This study investigates the influence of rare earth element Ce addition on the nanoscale precipitation, microstructure, and mechanical properties of Ti-containing secondary phases in high-strength low-alloy weathering steel. Mechanical property testing and microstructural characterization were performed on experimental samples subjected to rolling-aging treatment. The results demonstrate that the addition of Ce promotes coarsening of nanoscale precipitates, thereby diminishing their precipitation strengthening effect. At a 0.11% Ce content, an increase in inclusions was observed, leading to crack formation during hot deformation. However, Ce addition also refines inclusion size and modifies inclusion types, contributing to steel purification. Through austenite recrystallization zone rolling combined with an isothermal process, a high-strength ferritic weathering steel with nanoscale precipitates was fabricated, exhibiting a yield strength of 635 MPa, tensile strength of 750 MPa, and elongation of 21.2%. Precipitation strengthening plays a critical role in enhancing the room-temperature strength of ferritic steel.

When fabricating high-entropy alloy particle-reinforced metal matrix composites via friction stir processing, the relatively low heat input led to insufficient interfacial diffusion between the particles and matrix, thereby compromising the composite properties. To address this issue, this study introduced an electroless copper plating step followed by heat treatment to produce Cu-coated HEA particles with an interfacial diffusion layer. These modified particles were then incorporated into a copper matrix via friction stir processing to form composites with an intentionally designed interfacial diffusion layer. The results indicate that the diffusion layer structure contributed to excellent interfacial bonding. The resulting composite exhibited a simultaneous enhancement in both strength and ductility. The tensile strength and elongation reached 372.5 MPa and 34.2%, respectively, representing increases of 20.4% and 54% compared to pure copper. The wear rate of the composite reduced by 33.7% relative to pure copper. Quantitative analysis indicated that the contribution of fine-grain strengthening, Orowan strengthening, dislocation strengthening, and load transfer strengthening to the overall strength was 41.2 MPa, 0.3 MPa, 12.7 MPa, and 15.7 MPa, respectively.

The surface roughness (Ra) and coefficient of friction (COF) of acrylonitrile butadiene styrene (ABS) parts fabricated through fused deposition modelling (FDM) are key determinants of their functional service performance. However, these two objectives often present a trade-off relationship in single-objective optimisation. To achieve synergistic optimisation of surface quality and surface performance of FDM ABS parts, this paper proposes a multi-objective optimisation framework integrating response surface methodology (RSM) with a chaotic whale optimisation algorithm (CWOA). A Box–Behnken design (BBD) was employed to establish quadratic regression models for Ra and COF as functions of layer thickness (0.16–0.24 mm), extrusion ratio (0.9–1.0), infill density (20–100%) and extrusion temperature (240–270 °C). Based on analysis of variance (ANOVA) and response surface analysis, a non-linear mathematical model with dual responses was constructed. Pareto-dominated CWOA was introduced for multi-objective optimisation, and the optimal process parameter combination was selected using the TOPSIS method. The results showed that the optimal parameters were: layer thickness 0.16 mm, extrusion ratio 0.9, infill density 66%, and extrusion temperature 270 °C. Under these conditions, the experimentally measured Ra was 7.7921 μm (2.04% error from the predicted value) and COF was 0.1504 (2.80% error from the predicted value). Compared with the benchmark reference (the average value of the BBD central experimental runs), a synchronous decrease in Ra and COF was achieved (Ra reduced by 27.4% and COF reduced by 14.9%). Metallographic morphology analysis revealed that the optimal specimen surface exhibited wide filament ridges, narrow and well-defined inter-filament valleys, and no obvious forming defects, achieving synergistic low roughness and low friction. The proposed RSM-CWOA framework provides an effective method for multi-objective optimisation of FDM processes and can be extended to other polymer additive manufacturing systems.