This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Magnesium and its Alloys”.
1. What is the specific gravity of magnesium?
a) 1.74
b) 2.7
c) 6.3
d) 8.9
View Answer
Explanation: Magnesium is a silvery-white metal which has a specific gravity of only 1.74. It also has a low weight of 1.73 gm/cu cm. The specific gravities of aluminum and copper are 2.7 and 8.9 respectively.
2. What is the melting point of magnesium?
a) 419oC
b) 650oC
c) 1091oC
d) 2562oC
View Answer
Explanation: Magnesium is a common element which has a melting point of 650oC and a boiling point of 1091oC. It weighs less than aluminum, iron, and steel. It has the lowest density among common structural elements.
3. Which of the following is not a property of magnesium?
a) Low strength
b) Vulnerable to corrosion
c) Expensive
d) Heavyweight
View Answer
Explanation: Pure magnesium is not used due to its low strength. It is also prone to corrosion, due to which it is usually painted on. Since magnesium is costly, it is used only in cases where weight is a priority. This comes to use due to its low weight.
4. Magnalium is an alloy of magnesium, ________
a) Nickel and Tin
b) Zinc and Tin
c) Nickel and Zinc
d) Zirconium and Zinc
View Answer
Explanation: Magnalium, although considered an aluminum alloy, may contain over 50% magnesium and small amounts of nickel and tin. They are commonly used for engineering applications and pyrotechnics.
5. How does a high amount of magnesium affect alloys?
a) Increases strength
b) Increases corrosion resistance
c) Lowers density
d) Becomes brittle
View Answer
Explanation: Alloys with around 50% magnesium are more brittle and prone to corrosion. However, lesser quantities (5%) result in increased strength, corrosion resistance, low density, and weldability.
6. Dow metal contains ______ of magnesium.
a) 0%
b) 5%
c) 50%
d) 90%
View Answer
Explanation: Dow metal is an alloy of magnesium which contains 90% magnesium, 10% aluminum, and a small amount of manganese. It is extremely lightweight and easy to weld and machine. They are commonly employed in automobile and aircraft applications.
7. Which of the following is a type of aluminum alloy with magnesium?
a) Mag-Thor
b) Magnox
c) Birmabright
d) Elektron
View Answer
Explanation: Birmabright is an aluminum alloy containing 1-7% magnesium and less than 1% manganese. They have good weldability and corrosion resistance to seawater. The leftover choices are a few magnesium alloys.
8. A magnesium alloy containing 3% rare earth metal exhibits which of the following characteristics?
a) Creep resistance up to 250oC
b) Good founding properties
c) Die-casting alloy
d) Good overall properties
View Answer
Explanation: A magnesium alloy containing rare earth metal (3%) is a type of cast alloy. It also contains 2.5% of zinc and 0.6% zirconium. It has a creep resistance up to 250oC. It is also pressure tight, weldable, and has excellent castability.
9. Which of the following alloys is used in nuclear reactors?
a) Elektron
b) Magnox
c) Mag-Thor
d) Pyrotechnics
View Answer
Explanation: Magnox is a magnesium alloy used for which is used to contain fission products in nuclear reactors. It stands for Magnesium Non-Oxidising. Elektron is mainly used in aerospace and race car applications, whereas Mag-Thor is used in the aerospace industry. Magnesium is used in pyrotechnics.
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