Development of functionalized oxide films on Al-Si alloys by plasma electrolytic oxidation and study of their tribocorrosion behavior

摘要

Aluminium-silicon (Al-Si) cast alloys are widely used in the automotive industry due to thecombination of high strength-to-weight ratio as well as their excellent fluidity and castability.Nevertheless, the corrosion and wear resistance of these materials must be improved, as well asthe simultaneous action of both (tribocorrosion), in particular for those components continuouslysubmitted to aggressive conditions that accelerate their degradation and therefore shorten theiruseful life [1].Over the last years, plasma electrolytic oxidation (PEO) technique has arisen as one of the mostpromising ones to enhance the durability of Al-Si alloys, once it induces to the growth of hard, thickand well-adhered alumina films on their surfaces, with enhanced corrosion and wear properties.Through this technique, oxide films with different features may be fabricated, namely by varyingthe processing parameters such as the voltage applied, process duration and electrolytecomposition [1][2].In the present work, PEO films with different features were developed on Al-Si alloys with a highcontent of Si, by varying the current density applied during 1-hour processes, carried out in acommercial electrolyte. Furthermore, nanoparticles (NPs) of boron nitride (BN) were added into theelectrolyte, aiming their incorporation in the PEO films in a single-step. The main purpose of addingBN NPs was to enhance even more the tribo-electrochemical properties of the protective oxidefilms. Beyond the development of functionalized oxide films with BN NPs by PEO, the main aim ofthis work was to study the tribo-electrochemical behaviour of these materials and compare it withAl-Si substrates without any treatment. To achieve the main aims, tribocorrosion tests were carriedout using a pin-on-disc unidirectional sliding configuration in a corrosive media composed of NaCl0.06M. The resulting wear tracks were analyzed by means of optical microscopy, confocalmicroscopy and Scanning Electron Microscopy / Energy-Dispersive X-ray Spectroscopy (SEMEDS).Before tribocorrosion testing, the films were characterized in what concerns theirmorphology, topography, chemistry as well as their thickness and hardness.To conclude, the treatment of Al-Si alloys by PEO technique induced to the growth of oxide filmswith enhanced corrosion and wear resistance properties. This study provides new insights for thedevelopment of multifunctional PEO films able to extend the service life of automotive tribologicalcomponents.