Effect of MoS2 on microstructure and mechanical property of ultrasonically welded carbon fiber/polyamide 66

Porous defect induced by thermal decomposition is one of the most significant factors in determining the weld quality of ultrasonically welded thermoplastics. MoS2 has high thermal stability and a two-dimensional layer structure, which could play a key role in improving the thermal stability of the thermoplastics. In this study, MoS2 with 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt% loadings are incorporated into carbon fiber/polyamide 66 composite (CF/PA 66), and its effect on microstructure and mechanical properties of the joint is evaluated with the combination of finite element analysis. Results showed the incorporation of MoS2 slightly influenced tensile property of the composite while had a considerable effect on joint performance. With 1.5 wt% loading of MoS2, the highest peak load was enhanced to 6.20 kN from 5.05 kN and the difference in peak load became limited. This is mainly because the temperature of the workpiece under the horn rose above the thermal decomposition point of the composite during ultrasonic welding (UW). However, MoS2 filler improved the thermal stability of the workpiece and alleviated the thermal decomposition of PA 66 during UW. As a result, the workpiece with MoS2 addition can endure longer weld time to increase the weld area of the joint and improve the weld microstructure and porous defect, which results in higher peak load and stability. This work provides a new solution for improving the joint strength of ultrasonically welded thermoplastics.