surface in the Pacific Ocean at the Panama Canal Zone, Reference 16, 

 and in Port Hueneme Harbor, Reference 15. After 181 days of exposure 

 at the surface in the Pacific Ocean at Point Mugu, the corrosion rate 

 of 5 percent aluminum bronze was 1.1 MPY, slightly higher than at any 

 of the other locations, both surface and at depth. The 7 percent 

 aluminum bronze corroded the same at the surface at Point Mugu as at 

 the other locations except for one lot of specimens which were dealumi- 

 nified and corroded at nearly 3 MPY. Their corrosion rates in the sea 

 water and in the bottom sediments at both depths decreased slightly 

 with increasing time of exposure. 



The corrosion rates of the cast aluminum bronzes containing 10, 

 11, and 13 percent aluminum are shown in Figure 26. The corrosion 

 rates in the bottom sediments at the 6,000 foot depth were the same as 

 in the sea water irrespective of the aluminum content. They were the 

 same for the first 751 days of exposure and decreased slightly after 

 1064 days of exposure at the 6,000 foot depth. At the 2,500 foot depth 

 the corrosion rates in sea water were slightly lower than at the 6,000 

 foot depth and in the bottom sediments at 2,500 feet, the corrosion 

 rates were lower still, less than 0.1 MPY after 402 days of exposure. 

 After 181 days of exposure at the surface at Point Mugu, the corrosion 

 rates of the 10 and 13 percent aluminum bronzes were considerably high- 

 er than at either depth, 2.1 MPY versus 0.5 MPY at 6,000 feet. All 

 three of the alloys were attacked by dealuminif ication varying in 

 degree from very slight to severe; the first evidence being found 

 after 123 days of exposure at the 6,000 foot depth and 181 days of ex- 

 posure at the surface. 



Although the corrosion rates of the wrought and cast aluminum 

 bronzes were approximately the same as evidenced by comparing Figures 

 25 and 26 the types of corrosion were different: all the cast alloys 

 were dealuminif ied while there was dealuminif ication and pitting on 

 about half of the wrought 7 percent aluminum bronze specimens and uni- 

 form corrosion on most of the wrought 5 percent aluminum bronze speci- 

 mens . 



Williams, Reference 17, has reported that dealuminif ication was 

 found on wrought aluminum bronze containing 6.5 - 11 percent aluminum 

 after exposure in sea water and that an aluminum bronze containing 6 to 

 8 percent aluminum and 3.5 percent iron was not attacked by dealumini- 

 fication. In this investigation slight dealuminif ication was found on 

 an aluminum bronze containing 4.76 percent aluminum and less than 0.05 

 percent iron at the 6,000 foot depth. There was more dealuminif ication 

 on two lots of aluminum bronze containing about 7 percent aluminum and 

 3 percent iron at both the 2,500 and 6,000 foot depths. The perfor- 

 mance of the aluminum bronzes at depth in the Pacific Ocean was contrary 

 to that found at the surface in the Atlantic Ocean. 



The corrosion rates of the three nickel-aluminum bronze alloys are 

 shown in Figure 27. The corrosion rates in sea water and the bottom 

 sediments were the same irrespective of the depth, 2,500 and 6,000 feet. 

 This shows that variations in the nickel content from 4 to 5 percent. 



11 



