Synthesis of Intermetallics Based on the Fe-Al-Si-Zn Alloy System by Magneto-Mechanical Milling of Ductile Elemental Powders

The Zincalume hot-dip coating process is a well-established technique for excellent corrosion protection of steel products. This paper describes the study of two intermetallics based on the Fe- Al-Si-Zn alloy system, α-AlFeSi and α-AlFeSi(+Zn), pertinent to the Zincalume process. These intermetallics are difficult to characterize in-situ due to their formation at high temperature and because they form as very thin intermetallic layers on a steel substrate, which inhibits accurate quantitative analysis. Controlled magneto-ball milling and hot-pressing have been employed in an attempt to synthesise these intermetallic compounds. Magneto-ball milling, under a He atmosphere, was conducted in shearing mode to enable controlled milling of elemental powders, namely Zn and Al, without the excessive cold-welding often associated with milling of ductile powders with high coefficients of surface friction. XRD analysis indicated that uniform mixtures of highly reactive fine-structured powders were produced, as indicated by diffuse elemental peaks of low intensity. Hot-pressing was utilized to sinter the powders into compact intermetallic compounds without sintering aids. The intermetallics were characterized by DTA, XRD and elemental contrast mapping performed on an SEM with EDS.