Suppression of shrinkage porosity in laser-joining of CFRP and steel using a laser surface modification process Surfi-Sculpt®

The emergence of shrinkage porosity is a significant issue in the laser joining of carbon fiber reinforced polymer (CFRP) and steel. The joining process uses laser heating to melt a thermoplastic CFRP matrix in contact with a metal substrate to create a physical bond upon cooling. During the cooling process, melted CFRP at different location has different solidification rate, leading to the shrinkage porosity in the CFRP. In this study, the laser Surfi-Sculpt (R) is used to prevent the formation of shrinkage porosity in CFRP. The effects of the morphology characteristics (protrusion height and density) on shrinkage porosity are investigated, and the thermal distribution and history during the joining is simulated to examine mechanism of shrinkage porosity suppression. The results show that formation of shrinkage porosity can be suppressed with the laser Surfi-Sculpt (R), which is attributed to the change of heat conduction path. The protrusions conduct the heat from the interior of melted zone to steel, decreasing the heat accumulation at the interface and suppressing the formation of shrinkage porosity. After adopting this technique, the porosity can be reduced from 7.13% to 1.26% and the shear strength of the joint increases from 9.3 MPa to 30.8 MPa.