Effect of micro-arc oxidation treatment on laser joint microstructures of Ti-6Al-4V alloy/CFRP

Resin-based carbon fibre reinforced composite (CFRP) with excellent properties has been widely applied in aerospace industry. In this study, polyether ether ketone enforced composite (PEEK-CFRP) and Ti-6V-4V titanium alloy had been joined by laser welding process. Micro-arc oxidation (MAO) process was conducted on the surface of titanium alloy to improve the joint property. Fractures and mechanical properties of joints were analysed. Interfacial microstructures of the joints had been investigated, and the formation mechanism of joint had been figured out. The results showed that after MAO treatment, the joint strength had been greatly improved and the shear strength reached to 42.3 MPa compared with pretreated sample. The wettability of CFRP on titanium alloy was rising with the contact angle of 68.8°. Fracture showed that cohesive failure contributed to the main fracture mode. As joints were formed by both mechanical bonding and chemical bonding, ‘anchor-shaped’ structures were found in the joint to enhance the mechanical bonding effects due to the flowing of the melted resin. (−OH) bonds were identified at the surface of MAO-treated titanium alloy that provided conditions for hydrogen bond interaction. TiO₂, TiO and Ti–V–C phase were found at interface, whereas Ti–F and Ti–O–F bonds were generated during the welding process, which made great contribution to the chemical bonds between titanium alloy and CFRP.