Corrosion behaviour of a surface-treated AISI H11 hot work tool steel in molten aluminium alloy

Immersion tests in a molten aluminium alloy of a surface-treated AISI I-Ill hot work tool steel were carried out in order to study the corrosion mecha nisms and the effect of different surface treatments on the resistance of t he material. The steel has a great reactivity with molten aluminium, which causes a generalised attack on the exposed surface. Plasma nitriding and a proprietary gas oxynitriding treatment (NIPRE(R)) do not change the attack morphology, but improve the corrosion resistance because they reduce wettab ility and require the dissolution of the surface compound layer formed by t he diffusion treatment, before the alloy reacts with the steel. PVD coating s are able to greatly improve the corrosion resistance. They change the mec hanism from a generalised attack to a localised one. The improvement is fur ther enhanced by a preliminary nitriding of the base material. The coating density of through-coating defects and the resistance to the thermomechanic al stresses arising during immersion are the key properties of the coated s urfaces. (C) 2000 Elsevier Science S.A. All rights reserved.