Enhanced interfacial bonding strength of laser bonded titanium alloy/CFRTP joint via hydrogen bonds interaction

The bonding between titanium alloy and carbon fiber reinforced thermal plastic (CFRTP) has become a favorable approach to realize lightweight fabrication in the aviation and locomotive industries. However, the metal-plastic bonded joints were generally weak. Different from the traditional interfacial bonding mechanism, the role of hydrogen bonds between functional groups at the metal-plastic interface is currently of great interest. In this work, laser joining of Ti–6Al–4V (TC4) to CFRTP was performed. To enhance the bonding strength, surface modification including micro-arc oxidation (MAO) and silane coupling agent (SCA) treatment were adopted. The results indicated that porous structure after the MAO process could increase TC4 surface roughness and promote mechanical interlocking of TC4 surface to the molten CFRTP substrate. Simultaneously, the porous structure enhanced the adsorption content of hydroxyl groups on the surface of TC4 significantly, which optimized the chemical condition of TC4 surface. Selected silane coupling agent of γ-aminopropyl triethoxysilane (KH550) could directionally introduce amino groups (-NH2) to TC4 surface, while maintaining the physical morphology of TC4 surface. Hydrogen bonds were thus induced between functional groups, which were proved by red- and blue-shift of typical functional groups wavenumber. The interfacial bonded force reached maximum value of 1813 N, which was further increased by 29.96% due to the interaction of hydrogen bonds.