# Fabrication of an Anti-Icing Aluminum Alloy Surface by Combining Wet Etching and Laser Machining
## 2 Experiment
### Experiments Processing
#### 2.2.2 Hierarchical Structure Processing  
The microstructure (MS) was processed by laser engraving. The selected laser processing parameters had a scanning interval of 60 \(\upmu\)m, laser power of 14 W, scanning speed of 100 mm/s, pulse frequency of 20 kHz, pulse width of 10 ns, spot diameter of 55 \(\upmu\)m, wavelength of 1064 nm, and single pulse energy for 6 \(\times\) 10\({}^{-4}\) J, and the number of laser passes was 10. The fluorinated microstructure's contact angle (CA) can reach 149.2\({}^{\circ}\) at room temperature (25 \(\pm\) 1 \({}^{\circ}\)C). The nanostructure (NS) was prepared by wet etching, and the process sequence is shown in Figure 1. The reaction time was kept at 10 min, the reaction temperature was set at 30 \({}^{\circ}\)C, and the concentration of hydrochloric acid was selected as 3 M. Firstly, the sample was immersed in hydrochloric acid for reaction, and then it was dipped into dilute sodium bicarbonate solution to remove the residual acid solution on the sample surface. The samples were then taken out of the solution and underwent ultrasonic cleaning. After that, the samples were placed in a 0.8 wt% FAS-17 solution, soaked for 1 h, and heated in an oven at 140 \({}^{\circ}\)C for 1 h to obtain nanoscale superhydrophobic surface samples. After fluorinating, the CA of the nanostructure could reach 152.1\({}^{\circ}\) at room tem  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Cu** & **Mg** & **Mn** & **Fe** & **Si** & **Ti** & **Al** \\ \hline
4.45 & 1.48 & 0.66 & 0.005 & 0.035 & 0.023 & Bal \\ \hline \end{tabular}
\end{table}
Table 1: The technical parameters of 2524 aluminum alloy (wt%).  
perature. The average surface roughness of NS was 1.17\(\upmu\)m. Finally, laser machining and chemical etching obtained the hierarchical structure (H.S.). The process steps for preparing the hierarchical structure are shown in Figure 2. After preparing the layered structure, the sample was soaked in a 0.8 wt% FAS-17 solution for one hour, and then this was heated off in a 140 \({}^{\circ}\)C oven for one hour to obtain a hyper-hydrophobic surface sample. At the same time, the contact angle and rolling angle were tested. The CA of the sample reached 154.2\({}^{\circ}\), the rolling angle was approximately 8\({}^{\circ}\) at room temperature, and it showed good hydrophobicity. The SEM of MS, NS, and HS are shown in Figure 3a, b, c, and d, respectively. The groove spacing of the laser processed surface is approximately 60 \(\upmu\)m. There were remelted materials on both sides of the groove that depicted that the structure had excellent hydrophobic properties. After chemical etching, a large number of NS appeared on the sample surface, which led to its superhydrophobic properties. After laser processing and chemical etching, a nanoscale structure on the surface of the microgroove improved the contact angle of the hierarchical structure. It can be seen from Figure 3e,f that the depth of the groove on the HS surface was approximately 52 \(\upmu\)m, and the width of the groove was approximately 28 \(\upmu\)m.  
Figure 1: The wet etching procedure and key steps.  
Figure 2: The overall preparation process of the hierarchical structure.