Iron-based intermetallic particles formation in Al-Zn-Si alloy through powder metallurgy route

Abstract

Corrosion of the steel products is one of the significant challenges which is managed by coating with Al-Zn-based alloys. The Galvalume alloy (Al-55%, 43.5%-Zn, Si-1.5%) is coated on steel strips via a hot-dipping process. The dissolution of iron (Fe) from steel strips and the formation of Fe-based intermetallic particles is an inevitable phenomenon during the hot-dip coating process. These intermetallic particles are a primary source of massive bottom dross build-up in the coating pot and metal spot defects in the coated steel products. Therefore, it is important to investigate the formation of Fe-based intermetallic particles. In this study, Fe-based intermetallic particles are produced via the powder metallurgy route. High energy ball milling was used for mechanical alloying of aluminum (Al), iron (Fe), silicon (Si), and zinc (Zn) powders. Optimized ball milling conditions were identified after a series of trials. After cold pressing, the mechanically alloyed samples (pellets) were sintered at various conditions in a high vacuum sintering furnace. The X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy-dispersive X-ray diffraction (EDS) were used for the analysis of raw material, mechanically alloyed powders, and sintered pellets. It is concluded that the mechanical alloying of 6h and cold pressing at 9 tons for 30 min is sufficient to produce a dense compact material. It was found that Fe-based intermetallic particles were successfully fabricated which were α-AlFeSi. However, intermetallic particles similar to those found in the bottom dross of the coating pot are difficult to fabricate through the powder metallurgy route due to the volatilization of Zn during the sintering process.

Iron Intermetallic Compounds (IMCs) Formation Mechanism in the Molten Aluminium Zinc (Al-Zn) Coating Alloy

“…Once flat steel strips passed through the final rolling step, τ5c Fe-IMCs experience compressive forces. The Fe-IMCs are hard and brittle hence fractured and produced ents in the relatively ductile steel strips and overlay coating [20]. Such defects are called the metal spot defects which ultimately compromise the corrosion resistance and overall quality of coated steel products.…”