Integrating the electric motor with a multi-speed transmission is an effective way to improve the efficiency and performance of battery electric vehicles (BEVs). This paper innovatively proposes a design method for matching a single-motor and dual-speed dual-clutch transmission (2-Speed Wet DCT) powertrain system and constructs a variable speed efficiency model (VSEM) and constant speed efficiency model (CSEM) for the inverter, motor, and transmission. Research shows that the design parameters of the motor and transmission significantly affect the optimal powertrain system. This study uses an enhanced NSGA-II multi-objective genetic algorithm to optimize the driving performance of energy efficiency and powertrain cost under two different acceleration times (10 s and 12 s), with the key parameters of the motor and transmission as optimization variables and dynamic indicators as constraints, and compares VSEM and CSEM. The optimization results indicate that VSEM have better energy-saving effects than CSEM, with the energy consumption reduced by 3.7% and 3.3% under the two driving performances, respectively. The Pareto frontier further confirms that, for multi-speed transmission systems in electric vehicles, matching a high-power, high-torque motor with a smaller transmission ratio powertrain can achieve higher energy efficiency and thus longer driving range. Additionally, this study quantifies the correlation between energy efficiency and powertrain cost using grey relational analysis (GRA), with a result of 0.77431.

This study addresses the issues of coarse primary austenite dendrites and uneven graphite distribution in hypoeutectic gray cast iron. High-energy mechanical activation technology was used to prepare high-energy activated SiC particles (EASiCp), and the regulatory mechanisms of trace additions (0–0.15 wt.%) on the solidification process and microstructure properties of hypoeutectic gray cast iron were systematically investigated. The results indicate that high-energy activation treatment reduced the average particle size of SiC particles from 26.53 μm to 9.51 μm and increased their specific surface area from 0.35 m²/g to 1.78 m²/g. X-ray diffraction (XRD) analysis revealed that the grain size was refined from 55.5 nm to 17.4 nm, with significant lattice distortion. The absorption rate of EASiCp in the melt stabilized between 68–72%, with particles predominantly dispersed within the grains (78.12%) and at grain boundaries (21.88%) in sizes ranging from 0.3 to 2 μm. The addition of EASiCp enhanced the solidification undercooling from 5.3 °C to 8.4 °C and reduced the latent heat of crystallization from 162.6 J/g to 99.96 J/g due to its endothermic reaction in the melt (SiC + Fe → FeSi + C) and heterogeneous nucleation effects. In terms of microstructure, the addition of 0.15 wt.% EASiCp increased the primary austenite dendrite content by 35.29%, reduced the secondary dendrite arm spacing by 57.98%, shortened the graphite length from 0.46 mm to 0.20 mm, and refined the eutectic colony size from over 500 μm to 180 μm. The final material achieved a tensile strength of 308 MPa, an improvement of 12.82% compared to the unadded group. Mechanistic analysis showed that EASiCp facilitated direct nucleation, reaction-induced “micro-area carbon enrichment,” and a synergistic effect in suppressing grain growth, thereby optimizing the solidification microstructure and enhancing performance. This study provides a new method for the efficient nucleation control of hypoeutectic gray cast iron.