No abstract

Plasma electrolytic oxidation (PEO) is widely used to improve the corrosion and wear resistance of lightweight metals such as aluminium alloys by the formation of a ceramic oxide coating. However, the PEO process remains ineffective for ferrous metals and, when applied to magnesium alloys, oxide coatings are usually thin and porous. To overcome these limitations, the feasibility of applying a duplex treatment combining cold-spray deposition (CS) and PEO is investigated. Cold-sprayed aluminium coatings are deposited on magnesium (EV31) and steel (S235) substrates prior to PEO. Investigation of this duplex process evidences the efficiency of such a two-steps process to form thick, dense and crystalline alumina coatings on both magnesium and steel substrates. The growth kinetic of the duplex CS-PEO oxide layer is enhanced by a factor of 3 compared to single-step PEO processing of bulk aluminium substrates. Results are discussed by considering the effect of the porosity through the coldsprayed aluminium coating on the mechanism of oxidation during the subsequent PEO treatment.

Unlike their metal counterparts; composite structures do not readily conduct away the electrical currents generated by lightning strikes. Cost reduction and expected production growth of the next middle range airplanes require automated manufacturing process of polymer components. The development of an automated technology to metallize polymer based composite for lightning strike protection is the aim of the CO3 project (EU Grant agreement: ID831979). In this study; thermal and electrical conductivities of composites were achieved by cold spray deposition of Cu or Al coatings. Critical points to be addressed were substrate erosion during cold spray; lack of polymer-metal adhesion and poor deposition efficiency. Several strategies were tested: i) a thin polymer film was cocured at the substrate surface before cold spraying; to enable implantation of metallic particles in the film; helping coating build-up and protecting the fibers of the composite. ii) Cold spraying a mix of metal and polymer powders to improve coating adhesion and prevent fiber damage. iii) Supercritical Nitrogen Deposition technology; prior to cold spray; to mechanically anchor metallic particles into the polymer. Subsequent cold spraying of purely metallic coatings was more efficient and showed better adhesion. All coatings were tested in terms of adhesion strength and electrical conductivity.