Effect of process temperatures on joining aluminum alloy (AA5052) to polypropylene (PP) by friction lap welding

The joining of aluminum alloy 5052 (AA5052) and polypropylene (PP) by friction lap welding (FLW) was investigated under different process temperature conditions. Welding experiments were conducted at different tool rotational speeds, and the process temperatures were monitored using an infrared camera and thermocouples. The temperature distribution at the cross-section was determined using a validated numerical model. The joint quality was assessed by measuring tensile shear strength and examining the joint morphology. It was found that interfacial temperatures in the range of 156 °C–316 °C were optimal for achieving effective mechanical interlocking, attributed to the appropriate flow of molten PP into the textured aluminum alloy surface. Temperatures below 130 °C resulted in inadequate PP flow, leading to poor joint formation, while temperatures above 316 °C caused over-melting of PP, bubble formation, and approached the PP initial decomposition limit. Raman spectroscopy showed that the process temperatures did not cause significant chemical bonding and that mechanical interlocking was the main contributing joining mechanism. The results showed that dissimilar welding of metals and non-polar polymers can be optimized by the precise monitor and control of the temperature of the process.