AUDI Material Selection & Properties 3 — Questions and Answers
Question 1: Which heat treatment process is used to increase the hardness and wear resistance of Audi crankshaft bearing journals?
- Solution annealing
- Induction hardening (Correct answer)
- Precipitation hardening
- Normalizing
Correct answer: Induction hardening
Induction hardening selectively heats only the bearing journal surface, creating a hard martensitic layer while leaving the core tough and ductile.
Question 2: Audi uses magnesium alloy for certain engine components such as the crankcase. What is the biggest material handling concern with magnesium during machining?
- Magnesium is highly toxic when vaporized
- Magnesium chips and dust are highly flammable and can ignite spontaneously (Correct answer)
- Magnesium causes tool steel corrosion
- Magnesium has poor machinability requiring carbide tooling exclusively
Correct answer: Magnesium chips and dust are highly flammable and can ignite spontaneously
Magnesium swarf and fine dust are extremely flammable and can ignite spontaneously, requiring dry-chemical fire suppression and strict housekeeping procedures.
Question 3: What distinguishes a thermoplastic from a thermoset polymer used in Audi interior and exterior components?
- Thermoplastics can be remelted and reshaped; thermosets cannot (Correct answer)
- Thermosets are lighter than thermoplastics
- Thermoplastics have higher heat resistance than thermosets
- Thermosets are always reinforced with fibers; thermoplastics are not
Correct answer: Thermoplastics can be remelted and reshaped; thermosets cannot
Thermoplastics soften and can be reprocessed when heated, while thermosets undergo irreversible cross-linking during curing and cannot be remelted.
Question 4: Audi specifies titanium fasteners in certain high-performance applications. Compared to steel fasteners of the same size, titanium offers:
- Higher stiffness (Young's modulus)
- Approximately 45% lower density with comparable tensile strength (Correct answer)
- Better electrical conductivity
- Higher coefficient of thermal expansion
Correct answer: Approximately 45% lower density with comparable tensile strength
Titanium's density is about 4.5 g/cm³ versus steel's ~7.8 g/cm³, roughly 45% lighter, while high-grade titanium alloys match or exceed many steel grades in tensile strength.
Question 5: Which rubber compound is most suitable for Audi's turbocharger intake hoses that must withstand sustained temperatures up to 200°C?
- Natural rubber (NR)
- Ethylene propylene diene monomer (EPDM)
- Silicone rubber (VMQ) (Correct answer)
- Neoprene (CR)
Correct answer: Silicone rubber (VMQ)
Silicone rubber retains flexibility and sealing properties across a wide temperature range from -60°C to over 200°C, making it ideal for high-temperature turbo hoses.
Question 6: The tensile strength of a steel alloy is 800 MPa and its yield strength is 650 MPa. What does the difference between these values indicate?
- The steel has poor fatigue resistance
- The steel has a plastic deformation range before fracture, indicating ductility (Correct answer)
- The steel is unsuitable for structural use
- The steel requires heat treatment before use
Correct answer: The steel has a plastic deformation range before fracture, indicating ductility
The gap between yield and tensile strength represents the plastic deformation capacity of the material, which is a measure of its ductility and energy absorption ability.
Question 7: Audi uses phosphate coating on steel body parts before painting. What is the primary function of this process?
- To add decorative finish
- To improve corrosion resistance and paint adhesion (Correct answer)
- To increase surface hardness
- To reduce electrical conductivity
Correct answer: To improve corrosion resistance and paint adhesion
Zinc or iron phosphate coatings create a conversion layer that improves both corrosion protection and the mechanical bond between the steel substrate and subsequent paint layers.
AUDI Material Selection & Properties 3
Which heat treatment process is used to increase the hardness and wear resistance of Audi crankshaft bearing journals?