Materials Science in Automotive Flashcards

Which test method evaluates the resistance of automotive paint and substrate systems to corrosion induced by cyclic wet-dry-salt spray conditions?

Answer: SAE J2334 cyclic corrosion test

SAE J2334 cycles through humidity, salt solution, and air-dry phases to replicate real-world corrosion better than continuous salt spray.

What is the primary advantage of using magnesium alloys (e.g., AZ91D) for automotive instrument panel frames?

Answer: Lowest structural metal density (~1.74 g/cm³) enabling maximum weight reduction

Magnesium is the lightest structural metal, offering ~35% weight savings over aluminum and ~78% over steel for equivalent designs.

In automotive rubber compounding, which ingredient is responsible for vulcanization that converts natural rubber from a thermoplastic to an elastomeric network?

Answer: Sulfur

Sulfur forms polysulfide cross-links between polyisoprene chains during vulcanization, creating a three-dimensional elastomeric network with elastic memory.

Which coating technology is used to apply cathodic electrodeposition (e-coat) primer to automotive body-in-white for maximum corrosion protection?

Answer: Immersion in charged paint bath causing deposition on the negatively biased metal

In cathodic e-coat, the body is made cathode in a paint bath; electrochemical reduction deposits resin uniformly in cavities unreachable by spray methods.

What is the primary reason transformation-induced plasticity (TRIP) steels are used in automotive B-pillars?

Answer: Austenite-to-martensite transformation during crash absorbs energy while increasing strength

Retained austenite in TRIP steels transforms to martensite under crash strain, simultaneously releasing transformation energy and raising local strength for superior energy absorption.

Which phenomenon causes hydrogen embrittlement in high-strength automotive fasteners (>1200 MPa) during electroplating?

Answer: Atomic hydrogen absorbed during pickling or plating diffuses to grain boundaries and reduces cohesive strength

Atomic hydrogen generated during acid pickling or electroplating absorbs into steel and segregates to grain boundaries, drastically reducing ductility and fracture toughness.

In laser powder bed fusion (LPBF) additive manufacturing of automotive titanium brackets, what post-process is mandatory to relieve residual stresses before machining?

Answer: Stress relief annealing in inert atmosphere

Rapid thermal cycling during LPBF creates large tensile residual stresses; annealing at 600–800°C in argon or vacuum relaxes these stresses, preventing distortion during machining.