The effect of conversion bath convection on the formation of Zr‐based thin‐film coatings on multi‐metal surfaces

The present study investigates the effect of different conversion bath agitation and stirring conditions on the generation of Zr‐based thin film conversion coatings for steel, zinc galvanized steel, and aluminum substrates. Therefore, samples were immersed in a copper containing fluoric acid of zirconium. Film formation was monitored in situ via open circuit potential (OCP) measurements recorded during the pre‐treatment of the samples in solution. The resulting thickness and elemental distribution of the obtained Zr‐based coatings formed with and without stirring were analyzed ex situ by means of high‐resolution Auger electron spectroscopy (AES) depth profiles. Under the studied conditions, the conversion film thickness on AA6014 and cold rolled steel increased three and two times as a result of stirring. For hot dip galvanized steel, a thickness increase of 400% was achieved. The data point at mass transfer as the dominant factor for film formation. In this context, specific relations for each metal substrate type were detected.