Material Selection & Properties Flashcards

Audi uses a wax-injection process in hollow body cavities after painting. What is the purpose of this cavity wax?

Answer: To provide long-term corrosion protection in enclosed areas inaccessible to paint

Cavity wax penetrates into enclosed sections and seams, providing a moisture-displacing film that protects internal surfaces from corrosion throughout the vehicle's service life.

Which material property determines how much a connecting rod will elastically deform under combustion loads, and is therefore critical for engine bearing clearance design?

Answer: Young's modulus (modulus of elasticity)

Young's modulus defines the ratio of stress to elastic strain; a higher modulus means less elastic deflection under load, which directly affects bearing clearance calculations.

Audi's B-pillar reinforcements in the Q7 are made from boron-alloyed steel (22MnB5). What role does boron play in this alloy?

Answer: Boron significantly improves hardenability, enabling the ultra-high strength achieved after press hardening

Even small additions of boron (typically 0.001–0.005%) dramatically improve steel hardenability, allowing thin sections to achieve martensitic microstructure throughout when quenched during press hardening.

A repair technician must replace a section of an Audi's aluminum structural rail. Why must they avoid using steel MIG wire in an aluminum MIG welder?

Answer: Steel and aluminum cannot be fusion welded due to brittle intermetallic compound formation at the joint

Steel-aluminum welds form brittle intermetallic compounds (Fe2Al5, FeAl3) at the fusion boundary, resulting in joints with near-zero toughness that fail under minimal stress.

Audi specifies a minimum hardness of 58 HRC for camshaft lobes. Which hardness testing method is most appropriate for verifying this specification?

Answer: Rockwell C scale (HRC)

The Rockwell C scale is specifically designed for hard steels in the range of 20–70 HRC, making it the appropriate and directly comparable test method for this specification.

What is the function of the interstitial-free (IF) steel used for Audi's outer door skin panels?

Answer: Offers exceptional formability for complex panel shapes with minimal springback

IF steel has carbon and nitrogen removed to sub-ppm levels, eliminating interstitial atoms that impede dislocation movement and greatly improving deep drawability for complex stampings.

Audi's wheel bearings use bearing steel (e.g., 100Cr6 / SAE 52100). What combination of properties makes this alloy suitable?

Answer: High hardness and wear resistance with sufficient toughness to resist rolling contact fatigue

Bearing steel achieves 60–67 HRC surface hardness after heat treatment, providing wear resistance, while retaining enough core toughness to withstand the cyclic stresses of rolling contact fatigue.