Material Selection & Properties Flashcards

What is the primary reason Audi uses galvanized (zinc-coated) steel for underbody panels rather than bare steel?

Answer: Zinc provides sacrificial cathodic protection against corrosion

Zinc corrodes preferentially to the underlying steel (sacrificial anode effect), protecting exposed edges and minor scratches from rust formation.

Audi's R8 uses a dry-sump lubrication system with an aluminum oil tank. Which aluminum series is best suited for this application requiring corrosion resistance and weldability?

Answer: 5xxx series (magnesium-alloyed)

5xxx-series aluminum alloys offer excellent corrosion resistance, good weldability, and sufficient strength for fluid-containment applications like oil tanks.

A technician notices a white powdery residue at a joint between an aluminum subframe and a steel bolt on an Audi. This is most likely caused by:

Answer: Galvanic corrosion due to dissimilar metal contact in the presence of an electrolyte

When aluminum and steel are in direct contact with moisture present, galvanic corrosion occurs because aluminum is anodic relative to steel and corrodes preferentially.

Which property of carbon fiber reinforced polymer (CFRP) makes it particularly advantageous for Audi's high-performance driveshafts?

Answer: Exceptional specific stiffness (stiffness-to-weight ratio) and high torsional resonant frequency

CFRP driveshafts are significantly lighter than steel equivalents, which raises the critical whirl speed (torsional resonant frequency), enabling single-piece driveshafts at higher RPM.

Audi's DSG gearbox shift forks are made from a glass-fiber-reinforced polyamide (PA-GF). What advantage does this offer over a traditional aluminum fork?

Answer: Reduced weight, sufficient strength, and self-lubricating properties

Glass-fiber-reinforced polyamide provides adequate strength and stiffness for shift forks at reduced weight, and polyamide's inherent lubricity reduces friction on the gear collar.

What does the term 'work hardening' (strain hardening) mean in the context of Audi body panel forming?

Answer: The material increases in strength and hardness as it is plastically deformed during stamping

Work hardening occurs as dislocations accumulate during plastic deformation, increasing the material's yield strength and hardness in the deformed region.

Audi specifies a specific torque value for aluminum cylinder head bolts that is lower than the equivalent steel bolt specification. What is the primary reason?

Answer: Aluminum threads strip more easily due to lower shear strength

Aluminum has lower shear strength than steel, so threads in aluminum bores can strip at lower applied torque values, requiring more conservative clamp-force specifications.