Materials Science in Automotive Flashcards

Which heat treatment process produces a hard martensitic surface layer while keeping the core tough in automotive gear components?

Answer: Case hardening

Case hardening (carburizing + quenching) creates a high-carbon martensitic surface with a ductile low-carbon core, ideal for gears.

What is the primary reason aluminum alloys are used in automotive engine blocks instead of cast iron?

Answer: Lower density reducing vehicle weight

Aluminum's density (~2.7 g/cm³) is about one-third that of cast iron (~7.2 g/cm³), offering significant weight savings.

Which composite material architecture offers the highest in-plane stiffness-to-weight ratio for automotive structural panels?

Answer: Unidirectional (UD) fiber laminate

Unidirectional laminates align all fibers along the load axis, maximizing specific stiffness compared to other fiber architectures.

In the iron-carbon phase diagram, what phase exists at room temperature in a slowly cooled 0.8% carbon steel?

Answer: Pearlite

A 0.8% C steel is eutectoid; slow cooling through 727°C transforms all austenite to pearlite (alternating ferrite and cementite lamellae).

Which mechanism is responsible for age hardening (precipitation hardening) in aluminum alloys used in automotive structural components?

Answer: Coherent precipitate strain fields impeding dislocation motion

Fine coherent precipitates (e.g., GP zones, θ' in Al-Cu) create strain fields that act as barriers to dislocation glide, increasing strength.

What is the function of a corrosion inhibitor added to automotive coolant?

Answer: Form a protective oxide film on metal surfaces

Inhibitors like silicates and azoles adsorb on metal surfaces to form passivating films, preventing electrochemical corrosion in the cooling system.

Which property best describes a material's resistance to crack propagation under cyclic loading conditions in automotive suspension components?

Answer: Fatigue crack growth threshold (ΔKth)

ΔKth is the stress intensity range below which fatigue cracks do not propagate, directly governing durability under cyclic loads.