Engineering Materials - Study Mode
[#121] Addition of manganese to aluminium results in
Correct Answer
(B) Improvement of corrosion resistance
Explanation
Solution: When manganese is added to aluminum, its strength is increased slightly through solution strengthening and its strain hardening is also improved
[#122] Addition of copper to aluminium results in
Correct Answer
(C) One of the best known age and precipitation hardening systems
Explanation
Solution: The copper provides substantial increases in strength and facilitates precipitation hardening. The introduction of copper to aluminum can also reduce ductility and corrosion resistance.
[#123] Addition of lead and bismuth to aluminium results in
Correct Answer
(D) Improving machinability
Explanation
Solution: Addition of lead and bismuth to aluminium results in Improving machinability
[#124] Addition of silicon to aluminium results in
Correct Answer
(A) Improvement of casting characteristics
Explanation
Solution: addition of silicon is for ease of casting. Silicon is good in metallic alloys used for casting. This is because it increases the fluidity of the melt, reduces the melting temperature, decreases the contraction associated with solidification and is very cheap as a raw material
[#125] The hardness of steel primarily depends on
Correct Answer
(A) Percentage of carbon
Explanation
Solution: * Carbon's Role: The primary factor determining steel hardness is the amount of carbon it contains. More carbon generally leads to higher hardness. * Why Not the Others? * Percentage of alloying elements : Alloying elements (like chromium, nickel, etc.) can increase hardness, but their influence is secondary to carbon. They mostly affect other properties like corrosion resistance or strength. * Heat treatment employed : Heat treatment (like quenching, tempering) significantly alters hardness, but it primarily works by changing the microstructure of the steel, which is influenced by the carbon content. A steel with low carbon will not achieve very high hardness even with aggressive heat treatment. * Shape of carbides and their distribution in iron : Carbides (compounds of iron and carbon) are important, and their shape and distribution certainly affect hardness. But, the amount of carbon available to form these carbides is the fundamental control . In summary , while other factors play a role, the percentage of carbon is the most important and direct determinant of steel hardness.