in the sea water. There was general corrosion of Ni-Vee bronze C after 

 751 days of exposure in the sea water. Except for the three cases 

 mentioned above, the corrosion on these three alloys was of the uniform 

 type. After 181 days of exposure at the surface in the Pacific Ocean 

 at Point Mugu, these three alloys corroded at much higher rates than 

 at either depth, 1.9 MPY versus 0.7 MPY. 



The corrosion rates of all the bronzes both in sea water and in 

 the bottom sediments at both nominal depths of 2,500 and 6,000 feet are 

 summarized in Figure 30. Initially, all the corrosion rates except 

 those for the silicon bronzes were within the range of less than 0.1 to 

 0.8 MPY while those for the silicon bronzes at the 6,000 foot depths 

 were about twice as high (1.3 to 1.7 MPY). However, after 1064 days of 

 exposure at the 6,000 foot depth, the corrosion rates of all the alloys 

 were within the range of less than 0.1 MPY to 0.7 MPY. At the 2,500 

 foot depth the ranges were between less than 0.1 to 0.8 MPY after 197 

 days and less than 0.1 to 0.6 MPY after 402 days of exposure. In 

 general, it can be concluded that the bronzes corroded at nearly con- 

 stant rates except for the silicon bronzes which corroded at decreasing 

 rates with increasing time of exposure. There were a few values which 

 were outside these ranges, most of them (6 of 8) after 751 days of 

 exposure at a depth of 6,000 feet: they were aluminum bronzes, nickel- 

 aluminum bronzes and silicon bronzes. Most of the bronzes corroded at 

 greater rates at the surface in the Pacific Ocean at Point Mugu than 

 at either depth; the only exception was the silicon bronzes which 

 corroded at the same rate as at the 6,000 foot depth. 



Stress Corrosion 



Four of the bronze alloys, phosphor bronze A, phosphor bronze D, 

 aluminum bronze and manganese-silicon bronze were exposed in the stress- 

 ed condition to determine their susceptibility to stress corrosion 

 cracking. They were stressed at values equivalent to 35, 50 and 75 

 percent of their respective yield strength as shown in Table 12. They 

 were not susceptible to stress corrosion cracking for periods of ex- 

 posure of 400 days at either depth. 



Mechanical Properties 



The effects of exposure in the deep ocean environments on the 

 mechanical properties of the bronzes are given in Table 13 and shown in 

 Figures 31 through 34. The mechanical properties of the phosphor 

 bronzes, A and D, (Figures 31 and 32) were not affected by exposures 

 for as long as 402 days at a depth of 2,500 feet or 751 days at a depth 

 of 6,000 feet. The elongation of the aluminum bronze (Figure 33) was 

 decreased considerably (28%) especially after 403 and 751 days at the 

 6,000 foot depth which is attributed to pitting corrosion and dealumini- 

 fication. The tensile strength, yield strength and elongation of 



13 



