Materials, Hardware and Corrosion Control
What you must understand
Know the common aircraft materials: aluminium alloys (2024, 7075 and their heat treatment), titanium, steel and stainless steel, magnesium, and composites (fibre and resin, lay-up, and the meaning of a delamination or a disbond). Understand the properties that matter: strength, stiffness, fatigue resistance, corrosion resistance, and thermal expansion. Know the heat-treatment tempers and why a 2024 rivet is stored refrigerated and used within its life.
Hardware: rivet types and their use, bolts (AN, MS, close-tolerance), nuts, washers, cotter pins, lockwire, and the meaning of grip length and thread engagement. Know the difference between a tension fastener and a shear fastener, and why hole fit matters. Understand standard versus close-tolerance bolts and the use of a torque wrench with the correct procedure.
Corrosion: know the forms - general or surface, galvanic, pitting, intergranular, exfoliation, stress corrosion, fretting and microbiological. Know the conditions that promote each and the inspection clues. Understand protective treatments: anodising, alodine, primer, sacrificial coatings, sealants, and the role of drainage and ventilation.
Traps
A common trap is confusing exfoliation (layered lifting of grain structure) with intergranular corrosion. Another is fitting a bolt whose grip is too short, leaving threads in bearing.
Rule of thumb
Galvanic corrosion needs two dissimilar metals, an electrolyte and an electrical path. Remove any one and the corrosion stops - that logic answers most preventive questions.