6,000-foot depth, both in the seawater and in the 

 bottom sediments. The corrosion of the silicon 

 bronzes was greater than that of the other bronzes at 

 depth and at the surface; it decreased with increasing 

 duration of exposure until it was the same as the 

 other bronzes after 1,064 days of exposure. The 

 average corrosion of the bronzes in surface seawater 

 was greater than at depth, and it decreased with 

 increasing duration of exposure. 



3.3.2. Parting Corrosion 



Parting corrosion was found on all the aluminum 

 bronzes (dealuminification) and on the silicon 

 bronzes (coppering) as shown in Table 19. The 

 parting corrosion was most severe on the cast alloy 

 containing 10, 11, and 13% aluminum. There was 

 much less on the wrought aluminum bronzes with 

 there being very few cases of slight attack on the 

 alloy containing 5% aluminum and more cases on the 

 alloy containing 7% aluminum. The parting corrosion 

 on the silicon bronzes occurred only occasionally, but 

 its rating varied from slight to severe. 



3.3.3. Effect of Depth 



The effect of depth on the corrosion of the 

 bronzes after 1 year of exposure in seawater is shown 

 in Figure 9. The bronzes corroded slightly slower at 

 depth than at the surface, but the difference was not 

 considered to be significant. For practical purposes 

 depth does not influence the corrosion of the 

 bronzes. 



3.3.4. Effect of Concentration of Oxygen 



The effect of the concentration of oxygen in sea- 

 water on the corrosion of the bronzes after 1 year of 

 exposure is shown in Figure 10. The corrosion of the 

 bronzes increased linearly, but slightly, with 

 increasing oxygen concentration, and at 5.75 ml/1 

 oxygen they were corroding at the same rate as 

 copper and other copper alloys. 



3.3.5. Stress Corrosion 



Four bronzes, phosphor bronze A, phosphor 

 bronze D, aluminum bronze 5%, and silicon bronze 

 A, were exposed in seawater to determine their 



susceptibility to stress corrosion. They were stressed 

 at values equivalent to 35, 50, and 75% of their 

 respective yield strengths as shown in Table 20. They 

 were not susceptible to stress corrosion for periods of 

 exposure of 400 days at either depth. 



3.3.6. Mechanical Properties 



The effects of corrosion on the mechanical 

 properties of four bronzes are given in Table 21. The 

 mechanical properties of the phosphor bronzes A and 

 D were not affected by exposures at depth. The 

 decreases (12, 27, and 29%) in the elongation of the 

 aluminum bronze were attributed to parting cor- 

 rosion. Also, the decrease in the mechanical 

 properties of silicon bronze A after 403 days of 

 exposure in the bottom sediments at a depth of 6,000 

 feet was attributed to parting corrosion. 



3.3.7. Corrosion Products 



Chemical analyses of the corrosion products 

 removed from aluminum bronze showed the presence 

 of copper oxy-chloride, cupric chloride; major 

 elements, copper and aluminum; minor elements, 

 iron, magnesium, calcium, and silicon; chloride ion, 

 0.9%, and sulfate ion, 9.0%. 



3.4. COPPER-NICKEL ALLOYS 



The chemical compositions of the copper-nickel 

 alloys are given in Table 22, their corrosion rates and 

 type of corrosion in Table 23, their resistance to 

 stress corrosion in Table 24, and the changes in their 

 mechanical properties due to corrosion in Table 25. 



3.4.1. Duration of Exposure 



The effects of the duration of exposure on the 

 corrosion of the copper-nickel alloys in seawater at 

 depths, at the surface, and in the bottom sediments 

 are shown in Figure 13. 



Because the corrosion rates of all the copper- 

 nickel alloys were comparable, average values for any 

 one time, depth, or environment were used to con- 

 struct the curves in Figure 13. The average corrosion 

 at the surface and at the 6,000-foot depth, both in 

 seawater and in the bottom sediments, decreased 



46 



