The Effect of Temperature and Time on the Formation of a Reaction Interlayer During Aluminizing of a Carbon Steel
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The Effect of Temperature and Time on the Formation of a Reaction Interlayer During Aluminizing of a Carbon Steel R. Torres1, V.H. López 2, J.P. Arredondo 1, R. García 2, J.A. Verduzco2 and M.L. Mondragón3 1
Facultad de Ingeniería Mecánica, UMSNH, Morelia, Mich., México. Instituto de Investigaciones Metalúrgicas, UMSNH, P.O. Box 888, Morelia, Mich., 58000, México. E-mail; [email protected] 3 Instituto Tecnológico de Morelia, Morelia, Mich., México. 2
ABSTRACT A kinetic study was performed on the growth of a reaction interlayer between molten Al and carbon steel substrates at temperatures between 665 to 820°C by holding Al/flux/steel assemblies, in a tube furnace, at temperature for times up to 120 min. An Ar atmosphere and a K-Al-F based flux were used to enable spreading of molten Al on the steel substrates. Chemical and microstructural characterization of the samples revealed that the interlayer is composed of FeAl3 and Fe2Al5, being the second phase significantly thicker. The Fe2Al5 phase grows toward the steel with a tongue like morphology. Isothermal growth profiles of the reaction interlayer followed a parabolic behavior, meaning that at the beginning the reaction is very rapid and once that a continuous interlayer is formed the growth of the interlayer is controlled by interdifussion of species across the interlayer. INTRODUCTION Carbon steels are cheap materials widely used for a number of structural applications due to their stiffness and strength. However, their corrosion properties are lacking and therefore their use in even lightly aggressive environments is restricted. In order to reduce costs and overcome the degradation of carbon steels by corrosion, application of coatings is a suitable method to extend the service life of structural components. On the other hand, Al and its alloys are also popular materials employed in a wide range of applications due to their light weight, shiny appearance and outstanding corrosion properties. Thus the combination of the mechanical properties of steels with the surface properties of aluminum is desirable for many applications. Hot dip aluminizing is a versatile method which enables adhesion of molten Al onto steel by using fluxing agents that dissolve oxides. Once that liquid Al and solid steel come into contact and owing to the negligible solubility of Fe in liquid Al, Al-Fe intermetallic compounds precipitate at the solid/liquid interface and rapidly form a reaction interlayer. Intermetallics are brittle compounds which can readily crack and lead to peeling of the coating. Thus, it is critic to control parameters such as temperature of the melt and contact time in order to minimize the formation and growth of the interlayer [1,2]. This study aims to insight into the growth mechanism of the reaction interlayer and its kinetics when Al of commercial purity is deposited onto a plain carbon steel widely use.
EXPERIMENTAL DETAILS To perform the kinetic study, aluminum of commercial purity (99.4%) and a plain carbon steel (0.05 C, 0.35 Mn, 99.31 Fe, wt.%) were us
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