TITLE:
Importance of Surface Preparation for Corrosion Protection of Automobiles
AUTHORS:
Narayan Chandra Debnath
KEYWORDS:
Pretreatment Process; Tricationic Phosphating Formulations; SEM; XRD; EDX; Electrochemical Impedance Spectroscopy; Corrosion Protection
JOURNAL NAME:
Journal of Surface Engineered Materials and Advanced Technology,
Vol.3 No.1A,
February
28,
2013
ABSTRACT:
An overview of science and technology of pretreatment process suitable for automotive finishing with cathodic electrodeposition primer is presented in details in this paper. Both the theoretical principles and practical aspects of tricationic phosphating process that are used in automotive industry are discussed in details. The characteristic features of phosphate coatings of both conventional high zinc phosphating formulations and modern tricationic phosphating formulations on steel surface are compared in details by SEM, EDX and XRD techniques. The corrosion protection of the phosphated and painted steel panels were evaluated by both salt spray test and electrochemical impedance spectroscopy (EIS). The analysis of impedance data in terms of pore resistance (Rpo), coating capacitance (Cc) and breakpoint frequency (fb) as a function of salt spray exposure time provides a clear insight into the mechanism of superior corrosion resistance provided by the modern tricationic phosphating formulations compared with conventional high zinc phosphating formulations.