(2) 55% Al-Zn
a) Conditions at the cut. When the product is cut, the cross section shows coat-drooped part and exposed-substrate part.
b) Conditions in an early period. As zinc in the coating layer of the product provides sacrificial corrosion to protect the substrate, red rust (Fe oxide) develops on exposed-substrate part if it gets wet with rain or some other water in early stages of installation.
c) Exhaustion of Zn in the coating layer near the cut end and development of red rust on the cut end.
d) Conditions after certain years. Corrosive growth of Al, Zn, S and O develops over red rust some years after installation and such growth works to suppress corrosion of the coating layer and substrate.

Fig.-5. Sketches depicting changes noted on the cut end of 55% Al-Zn over certain lengths of time.



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