Auto manufacturers started increasing their use of aluminum in 2015. Compared to galvanized steel, aluminum results in a lighter, more fuel-efficient vehicle that can protect passengers in a crash.
Unfortunately, the myth that aluminum does not rust continues to persist. While this metal may not develop rust in the same way as steel, it can corrode. If you have a newer vehicle made with mainly aluminum parts, here’s what you should know about corrosion and how to prevent it.
Rust Versus Corrosion
Aluminum corrosion can be more superficial, less likely to alter the metal and the vehicle’s structural integrity. By contrast, rust starts on the surface and can have a pervasive effect that eventually compromises how well the vehicle protects passengers.
We often use the terms “rust” and “corrosion” interchangeably, but there are several differences:
- Rusting: Starts with a chemical reaction involving oxygen and often a “catalyst” substance like water or salt that speeds up the process, resulting in ferric oxide. These molecules are larger than those that make up steel. When rust spreads across the metal, it weakens the structure and may cause steel to flake or peel.
- Galvanic Corrosion: Aluminum acts as an anode but can transfer electrons to a cathode material through an electrolyte like water or salt. Both metals will start to weaken, so auto body work keeps aluminum and steel parts separate. However, aluminum can start to display “spots” or “lesions” on the surface.
Aluminum also has the potential to bond with oxygen, resulting in a compound called aluminum oxide. Unlike rusting, this process creates a hard filmy layer over the surface that can disrupt paint quality in cars.
Types of Aluminum Corrosion
Corrosion of aluminum auto parts falls into one of the four following types:
- Crevice Corrosion: A liquid containing an electrolyte passes through a seam, joint or two panels. The liquid invites corrosion, creating a pitted or etched appearance, potentially affecting both aluminum and steel parts.
- Filiform Corrosion: Mostly an aesthetic concern that affects the aluminum below coatings and paint, this type of corrosion spreads below the metal, causing paint to bubble and flake off. Unlike with rust, you may also see a white, powdery coating below the paint when this occurs.
- Galvanic Corrosion: When an electrolyte like water or salt is present, this kind of corrosion occurs from a reaction between two dissimilar metals. You might see a similar white powdery film or “spots” along the aluminum part where the paint starts to bubble and flake.
- Aluminum Oxide: This occurs when bare, unfinished aluminum is exposed to oxygen and moisture. These factors cause a hard film to develop, which can affect how well aluminum welds, keeps paint on the surface and adhesives, putty and filler hold. Unlike other forms of corrosion, aluminum oxide can form within minutes and will need to be removed before any work can begin.
How to Reduce Corrosion of Aluminum Car Parts
Reducing the corrosion of aluminum car parts involves lessening exposure to an electrolyte, as well as ensuring bare aluminum gets treated immediately after sanded. When caring for your vehicle and considering auto body work:
- Do not share tools between aluminum and steel parts. Separate sets help avoid potential galvanic corrosion.
- Limit exposure to moisture and rock salt during winter.
- Make sure appropriate sealers, primers, fasteners and coatings are applied to the metal and between parts to prevent crevice corrosion and shield aluminum and steel parts from direct contact. These substances will be recommended by the original equipment manufacturer.
- Never work on steel and aluminum parts in the same area, as dust from tools and grinding can spread between metals. This is known as cross-contamination and certified aluminum repair facilities have separate work areas to prevent it from happening.
- As aluminum oxide melts at a significantly higher temperature than aluminum alone, it’s recommended to scrape off any accumulation before welding the metal or painting the surface.
DaSilva’s Auto Body is a certified aluminum repair facility that provides rust removal and rustproofing services. To set up an appointment, contact us today.