## 4 Results and Discussion
### The Effect of the LSP Process on the Crystalline State of the Electrodes  
Figure 6 displays the effects of the LSP process and pulse density on the crystalline state of the treated surface and sub-surface Al6061 T6 electrodes. There is an increasing intensity of the diffraction peaks, which is depicted by the texturing of the (111) direction upon the rise of the pulsed density applied during the microstructuring process; see the inset diffraction peak shown in Figure 6. This is due to the following events induced by the laser energy and the related cooling cycles: (a) grain refinement related to the severe plastic deformation processes that induce microstructural defects and high amounts of dislocations and (b) the residual stress redistribution caused by the lattice decrease. There is a small shift in the 20 angles of the diffraction peak of the (111) direction to higher 20 values that points out the lattice decrease; see the inset image in Figure 6. Compressive residual stress achieved by work hardening and grain refinement revealed by the micro-hardness increase up to several hundreds of micrometers, which is caused by the wave impact during the LSP process that has been extensively investigated and reported in the literature [20; 21; 22]. Those investigations have been carried out mainly to improve the mechanical properties of the treated alloys. The Effect of the LSP Treatment with Different Pulse Densities on Nucleation Temperature as a Function of High DC Voltage  
Figure 7 shows four typical temperature-time curves that were obtained during the cooling experiments of 1 mL of deionized water. The curves correspond to experiments performed before the application of voltage using an electrode without the LSP treatment (black line), an electrode treated with LSP with 900 pulses/cm\({}^{2}\) (red line), an electrode treated with LSP with 1600 pulses/cm\({}^{2}\) (blue line), and an electrode treated with LSP with 2500 pulses/cm\({}^{2}\) (green line). All curves start their cooling at 5 \({}^{\circ}\)C and then they present a very similar cooling slope between them without any apparent effect due to the different pulse densities of the LSP treatment applied on the electrodes. Subsequently, the curve of the experiment with the electrode without LSP presents a nucleation temperature of \(-12.04\)\({}^{\circ}\)C, while the curve of the experiment with the electrode with LSP with a density of 900 pulses/cm\({}^{2}\) presents a nucleation temperature of \(-12.34\)\({}^{\circ}\)C. On the other hand, the experiment with the electrode with a pulse density of 1600 pulses/cm\({}^{2}\) showed a nucleation temperature of \(-11.25\)\({}^{\circ}\)C, and finally, the nucleation temperature of the experiment with the electrode with the LSP treatment with a pulse density of 2500 pulses/cm\({}^{2}\)  
Figure 6: The effect of the pulse density during the LSP treatment on the crystalline state of the Al6061 T6 alloy. was \(-11.88\)\({}^{\circ}\)C. The freezing temperature of the deionized water during the four experiments was close to \(0^{\circ}\). Figure 8 presents the cooling curves from the electrofreezing experiments conducted with electrodes that did not undergo the LSP treatment. It was observed that the nucleation temperature increased with the applied voltage, exhibiting a generally linear trend across the range of voltages tested. Figure 9 shows the cooling curves for the experiments using electrodes treated with 900 pulses/cm\({}^{2}\). In this case, the nucleation temperatures exhibited a significant shift to higher values compared to the untreated electrodes, including the temperature at 5 kV, which reached \(-7.623\)\({}^{\circ}\)C--slightly higher than that of the untreated electrode. Figure 10 displays the cooling curves for the electrofreezing experiments with electrodes treated with 1600 pulses/cm\({}^{2}\). In this case, the shift towards higher nucleation temperatures was significant compared to the untreated electrodes.