Thin Al2O3 Coatings Produced by Electrochemical Method, Subjected to Thermo-Chemical Treatment

Mateusz Niedźwiedź,Marek Bara,Władysław Skoneczny,Grzegorz Dercz

doi:10.3390/coatings11111294

Abstract

The article presents the effect of the anodizing parameters, as well as the thermo-chemical treatment, of Al2O3 layers produced on an aluminum alloy on the characterization of structure, geometrical structure of the surface (SGS), the thickness of the oxide layers, the phase composition, and their microhardness. The oxide layers were produced by the method of direct current anodizing in a three-component electrolyte. Then, thermo-chemical treatment was carried out in distilled water and aqueous solutions of sodium dichromate and sodium sulphate. The anodizing parameters and compounds for the thermo-chemical treatment were selected on the basis of Hartley’s plans. The research showed the effect of anodizing parameters on the thickness of the Al2O3 layers and the increase in the thickness of the layers as a result of the thermo-chemical treatment. The research showed a significant increase in the microhardness of the layers as a result of thermo-chemical treatment and its influence on the phase composition of Al2O3 layers. A significant influence of the thermo-chemical treatment on the geometrical structure of the surface was also found.

Highlights

The development of technology has contributed to the search for and use of a very wide spectrum of materials
The temperature of the electrolyte during anodizing is important for the thickness of the oxide layer
An increase in the electrolyte temperature during a constant current density and constant process time contributes to a reduction in the oxide layer thickness

Summary

Introduction

The development of technology has contributed to the search for and use of a very wide spectrum of materials. A very popular process that increases corrosion resistance [9,10] and closes the porous oxide layer [11] is thermo-chemical treatment, which preserves the advantages of the Al2 O3 layer [12] This process transforms the Al2 O3 layer of aluminum oxide into its hydrated forms, such as boehmite γ-AlOOH and hydrargillite γ-Al(OH). The thermo-chemical treatment of Al2 O3 layers is one of the processes consisting of a series of treatments leading to a change in the properties (usually surface) and the chemical composition of the treated material, especially its surface It is most often conducted in order to improve the physicochemical or mechanical properties. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

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