EFFECTS OF Cr PLATING LAYER ON SHEAR STRENGTH AND INTERFACE BONDING CHARACTERISTICS OF MILD STEEL/CFRP JOINT BY LASER HEATING

The carbon fiber reinforced polymer (CFRP) has been widely used in aerospace and military fields, whereas it is still at its initial stage in the field of automobile manufacturing, wind power generation and so on. One of the main reasons to restrict its wide application is that the strength of metal/CFRP joint is very low and cannot meet the industrial requirements. In this study, an investigation of the laser joining between CFRP and mild steel with Cr electroplating was presented. The influence of Cr plating layer on shear strength of mild steel/CFRP lap joint was studied and the bonding characteristics of the joint interface were analyzed by SEM and XPS. The results show that Cr plating layer can greatly improve the shear force and shear strength of mild steel/CFRP joint. The shear force increases from 2237.37 N to 6127.81 N and the shear strength increases from 9.32 MPa to 22.14 MPa. For the mild steel/CFRP joint without Cr plating, the shear failure happens at the interface. However, for the mild steel/CFRP joint with Cr plating, the shear failure happens at the porosities zone in the CFRP. It means that the Cr plating can improve the interfacial bonding strength. The results of SEM observation and XPS analyses show that the mechanical bonding represented as the "anchoring effect" is achieved at the mild steel/CFRP interface both with and without Cr plating. But the chemical bonding is detected only at the mild steel/CFRP interface with Cr plating, which is considered as an important reason that the Cr plating can improve the bonding strength of the mild steel/CFRP joint.