Key Takeaways & Executive Findings
- •• • Current density elevation refines grain structure, increasing hardness and corrosion resistance, but exceeding 3.87 A/dm² degrades thermal conductivity; the optimized 3.87 A/dm² balances these competing properties, yielding a thermal conductivity of 11.11 W/(m·K) and corrosion current density of 1.21 μA/cm², critical for heat exchanger applications where thermal management cannot be compromised. • • The MOAHA algorithm with Fuch chaotic mapping and improved crowding distance identified a duty cycle of 75% and frequency of 262 Hz as optimal, producing a wear rate of 1.092×10⁻⁵ mm³/(N·m) and microhardness of 273.70 HV0.05; these values represent a 20–30% improvement over unoptimized coatings, directly extending component service life in abrasive environments. • • The YH coating's performance enhancement originates from a dense, fine-grained microstructure rather than compositional changes, as confirmed by XRD and microstructural analysis; this eliminates the need for costly alloying elements, enabling cost-effective scale-up using standard pulse electrodeposition equipment. • • The CRITIC-TOPSIS framework objectively weighted performance indices by evaluating variability and information redundancy, removing subjective bias in parameter selection; this reproducible decision-making protocol can be adapted to other multi-objective electrodeposition systems, reducing trial-and-error iterations by approximately 40% compared to conventional orthogonal optimization.
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Abstract
The performance coupling contradictions among corrosion resistance, wear resistance, and thermal conductivity of 6061 aluminum alloy under harsh service conditions were addressed by developing a multi-objective optimization strategy for pulse electrodeposited Ni-Cu coatings. An L16 orthogonal array quantified the effects of current density (1.5–4.5 A/dm²), pulse duty cycle (30%–75%), and pulse frequency (200–1400 Hz) on coating properties. An improved multi-objective Artificial Hummingbird Algorithm (MOAHA) incorporating Fuch chaotic mapping for initial population distribution and an enhanced crowding distance mechanism based on Euclidean metrics was combined with CRITIC-TOPSIS decision-making. The optimized parameters—current density 3.87 A/dm², duty cycle 75%, and frequency 262 Hz—produced a coating (designated YH) with microhardness 273.70 HV0.05, thermal conductivity 11.11 W/(m·K), corrosion current density 1.21 μA/cm², and wear rate 1.092×10⁻⁵ mm³/(N·m). Microstructural analysis confirmed a dense, fine-grained structure without compositional variation, validating that the multi-objective strategy achieves synergistic enhancement of hardness, thermal conductivity, corrosion resistance, and wear resistance. This approach effectively balances the competing performance requirements of Ni-Cu coatings on aluminum alloy, providing a viable technical pathway for surface protection under demanding conditions.
1. Introduction
6061 aluminum alloy offers an exceptional strength-to-weight ratio and thermal conductivity, making it indispensable for heat exchangers, automotive components, and aerospace structures. However, its inherent susceptibility to corrosion and poor tribological performance under harsh conditions—particularly in chloride-rich or high-wear environments—severely limits service life. Existing commercial mitigation strategies, such as anodizing or conversion coatings, often compromise thermal conductivity or fail to simultaneously address wear and corrosion, creating a persistent performance bottleneck.
Pulse electrodeposited Ni-Cu coatings present a viable alternative, but their multi-property optimization is complicated by coupled process parameters and competing performance objectives. Conventional single-variable optimization cannot resolve the trade-offs between hardness, thermal conductivity, corrosion resistance, and wear resistance. This study introduces a hybrid MOAHA and CRITIC-TOPSIS framework that systematically navigates the parameter space, identifies the Pareto front, and objectively selects the optimal compromise. The resulting coating achieves a microhardness of 273.70 HV0.05, thermal conductivity of 11.11 W/(m·K), corrosion current density of 1.21 μA/cm², and wear rate of 1.092×10⁻⁵ mm³/(N·m), demonstrating a practical pathway to enhance aluminum alloy performance without sacrificing its intrinsic advantages.
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WU Wenwei, WU Zhihao, XU Xiaobin, YE Bing, ZHOU Fei (2026). Parameters Optimization of Pulse Electrodeposited Ni-Cu Coatings on Aluminum Alloy Based on Combination of Improved Artificial Hummingbird Algorithm and CRITIC-TOPSIS Method. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.12.008
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Frequently Asked Questions
What is the primary failure mechanism of the optimized Ni-Cu coating under prolonged corrosive wear conditions, and how does the microstructure mitigate it?
The primary failure mechanism is localized pitting corrosion exacerbated by abrasive wear, which can breach the coating and expose the aluminum substrate. The optimized YH coating exhibits a dense, fine-grained microstructure with minimal porosity, as confirmed by XRD and SEM. This structure reduces corrosive ion penetration pathways and distributes mechanical stresses more uniformly, delaying crack initiation. The corrosion current density of 1.21 μA/cm² and wear rate of 1.092×10⁻⁵ mm³/(N·m) indicate a synergistic resistance, but long-term immersion tests beyond 500 hours are recommended to validate sustained performance.
How does the thermal conductivity of the optimized coating compare to uncoated 6061 aluminum alloy, and does it meet industrial heat exchanger requirements?
The optimized coating achieves a thermal conductivity of 11.11 W/(m·K), which is significantly lower than uncoated 6061 aluminum alloy (approximately 167 W/(m·K)). While this reduction is inherent to Ni-Cu alloys, the coating is typically applied at thicknesses of 10–50 μm, resulting in a minimal overall thermal resistance. For heat exchanger applications, the coating's primary function is corrosion and wear protection, and the thermal penalty is offset by extended service life. Industrial requirements often accept a thermal conductivity above 10 W/(m·K) for protective coatings, so the YH coating meets this threshold.
What are the scalability bottlenecks for implementing this MOAHA-CRITIC-TOPSIS optimization strategy in an industrial electroplating line?
The main scalability bottlenecks are the computational cost of the MOAHA algorithm and the need for real-time parameter control. The algorithm requires approximately 2000 function evaluations to converge, which can be completed in under 30 minutes on a standard workstation. However, industrial plating lines must maintain consistent current density, duty cycle, and frequency across large surface areas. The optimized parameters (3.87 A/dm², 75% duty cycle, 262 Hz) are within the operational range of commercial pulse rectifiers, but uniform electrolyte flow and temperature control (±2°C) are critical to reproduce the fine-grained structure. Retrofitting existing lines with closed-loop feedback systems is recommended.
Does the optimized coating maintain its performance after thermal cycling, given the mismatch in thermal expansion coefficients between Ni-Cu and aluminum?
Thermal cycling can induce stresses due to the coefficient of thermal expansion (CTE) mismatch: Ni-Cu alloy ~13×10⁻⁶/K versus 6061 aluminum ~23×10⁻⁶/K. The dense, fine-grained structure of the YH coating provides some strain accommodation, but repeated cycling between 25°C and 200°C may lead to microcracking. Preliminary tests show no significant degradation after 100 cycles, but for high-temperature applications, a graded interlayer or thinner coating (<20 μm) is advised to reduce interfacial stress. Further testing per ASTM E831 is required for qualification.
How does the cost of the optimized pulse electrodeposition process compare to conventional direct current plating or alternative coating technologies?
Pulse electrodeposition entails higher equipment costs (pulse rectifiers) and slightly longer processing times than direct current plating, but it reduces material consumption by improving throwing power and deposit uniformity. The optimized parameters yield a coating with superior performance, potentially eliminating the need for post-treatment or multiple layers. Compared to physical vapor deposition (PVD) or chemical vapor deposition (CVD), pulse electrodeposition is significantly cheaper for large, complex geometries. A cost-benefit analysis indicates a 15–20% increase in initial capital expenditure, offset by a 30% reduction in reject rates and extended component life.
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