Automotive Materials
Automotive Materials
This domain tests the properties and uses of ferrous and non-ferrous metals, plastics, rubber, composites and heat treatments. Questions ask why a piston is aluminium or why a cylinder liner is cast iron.
Core rules
- Ferrous: cast iron (cylinder blocks, liners, brake discs - wear resistant, brittle), mild steel (brackets, chassis), high-carbon and alloy steels (gears, shafts, springs), stainless steel (exhaust parts).
- Non-ferrous: aluminium alloys (pistons, cylinder heads, wheels - light, good heat conduction), copper (wiring), brass (radiator cores, fittings), bronze (bushes), zinc (coatings).
- Plastics and composites: PP, ABS, PA for trims, bumpers, covers; glass-fibre and carbon-fibre composites for panels and driveshafts - light and strong but costly to repair.
- Rubber: tyres, seals, hoses, mounts - resilience and damping; degraded by ozone, heat and oil.
- Heat treatment: annealing softens and relieves stress; hardening (quenching) increases hardness but makes steel brittle; tempering restores toughness after hardening.
Worked example
A piston is specified as an aluminium-silicon alloy rather than cast iron. Reasoning: the piston must reciprocate at high speed, so low mass reduces inertia loads. Aluminium has about one-third the density of steel or cast iron and conducts heat well, helping to control crown temperature. Silicon lowers thermal expansion and improves wear resistance. Cast iron would be stronger at high temperature but too heavy; hence the aluminium piston runs in a cast-iron or coated liner that provides the wear surface.
Traps
- Confusing hardness with toughness.
- Saying aluminium is stronger than steel in absolute terms.
- Recommending annealing to harden a component.
- Using the wrong rubber or sealant where oil resistance is needed.