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Electric vehicles (EVs) and hybrid cars are widely recognised as the future of sustainable transportation, offering lower emissions. However, corrosion is an often-overlooked problem that can compromise the durability of these advanced vehicles. Understanding how corrosion affects EVs and hybrids and knowing the best strategies to prevent it ensures you get the most out of your investment.
It may seem counterintuitive since EVs don’t have a traditional exhaust system, but they face unique challenges that make them quite susceptible to corrosion.
EV and hybrid batteries are heavy. To compensate for the weight and maintain decent efficiency, automakers have to make the rest of the car lighter. This often means swapping out traditional, heavy steel components for lighter metals like aluminium and magnesium in the chassis, body panels and subframes.
However, the presence of mixed materials increases the risk of corrosion, and when they come into contact with oxygen and moisture, they can form aluminium oxide and lead to rusting.
Mixing different types of metals can increase the risk of galvanic or bimetallic corrosion. This can happen when aluminium comes into contact with more noble or dissimilar metals, such as steel frames, fasteners, or screws.
Because EVs incorporate a blend of materials, numerous connection points are vulnerable to this type of corrosion if not properly protected or insulated. When moisture and salt penetrate a joint between steel and aluminium, the resulting electrochemical reaction accelerates corrosion rapidly.
Corrosion in the battery compartment housing on an EV’s underside often results from chloride-containing road salts. However, deicing salts are well-known corrosive agents that can adhere to the vehicle for prolonged periods, especially in hard-to-clean areas, which accelerates corrosion.
Smaller EVs face an added challenge. Because of their compact size, batteries are positioned higher up, closer to the wheels than in combustion engine vehicles. This placement exposes the battery to increased moisture, temperature fluctuations, and salty water from gritted UK roads, especially during the winter months.
Corrosion can manifest in many ways. Here’s how the different types can impact a green vehicle’s longevity.
Galvanic corrosion occurs when two dissimilar metals — such as aluminium and steel — come into electrical contact with an electrolyte, like water. This issue is particularly relevant since EVs often use lightweight, mixed structures to reduce weight. Road salt and moisture can readily complete the electrical circuit, which accelerates corrosion of the less noble metal at joints or connection points.
Small pits on the underside of an EV are typically caused by pitting corrosion. This type of corrosion commonly develops on metals that depend on a protective surface layer, such as stainless steel or aluminium alloys. These pits can be difficult to detect until they compromise the battery enclosure’s structural integrity, presenting risks to both longevity and safety.
Crevice corrosion is another concern in EVs. This localised form of corrosion occurs in confined spaces where components are tightly joined, restricting oxygen access. EVs contain numerous seams, seals and bolted joints, especially around the battery pack enclosure and subframes, where multiple elements converge. Such crevices readily trap salt and moisture and the restricted oxygen flow can compromise the integrity of essential seals.
EV owners can invest in the right maintenance to preserve the longevity of their vehicles. Here are key steps to help ensure your EV remains reliable for years to come.
The areas most susceptible to corrosion are often found in the underbody and the electrical or structural components. Keep an eye out for the following parts:
Applying nonconductive coatings — such as undercoating or rustproofing — to vulnerable areas is an effective way to resist corrosion. For instance, electroless nickel-phosphorous coatings provide exceptional corrosion resistance, strong adhesion and increased hardness.
Rustproofing sprays, typically oil or lanolin-based, penetrate crevices and seams, actively displacing moisture and forming a self-healing barrier against corrosion. For best results, use a dielectric product and have it applied by a professional.
Corrosion typically occurs in hard-to-see areas, such as tight joints, making regular inspections essential to identify issues before they develop into significant problems. Even with advanced protective features in your vehicle, it is highly recommended to have an annual inspection performed by a professional.
You should promptly address any paint chips or scratches on the body panels or battery pack casing, as exposed metal can quickly become the starting point for pitting corrosion.
Corrosion poses a significant risk to the long-term durability of EVs and hybrid vehicles. Investing in specialised coatings, regular undercarriage cleaning and thorough inspection helps ensure your vehicle remains safe and reliable for years to come.
With an extensive background in automotive journalism, Jack Shaw brings a wealth of knowledge and enthusiasm to the table. As a contributing writer for the National Motorists Association, MOTOR, Tesla Oracle and other leading publications, his articles provide readers with expert insights and captivating stories from the world of automotive repair and manufacturing.
