Influence of pre-treatment on zirconium based conversion coating on AA2024

Matilda Zemanová 1 , Ján Lokaj 2 , Mária Karľová 2 , and Jana Madejová 3
  • 1 Institute of Inorganic Chemistry, Technology and Materials, Faculty of Chemical and Food Technology STU in Bratislava, Radlinského 9, 812 37 , Bratislava, Slovak Republic
  • 2 Institute of Inorganic Chemistry, Technology and Materials, Faculty of Chemical and Food Technology STU in Bratislava, Radlinského 9, 812 37 , Bratislava, Slovak Republic
  • 3 Institute of Inorganic Chemistry, SAS, Dúbravská cesta 5, 845 36 , Bratislava, Slovak Republic

Abstract

A comparison of the influence of two alloy pre-treatments and temperature treatments on the formation and composition of zirconium based conversion coating on the AA2024 alloy has been performed. The investigation employed mass changes, atomic force microscopy (AFM), XRD dispersive spectroscopy (EDX), infrared spectroscopy (IR) and electrochemical tests by open circuit potential (OCP) measurements. Pre-treatment using only alkaline etching is called alkaline pre-treatment. When alkaline etching is followed by de-oxidization in a phosphoric acid solution the process is called acidic pre-treatment. Conversion coatings were formed in Pragokor BL. IR analysis revealed the formation of a phosphate on the alloy surface. EDX analysis showed Mg dissolution. The Zr content increased with the temperature of the conversion coating formation. Both pre-treatment methods provided a phosphate layer on the alloy surface.

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