How do solid-phase welding processes join metals without melting them?

Solid-phase welding processes join metals without melting the base material or adding filler metal. Instead, these methods rely on the application of pressure to achieve coalescence, typically supplemented by heat.1

The specific mechanisms used to facilitate this bonding include:

• Pressure: This is a fundamental requirement in all solid-phase processes to bring the metal surfaces into intimate contact.1
• Heat: While the base material does not reach a molten state, heat is often provided to assist the process. For example, frictional heat is generated in friction welding and ultrasonic joining, while furnace heating is commonly used in diffusion bonding.12

By avoiding the molten state, these processes bypass the formation of a cast structure and the associated risks of oxidation or contamination that can occur in fusion welding. The integrity of the joint is instead achieved through the controlled application of force and thermal energy, which allows the metallic structures to bond at the interface.1