Determination of the Hardness of the Oxide Layers of 2017A Alloys

Abstract

In order to improve the resistance of materials to surface damage by mechanical and environmental action, considerable research has been conducted to increase the hardness of the surface of mechanical parts. This is achieved, for example, by anodisation of aluminium alloys. The objective of designing films possessing optimum mechanical properties cannot avoid the determination of their hardness as precisely as possible. Unfortunately, direct measurement of film hardness by conventional micro-hardness testing is not possible for a large range of indentation loads because the substrate also participates in the plastic deformation occurring during the indentation process. It is often assumed that this phenomenon, which involves the two materials, begins to be noticeable for loads such that the depth of the indent exceeds one tenth of the film thickness. In this situation, the hardness number is thus the result of the combined substrate and film contributions. In order to determine the true hardness of the film, it is necessary to separate these contributions. Numerous mathematical models were proposed for that purpose on the basis of different assumptions. The objective of the present work is to study hardness response of oxide film developed by sulphuric anodisation on annealing aluminium alloys substrates (2017A) over a range of applied loads. The hardness values were determined experimentally using conventional Vickers microhardness measurements. The results were analysed using the work-of-indentation model for the hardness of coated systems. Both experimental measurements and modelling work in this area will be aimed at obtaining the estimates mechanical properties of oxide layer.