Mechanism of surface hardness enhancement of aluminum alloy 2024-T3 by laser-induced plasma electrolyte jet machining

Abstract

Laser-induced plasma electrolyte jet machining (LIPEJM), as an efficient machining method with low machining deformation and no environmental pollution, has potential applications in the forming machining of aerospace thin-walled components. However, the change in surface hardness after LIPEJM remains unclear. This study utilized the nanoindentation technique to directly measure unmachined aluminum alloy 2024-T3 substrates, traditional electrolyte jet machining (EJM) and LIPEJM surfaces. The results showed that the hardness of the LIPEJM surface increased by 38.29 % compared to EJM, which was related to the laser-induced thermal and force effects. The laser-induced thermal effects, observed through an increase in the surface oxide layer at a laser energy density of 122.65 J/cm², contribute significantly to this enhancement. Additionally, a machining vibration monitoring device reveals the effects of laser-induced force during the machining process, providing insights into the underlying mechanisms. Grain refinement, induced by both thermal and mechanical impacts from the laser, is identified as the primary mechanism for surface hardness improvement. The laser-induced force exceeds the dendrite strength at high temperatures, resulting in fragmentation and increased equiaxial crystal formation sites. Furthermore, the laser-induced force effect temporarily elevates the melting point, increasing supercooling and promoting dynamic nucleation of non-uniform phases.