Optimization of machining quality for carbon fiber reinforced thermoplastic polymer/aluminum hybrid laminates via ultrasonic-assisted processing and interfacial modification

Fiber metal laminates (FMLs) are lightweight structural materials composed of metal sheets and carbon fiber reinforced thermosetting polymer (CFRP) composites. These hybrid materials overcome the limitations of single metals and fiber-reinforced composites in industrial applications by offering lower weight, higher strength, and superior fatigue resistance. While the mechanical properties of FMLs such as tensile, flexural, and impact strengths generally exceed those of their individual constituents, overall performance strongly depends on the specific material composition and laminate structural designs. Additionally, FMLs exhibit improved impact resistance and damage tolerance compared to pure composites, making them attractive for aerospace and transportation applications. However, due to the significant mismatch in interfacial properties between composites and metals, delamination frequently occurs during machining, particularly drilling. To address this challenge, a novel interfacial modifier was employed in this study to enhance the bonding strength between aluminum alloys and carbon fiber reinforced thermoplastic polymer (CFRTP) composites. This innovative adhesive-free modification enables the fabrication of carbon fiber reinforced aluminum laminates (CARALL) FMLs improved interfacial integrity. Ultrasonic-assisted drilling (UAD) was applied to investigate the machining characteristics, with three drilling parameters evaluated using the Taguchi method: spindle speeds of 1500, 3000, and 4500 RPM, feed rates of 0.05, 0.10, and 0.15 mm/rev, and ultrasonic amplitudes of 0, 5, and 10 μm. Experiments conducted using an L9 orthogonal array, with post-drilling flexural strength and delamination factor as evaluation metrics, revealed that the optimal parameter combination—identified via Taguchi S/N ratio analysis using the larger-the-better criterion—was a spindle speed of 1500 RPM, a feed rate of 0.05 mm/rev, and an ultrasonic amplitude of 10 μm. This combination significantly improved machining quality and mechanical performance. The strong correlation between the experimental results and Taguchi-based predictions validates the effectiveness of the proposed optimization strategy and underscores the synergistic benefits of ultrasonic-assisted drilling and interfacial modification in improving FML structural performance. Furthermore, the use of thermoplastic CFRTP and an adhesive-free interfacial modifier enables potential recyclability, offering a sustainable and scalable approach for lightweight structural components in aerospace, automotive, and transportation industries.