This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Magnesium Alloys”.
1. Pure magnesium melts at what temperature?
Explanation: The temperature at which the pure form of magnesium gets ignited by itself is 473°C, and the temperature at which magnesium in its purest form is found to melt is 650°C.
2. Which of the following metals is least used in making magnesium alloys?
Explanation: Magnesium metal in itself is not one of the strongest metals and is hence adulterated with other materials to form strong alloys. Among the following, aluminium, zinc and manganese are highly used in making magnesium alloys.
3. Which of the following can be the casting temperature for magnesium alloys?
Explanation: When it comes to casting of magnesium alloys, the casting temperatures have to be kept in real control, that is, if the temperatures go too high, the metal might catch fire. The temperature range for casting magnesium alloys is 720°C to 800°C.
4. Which of the following is not a property of a magnesium alloy?
a) High damping capacity
b) High electrical conductivity
c) Good fatigue strength
d) High thermal resistivity
Explanation: Magnesium on getting mixed with other elements starts possessing many different properties. It contains good damping capacity, good electrical conductivity and good fatigue strength, but not, thermal resistivity.
5. What is the color of pure magnesium metal?
Explanation: The purest form of magnesium is considered to be in its weakest form, and hence other elements are added in it to enhance its quality. The physical qualities too change on addition of other elements. Originally, the color of pure magnesium metal is silvery white.
6. What should be the temperature of the mixture while alloying takes place?
Explanation: During the mixture getting processed, first the magnesium is melted, and then zinc metal is added. Aluminum is mixed in it through stirring. While this is happening, it has to be ensured, that the complete alloying process takes place at 700°C.
7. In magnesium alloys, what is the maximum amount of allowed aluminum?
Explanation: Magnesium alloys are basically a composition of various metals mixed with magnesium to improve its physical, chemical, mechanical and thermal properties. In this, the maximum allowable aluminum that can be added is only 11%.
8. What should the temperature ideally be to remove the casting after making of magnesium alloys?
a) Below 450°C
b) Below 300°C
c) Below 350°C
d) Below 300°C
Explanation: It is always advisable that, the castings should never be removed too quickly, as it might lead to distortion of the cast, because it is still hot. Therefore, when the temperature of the cast is below 300°C, the magnesium alloy cast can be removed.
9. In grain refinement process, only hexachlorobenzene is used.
Explanation: In grain refinement process, there is another process called carbon inoculation, in which, tablets of organic compounds are used, namely hexachlorobenzene and hexachloroethane.
10. Magnesium alloys have a low strength to weight ratio.
Explanation: Magnesium alloys possess many desirable mechanical, physical and thermal properties, which may help in better casting processes. One of these property is a high strength to weight ratio.
11. In sand casting of magnesium alloys, what is the amount of silica sand used in an American mix?
a) 80 lb
b) 90 lb
c) 100 lb
d) 110 lb
Explanation: It is mainly observed that, magnesium alloys are manufactured with the help of sand molds only. The amount of silica sand used in magnesium alloys is 100 lbs in both British mix and American mix.
12. In sand casting of magnesium alloys, what is the amount of bentonite sand used in a British mix?
a) 3 lb
b) 4 lb
c) 5 lb
d) 6 lb
Explanation: In the production of magnesium alloys, there are variety of sands employed. For this, bentonite sand has to be used for the sand casting of the alloys. The amount of bentonite sand used is 4 lbs in both British as well as American mix.
Sanfoundry Global Education & Learning Series – Casting, Forming and Welding.
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