Effect of linear heat input on the interface and mechanical properties of steel/CFRP laser welding joint

An investigation on laser joining of PA66 carbon fiber reinforced plastic (CFRP) to DP780 dual-phase steel was presented. Effect of linear heat input on the interface and mechanical properties of steel/CFRP joint was per-formed. When linear heat input increases, the softening phenomenon is not observed in heat-affected region of dual-phase steel. Meanwhile, the melting point and decomposition temperature of resin are less impacted. The maximum tensile-shear force of steel/CFRP joint reaches 1959.4 N. The interface temperature is contained be-tween melting and decomposition temperature of resin, the spreading of resin on steel surface is promoted, and a favorable steel/CFRP bonding interface is obtained. In addition, the new chemical bonds such as M-C and M-O are formed, which is conducive to the chemical connection of steel/CFRP interface. However, as excessive linear heat input is applied, the interface temperature will exceed the decomposition temperature of resin, resulting the generation of decomposing pores. Moreover, due to excessive heat on resin, its crystallinity decreases, the interface between resin and fiber is weakened, so that the fracture behaves as a mixed fracture mode of interface and cohesion fractures, which deteriorates steel/CFRP joint properties.