanized
Galvalume
Galvalume
8
Exposure Time, Years
Exposure Time, Years
Corrosion Loss in Micrometers
Corrosion Loss in Micrometers
Severe Marine Atmosphere
Marine Atmosphere
15
10
5
0
0
2 4 6 8 10 12 14 16
×
×
×
×
×
×
×
×
×
Galvanized
Galvalume
Exposure Time, Years
Corrosion Loss in Micrometers
Industrial Atmosphere
15
10
5
0
0
2 4 6 8 10 12 14 16
×
×
×
×
×
FigurE 8.15
Thirteen-year exposure of Galvalume in marine and industrial atmospheres.