Influence of substrate topography on formation of FeZn phases and properties of galvanneal coatings

The influence of cold rolled topography on titanium (Ti) and titanium niobi um (TiNb) interstitial free steels has been investigated with respect to Fe Zn intermetallic phase development and the adhesion properties of hot dip g alvanised and galvannealed coatings. It is shown that substrate chemistry d etermined the initial reactivity in the galvanising bath and the consequent development of FeZn intermetallic phases. TiNb steels were found to have a lower susceptibility to coating failure, in particular flaking, during for ming operations. The results suggest that this is due to the higher interfa cial strength of TiNb material, which in part is determined by the nucleati on of orientated FeZn crystals with slow growth rates on {111} alpha Fe gra ins. this reduces the effective surface area of the brittle Gamma phase and increases the microroughness of the galvanneal coating and the substrate/c oating interface. An interaction between FeZn phase growth and topographica l features was found, However, the consequent effect on coating performance remains unclear and is the subject of further research.