1991 Volume 40 Issue 7 Pages 470-477
To estimate the corrosion resistance of hot-dipped Zn-Al alloy coatings used for protective coatings for outdoors telecommunications plants in coastal areas, the corrosion behaviour of Zn-Al coatings containing 0.2 to 30wt% aluminum was investigated by polarization measurements in NaCl solution and salt spray testing.
The results are summarized as follows:
a) Corrosion potential of Zn-Al coatings of any aluminum content were almost the same as that of pure zinc in a 3% NaCl solution. This indicate that Zn-Al coatings of any aluminum content can be expected to provide the same galvanic protection to a steel substrate as a pure zinc coating.
b) The polarization curves for Zn-Al coatings in the NaCl solution were also the same as that of pure zinc coatings.
c) The polarization curves of Zn-Al coatings with crevices were almost the same as that of non-creviced specimens, despite the accelerated anodic polarization current of creviced specimens of pure aluminum coating, whose crevice corrosion in coastal areas is well known. Consequently, the crevice corrosion of Zn-Al coatings need not be considered.
d) The weight loss of Zn-Al coatings in the salt spray testing was reduced in proportion to increasing aluminum content.
e) The corrosion products of Zn-Al coatings after salt spray testing consisted mainly of ZnCl2·4Zn (OH)2.
