Microstructure evolution of a 55Â wt.% Al-Zn coating on press hardening steel during rapid heating

The surface alloying of 55 wt.% Al-Zn coated press hardening steel during a press hardening heat treatment was evaluated. Austenitization resulted in the formation of a surface layer containing FeAl and Fe2Al5. The use of an increased heating rate during the austenitization cycle resulted in a high volume fraction of Zn at FeAl grain boundaries, and the presence of Zn islands in Fe2Al5 grains. These microstructural features suppressed the high temperature oxidation and evaporation of Zn. Zn was found to provide a pronounced cathodic protection, and the alloyed coating did not cause liquid metal induced embrittlement.