AME 2 Q5

C. The increase in strength of aluminum due to plastic deformation.

Work hardening, also known as strain hardening, is the process by which a metal's strength increases as it is subjected to plastic deformation. This occurs because the metal's crystal structure changes as it is shaped, making it more resistant to further deformation.

Why the other answers are incorrect:

• A. A process of heating aluminum to increase its strength. This describes heat treatment, not work hardening. Work hardening occurs through deformation, not heat.
• B. A process of cooling aluminum rapidly to increase its hardness. This describes quenching, a heat treatment process. Work hardening is related to plastic deformation.
• D. The process of adding impurities to aluminum to improve its properties. This describes alloying, not work hardening. Work hardening is a result of the metal's internal structure changing due to deformation.

Work hardening is a physical process that occurs when a metal, like aluminum, is shaped or deformed. It doesn't involve heat treatment or adding impurities.

B. Increases strength, decreases ductility.  

1. ENGINEERING FUNDAMENTALS Refresh: Ductility, Strain, and Toughness | Fictiv

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Work hardening increases the strength of aluminum by hindering the movement of dislocations within the metal's crystal structure. However, this process also reduces the metal's ability to deform without fracturing, leading to decreased ductility.

Why the other answers are incorrect:

• A. Increases both strength and ductility. While strength increases, ductility decreases during work hardening.  
  1. [Solved] The ductility of a material with work hardening - Testbook

  

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• C. Decreases both strength and ductility. This is the opposite of what happens during work hardening. Strength increases.
• D. Increases ductility, decreases strength. Ductility decreases during work hardening, while strength increases.  
  1. [Solved] The ductility of a material with work hardening - Testbook

  

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B. Grain size decreases and elongated grains form, leading to increased strength.  

1. Effects of Grain Size: Strength, Ductility, Hardness - Vaia

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When aluminum undergoes work hardening, the grains within its structure become smaller and elongated due to the plastic deformation. This change in grain structure increases the strength of the material by hindering the movement of dislocations, which are defects within the crystal lattice that allow for plastic deformation.

Why the other answers are incorrect:

• A. Grain size increases, leading to increased strength. This is opposite to what happens during work hardening. Grain size actually decreases.
• C. The crystal structure remains unchanged, but the metal becomes denser. The crystal structure changes significantly during work hardening, and density is not a primary factor in this process.
• D. The aluminum atoms rearrange to form a new crystal structure. While there is some rearrangement at the atomic level, the overall crystal structure doesn't change dramatically. The primary change is in the grain size and shape.

Work hardening is primarily characterized by a decrease in grain size and the formation of elongated grains, which together contribute to the increased strength of the material.

B. By heating the aluminum to a specific temperature, holding it there, and then cooling it slowly.

Annealing is a heat treatment process that involves heating a metal to a specific temperature, holding it there for a sufficient time, and then cooling it slowly. This process softens the metal and improves its ductility. While it's challenging to achieve precise temperature control and slow cooling on a moving vessel, it's theoretically possible with careful planning and equipment.

Why the other answers are incorrect:

• A. By rapidly cooling the aluminum from a high temperature. This describes quenching, which is used to harden metal, not anneal it.

   

  1. Metal Hardening | Metal Quenching | Metal Tempering - Metlab | Heat Treating

  

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• C. By deforming the aluminum to increase its strength and ductility. This describes work hardening, which is the opposite of annealing.
• D. By adding impurities to the aluminum to change its properties. This describes alloying, not annealing. Annealing is a heat treatment process.  
  1. Annealing is a heat treatment process which alters the microstructure... - Bodycote

  

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Annealing involves heating the metal to a specific temperature, holding it there, and then cooling it slowly to soften it and improve its ductility.