FERROUS & NON - FERROUS ALLOYS SET 07

FERROUS & NON - FERROUS ALLOYS SET 07

1. 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
 

Answer: b
 

Explanation:In the production of magnesium alloys, there are a 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.
 

2. In general, magnesium alloy components tends to have fine grain structure in it.
a) True
b) False
 

Answer: b
 

Explanation: In general, magnesium alloy component tends to have coarse grain structure unless some suitable procedures are taken to insure the formation of fine grains. The procedure involves superheating of molten metal to 2500 or 3000 ⁰C. And then after holding it there for a certain period of time, it cools down to the desired temperature and pouring operation takes place without any delay.
 

3. Magnesium is a very light material that can be suitable in aircraft applications.
a) True
b) False
 

Answer: a
 

Explanation: Magnesium is very light metal in comparison with other structural metals. Magnesium is commonly used in a wide range of markets and applications, from automobiles to aircraft applications. In most of the cases of manufacturing, weight reducing is the primary objective for magnesium alloys.
 

4. Magnesium metal is very light material, but not lighter than aluminium metal.
a) True
b) False
 

Answer: b
 

Explanation: Magnesium is mainly distinguished by its low density, which is nearly about 25% of steel and about 60% of the aluminium metal. This property makes magnesium to use for very lightweight construction. In expensive cars, it is highly used in the construction of crankcase and in other parts to increase power to weight ratio.
 

5. Magnesium cannot be used extensively for precision casting applications.
a) True
b) False
 

Answer: a
 

Explanation: Magnesium cannot be used extensively for precision casting applications because it is highly reactive with silica containing constituents like plaster or other mould materials. Silica is mostly present in slurry in which it acts like binding material. Reaction of magnesium with silica produces magnesium oxide and magnesium silicide which may imparts defects in the casting components.
 

6. Adding of zirconium in magnesium metal results in the formation of magnesium-zirconium alloy of enhanced ductility.
a) True
b) False
 

Answer: b
 

Explanation: The grain size is highly affected by adding zirconium in magnesium metal. Addition of less than 0.6% zirconium in magnesium is sufficient to obtain grain size less than 80 microns in casted components. This further increases hardness in the material due to formation of fine grains and ductility also decreases simultaneously.
 

7. Inhibitors are generally used in mould to avoid reaction of magnesium with moulding materials.
a) True
b) False
 

Answer: a

 

Explanation: When moulding materials like silica, moisture and binders make contact with magnesium, the reaction takes place which arise problems in the castings of magnesium alloys. To avoid reaction, the mould is modified by using some techniques like drying and by including inhibitors in the moulding materials.
 

8. Which of the following compounds can be used as an inhibitor in moulding materials for avoiding chemical reaction with magnesium alloys?
a) Sodium silicate
b) Water
c) Hydrogen silicate
d) Potassium borofluoride
 

Answer: d
 

Explanation: Moulding materials are effectively inhibited by adding 1 to 2 percent of potassium borofluoride. And controlling of inhibitor content in moulding materials is very important because they can affect setting times. Sometimes elimination of silica content from moulding materials also takes place to avoid chemical reactions.
 

9. Magnesium metal possesses better noise and vibration damping characteristics than aluminum.
a) True
b) False
 

Answer: a
 

Explanation: Magnesium is the lightest material in all the engineering materials. It has good ductility, better noise and vibration damping features than aluminium and also has excellent cast-ability. Alloying of magnesium metal with aluminium, manganese increases the strength of the components and also reduces the weight of the casted parts, so magnesium alloys are very important materials for applications where weight saving is a dominant objective.
 

10. Magnesium alloys do not require any special coating as they are self protective from corrosion.
a) True
b) False
 

Answer: b
 

Explanation: Different types of coatings are applied to magnesium alloys to increase corrosion resistance. Coatings for magnesium alloys are applied by using hexavalent chromium material which provides excellent protection, but do not considered as eco-friendly. To avoid environmental problems, Teflon resin is basically applied instead of any other coatings.