Chemical reactivity of iron base substrates with liquid Mg–Zr alloys Original Research Article

The chemical interaction between pure iron, mild steel or cast iron substrates and liquid magnesium containing 0.10–0.18 at% of zirconium has been investigated at 1000 K. As long as the Mg–Zr melt is pure and fully saturated in zirconium (0.18 at% Zr), a continuous reaction layer of zirconium carbide ZrCx is formed at the substrate surface. When active impurities such as Si or Mn are present in the Zr-saturated melt, thin segmented ZrCx layers with globular Fe2Zr crystals stuck to their outer side are found undulating in the liquid at 10–50 μm from the substrate surface. These observations are interpreted in terms of a competition between a direct interaction in which Fe–Zr compounds grow in the melt by dissolution-crystallization and an indirect reaction in which a protective ZrCx surface layer develops by solid state diffusion of carbon initially present in the bulk of the substrates.