Formation of microstructural features in hot-dip aluminized AISI 321 stainless steel

Abstract

Hot-dip aluminizing (HDA) is a proven surface coating technique for improving the oxidation and corrosion resistance of ferrous substrates. Although extensive studies on the HDA of plain carbon steels have been reported, studies on the HDA of stainless steels are limited. Because of the technological importance of stainless steels in high-temperature applications, studies of their microstructural development during HDA are needed. In the present investigation, the HDA of AISI 321 stainless steel was carried out in a pure Al bath. The microstructural features of the coating were studied using scanning electron microscopy and transmission electron microscopy. These studies revealed that the coating consists of two regions: an Al top coat and an aluminide layer at the interface between the steel and Al. The Al top coat was found to consist of intermetallic phases such as Al<inf>7</inf>Cr and Al<inf>3</inf>Fe dispersed in an Al matrix. Twinning was observed in both the Al<inf>7</inf>Cr and the Al<inf>3</inf>Fe phases. Furthermore, the aluminide layer comprised a mixture of nanocrystalline Fe<inf>2</inf>Al<inf>5</inf>, Al<inf>7</inf>Cr, and Al. Details of the microstructural features are presented, and their formation mechanisms are discussed. © 2018, University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature.