1.
1XX.X designation is given to ___________ type of aluminium alloys.
Correct Answer
B. Cast
Explanation
The 1XX.X designation is given to cast type of aluminium alloys. This means that alloys with this designation are specifically used for castings, which are produced by pouring molten metal into a mold and allowing it to solidify. Cast aluminium alloys have different properties compared to other types of aluminium alloys, making them suitable for applications where casting is required, such as automotive parts, aerospace components, and household appliances.
2.
Which of these is unused in 4-digit designation of aluminium alloys?
Correct Answer
D. 6XX.X
Explanation
The 6XX.X designation is unused in the 4-digit designation of aluminium alloys.
3.
Magnesium decreases __________ of Al alloys.
Correct Answer
C. Density
Explanation
Magnesium decreases the density of Al alloys. When magnesium is added to aluminum alloys, it forms a solid solution, which leads to a decrease in the overall density of the alloy. This is because magnesium has a lower atomic mass than aluminum, resulting in a lighter material. The reduced density can be advantageous in various applications where weight reduction is desired, such as in the automotive and aerospace industries.
4.
Cu is usually kept ___________ in non-heat treatable wrought alloys to avoid formation of insoluble intermetallic phases.
Correct Answer
C. <0.3
Explanation
Cu is usually kept
5.
The strongest aluminium alloys are produced by ___________ .
Correct Answer
B. Age hardening
Explanation
Age hardening is a process used to strengthen aluminium alloys by subjecting them to a combination of heat treatment and rapid cooling. This process involves the precipitation of small particles within the alloy, which hinders the movement of dislocations and increases the strength of the material. Age hardening is particularly effective in strengthening aluminium alloys, making them stronger and more resistant to deformation and wear.
6.
____________ causes hot cracking in 5XXX alloys.
Correct Answer
A. Sodium
Explanation
Sodium causes hot cracking in 5XXX alloys. Hot cracking, also known as solidification cracking, occurs during the solidification process of the alloy. Sodium is known to have a detrimental effect on the solidification process, leading to the formation of cracks. It has a low melting point and can easily penetrate the grain boundaries, causing weakening and cracking of the alloy. Sodium is particularly problematic in 5XXX alloys, which are commonly used in structural applications and require high strength and good weldability. Therefore, the presence of sodium can significantly compromise the mechanical properties of the alloy, making it susceptible to hot cracking.
7.
Nickel and Chromium _________ and ________ corrosion resistance respectively.
Correct Answer
B. Decrease, improve
Explanation
Nickel and chromium are both known for their corrosion resistance properties. Nickel helps to decrease corrosion by forming a protective layer on the surface of the metal, preventing it from coming into contact with corrosive elements. On the other hand, chromium improves corrosion resistance by forming a thin oxide layer on the surface of the metal, which acts as a barrier against corrosion. Therefore, the correct answer is "decrease, improve" as nickel decreases corrosion and chromium improves corrosion resistance.
8.
Non heat-treatable alloys can be ________ to increase strength.
Correct Answer
C. Cold worked
Explanation
Cold working is a process in which a metal is deformed at room temperature, usually through processes like rolling, bending, or drawing. This deformation causes dislocations in the crystal structure of the metal, which increases its strength. Therefore, cold working can be used to increase the strength of non heat-treatable alloys.
9.
Grain refinement in Al alloys is achieved by :
Correct Answer
D. All of the above
Explanation
Grain refinement in Al alloys can be achieved through multiple methods. Fast cooling of the melt helps in reducing the grain size by preventing the growth of grains during solidification. Adding grain refinement elements, such as titanium or zirconium, promotes the formation of fine grains in the alloy. Cold working, which involves plastic deformation of the material at low temperatures, also contributes to grain refinement by breaking down existing grains and creating new smaller grains. Therefore, all of the mentioned methods - fast cooling of melt, adding grain refinement elements, and cold working - can be used to achieve grain refinement in Al alloys.
10.
Silicon :
Correct Answer
D. None of the above
Explanation
Silicon is known for its ability to enhance fluidity and corrosion resistance in materials. However, it does not increase the thermal expansion coefficient. Therefore, the correct answer is "none of the above" as silicon does not reduce fluidity, corrosion resistance, or increase the thermal expansion coefficient.