# Interface Block and Microstructure Evolution in Ultrasonic Welding of Aluminum

## TL;DR

This paper studies how ultrasonic welding creates strong bonds in aluminum by analyzing interface block and microstructure changes during the process.

## Contribution

A new concept called 'Interface Block' is introduced to explain metallurgical bonding in ultrasonic additive manufacturing.

## Key findings

- LMD increases with welding time and decreases with welding pressure.
- Surface deformation obstruction leads to non-straight interfaces that enhance bonding.
- Recrystallization occurs at the joint interface after plastic deformation.

## Abstract

Ultrasonic welding, as a solid-state connection technology, has attracted considerable attention. The traditional ultrasonic welding sonotrode is not conducive to the study of the bonding mechanism of a straight interface, while the ultrasonic additive sonotrode does not have this problem. In this study, a special ultrasonic welding sonotrode was designed to form the joint, which is identical to ultrasonic additive manufacturing, to reveal its interfacial bonding mechanism between layers. Firstly, the linear metallurgical bonding density (LMD) of the joint is found to be positively correlated with welding time and negatively with welding pressure. Furthermore, the joint interface undergoes recrystallization after intense plastic deformation, with the obstruction of surface deformation by interface block resulting in the formation of a non-straight interface, which is beneficial to the formation of metallurgical bonding. Finally, a new concept of “Interface Block” was proposed, which can be applied to explain the formation of metallurgical bonding at the interface in ultrasonic additive manufacturing.