Fiber-reinforced composites are finding increased applications in different fields where high strength-to-weight ratios are of priority. In particular, carbon fiber reinforced thermoplastic composite (CFRTP) materials have been extensively used in aerospace and automobile applications owing to their remarkable properties. Generally, it is highly recommended to connect CFRTP with metals to form a hybrid structure to achieve the full potential of the composites. The joint formation process is of great significance, considering that the service life and functionality of the resulting hybrid structure depend on the quality of the joint formation process. Laser welding technology has been identified as a promising candidate for joining CFRTP-metal hybrid structures. It is highly efficient, flexible and suitable for high precision. The use of laser welding in this field has been extensively studied in recent years. These studies have involved joining CFRTP with different metals and analyzing the properties of the resulting structures. Specifically, the CFRTP-metal interface has been identified as the main factor influencing the joining process.
Several methods have been put forward to enhance interface performance and joint strength. Among them, micro-texturing machining is the most commonly used surface pretreatment to improve CFRTP-metal joining strength. However, it is characterized by the formation of mechanical interlocks at the joint interface. Additionally, the failure of the molten resin to fill the micro-textures completely results in the formation of microstructure holes at the interface. These inadequacies significantly affected joint strength and resistance. Thus, developing more effective strategies to eliminate or reduce the formation of micro-textures holes is highly desirable.
To overcome the above challenges, Professor Junke Jiao and his research team from Yangzhou University proposed a new interface metal surface laser plastic-covered method for efficient joining of CFRTP and TC4 alloys, which are becoming common materials in aerospace manufacturing. The joining process was facilitated by high-speed laser rotational welding technology. The process was implemented and the fatigue resistance, mechanical properties as well as failure mechanisms were investigated. Their main objective was to reduce the occurrence of the micro-textured holes and improve the strength and performance of the CFRTP-TC4 joint. Their work is currently published in the research journal, Composites Part B: Engineering.
The research team showed that the fatigue resistance and strength of the CFRTP-TC4 joint were significantly improved, resulting in the formation of a 189-265µm thick laser hardened layer on the TC4 surface. This was also attributed to the increased amount of resin at the interface and full combination of the resin and the micro-textures. The joint attained a maximum shear strength of 30.4 MPa higher than that produced through micro-texturing pretreatment. The joint fracture and fracture mode was observed in the CRFTP layers and CRFTP interlaminar tearing, respectively. In addition, the welding area also exhibited a higher average micro-hardness layer compared to the TC4 base metal.
In summary, the study proposed a metal surface laser plastic-covered pretreatment method to improve the quality and perforce of the CFRTP-TC4 laser joint. The proposed approach proved to be effective in enhancing the quality and performance of the joint, and it is superior to the traditional line laser welding. This makes it a promising approach for industrial application. In a statement to Advances in Engineering, Professor Junke Jiao stated that the study advances an effective application of CFRTP-metal laser-assisted joining technology in the automobile and aerospace industries.
Jiao, J., Zou, Q., Ye, Y., Xu, Z., & Sheng, L. (2021). Carbon fiber reinforced thermoplastic composites and TC4 alloy laser assisted joining with the metal surface laser plastic-covered method. Composites Part B: Engineering, 213, 108738.