Automotive Materials
This domain tests ferrous and non-ferrous metals, plastics, composites, heat treatment and material selection for engine, transmission, body and trim components. Questions link properties to service requirements.
Core rules
Ferrous materials include cast iron and steels; non-ferrous include aluminium, copper, brass and magnesium. Strength, hardness, toughness, ductility, thermal conductivity, density and corrosion resistance drive selection. Cast iron is wear-resistant and damping but heavy; aluminium is light and conducts heat well but has lower strength at temperature and higher expansion. Steel can be hardened and tempered; case hardening gives a hard wear surface with a tough core. Plastics are chosen for weight, corrosion resistance, insulation and cost. Galvanic corrosion occurs when dissimilar metals and an electrolyte form a cell.
Worked example
A piston is made from an aluminium-silicon alloy rather than mild steel. Aluminium has about one-third the density of steel, reducing reciprocating mass, and its thermal conductivity is roughly three to four times higher, helping the piston shed heat. Its coefficient of expansion is greater, so the piston-to-bore clearance and ring design must allow for expansion. A cast-iron cylinder liner or a wear-resistant bore surface is used because aluminium alone has poor sliding wear resistance.
Traps
Confusing hardness with toughness; assuming stainless steel cannot corrode; heating high-strength steel without checking the repair procedure; and joining aluminium to steel without isolating the galvanic couple. Tempering reduces hardness and increases toughness after hardening.