Final answer:
Solid-state welding heats the material until it softens enough to be deformed plastically without reaching its melting point, making it pliable for joining.
Step-by-step explanation:
Solid-state welding involves joining materials without melting them. Unlike fusion which is a process where a solid becomes a liquid at its melting point, solid-state welding relies on the material being heated until it is softened but not fully melted. As defined by the properties of solids and the process of melting and freezing, the heating in solid-state welding does not cause the solid to transition into liquid, but rather induces plastic deformation.
This plastic deformation occurs when the material is heated to a point where it softens and becomes pliable enough to be joined with another material under pressure.