What does the term 'cooling of pure metal' refer to?

The term 'cooling of pure metal' refers to the reduction of temperature until the metal solidifies. This process is crucial in metallurgy and materials science because as a pure metal cools, it transitions from a liquid to a solid state. During this cooling process, the atoms in the liquid metal lose energy and begin to arrange themselves into a fixed structure, which is a solid.

This solidification process is essential in manufacturing and shaping metals, as it defines the physical and mechanical properties of the final product. Understanding the cooling rates and solidification mechanisms is crucial in applications such as casting, welding, and forging, where the characteristics of the metal can significantly affect the performance of the final product.

The other options do not accurately reflect the concept of cooling in terms of metallurgy. Changes in color pertain to different phenomena, while introducing impurities is related to altering melting points rather than the cooling process itself. Mechanical processing involves shaping metals but does not specifically refer to the cooling process.