Effect of Stacking Sequence on Thermal Damage Evolution and Plume Shielding During High-Power Laser Cutting of Thick CFRP/Ti–6Al–4V Dissimilar Stacks

Abstract Laser cutting provides a highly promising non-contact machining approach for thick carbon fiber–reinforced polymer (CFRP)/titanium alloy stacks, yet it is highly prone to inducing severe interfacial thermal damage. In this study, single-pass penetration cutting of 20-mm-thick CFRP/Ti–6Al–4V stacks using a high-power continuous-wave laser was conducted to systematically reveal the stacking-sequence-dominated plume dynamics evolution and the coupled thermophysical–chemical interfacial damage mechanisms. In situ monitoring demonstrated that the Ti–6Al–4V–CFRP (T-C) configuration improved the bottom exhaust channel, significantly mitigating the Rayleigh scattering and laser extinction effects caused by carbon particle accumulation. Consequently, the cutting depth at 5 kW increased by 19.4% compared to the CFRP–Ti–6Al–4V (C-T) configuration, and full-penetration cutting was achieved at 7.5 kW. Microstructural and chemical characterizations confirmed that the high thermal resistance and physical barrier of the titanium alloy led to extreme transverse heat dissipation at the interface, resulting in a heat-affected zone (HAZ) approximately 66% wider than that on the open surfaces. Within this restricted high-temperature region, the CFRP side not only exhibited a gradient physical damage morphology comprising a “dense carbon layer–fragmented carbon layer–bare fibers” transition, but its resin matrix also underwent profound secondary thermal depolymerization. This process generated a highly viscous, brown residue predominantly composed of bisphenol A (BPA) and naphthalene. This study elucidates the thermal damage mechanisms of heterogeneous stacks, providing critical theoretical support for optimizing the high-efficiency and low-damage laser processing of thick laminated plates.