Bubble Nucleation-Induced Interfacial Delamination of a Lap-Shear Aluminum/Glass Fiber-Reinforced Polycarbonate Specimen by CO2 Gas Impregnation and Subsequent Heating

The separation of the metal/polymer interface in a multimaterial product requires a significant workload in the material recycling industry. This study demonstrated that gas bubble nucleation separated a metal/polymer interface and reduced the maximum load. A lap-shear test piece was prepared by joining a laser-graved aluminum alloy (Al) with a 40 wt % glass fiber-reinforced polycarbonate (PCGF40) using injection molding. PCGF40 infiltrated into Al's graved microcavity and exhibited 20 MPa of adhesive strength by the anchoring effect. The Al/PCGF40 lap-shear part was saturated with high-pressure CO2 gas of 5, 7.5, and 10 MPa at 80 °C in a high-pressure vessel for 24 h. Then, it was heated at 110–150 °C to bring about the dissolved gas supersaturation state and induce bubble nucleation for 3 min. The specimen was subjected to an ISO19095-3 tensile lap-shear measurement fixture. The maximum separation load decreased with increased CO2 pressure and heating temperature. We found two separation modes: cohesive failure and interfacial delamination depending on the heating temperature. The cohesive failure occurred at a temperature higher than 130 °C, saturated at 5 and 7.5 MPa, and remained resin on the Al substrate. X-ray computational tomography (X-ray CT) imaging clarified that bubble nucleation formed numerous voids far from the Al/PCGF40 interface and initiated cohesive failure. The interfacial delamination occurred at a lower temperature, 110–130 °C, and a high pressure, 10 MPa. X-ray CT clarified that many voids existed at the interface and suggested the initiation of interfacial delamination. The small maximum delamination load with the realization of the smallest remaining resin was obtained at 10 MPa and 130 °C. Our method reduced the maximum load by 50% compared with the control and paved the way for recycling multimaterial products.