Preparation and Characterization of Synchronous Chemical Conversion Coating on 6061 Aluminum Alloy/7075 Aluminum Alloy/Galvanized Steel Substrates

Abstract

This paper aimed to develop synchronous chemical conversion coating on multi-metal substrates with good corrosion resistance to meet the primer process of new energy light vehicle bodies. Titanium/zirconium-based chemical conversion coatings were prepared on 6061 aluminum alloy/7075 aluminum alloy/galvanized steel substrates. By measuring the open circuit potential (OCP), the formation of a muti-metal synchronous conversion coating can be roughly divided into three steps. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques showed that the self-corrosion current density of the conversion coating decreased significantly while the resistance increased. The surface morphology and composition of the conversion coatings were observed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Additionally, the micro-zone characteristics of conversion coatings were analyzed by an electron probe microanalyzer (EPMA). The synchronous conversion coatings exhibit uniformity and relative smoothness. Additionally, a number of tiny cracks, pores, intermetallic compounds, enrichments and inclusions provide efficient active sites for the nucleation of chemical conversion. Consequently, in the synchronous conversion coating, the structure of aluminum alloy mainly consists of Al2O3/TiO2/ZrO2/ZrF4, while the structure of conversion coating of galvanized steel contains TiO2/Fe2O3/ZrO2.