Aircraft Materials - Non-Ferrous
Core concepts
Aluminium alloys are the backbone of the airframe. 2024 (copper) has good strength and fatigue resistance but poor corrosion resistance, so sheet is usually Alclad - clad with a thin layer of pure aluminium that protects the core galvanically. 7075 (zinc) is the strongest common alloy and the least corrosion resistant. 6061 (magnesium-silicon) is weldable and corrosion resistant; 5052 is a good general-purpose sheet alloy. Tempers matter: O is annealed, T3 solution-treated and cold worked, T4 solution-treated and naturally aged, T6 solution-treated and artificially aged. Solution treatment is around 500 C followed by a quench; artificial ageing is done at a much lower temperature, and that ageing temperature is the ceiling for later paint-baking or repair heating.
Magnesium alloys are light but corrode readily and can burn; they need chromate-type protective treatments and isolation from other metals. Titanium has excellent strength-to-weight, poor thermal conductivity, galls easily and absorbs oxygen if heated in air, so welding needs inert-gas shielding. Copper alloys (brass, bronze) serve as bushes and fittings.
Traps in questions
Assuming stronger is always better: 7075-T6 is strong but less tough and less corrosion resistant than 2024-T3, which is why cladding and protection matter. Thinking anodising adds strength - it only builds a brittle oxide layer for corrosion resistance and paint adhesion. Confusing Alclad (pure aluminium) with plating.
Rule of thumb
2024 - copper, strong, needs cladding; 7075 - zinc, strongest, needs protection; 6061 - weldable, corrosion resistant. Never heat a heat-treated part above its artificial ageing temperature.