Plasma electrolytic oxidation (PEO) as surface treatment for high strength Al alloys produced by L-PBF: Microstructure, performance, and effect of substrate surface roughness

In recent years, additive manufacturing of Aluminium alloys has achieved remarkable developments, allowing for the replacement of casted components in industrial fields such as aerospace and automotive. However, the main issue affecting these alloys during operation at high temperatures and in critical environments is poor corrosion and wear resistance. The present work aims to produce a coated layer using an innovative surface treatment, Plasma Electrolytic Oxidation (PEO), on two high-strength Al alloys, AlSi10Mg and A205, processed by Laser-Powder Bed Fusion (L-PBF), in order to increase the corrosion and wear performance of the material. For each material, PEO coating was produced on two different surface conditions (as-fabricated and polished) and characterised in terms of morphology and composition through scanning electron microscopy (SEM) and digital microscope analysis. A PEO coating thickness of over 40 μm was achieved for both alloys, while the porosity was found around 13 % and 3 % for AlSi10Mg and A205, respectively. Additionally, nano-hardness analyses were carried out to understand the differences compared to the virgin material, highlighting an increase in hardness of the PEO coating at least 10 greater than the substrate for both materials. Finally, friction and corrosion tests were performed. The results in terms of wear rate and corrosion rate were compared with those obtained on uncoated manufactured samples. In particular, an increase in the wear and corrosion performance of 26.4 % and 37.5 %, respectively for the AlSi10Mg, and 88.4 % and 53.1 % for the A205, were evaluated. It was demonstrated that the presence of the oxidised layer improved the mechanical properties of the surface and, accordingly, the general performance of the material. Furthermore, performing a surface polishing treatment before PEO treatment helped to further increase the tribological and corrosion properties.