Electrochemical Properties of Zn-Based Coatings on Direct Press Hardened Steels

The automotive industry is increasing its usage of Zn-coated press-hardened steels (PHS) in automotive safety and weight reduction applications, due to its ability to provide high strengths whilst also providing corrosion protection. However, there is some debate as to the fundamental corrosion mechanisms by which the mixed phase α-Fe(Zn) + Γ-Fe3Zn10 coatings provide cathodic protection. To this end, the objective of this research is to determine the fundamental mechanisms by which the mixed phase coatings provide cathodic protection, with an emphasis on the relative phase fractions of the Γ-Fe3Zn10 and α-Fe(Zn) phases in the coatings and their electrochemical characteristics. It was determined that small volume fractions of Γ-Fe3Zn10 in the coatings dominated the potentiodynamic characteristics of the coatings, indicated that this phase is essential in providing robust corrosion protection for Zn-coated PHS.