Cast aluminium alloys are widely utilized in various industrial applications due to their favourable properties. A comparative analysis of fracture surfaces for EN AC 5083 cast aluminium alloy specimens processed in a single-pass by friction stir processing (FSP) and submerged friction stir processing (SFSP) has been carried out in this paper. Fracture surface evaluation involves mechanical tensile tests, microscopic investigations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to analyse the microstructure, fracture characteristics and elemental composition of the processed material. The findings provide valuable insights into the fracture behaviour of EN AC 5083 aluminium alloy FSP and SFSP processed, contributing to further research on optimizing friction stir processing techniques in ambient and submerged process conditions.

In recent years, the field of ultrasound has seen remarkable advancements, mainly due to its close ties with the mechanical industry, recognized as the most dynamic industry of the last forty years. The application of ultrasound in the mechanical field has been guided by the advantages it offers, while the most significant advancements are related to the relatively low surface temperature compared to eroded surfaces, the evident localized accumulation, and the possibility of achieving dimensional improvements ranging from sub-millimeter values to centimeter values.

Ultrasonic welding is a process that has been in continuous development since it was first introduced in the 1940s. The process is widely used to join or reform plastic or metal materials using mechanical vibrations propagated at frequencies ranging from 20.000 Hz to gigahertz levels. These vibrations produce heat that melts the materials to be welded at their contact surface. In addition to the heat produced by the vibrations, a preset pressure is applied from the control panel of the welding machine to ensure perfect contact between the welded parts.[1] The ultrasonic welding process is time-efficient, taking less than 0.2 seconds in some cases, and does not damage the outer surface of the parts. The whole paper is structured in two parts, one theoretical and one practical, these parts are divided into six chapters. The first chapter of the paper explains the propagation process of ultrasound and what it actually is, as well as a brief history of ultrasound. In the second chapter there are generalities about ultrasonic welding and how this process is carried out and a history of ultrasonic welding. The third chapter introduces us to the subject of the paper, namely ultrasonic welding of plastics. Chapter four deals with the materials used to produce seat belts and their evolution over time. In chapter five we present all the equipment used for the case study. Chapter six is the case study and the explanation of all the steps performed to find out some results about ultrasonic welding of seat belt samples. Finally, I presented the conclusions drawn from the whole research process and the results obtained for the ultrasonic welding process of seat belts.