Corrosion

Cleaning and Corrosion Protection

• Ordinary or non-approved cleaning compounds should not be used on aircraft as they can result in damage.

Cleaning Magnesium Engine Parts

• Magnesium engine parts can be cleaned using a recommended solvent.

Chemical Cleaning and Depainting/Stripping Agents

• Acceptable practices when using chemical cleaning and/or depainting/stripping agents on aircraft include:
  • Not using synthetic fiber wiping cloths with flammable agents.
  • Not using atomizing spray equipment.
  • Using cotton fiber wiping cloths with non-flammable agents.

Cleaning Acrylics and Rubber

• A specific solvent is recommended for cleaning acrylics and rubber.

Fayed Surfaces and Chemical Cleaning

• Fayed surfaces cause concern in chemical cleaning due to the danger of creating scratches.

Caustic Cleaning Products and Aluminum Structures

• Caustic cleaning products used on aluminum structures produce hydrogen gas, which can lead to embrittlement.

Cleaning Transparent Plastic Surfaces

• An acceptable first step to prevent scratching when cleaning a transparent plastic surface is to use a soft, dry cloth to remove any dirt or debris.

Preventing Rapid Deterioration of Tires

• To prevent rapid deterioration when oil or grease come into contact with a tire, the tire should be cleaned and dried immediately.

Corrosion of Aluminum Alloys

• Intergranular corrosion attacks grain boundaries of aluminum alloys that are improperly or inadequately heat-treated.

Corrosion Process

• Corrosion is a process where metal returns to its natural oxide state.

Galvanic Corrosion

• Galvanic corrosion is primarily caused by the difference in electric potential between two dissimilar metals in contact with each other.
• If mercury is spilled on aluminum, the most likely result will be the formation of a galvanic cell, leading to corrosion.

Galvanic Series for Metals

• In the Galvanic or Electro-Chemical Series, most anodic metals are those that give up electrons most readily.
• If the surface area of the anodic metal is smaller than the cathodic metal, crevice corrosion will occur.

Cathodic Materials

• Titanium is the most cathodic material.

Protecting Aluminum Structures

• Pure aluminum forms a non-porous oxide coating when exposed to air, but it's necessary to chemically treat and/or provide a barrier material when it's used in aircraft structures to prevent corrosion.

Improper Heat Treatment and Corrosion

• Improper heat treatment of aluminum alloys will increase the rate of corrosion.

Fretting Corrosion

• Fretting corrosion is caused by the repeated sliding or vibrational motion of two surfaces in contact.

Anodic Materials

• Magnesium is the most anodic material.

Bicarbonate of Soda (Baking Soda)

• Bicarbonate of Soda (Baking Soda) is used in a container (Vent Jar) located in the vent system to absorb moisture and prevent corrosion.

Protecting Steel Tubing

• Linseed oil is used to protect the inside of steel tubing such as frames, spars, and engine mounts from corrosion.

Neutralizing Nickel-Cadmium Battery Electrolyte

• Nickel-Cadmium battery electrolyte can be neutralized with Bicarbonate of Soda (Baking Soda).

Non-Destructive Inspection (NDI) for Corrosion

• One of the most effective NDI inspections for detecting corrosion is X-ray or radiography.

Intergranular Corrosion Detection

• Intergranular corrosion can be detected through visual inspection with a 10X magnifying glass.

Mechanically Cleaning Aluminum Surfaces

• The accepted means of mechanically cleaning aluminum surfaces to remove corrosion is by using a wire brush or abrasive paper.

Removing Corrosion from Aluminum Surfaces

• Medium grit aluminum oxide paper is used to remove corrosion on aluminum surfaces.
• Stiff hog-bristle brushes are used to remove corrosion from crevices or tight spaces.

Corrosion Preventative Material

• When an engine has been pickled, or the final spraying of fogging oil or corrosion preventative mixture has been added, the seal of the corrosion preventative material will be broken if the propeller shaft is rotated.

Stress Corrosion and Cracking

• One process of increasing a metal's resistance to stress corrosion and cracking is by shot peening.

Damaged Anodized Surface Treatment

• If an anodized surface treatment is damaged, it can be partially restored by re-anodizing.

Paint Remover and Enamel Finish

• Paint remover swells the finish and breaks the bond between the enamel finish and the metal.

Chrome Acid Pickling

• Chrome acid pickling protects magnesium sheets from corrosion.

Anodizing

• Anodizing is an electrolytically formed oxide film to protect aluminum alloys from corrosion.

Galvanizing Aluminum Alloy

• Aluminum alloy is not protected from corrosion by galvanizing the metal.

Removing Corrosion from Aluminum Alloy

• One way to remove corrosion from aluminum alloy is by using a chemical conversion coating or a paint system.