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

Abstract 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 ZrC x is formed at the substrate surface. When active impurities such as Si or Mn are present in the Zr-saturated melt, thin segmented ZrC x layers with globular Fe 2 Zr 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 ZrC x surface layer develops by solid state diffusion of carbon initially present in the bulk of the substrates.