55 % Al-Zn Coating for Press Hardening Steel

Abstract

Press hardening is the most efficient process to produce high strength steel parts. Al-Si and Zn coated PHS are currently in use despite the fact that these coatings have obvious drawbacks such as delamination and liquid metal induced embrittlement (LMIE). The 55 % Al-Zn alloy coating can be used as a coating for PHS because it provides both a barrier protection, due mainly to Al, and an effective cathodic protection, due to the presence of free Zn. The microstructural evolution of this alloy coating during and after heat treatment prior to hot press forming has been investigated in depth in the course of the present work. During the heat treatment, the coating was transformed to an alloy layer consisting of a Fe2Al5 layer and a Fe-Al diffusion layer. The Zn was partitioned out of the Fe-Al intermetallic compound and accumulated at the grain boundaries of the reacted alloy layer. This phenomenon was found to be beneficial for cathodic protection.