High Resolution Transmission Electron Microscopy of Aluminum/Mo-Coated Glass Substrate Interface Bonded by Ultrasonic Wire Welding

Abstract

Ultrasonic welding is an attractive joining method, because bonding is quickly obtained without extra heat or welding metal. Thus far, there have been several researches about the bonded interface structure and process of the ultrasonic welding. However, atomic structure analysis of the bonded interface was limited and sometimes controversial results were obtained. Besides, there were only few studies about application of the ultrasonic welding to Al/Glass substrates and detailed bonding mechanism was unclear. In this report, the ultrasonic bonded interface between an Al wire and a Mo coated glass substrate was observed by high resolution transmission electron microscopy and the bonding mechanism was discussed. The bonded sample was cut perpendicular to the interface and, the atomic structure and chemical composition of the cross-section of the sample were analyzed. Grains in a Mo layer on the glass observed before bonding extended perpendicular to the glass substrate and terminated with nano sized pyramids. Structure of Mo grains remained unchanged after the bonding. Around the interface between Al and Mo, several dislocations and Al sub-grains were produced in Al and no intermetallic compounds were observed. Al and Mo lattices were directly connected at the interface. This indicates that dislocations generated at the interface moved to form low angle grain boundaries during a recovery process without intermetallic formation. During the ultrasonic welding process, the pyramids of Mo surface were considered to work effectively to break a native oxide and produce the bonded interface.