Effect of interfacial temperature on the bonding morphology and fracture mechanism of TC4-CFRTP laser bonding joints with polymer interlayer

Carbon fiber reinforced thermoplastic composites (CFRTP) and TC4 are widely utilized in aerospace. Incorporating a polymer interlayer during laser bonding of CFRTP/TC4 stacked structures enhances joint performance. However, challenges such as thermal defects and poor bonding at the interface persist. In this paper, the effect of interfacial temperature characteristics on the performance of joints containing polymer layer is systematically analyzed in conjunction with the peak interfacial temperature and its distribution, as well as the polymer melting time. The interfacial temperature characteristics with different powers and their effects on joint mechanical property, bonding morphology, and fracture mechanism, were analyzed through laser joining experiments and temperature field simulations. And the optimal temperature conditions for achieving the high-quality joint were determined. Results indicated that different temperature conditions directly lead to different bonding morphologies and fracture forms. The nonuniform distribution of interface temperature within the laser scanning area causes different fracture forms to occur simultaneously in the joint. Low interfacial peak temperatures and insufficient polymer melting times lead to poor bonding at the interlayer/CFRTP interface, causing failure; Under optimal temperature conditions, the mechanical anchoring structure at the TC4/interlayer interface is unable to withstand shear force, resulting in failure by fracture; When the interfacial peak temperature significantly exceeds the polymer's decomposition temperature, thermal defects cause stress concentration and lead to failure. The temperature conditions for achieving an optimal joint include a peak temperature of 440 degrees C, a polymer melting time of 9 s, and as uniform an interface temperature distribution as possible.