Enhancing the ultrasonic plastic welding strength of Al/CFRTP joint via coated metal surface and structured composite surface

Ultrasonic plastic welding (UPW) is a promising technology for joining metal to carbon fiber reinforced thermoplastic composite (CFRTP) but shows poor joint strength in the existing studies. This work conducts UPW of AA6061 aluminum alloy to carbon fiber reinforced PA66 (CF/PA66) by employing a polymer coating as an interlayer. Simple metal surface grinding and silane coupling agent (SCA) treatment are used to strengthen the bonding of the metal/coating interface. Structured CF/PA66 surface fabricated by ultrasonic embossing acts as energy directors to improve the bonding strength of the coating/plastic interface. The results show that relatively high tensile-shear strength (about 31.0 MPa) can be obtained. Micro-mechanical interlocking and chemical bonding (Al-O-C and Al-O-Si bonds) are considered as the bonding mechanism of the metal/coating interface.