Materials used in electric vehicles are subjected to long-term exposure to environmental factors such as air pollution, rain/snow erosion, and direct sunlight. These conditions can alter their mechanical performance and durability, posing potential safety risks. Electroplating, a commonly employed surface treatment technique in industrial manufacturing, deposits a metallic film onto raw automotive materials through electrolysis. This process not only enhances the base material’s protection performance but also improves the vehicle’s aesthetic appeal through a metallic finish. Furthermore, the functional properties of the plating expand the application scope of certain materials.
Lightweight design in new energy vehicles is a vital strategy for achieving energy conservation and emissions reduction, and electroplating plays an important role in this context. By modifying material properties and structures through surface metallization, electroplating technology enriches the utilization of lightweight materials in automotive applications. This paper analyzes the current application status of electroplating technology in NEVs, aiming to support the optimization of New Energy Vehicle quality.
Benefits of Electroplating in New Energy Vehicles
Corrosion Protection by Electroplating
NEV components primarily consist of metallic, organic, and inorganic materials. During vehicle service, environmental changes, corrosive gases, and road debris can cause components to suffer damage, aging, deformation, and corrosion. Electroplating provides a corrosion-resistant surface treatment that extends the material’s service life.
Metallic Components: Corrosion is related to the material’s surface condition, composition, and environment (temperature, humidity).
Organic Materials: Aging during the vehicle’s service life can lead to issues such as poor sealing and embrittlement.
Battery Gas Diffusion Layer: This critical component, composed of carbon fiber, carbon black, and a hydrophobic agent, significantly impacts battery stability. The GDL’s thickness and surface treatment status can impede battery heat conduction, potentially leading to corrosion of the motor materials.
To mitigate the corrosion susceptibility of metal bipolar plates in NEV batteries, electroplating is employed to secure the overall electrode performance. The coating varies depending on the bipolar plate substrate, and different platings ensure optimal conductivity and corrosion resistance. For stainless steel or titanium alloy bipolar plates, their performance can be enhanced by electroplating with Ni-W-P, Ni-Cu-P, or Ni-Cu coatings. Furthermore, pre-treatment of the substrate material before electroplating improves coating adhesion.
On the anode side of the metal bipolar plate, low-stress electroplated nickel is typically selected. This process enhances the coating’s adhesion, conductivity, and corrosion resistance. Alternatively, adjusting the parameters of the electroplated nickel process can impart a degree of hydrophobicity to the coating, ensuring the battery is not easily wetted by the electrolyte solution during operation.
Aesthetic Enhancement
Beyond improving corrosion resistance and impact resistance, electroplating process enhances the vehicle’s visual appeal, capturing consumer attention and stimulating purchase intent. For example, electroplating new energy vehicle wheel hubs makes their exterior more attractive, elevating the vehicle’s overall aesthetic.
Wheel hub electroplating processes mainly include silver plating, water electroplating, and pure electroplating:
Silver Plating: These provide a smooth, textured appearance but have relatively poor resistance to stone chipping, corrosion, and stability. They are suitable for younger demographics seeking aesthetics and novelty.
Electroplating: This process is characterized by high production cost, but superior stability and durability, making it suitable for middle-aged consumers who prioritize quality.
Electroplating for product appearance is referred to as decorative electroplating. This process on NEV wheel hubs involves casting, heat treatment and electroplating to apply a bright, lustrous metallic film to the surface. Compared to functional plating, decorative electroplating requires a longer pre-treatment time, approximately 30-40 minutes. With the rising cost of metallic nickel, the decorative nickel plating process is being impacted, necessitating the active search for alternative materials to reduce plating costs at the source.
Vacuum electroplating involves high-temperature spraying of two base layers onto the NEV surface, followed by electroplating in a vacuum chamber. This process significantly reduces the consumption of electroplating metals, offering an effective solution to the problem of escalating plating costs.
Applications of Electroplating in EV
As global focus on new energy vehicles intensifies, the development of related materials and processing technologies is becoming more sophisticated. Electroplating, by modifying material properties through surface deposition, is of great significance for optimizing NEV quality, enhancing appearance, and promoting lightweighting.
Electroplating for Metals
Metal materials are used extensively in the NEV chassis, structural frames (seats, dashboards), brackets (steering columns), and wheel hubs, forming the foundation of the vehicle’s overall structure. To meet the demands for surface protection in harsh service environments, electroplating is the standard surface treatment method.
Steel: As the most prevalent material in NEVs, steel is often surface-treated with zinc electroplating. However, in complex service environments, the corrosion resistance of a pure zinc coating is often insufficient. Automotive manufacturers favor the superior corrosion resistance of zinc-iron, zinc-nickel, zinc-cobalt, and zinc-manganese alloys over simple zinc plating.
High-strength steel materials used in NEVs require electroplating processes that meet the demanding specifications of the Neutral Salt Spray Corrosion Test. Specifically, high-strength steel electroplated with a nickel-zinc alloy offers higher corrosion resistance, along with a stable, low wear rate and low hydrogen embrittlement sensitivity, broadening its application scope. Recent R&D efforts have resulted in composite coatings with enhanced wear resistance, achieved by adding nano-oxides (TiO2, Al2O3, SiO2, etc.) or a third element (Fe, P, Mo, Mn, etc.) to the zinc-nickel alloy plating bath. Furthermore, some automakers choose to electroplate high-strength steel with zinc or zinc-nickel alloys to achieve colored or blue coatings, which provides color masking while boosting the material’s corrosion and wear resistance.
Aluminum Alloys: As an excellent alternative to steel, aluminum alloys possess low density, high strength, and high plasticity, making them a crucial raw material for NEV components such as structural frames, body shells, cylinder blocks, and pistons. To address the corrosion challenge, surface electroplating is the primary solution. The zinc-immersion process has evolved from an initial zinc-iron alloy to modern zinc-iron-nickel or zinc-iron-nickel-copper alloys, resulting in stronger coating adhesion to the aluminum substrate. The 6000-series aluminum alloy is a preferred choice for many NEV manufacturers. However, due to its minor magnesium and silicon content, its hardness and corrosion resistance are relatively low. Electroplating the surface of an aluminum alloy with a Ni-W-P alloy can achieve a microhardness of 320HV to 360HV. Subsequent heat treatment can further increase the coating’s hardness to over 600HV, while maintaining good electrical conductivity.
Electroplating for Plastics
In NEV design, engineers must consider both the strength and safety of components and the overall lightweighting strategy to minimize energy consumption. As high-molecular synthetic materials, plastics are widely used for NEV interiors, exteriors, structural parts, and functional components due to their low cost, light weight, and ease of molding. After electroplating, plastics acquire a metallic appearance, enhancing their decorative appeal, mechanical strength, and durability. Common automotive plastics include Acrylonitrile-Butadiene-Styrene (ABS), Polypropylene (PP), and Polyamide (PA).
ABS: A thermoplastic often compounded with other polymers to create modified plastic alloys in the NEV sector:
ABS electroplating involves three stages: pre-treatment, chemical plating, and electroplating. Current research hotspots include pre-treatment optimization, process simplification, and the upgrading of environmentally friendly plating solutions. For example, using a graphene composite conductive paste for ABS pre-treatment has been shown to improve the conductivity of the plated part while giving it a non-shedding metallic luster. Another approach utilizes two-dimensional graphene material for ABS pre-treatment, achieving excellent conductivity and cost savings while simplifying the traditionally complex process.
PP: A lightweight, general-purpose plastic with good heat resistance, insulation, and mechanical strength. Its comprehensive properties can be enhanced by incorporating reinforcing agents and tougheners, altering its molecular structure:
PA (Nylon): A thermoplastic resin with excellent heat resistance, wear resistance, flame retardancy, and mechanical properties. Its performance can be enhanced by blending it with glass fibers and other fillers.
Before electroplating PA materials, stress testing is required to eliminate the material’s internal stress. One study incorporated modified minerals treated with coupling agents and rare-earth ions, along with compatibilizers, into PA, resulting in a modified material with superior rigidity, toughness, and electroplating properties. Another study used a blend of talc and mica to obtain PA6, significantly improving its heat resistance and stability, making it suitable for the production of electroplated components such as headlamp housings.
