in the aluminum content from 9 to 11 percent, or in the manganese con- 

 tent from 0.5 to 3 percent had no effect on the corrosion of these 

 alloys. Nickel-aluminum bronze No. 2 tended to corrode at a slightly 

 higher rate at a depth of 4,250 feet in the Atlantic Ocean, Reference 

 13, than at either depth in the Pacific Ocean. Also, nickel-aluminum 

 alloy No. 2 exposed at the surface in the Pacific Ocean at Point Mugu 

 corroded at a rate nearly three times greater than at either depth in 

 the Pacific Ocean. The corrosion rates at depth decreased slightly 

 during the first year of exposure and thereafter, became constant with 

 increasing time of exposure. In addition to the uniform type of cor- 

 rosion there was some pitting and crevice corrosion and slight dealumi- 

 nif ication. 



The corrosion rates of the silicon bronzes (3 percent silicon and 

 3 percent silicon - 1 percent manganese (silicon bronze A)) are shown 

 in Figure 28. Both silicon bronzes corroded at the same rate in sea 

 water and in the bottom sediments at the 6,000 foot depth and the cor- 

 rosion rate decreased gradually with increasing time of exposure. At 

 the 2,500 foot depth their corrosion rates in sea water and in the 

 bottom sediments were lower than at the 6,000 foot depth with those in 

 the bottom sediment being lower than those in the sea water. In 

 general, the corrosion rates at a depth of 2,500 feet were constant 

 with time. The corrosion rate of 3 percent silicon bronze at the sur- 

 face of the Pacific Ocean, Panama Canal Zone, Reference 16, decreased 

 sharply between one and two years of exposure and thereafter, became 

 constant with increasing time of exposure; and, after two years of ex- 

 posure was the same as at the 6,000 foot depth in the Pacific Ocean. 

 After 181 days of exposure at the surface of the Pacific Ocean at Point 

 Mugu, the corrosion rates of the silicon bronzes were about the same 

 as at the 6,000 foot depth. In general, the silicon bronzes were uni- 

 formly corroded except for some selective attack at the 6,000 foot 

 depth. This attack is designated "coppering" because of the thin layer 

 of copper on the surfaces of the specimens after exposure. It is pos- 

 tulated that the silicon is either selectively removed by corrosion or 

 that the alloy corrodes as such and copper is subsequently redeposited 

 on the surface of the specimens. 



The corrosion rates of the Ni-Vee bronzes A, B and C (copper - 

 nickel - tin - zinc alloys) are shown in Figure 29. They corroded at 

 essentially the same rates in sea water and in the bottom sediments at 

 the 6,000 foot depth and in sea water at the 2,500 foot depth. They 

 decreased slightly and became asymptotic with increasing time of ex- 

 posure. The corrosion rates were less than 0.1 MPY (insignificant) in 

 the bottom sediments at the 2,500 foot depth. After periods of exposure 

 of 2 years or more at the 6,000 foot depth, the corrosion rates were 

 less than 0.5 MPY except for Ni-Vee bronze A and C in sea water after 

 751 days of exposure and Ni-Vee bronze A after 1064 days of exposure. 

 There was one area of very severe corrosion on Ni-Vee bronze A after 

 751 days of exposure and a pit 20 mils deep after 1064 days of exposure 



12 



