Effect of interfacial thermal history on bonding mechanism of laser assisted joining of QP980-CFRTP with adjustable flat-top rectangular laser beam

Carbon fiber reinforced thermoplastic composite (CFRTP) - metal hybrid structures, which have been increasingly used in the industry, can significantly reduce structure weight and energy consumption. In this paper, an adjustable flat-top rectangular diode laser beam was used as a heat source to join the quenched and portioned QP980 steel and CFRTP in a lap joint configuration. Compared to conventional laser beam scanning process in the literatures, the rectangular laser beam provides a relatively uniform temperature distribution at interface. The relationship between interfacial thermal history and the joint performance was explored. Experimental results showed that thermal history had a significant impact on interfacial chemical compositions and the formation of joint defects via affecting the resin state, resulting in change of the joint fracture behaviors. Furthermore, higher interfacial temperature and sufficient heating/holding time contributed to the complete melting and diffusing of resin matrix on QP980 surface, filling the micro pores of the interface, and promoting the chemical bonding between QP980 and CFRTP. On this basis, a novel strategy to achieve excellent interfacial bonding via adjusting the interfacial thermal history was proposed to produce a high-quality joint with the peak load higher than 10 kN and the shear strength of 22 MPa.