Influence of Augmentation Compositions and Confinement Layers on Flyer Velocity in Laser Impact Welding

Small-scale impact welding may have several advantages over rivets: the strength can be higher, it can be applied right at the edges in lap joints, and it can be lighter and more easily installed if simple systems can be developed. Laser Impact Welding (LIW) is compact and simple, adapting the technologies of laser shock peening. It is limited in terms of the energy that can be delivered to the joint. Augmented Laser Impact Welding (ALIW) complements optical energy with a small volume of an exothermic detonable compound and has been shown to be an effective welding approach. The scope of this study is extended to build upon previous work by investigating varied augmentation chemistries and confinement layers, specifically borosilicate glass, sapphire, and water. The evaluation of these compositions involved the use of two aluminum alloys: Al 2024 and Al 6061. Photonic Doppler Velocimetry (PDV) was utilized to measure the flyer velocity and assess the detonation energy. The findings indicated that adding micro-air bubbles (GPN-3 scenario) to the original GPN-1 enhanced the flyer velocity by improving the sensitivity, which promoted gas release during detonation. Hence, employing 1 mm thick Al 2024 as a flyer with GPN-3 enhances the flyer velocity by 36.4% in comparison to GPN-1, thereby improving the feasibility of using 1 mm thick material as a flyer and ensuring a successful welded joint with the thickest flyer ever welded with laser impact welding. When comparing the confinement layers, sapphire provided slightly lower flyer velocities compared to borosilicate glass. However, due to its higher resistance to damage and fracture, sapphire is likely more suitable for industrial applications from an economic perspective. Furthermore, the lap shear tests and microstructural evaluations confirmed that GPN-3 provided higher detonation energy, as emphasized by the tendency of the interfacial waves to have a higher amplitude than the less pronounced waves of the original GPN-1. Consequently, this approach demonstrates the key characteristics of a practical process, being simple, cost-effective, and efficient.