Investigation on mechanical property and fracture behavior of galvanized steel-CFRTP joints fabricated via induction heating

Abstract

As multi-material design becomes mainstream in automobile industry, the technology for joining different materials is becoming increasingly critical. This study proposes a strategy for directly joining carbon fiber thermoplastic (CFRTP) and galvanized steel (GS) using electromagnetic induction heating. A simple hot water treatment (HWT) method was utilized to produce nanostructures on the GS surface to enhance the joining strength. The effect of HWT time on the surface wettability and joining quality was investigated. The influences of induction heating conditions on the joining quality were also evaluated by joining interface temperature measurement and tensile shear test. The contact angles on GS surface were lower than 10° when HWT duration exceeded 20 min, demonstrating the superhydrophilicity. The optimized joining strength reached 39.8 MPa with the optimum joining interface temperature around 300 °C. The fracture mechanism was investigated through SEM observation of the facture surfaces and cross sections. Insufficient interface temperature can lead to inadequate fluidity of the molten CFRTP matrix, whereas excessively high temperature can precipitate the deterioration of both the matrix and the galvanic coating. Under optimized condition, the failure mechanism was identified as the occurrence and propagation of cracks within the CFRTP, attributed to the strong anchoring effect formed at the joining interface. The excellent mechanical properties of carbon fibers partially inhibited the propagation of cracks and contributed greatly to the high joining strength. In addition, a thermal cycle test was conducted to evaluate the reliability and durability of the joints. The result demonstrated the capacity of the joints to withstand environmental temperature change, with strength reduction within 5 % after 50 cycles.