6061 Aluminium alloy was treated with plasma electrolytic oxidation (PEO) in an alkaline silicate-base electrolyte. Recycled glass particles from consumer goods waste were added to the electrolyte in order to investigate the impact of these particles on corrosion and wear resistance of the alloy. A comparison of glass particles from different sources (liquid crystal display (LCD) glass, borosilicate (BS) glass, and soda-lime (SL) glass) has been made. Also, the effect of different current modes, direct (D) and pulsed (P), on glass incorporation and the coatings morphology was studied. The microstructure and thickness of the produced coatings were studied through SEM–EDS analysis and XRD. The wear resistance was evaluated by dry sliding tests vs AISI 52100 bearing steel (block-on-ring contact geometry). The corrosion behavior was analyzed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), and localized electrochemical characteristics were determined by scanning electrochemical microscopy (SECM). The results evidenced that the addition of glass improved the corrosion resistance of the samples due to the sealing effect on the typical pores of the PEO layer. In detail samples filled with glass particles show from EIS tests polarization resistances up to one order of magnitude higher than the untreated sample in the case of direct current mode and up to two order of magnitude higher in the case of pulsed current mode. The effect on wear resistance is instead strictly related to the type of glass as, if compared to the base PEO layer, it is improved only by selected additives with the more promising results obtained with the LCD glass in direct current mode that produce a decrease of the wear depth of around one order of magnitude in comparison with the sample PEO treated without glass addition. Globally the more promising type of glass particles, both in term of improvement of the wear and of the corrosion properties, seem to be the LCD glass particles. This fact was related to the particular chemical composition of this type of glass and in particular with the alkali-free composition of the glass. Graphical Abstract

Black coatings were successfully formed on Grade 2 (G2) and Grade 5 (G5) titanium alloy by means of a direct-current Plasma Electrolytic Oxidation (PEO) process at a very low current density of 0.05 A/cm². The impact of two different treatment times (30 min and 60 min) was examined. The electrolyte for the PEO process was a phosphate base solution Na₅P₃O₁₀ containing FeSO₄ and (NH₄)₆Mo₇O₂₄ as coloring additives. PEO-coated samples were subjected to optical, morphological, structural, chemical, and electrochemical characterization. XRD, EDS, and XPS data analyses revealed that anion ${\mathrm{MoO}}_4^{2-}$ and metal cation Fe³⁺ were successfully incorporated into the coatings. The results demonstrated that PEO-coated samples prepared after 60 min exhibit a stronger black color than those created after 30 min, with an absorptance maximum of 0.86. Furthermore, all prepared PEO coatings improve the corrosion resistance of bare titanium. Among them, the 60-minute PEO coatings on both alloys were the ones with the best corrosion properties.

In this work, a unique approach was used to synthesise black coatings on aluminium alloys (AA) 6061 and 7075 for applications in the aerospace field. In detail, plasma electrolytic oxidation (PEO) technology was used, maintaining the voltage constant at a relatively low value (V_max ≤ 292 V) during the process. NaVO₃ additive was used in the silicate-based electrolyte to obtain a black colour. The coatings were characterised by SEM-EDS, XPS, XRD, VIS-NIR spectroscopy, and EIS. The presence of vanadium oxides in the PEO coatings was detected by EDS, XPS, and XRD analyses. PEO coatings on AA7075 produced with 10 g/L of NaVO₃ exhibited exceptional optical characteristics, with a solar absorptance value of 95.3% in the VIS-NIR spectrum (wavelength range of 400–2000 nm). All the coatings improved the corrosion performances of the tested AA6061 and AA7075 by two or three orders of magnitude in 3.5 wt. % aqueous NaCl. Moreover, there was no sign of delamination, cracks, or any visible changes on coatings after thermal shock, performed by cycling samples between two extreme temperatures, −196 °C and 150 °C, respectively.