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Surface preparation: How do aircraft manufacturers try to prevent corrosion?

Corrosion is the gradual deterioration of metal caused by a chemical reaction with the environment – often involving moisture, oxygen, and salts. Aircraft, especially those made from aluminium alloys and other metals, are particularly vulnerable.

Several types of corrosion can affect aircraft, including:

• Galvanic corrosion: Occurs when two dissimilar metals come into contact, creating an electric current that accelerates corrosion.
• Pitting corrosion: Small, localised holes form on the metal surface, often caused by moisture.
• Crevice corrosion: Develops in areas where moisture is trapped, like joints and fasteners.
• Stress corrosion cracking: Caused by the combined effects of stress and a corrosive environment, leading to cracks in the metal.

To combat these risks, manufacturers use a meticulous surface preparation process to ensure that protective coatings adhere properly and provide long-term defence.

1. Cleaning and degreasing: The first step is to thoroughly clean the aircraft’s surface, removing oils, grease, dirt, and oxidation. According to the Civil Aviation Authority (CAA), they emphasise the importance of preventing and addressing aircraft corrosion, stating that it’s a critical factor in maintaining structural integrity and airworthiness, potentially leading to catastrophic failure if left unchecked. Specialised cleaners and solvents ensure that no contaminants remain, as even the smallest residue can prevent coatings from bonding effectively.
2. Abrasive blasting and mechanical abrasion: Next, abrasive blasting or mechanical abrasion is used to remove existing coatings, oxidation, and surface irregularities. This process is crucial for ensuring that protective layers bond effectively to the metal surface. Techniques include:

• Abrasive blasting: Plastic media blasting is preferred for aircraft maintenance because it’s a soft, versatile, and environmentally friendly method for cleaning and preparing components, especially delicate ones, without causing damage or leaving behind harmful residues.
• Mechanical abrasion: Sanding or using abrasive pads to carefully smooth the surface, often preferred in delicate areas to avoid damage.

1. Chemical treatments: Chemical treatments further enhance corrosion resistance. Acid etching or alkaline washes modify the metal surface to improve the adhesion of subsequent coatings and provide an additional barrier against environmental factors.
2. Inspection and testing: Before any coatings are applied, the surface undergoes thorough inspection. Tests check for cleanliness, surface roughness, and the removal of oxidation to ensure the surface is properly prepared.

Once the surface is ready, a series of protective layers are applied:

1. Priming: Primers act as the first line of defence against corrosion. Zinc chromate primers were traditionally used for their excellent corrosion resistance. Today, epoxy-based primers are more common due to their superior adhesion and protective properties.
2. Top coats: After priming, a top coat – often a polyurethane paint – is applied. This final layer shields the aircraft from moisture, UV radiation, and chemical exposure, while giving it a smooth, durable finish.
3. Sealing joints and fasteners: Moisture tends to accumulate in hard-to-reach places like joints and fasteners, making these areas particularly vulnerable to corrosion. Special sealants are applied to prevent water ingress, providing long-term protection. Regular inspections ensure that these seals remain intact and effective over time.

Corrosion prevention doesn’t stop once coatings are applied. Aircraft undergo routine inspections to detect early signs of wear or damage. Any compromised areas are addressed promptly, with touch-ups or reapplications of protective coatings, keeping the aircraft protected throughout its service life.

The aerospace industry continues to innovate, developing new materials and coating technologies to enhance corrosion resistance. Advancements in nanotechnology have led to the development of nanocoatings, offering enhanced protection with minimal environmental impact. These coatings provide a sustainable alternative to traditional methods, aligning with industry efforts to adopt greener practices. By integrating these comprehensive surface preparation techniques and embracing innovative solutions, aircraft manufacturers effectively combat corrosion, ensuring the safety and durability of their fleets.

Surface preparation is much more than a preliminary step in aircraft manufacturing – it’s a critical process that ensures safety, reliability, and longevity. Every stage, from cleaning to coating, plays a vital role in protecting aircraft from corrosion, enabling them to fly safely for years to come.

At Airblast Eurospray, we’ve been producing surface preparation and finishing facilities for the civil and defence aviation sectors for over three decades. Our rich heritage in designing and constructing these specialist facilities has seen us build some of the largest, most technologically advanced surface preparation and finishing buildings for leading aerospace organisations. Backed by a skilled workforce and deep technical knowledge, we continue to support the aerospace industry with solutions that enhance safety, performance, and durability.