Effect of Phosphorus in Iron on Formation of Intermediate Phase at Fe/Zn Interface

Abstract

The aim of this study is to clarify the effect of P on the microstructure of Al-free galvanized coatings. Fe-0.093wt%P binary alloy was galvanized using zinc bath without Al. It was found that P homogenizes the microstructure of galvanized coatings. Over a large part of the stereographic triangle extending from the (111) αcorner, where react diffusion is suppressed compared with that on other Fe planes, the intermetallic layer formed on Fe-P substrates is thicker than that on Fe substrates. On the Fe planes occupying the remainder of the triangle, the intermetallic layer on Fe-P is thinner than that on Fe. On Fe-P, FeZn₁₃(ζ) crystals randomly orient even on the Fe planes near (111) a where ζ crystals are formed heteroepitaxially with respect to underlying Fe substrates. The reason for that the intermetallic layer on Fe-P planes near (111) αis thicker than that on Fe planes near (111)αmay, therefore, lie in the grain boundary structure in ζ crystals. High angle boundaries in ζ crystals on Fe-P may allow high diffusivity of Zn toward substrates with eventual formation of thicker intermetallic, whereas low angleζboundaries on Fe planes near (111) α suppress the Zn diffusivity, which consequently retards the growth of the intermetallic layer.