In situ chemical bonding at the 30 wt.% GF/PA6-A2024 aluminium alloy interface via ultrasonic-assisted injection moulding

Abstract

In injection moulding processes with metal inserts, chemical bonds cannot be directly formed at the interface between polymers and metals without the application of special intermediate agents to form chemical bridges, which involves cumbersome steps and reduces production efficiency. This work successfully achieved in situ chemical bonding on a 30 wt.% GF/PA6-A2024 joint during the injection moulding process with the assistance of ultrasonic vibration. Effects of ultrasonic time and ultrasonic power on the interfacial bonding strength at different temperatures were analysed. The mechanism of in situ chemical bonding generated by ultrasonic-assisted injection moulding was explored in depth through experimental characterization combined with molecular dynamics. An appropriate ultrasonic energy (the product of ultrasonic time and ultrasonic power) can reduce the viscosity of the melted polymer and increase the surface free energy of the metal, resulting in rapid interfacial bonding. Notably, ultrasonic vibration can also cause a sharp increase in the interfacial temperature, converting molten PA6 into an oxygen-rich state and realizing in situ C‒O‒Al and hydrogen bonds at the interface under cavitation impact. With an ultrasonic time of 10 s and an ultrasonic power of 400 W, the normal-temperature tensile shear strength of 30 wt.% GF/PA6-A2024 reached 40.98 MPa, which is a 97.9% improvement over that without ultrasonic vibration. This work can help eliminate the need to apply intermediate agents, enabling in situ chemical bonding at the interface during the injection moulding process and providing an environmentally friendly and efficient method for enhancing the interfacial bonding strength of metal‒polymer joints.