ENHANCED BOND STRENGTH AND CORROSION PREVENTION IN COMPOSITE AND METAL STRUCTURES THROUGH PLASMA MODIFICATION

As a lightweight and strong alternative to metals, composites have become a dominant aerospace manufacturing material. Traditional fastening methods damage the underlying fibers, degrade the long-term performance, and the hardware offsets the weight savings. As a result, adhesives are used in the manufacturing process for composite-to-composite and composite-to-metal bonding. However, composites are non-polar, with low surface free energies (SFEs), and require surface preparations to achieve structural bond strengths. Common methods often require harsh mechanical or chemical treatments and pose high operator and environmental safety hazards. Atmospheric pressure plasma jets (APPJs) are a nondestructive surface preparation method that removes contaminants and activates surfaces, increasing SFE, to initiate covalent bonding to adhesives. Air-based plasma achieves cleaning and activation by producing reactive electrons, ions, and free radicals that modify surfaces without etching material. APPJs are scalable, energy efficient, and produce no hazardous waste. Plasma treatments were also compared to other surface modification methods such as solvent wiping, laser ablation, hand sanding and grit blasting. Plasma treatment resulted in higher bond strength than the other methods, without damage or exposure of carbon fibers. This is important as exposed carbon fibers in carbon fiber reinforced polymers used in composite-to-metal bonding create a conductive channel for galvanic corrosion. Plasma treatment provides similar or better bond strength while mitigating the corrosion pathway. Corrosion prevention can be further improved through plasma deposition of a nanoscale anticorrosion barrier tie layer added to metallic substrates. The coating prevents ingress of moisture into the bond line and validated with resistance to a copper sulfate test solution on aluminum coupons.