Nanoindentation investigations of electrodeposited on steel substrate corrosion protective zinc coating additionally improved by Cr III conversion layer

Abstract

The protective Zn coatings on steel substrates are preferable because the zinc layers play a role of "sacrificial coatings" due to their more negative electrode potential compared to steel substrate. Besides, their protective ability strongly depends from aggressive nature of environment, which determines the need of additional efforts. Vastly improvement of the chemical stability and protective ability of the Zn coatings give the additional treatments aiming the formation of "finishing" conversion layer with desired chemical-resistant composition on the Zn surface influencing against corrosion attack. Having in mind the chemical nature of the conversion layers, it is possible to predict the improvement of the chemical and mechanical properties of the system "Conversion layer"/"Zinc coating"/"Steel substrate". The present study shows the results obtained concerning the indentation modulus and indentation hardness of the Cr III conversion layers and their dependence in the depth of indentation for the studied systems. The thickness of the steel substrate, protective Zn coating and finishing conversion layer are 820, 5 and 0,15 µm, respectively. It was established that the system "Conversion layer"/"Zinc coating"/"Steel substrate" is characterized with higher indentation hardness and modulus than the system "Zinc coating"/"Steel substrate", which improves their wear resistance and corrosion protection.