Automotive Materials
What the exam tests
Automotive materials covers ferrous and non-ferrous metals, plastics, composites, properties and heat treatment. You must select materials for pistons, blocks, gears, springs and body panels, and justify the choice.
Core rules and concepts
- Cast iron is wear-resistant and dampens vibration; it suits cylinder blocks and brake discs.
- Steel is strong and tough; alloying and heat treatment adjust hardness and strength.
- Aluminium reduces weight; it suits pistons, heads and wheels but has lower wear resistance.
- Copper conducts electricity and heat; it is used in wiring and radiators.
- Plastics and composites reduce weight and resist corrosion, but may degrade at high temperature.
- Properties include strength, hardness, toughness, ductility, fatigue resistance and thermal conductivity.
Worked example
A 10 mm diameter steel rod carries a tensile load of 5 kN. Area A = π/4 × (0.010)² = 7.854 × 10⁻⁵ m². Stress σ = F/A = 5,000/7.854 × 10⁻⁵ = 63.7 MPa. If the steel yield strength is 250 MPa, the safety factor is 250/63.7 ≈ 3.9. The rod is safe for this load, but fatigue, threads or corrosion could reduce the margin.
Traps that cost marks
- Confusing hardness with toughness.
- Using diameter as radius in area calculations.
- Choosing aluminium for a high-wear surface without a liner or coating.
- Ignoring temperature and corrosion in material selection.