Influence of pretreatment methods on electrodeposition of magnetic Fe-Co coatings on carbon fibres

Abstract Magnetically responsive carbon fibres that can be actively aligned during composite manufacturing are of interest for improving the load bearing applications of fibre-reinforced lightweight structures. This work investigates thermal and chemical pretreatment methods to remove the epoxy sizing layer and enable a uniform galvanic coating with Fe-Co. Since the epoxy-based sizing layer on commercial carbon fibres limits wettability and prevents uniform metal deposition, its removal is essential for successful coating. To address this, thermal pretreatment was carried out between 350 °C and 500 °C in air while chemical pretreatment involved acetone and nitric acid. Thermal treatment in air progressively improves fibre dispersibility with increasing temperature above 450 °C. Acetone treatment produces only minor improvements, whereas acid treatment enhanced dispersibility by oxidising the fibre surface and increasing its polarity. Limited coating coverage is obtained after low-temperature thermal treatment and acetone treatment, while fibres pretreated thermally at 450–500 °C show continuous and uniform coatings. Acid treatment further improves coating coverage compared with acetone but remains less effective than thermal desizing. The resulting Fe-Co coatings had an average thickness of approximately 1 μm with an average composition of 64% Fe and 36% Co. The magnetic properties of the Fe-Co coatings are described by its low coercivity (approximately 30 Oe) and high saturation magnetisation (approximately 80 emu/g). Overall, thermal desizing at 450 °C and above proved to be the most effective pretreatment for producing homogeneous magnetic Fe-Co coatings on carbon fibres.