## 3 Results  
### Cavitation Erosion Behavior on Different Metallic Metals  
Figure 2(a) shows the cavitation flow during the experiment, and Figure 2(b) shows the shape and size of the disturbing element. The length of the disturbing element was 35 mm, its width was 40 mm, the height was 35 mm, and the angle was 45 degrees. Two grooves were machined at its bottom, and were fixed by bolts. It could be seen that the cavitation clouds originated in the back of the disturbing element, which flowed downstream and collapsed later. The intensity of the cavitation clouds decreased gradually far away from the disturbing element. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **H62 Brass** & \begin{tabular}{c} **T2 Red** \\ **Copper** \\ \end{tabular} & \
\begin{tabular}{c} **6061** \\ **Aluminum-Alloy** \\ \end{tabular} &
\begin{tabular}{c} **1060 Industry** \\ **Pure Aluminum** \\ \end{tabular} \\ \hline Yield strength (MPa) & 120 & 70–90 & 103 & 35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The yield strength of the four selected metallic materials. In order to calculate the cavitation damage of the metallic metals under the condition of cavitation flow quantitatively, the weight loss of the four different metallic samples under the action of cavitation flow from 2 h to 20 h was calculated. The weight loss was calculated as follows:  
\[\Delta W=W_{0}-W_{i} \tag{1}\]  
The cavitation erosion rate was calculated as follows:  
\[\Delta W^{\prime}=\left(W_{i-1}-W_{i}\right)/\Delta t \tag{2}\]  
where \(\Delta W\) is the weight loss of metallic sample; \(W_{0}\) is the original weight before testing; \(W_{i}\) is the actual weight after testing; \(\Delta W^{\prime}\) is the cavitation erosion rate; \(\Delta t\) is the cavitation acting time. Figure 4 is the weight loss of the metallic sample with increasing acting time. The right column is the surface morphology of the four different metallic materials after a 10 h cavitation acting time. It could be seen that the weight loss of the four selected metallic material samples increased gradually with the increasing acting time, and there were obvious differences among the surface morphologies of the four metals after cavitation erosion. As mentioned in Table 1, the yield strength of the four metallic material samples was: H62 brass > 6061 aluminum alloy > T2 red copper > 1060 industry pure aluminum. The 1060 industry pure aluminum material had the lowest yield strength, so the industry pure aluminum sample suffered the most severe cavitation damage during the experiment. This is the reason why the weight loss of the 1060 industry pure aluminum sample was much higher than other metallic materials. Large corrosion pits could be found on the surface of the industry pure aluminum specimen. H62 brass had the highest yield strength and good mechanical properties, so the cavitation damage in the experiment was the least. A small number of erosion pits appeared on the surface of the H62 brass, and most areas did not change significantly. Although the yield strength of the 6061 aluminum alloy was slightly higher than of the T2 red copper, the weight loss was obviously higher than red copper. A large number of corrosion pits appeared on the surface of the red copper samples because of the reciprocal action by the microjet and shock wave generated during the collapse of cavitation flow, which may be caused by the plastic deformation of the material surface. The relatively serious cavitation damage on the surface of the aluminum alloy was mainly because aluminum alloy materials often have coarse-grain defects, which will reduce the mechanical properties and fatigue resistance of the material. Figure 5 shows the change in the cavitation erosion rate of the metallic sample with increasing acting time. The right column is the partially enlarged drawing of the damage morphology subjected to 10 h cavitation flow.