Engineering Materials

Non-Ferrous Materials

Fundamentals of non-ferrous materials for Mechanical Engineering and GATE & IES preparation.

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7 Active Questions

Answers & Explanations Included

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Question 1 of 7

Original Exam: GATE (2018)

Which of the following elements is primarily added to aluminium to create an alloy that can be precipitation hardened to high strengths typical of structural aerospace applications?

A. Copper B. Silicon C. Manganese D. Lead

✓ Correct Answer: A

Explanation:
Copper is the primary alloying element in the 2xxx series aluminium alloys (e.g., 2024). These alloys undergo precipitation hardening (age hardening) via the formation of Al2Cu (theta prime) precipitates, which significantly block dislocation movement and increase structural strength.

Difficulty: intermediate Type: conceptual

Question 2 of 7

Original Exam: IES (2021)

Anodizing of aluminium components is primarily carried out to achieve which of the following surface properties?

A. To increase electrical conductivity B. To form a thick, stable, and protective oxide layer (Al2O3) for corrosion resistance C. To induce compressive residual stresses on the surface D. To decrease the surface roughness significantly

✓ Correct Answer: B

Explanation:
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts, particularly aluminium. This artificially thickened Al2O3 layer improves corrosion resistance and wear resistance.

Difficulty: basic Type: application

Question 3 of 7

Original Exam: GATE (2015)

Which non-ferrous alloy exhibits a unique shape memory effect due to a thermoelastic martensitic transformation?

A. Cu-30%Zn (Cartridge Brass) B. Ni-Ti alloy (Nitinol) C. Al-4.5%Cu (Duralumin) D. Mg-6%Al (AZ61)

✓ Correct Answer: B

Explanation:
Nitinol (Nickel-Titanium alloy) is a well-known shape memory alloy. Its shape memory properties stem from a reversible, diffusionless, thermoelastic martensitic transformation between a high-temperature austenite phase and a low-temperature martensite phase.

Difficulty: intermediate Type: conceptual

Question 4 of 7

Original Exam: GATE (2020)

What is the primary microstructural constituent responsible for the high fluidic castability of a binary Al-Si alloy near 12 wt.% Silicon composition?

A. Hypereutectic primary Si crystals B. Eutectic mixture of alpha-solid solution and silicon phase C. Pure intermetallic Al3Ni compounds D. Single-phase alpha solid solution

✓ Correct Answer: B

Explanation:
The Al-Si system has a eutectic point at approximately 11.7-12.6 wt.% Si. Eutectic compositions melt and freeze at a single discrete low temperature, minimizing the freezing zone length, which drastically improves fluidity and castability while eliminating macrosegregation.

Difficulty: intermediate Type: conceptual

Question 5 of 7

Original Exam: IES (2019)

The addition of zinc to copper to form alpha-brass influences its mechanical properties primarily through which mechanism?

A. Dispersoid strengthening by stable carbides B. Solid solution strengthening by substitution of zinc atoms into the copper FCC lattice C. Martensitic shear transformation upon rapid quenching D. Coherent precipitate formation during aging

✓ Correct Answer: B

Explanation:
Zinc dissolves substitutionally in the Face-Centered Cubic (FCC) lattice of copper up to roughly 35 wt.%, producing alpha-brass. The size mismatch between Zn and Cu atoms creates localized lattice strain fields that restrict dislocation motion, resulting in solid solution strengthening.

Difficulty: basic Type: conceptual

Question 6 of 7

Original Exam: IES (2023)

Titanium alloys are highly favored in marine and bio-implant sectors predominantly because of:

A. Low production costs and easy machinability B. High magnetic susceptibility and thermal expansion coefficient C. Excellent biocompatibility and a highly stable passive TiO2 surface film D. Low specific strength coupled with high density

✓ Correct Answer: C

Explanation:
Titanium forms a highly stable, continuous, adherent, and protective titanium dioxide (TiO2) film instantly upon exposure to oxygen. This provides outstanding resistance to chloride-induced pitting in marine environments and body fluids, making it safe and biocompatible.

Difficulty: basic Type: application

Question 7 of 7

Original Exam: GATE (2017)

Babbitt metals are special non-ferrous alloys optimized for use in plain journal bearings. Their microstructural design typically consists of:

A. Hard intermetallic compounds embedded uniformly within a soft, ductile tin or lead matrix B. A fully brittle, single-phase intermetallic structure to maximize hardness C. Alternating macro-layers of pure copper and pure zinc plates D. Amorphous metallic glasses containing zero crystal boundaries

✓ Correct Answer: A

Explanation:
Bearing alloys like Babbitt metals require a combination of low friction, wear resistance, and conformability. The soft tin/lead matrix deforms slightly to redistribute local high-contact pressures and allows debris encapsulation, while the hard compounds (like SbSn or Cu6Sn5) support the structural load.

Difficulty: intermediate Type: conceptual