Optimization of friction lap joining parameters and exploration connection mechanism of CFRPA6/6061-T6 aluminum alloy hybrid structures

Abstract

Carbon-fiber-reinforced thermoplastics (CFRTP) and lightweight-metal hybrid structures have been applied in the automotive and aerospace industries. Nonetheless, due to the enormous differences in physical and chemical properties of materials, the stability of the CFRTP and the lightweight-metal hybrid joint interface is challenging to ensure. In current work, the influence of welding parameters (rotational speed, welding speed, and plunge depth) on the stability of friction lap joining (FLJ) hybrid joints between carbon-fiber reinforced polyamide6 (CFRPA6) and 6061-T6 aluminum alloy (6061) was studied. The analysis of variance (ANOVA) showed that the rotational speed was the greatest factor affecting joint strength. By optimizing the welding parameters, a high-strength hybrid joint with a maximum tensile force of 2.5 kN was obtained. To further understand the mechanism of interface connection, experimental methods and density functional theory (DFT) calculations were systemically performed. The results show that the nitrogen and oxygen atoms in CFRPA6 will bond with aluminum on the 6061 surfaces to produce the interfacial Al-N and Al-O covalencies due to the p-orbital hybridization between bonding atoms.