A multiscale interfacial engineering to enhance the strength of CFRTP/aluminum FSpJ hybrid joints

Abstract

Carbon-fiber-reinforced thermoplastics (CFRTP)/aluminum hybrid joints are promising for lightweight aircraft design. Welding methods such as friction spot joining (FSpJ) minimize damage to CFRTP fiber structures, making them ideal for hybrid joint fabrication. However, the inherent chemical and physical incompatibility between CFRTP and aluminum hinder strong bonding. To address this, we propose a multiscale interfacial engineering strategy combining mechanical interlocking, covalent/hydrogen bonding, and process optimization. Biomimetic papilla was textured on A6061-T6 aluminum (6061) by femtosecond laser to realize the mechanical interlock with micro and nano scales. Hydroxy group was grafted onto CFRTP to induce the formation of Al–O covalencies and hydrogen bonds, reconstructing the interfacial bonding behavior. The surficial modifications of 6061 and CFRTP worked together to improve the compatibility of the two dissimilar materials. An orthogonal experiment was carried out to optimize the process parameters of friction spot joining (FSpJ), which restrained the formation of the welding defects and increased the density of the interfacial covalent bonds of the hybrid joints. An orthogonal experiment optimized FSpJ parameters, reducing defects and increasing bond density. Meta-learning validated strength prediction with minimal data, supporting parameter selection. The resulting joints achieved highest joining strength of 44.82 MPa and efficiency of 84.57 %. Current work offers a scalable approach for high-reliability CFRTP/metal joints in aerospace and automotive applications.