Plasticity refers to the ability of metal materials to produce permanent deformation (plastic deformation) without being damaged by breaking deformation under the action of load external force. When a metal material is stretched, its length and cross-sectional area will change. Therefore, the plasticity of a metal can be measured by two indicators: the elongation of the length (elongation) and the shrinkage of the section (shrinkage of area).
The greater the elongation and reduction of area of a metal material, the better the plasticity of the material, that is, the material can withstand greater plastic deformation without breaking. Generally, metal materials with an elongation greater than 5% are called plastic materials (such as low carbon steel, etc.), and metal materials with an elongation less than 5% are called brittle materials (such as gray cast iron, etc.).
A material with good plasticity can produce plastic deformation in a large macroscopic range, and at the same time as plastic deformation, the metal material is strengthened by plastic deformation, thereby improving the strength of the material and ensuring the safe use of parts. In addition, materials with good plasticity can be smoothly processed by certain forming processes, such as stamping, cold bending, cold drawing, and straightening. Therefore, when selecting metal materials for mechanical parts, certain plasticity indexes must be met.
