Comprehensive influence of silane layer and interfacial thermo-mechanical effect on joining mechanism of silane pretreated Al/CFRP FSLW joint: FEA and experiment

Abstract

Al/CFRP composite structure has the advantage of lightweight and high specific strength, making it a promising material for aviation, railway, and automotive applications. Silane coupling pretreatment is a chemical surface pretreatment method that can improve the mechanical properties of the Al/CFRP friction stir lap welding (FSLW) joint. To further investigate the strengthening mechanism of silane-treated Al/CFRP FSLW joint, a 6061-T6 Al/CF-PA66 FSLW experiment was carried out and the finite element analysis (FEA) was used. The thermophysical properties of semi-crystalline resin during the welding process were also considered. The joining mechanism of silane surface pretreated Al/CFRP FSLW joints was further revealed by comparing the changes in interface morphology, temperature, stress, and mechanical properties. The results indicated that the silane coupling agent forms a silane film by an Al-O-Si chemical bond at the interface. The silane film can enhance the Al/CFRP interface's tightness and reduce interfacial defects. The FSLW process affected the joint morphology and mechanical properties through interfacial temperature and stress, which were decided by welding parameters and thermophysical properties of the resin. By adjusting the thermal-mechanical effect of the Al/CFRP interface, defects can be reduced and the joining force can be improved. According to the analysis of interfacial chemical bonds and mechanical properties, the introduction of silane film enhances the hydrogen bond between Al and resin and thus enhances the mechanical properties of the interface. This study provides a new method for revealing the strengthening mechanism of silane-pretreated FSLW Al/CFRP joint.