Ultrasonic welding (UW) is an important joining technique in the electrical industry. Molecular dynamic simulation has been shown to possess several advantages for revealing the evolution of the atomic-scale structure and the interpretation of diffusion mechanisms at the microscopic level. However, voids associated with the understanding of microstructure evolution in the weld zone and dynamic processes that occur during ultrasonically welded materials still exist, and no UW studies at the atomic scale have so far been reported. In this study, molecular dynamic simulations of UW between Al and Cu were performed to investigate the diffusion behaviors of Al and Cu atoms. The results confirmed the occurrence of asymmetrical diffusion at the Al/Cu interface during UW. Meanwhile, recovery was noticed in the disordered Al blocks at low temperature. The thickness of the diffusion layer increased with the welding time. For relatively long welding times (1 ns), the concentrations of Al and Cu revealed the appearance of phase transitions. In addition, the diffusion during UW was identified as a dynamic and unsteady process. The diffusion coefficient was much larger than that underwent during the steady diffusion process despite the low interfacial temperature (below 375 K), which was mainly attributed to shear plastic deformation at the interface.

Amorphous alloys have emerged as important materials for precision machinery, energy conversion, information processing, and aerospace components. This is due to their unique structure and excellent properties, including superior strength, high elasticity, and excellent corrosion resistance, which have attracted the attention of many researchers. However, the size of the amorphous alloy components remains limited, which affects industrial applications. Significant developments in connection with this technology are urgently needed. Laser welding represents an efficient welding method that uses a laser beam with high energy-density for heating. Laser welding has gradually become a research hotspot as a joining method for amorphous alloys due to its fast heating and cooling rates. In this compact review, the current status of research into amorphous-alloy laser welding technology is discussed, the influence of technological parameters and other welding conditions on welding quality is analyzed, and an outlook on future research and development is provided. This paper can serve as a useful reference for both fundamental research and engineering applications in this field.

In this study, butt welds of QP980 steel were produced using small laser spot (0.1 mm) oscillating welding. The effect of beam oscillation with a circular trajectory on weld morphologies, microstructures, and mechanical properties was characterized. As the oscillating amplitude rose, the energy accumulation range enlarged, and the energy peak value was decreased, leading to the appearance of the cross-section changing from a nail-like shape to a cup-cone-like shape and then to a W-type shape. The weld zone is divided into the fusion zone, inner heat-affected zone, and outer soften zone. The fusion zone and inner heat-affected zone are full of typical lath martensite and have the highest hardness. The soften zone is composed of pre-existing martensite, temper martensite, ferrite, and retained austenite and has the lowest hardness. Compared to laser welding, beam oscillation could reduce the pre-existing block martensite to decompose, leading to a narrower width and higher hardness soften zone. Although the width of the fusion zone and soften zone increases with the oscillation amplitude, all welded samples failed at the base metal with 97% joint efficiency.

Eutectic structures in Ag-based brazing filler metals play an important role in improving the properties of alloys and brazed joints. The typical microstructures and morphological evolution of Ag-Cu eutectic structures in Ag-based brazing filler metals solidified at various cooling rates and with the addition of different Sn contents were investigated. The formation mechanisms of anomalous eutectic structure (AES) and the morphological transition from lamellar eutectic structure (LES) to AES were elucidated. The microstructures in alloys solidified at a slow cooling rate and with low Sn content consisted of the full AES, which was attributed to the remelting of the LES during recalescence. Increasing the Sn content and cooling rate promoted the formation of developed Ag dendrite, eutectic dendrite with branches, and AES with large dimensions. The AES in rapidly solidified filler metals with a high Sn content was ascribed to the decomposition of the Ag-rich dendrite skeleton and the growth of Cu-rich between the ternary dendrite arms.

In this paper, the interfacial stabilities of six different stacking interface configurations of Ni(100)/Ni₃Al(100) eutectic structures with AlNi termination and Ni termination are calculated by using first-principles methods. The calculated adhesion work and interface energy indicate that the “Center” site stacking interface configurations are more stable than the “Top” and “Bridge” site stacking interface models. The partial density of states (PDOS) and the charge density difference confirm that the bonding characteristic of the Ni-terminated “Center” site stacking interface of the Ni(100)/Ni₃Al(100) eutectic structure is metallic, while the bond at the AlNi-terminated “Center” site interface is a combination of covalent and metallic bonds. A comprehensive analysis of the interface energy, PDOS and charge density difference confirms that the AlNi-terminated “Center” site stacking interface configuration of the Ni(100)/Ni₃Al(100) eutectic structure is the most stable eutectic interface model.