Aircraft Materials, Identification and Corrosion Control

Airframes combine materials for strength per unit weight: aluminium alloys for skins and structures, steels for fittings and landing gear, titanium and magnesium in hot or weight-critical areas, composites and transparent plastics elsewhere. Identify metals by markings, by magnet test, by weight and by spark test.

Alloy designation includes the temper code, which records how the material was heat treated — for example a solution-treated and aged condition. Cold work and welding harden an alloy, and overheating it without the prescribed re-treatment permanently weakens it. Never substitute a material or temper without approved data.

Nonmetallic parts — seals, gaskets, hoses, tyres and transparencies — age with heat, ultraviolet light and chemicals and carry shelf lives and cure dates. Check the date before installation and dispose of expired stock correctly.

Corrosion is electrochemical decay, and each metal fails differently: aluminium pits, powders white and exfoliates under the paint; steel rusts red; dissimilar metals in moisture corrode galvanically, which is why isolation, sealing and the correct fasteners are specified.

Most serious cracks begin invisible, so inspection is organised by zone and never rushed. Dye penetrant reveals surface-breaking flaws in nonmagnetic parts; magnetic particle finds surface and near-surface flaws in ferromagnetic steel; eddy current finds subsurface cracks around installed fasteners without disassembly; ultrasonic and radiographic methods reach deeper. No method replaces another — the manual dictates which applies to each part. Treat corrosion by removing all of it within blend limits, converting and priming, restoring the protective system, and eliminating the trapped moisture that caused it.