is shown in Table 5. The mechanical properties of oxygen-free copper 

 and not welded and welded beryllium- copper , by both the MIG and TIG 

 processes were not significantly affected by exposure in sea water at 

 nominal depths of 2,500 and 6,000 feet. 



COPPER-ZINC ALLOYS (BRASSES) 



The chemical compositions of the copper-zinc alloys (brasses) are 

 given in Table 6, their corrosion rates and types of corrosion in Table 

 7, their resistance to stress corrosion cracking in Table 8, and the 

 effect of exposure in the sea water on their mechanical properties in 

 Table 9. 



Corrosion 



Corrosion of the copper-zinc alloys usually occurs as uniform, 

 pitting, crevice, dezincif ication or stress corrosion cracking. The 

 tendency for the copper-zinc alloys to corrode by dezincif ication and 

 stress corrosion cracking varies with the zinc content; the higher the 

 zinc content of the alloy the greater the susceptibility. Pitting and 

 crevice corrosion are usually caused by differential aeration cells. 



Dezincif ication is the selective corrosion of copper-zinc alloys 

 (brasses) by which the original alloy is converted into a spongy mass 

 of copper which has poor mechanical strength. The most favored theory 

 of this mechanism is that the metal corrodes as an alloy and the copper 

 is subsequently redeposited. 



Because it is not possible to remove all the corrosion products 

 (redeposited, spongy copper) it is not possible to obtain true weight 

 losses from which to calculate corrosion rates. Therefore, corrosion 

 rates so obtained are always lower than they are actually. Hence, 

 corrosion rates determined for dezincified copper-zinc alloys are not 

 reliable for assessing the corrosion of such alloys. 



The corrosion rates of the copper-zinc alloys are shown graphi- 

 cally in Figures 5 through 16. 



The corrosion rates of commercial bronze, shown in Figure 5, were 

 constant with duration of exposure through 751 days of exposure in the 

 sea water at the 6,000 foot depth and decreased slightly thereafter. 

 The corrosion rates in sea water at the 2,500 foot depth were lower 

 than those at the 6,000 foot depth and decreased with increasing dur- 

 ation of exposure. However, in the bottom sediments at the 6,000 foot 

 depth the corrosion rates increased with duration of exposure while 

 those at the 2,500 foot depth decreased with increasing duration of 

 exposure and they were lower than those at the 6,000 foot depth. The 

 corrosion rates of commercial bronze at both depths, both in the sea 

 water and in the bottom sediments were lower than those at the surface 

 of the Pacific Ocean, at NCEL and at Fort Amador, Panama Canal Zone, 

 Reference 16, as shown in Figure 5. 



