455 



Table 2 Chemical Composition and Mechanical Properties 



hardness, requiring heat treatment to remove this 

 work hardened layer. Following the Japanese 

 Industrial Standards , pure aluminum and aluminum 

 alloy H4163-2 were annealed for 1 hour at 400°C 

 and foils made of aluminum alloy H4163-5, were 

 annealed for 1 hour at 205°C. 



The surface hardness before and after annealing 

 are shown in Figure 2. This test was made using 

 a micro Vickers hardness tester. The tensile test 

 results are shown in Figure 3 and summarized with 

 the composition of the materials in Table 2. 



in SR are formed at the first stage of erosion. 

 At this stage there is no weight loss. This initial 

 period is called the incubation period where after 

 an initial increase, the SR value asymptotically 

 approaches a larger value. 



It is well known that MDP remains zero during 

 the incubation period. The time rate of MDP/(MDPR) 

 increases to the maximum (acceleration period) then 

 decreases gradually (deceleration period) . As a 

 measure of erosion intensity the value of MDD, pro- 



Surface Roughness (SR) , Mean Depth of Penetration 

 (MDP) , and Mean Depth of Deformation (MDD) 



For this study a NACA 16021 foil section was 

 tested for 9 hours to find the relation among SR, 

 MDP, and MDD. The result is shown in Figure 4. 

 When a ductile material such as aluminum is exposed 

 to cavitation, small pits detected by an increase 



60 



10 



^ 20 



\, 



•0-0 — o- 



PuRE Aluminum (H2102-2) 



Non-Annealed 



Annealed 



200 ^00 

 Static Load (g) 



60( 



FIGURE 2. Result of Vickers hardness test [pure 

 aluminum (H2102-2) ] . 



FIGURE 3. Comparison of tensile test result. 



