Ultrasonic welding of metal is a technology that uses high-frequency ultrasonic vibration to realize welding. In the welding process, the welding head transfers the kinetic energy of high-frequency vibration to two metal surfaces to be welded, so that they rub against each other. The heat generated by this friction can locally heat the metal surface, thus promoting the diffusion and recrystallization of metal molecules. In this way, the welding head can firmly connect two metal objects together. Recrystallization thickness is an important parameter in ultrasonic welding of metals. Recrystallization thickness refers to the depth or thickness of metal recrystallization in the welding area. In order to ensure the strength and reliability of welding, the thickness of recrystallization should be at least 0.01mm. This is because the thin recrystallization layer can not provide enough bonding strength, which leads to the brittleness or fracture of the weld.