This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Aluminium and its Alloys, Zinc and its Alloys”.
1. What is the melting point of pure aluminum?
a) 520-600oC
b) 600oC
c) 800oC
d) 950oC
View Answer
Explanation: Aluminum is an element which is available in abundance on earth. Its melting point is 600oC. Pure aluminum has low strength, due to which it is added with alloying elements.
2. What is the tensile strength of aluminum?
a) 122.5 GPa
b) 220 MPa
c) 70.5 GPa
d) 45 MPa
View Answer
Explanation: Pure aluminum has a low tensile strength of 45 MPa and Young’s modulus of 70.5 GPa. Copper has a tensile strength of 220 MPa and Young’s modulus of 122.5 GPa.
3. Compared to copper, how is the electrical conductivity of aluminum?
a) Higher
b) Lower
c) Equal
d) Zero
View Answer
Explanation: When equal weights are compared, aluminum is a better conductor than copper. It was found that aluminum conducts 201% more current than copper.
4. _______ is coated onto aluminum to improve its soldering ability.
a) Magnesium
b) Lithium
c) Tin
d) Copper
View Answer
Explanation: To improve soldering or joining ability of aluminum, it is coated with tin and then plated with other metals. Magnesium, lithium, and copper are better suited to form alloys to serve various purposes.
5. Which aluminum alloy is known as aircraft aluminum?
a) 6061
b) 6063
c) 7068
d) 7075
View Answer
Explanation: Aluminum alloy 7075 consists of zinc as its primary element, along with a bit of magnesium and copper. Due to its high strength and good corrosion resistance, it is often used in aircraft, and also known as aerospace aluminum. However, the other alloys are also employed in a few aerospace functions and structures.
6. Which of the following is not a classification of aluminum alloys?
a) Crucible alloys
b) Wrought alloys
c) Cast alloys
d) Heat-treatable alloys
View Answer
Explanation: Aluminum alloys are categorized into wrought alloys, cast alloys, heat-treatable, and non heat-treatable alloys. An example of each is 2.5% Mg, 0.25% Cr, and rest Al (wrought), 12% Si and rest Al (cast), 0.4-0.9% Mg, 0.3-0.7% Si, and rest Al (heat-treatable), and (0.8-1.5% Mn and rest Al (non heat-treatable).
7. Which of these is not a property of duralumin?
a) High strength
b) 1/3 the weight of steel
c) Excellent casting and forging abilities
d) Poor machinability
View Answer
Explanation: Duralumin contains 4% Cu along with 0.4-0.7% of both Mn and Mg. This provides it excellent casting and forging abilities and high strength while maintaining only 1/3 of the weight. It also possesses high machinability.
8. Which among the following is an example of a non heat-treatable alloy?
a) Al-Cu
b) Al-Li
c) Al-Mg-Si
d) Al-Mn
View Answer
Explanation: Non heat-treatable alloys can be strengthened by cold-working operations. Al-Mn alloy is an example of a non heat-treatable alloy. The leftover choices are examples of heat-treatable alloys. Duralumin and Y-alloy are the important Al-Cu alloys.
9. Artificial aging process takes place at a temperature range of ________
a) 190-260oC
b) 260-300oC
c) 300-350oC
d) Room temperature
View Answer
Explanation: Ageing of alloys at 190-260oC accelerates the aging process and reduces the overall time. This phenomenon is known as artificial aging. Natural aging occurs at room temperature.
10. What happens when the maximum strength is achieved by the aging process?
a) Precipitate hardening
b) Age hardening
c) Over-aging
d) Natural ageing
View Answer
Explanation: As the aging temperature decreases, the maximum strength increases and reaches its peak. At the peak strength, the strength starts to decrease. This is referred to as over-aging.
11. Which of these is not a stage in precipitation hardening treatment?
a) Solution treatment
b) Tempering
c) Quenching
d) Ageing
View Answer
Explanation: The alloy is heated to a certain temperature and treated at that temperature. Then it is quenched (rapid cooling) and finally heated below solvus temperature; this is known as aging.
12. How much copper is present in Y-alloys?
a) 4%
b) 2%
c) 1.5%
d) 1%
View Answer
Explanation: Y-alloy is an important type of Al-Cu alloy. Similar to duralumin, it contains 4% copper. Addition of 2% nickel and 1.5% magnesium is done to make Y-alloys.
13. What is the melting point of zinc?
a) 419oC
b) 600oC
c) 907oC
d) 950oC
View Answer
Explanation: Zinc has a relatively low melting point of 419. 5oC. Its boiling point, on the other hand, is at 907oC. The melting point of aluminum is 600oC.
14. With the addition of which element, does zinc create resistance to creep?
a) Pb
b) Cd
c) Mg
d) Cu
View Answer
Explanation: When magnesium is added to copper, it increases its resistance to creep. Lead affects intercrystalline corrosion, while cadmium improves hardening effect. Copper makes the Cu-Zu alloys more ductile.
15. The most common casting process for zinc alloys is _______
a) Sand casting
b) Die casting
c) Investment casting
d) Centrifugal casting
View Answer
Explanation: Die casting is generally employed for zinc alloys. These die-castings range from a few grams to 20 kilograms. Zinc base dies casting alloys to find applications in hardware items like car body, grills etc.
16. What is the appearance of zinc?
a) Bluish-grey
b) Red
c) Yellow
d) Green
View Answer
Explanation: Zinc is a metallic element whose color looks blue and grey. It has a lustrous property and is diamagnetic in nature.
17. What is the temperature at which zinc become malleable
a) <100 oC
b) 100-150 oC
c) >210 oC
d) 419 oC
View Answer
Explanation: Zinc is brittle at most temperatures. However, it becomes malleable between 100 and 150 oC. Above 210 oC, it becomes brittle again, reaching its melting point at 41 oC.
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