ALUMINUM ALLOYS 



The chemical compositions of the aluminum alloys are given in 

 Table 2, their corrosion rates and types of corrosion in Table 3, and 

 changes in their mechanical properties after exposure in Table 4. 



The corrosion rates of alloys 1100-H14, Alclad 3003, and 5052-0 

 were lower in the surface waters than at depths of 2,500 and 6,000 feet; 

 those of 3003, and 5456-H321 were lower at the surface than at the 

 2,500 foot depth; those of 2024-0, were lower at the surface than at 

 the 6,000 foot depth. The corrosion rates of the following alloys were 

 higher at the surface than at depth: 2024-0 than at 2,500 feet; 

 2219-T6 than at both 2,500 and 6,000 feet; 3003 than at 6,000 feet; 

 5086-H34 than at both 2,500 and 6,000 feet; 5456-H321 than at 6,000 

 feet; 6061-T6 than at 6,000 feet. The corrosion rates of all the alloys, 

 except 2024-0 and 2219-T81, immersed at the surface varied from 0.9 to 

 1.4 MPY with the average being 1.1 MPY. Those of 2024-0 and 2219-T81 

 were 3.8 and 3.5 MPY, respectively. 



Pitting corrosion during the 6 months of immersion was insignifi- 

 cant except on alloys 2024-0, 2219-T81, 3003-H14 and 5456-H321. The 

 maximum depths of the pits were deeper for surface waters than at 

 depth for comparable periods of exposure for the following alloys: 

 2024-0 at both depths, 2,500 and 6,000 feet; 2219-T81 at 6,000 feet; 

 3003-H14 at 6,000 feet; 5086-H34 at 6,000 feet; and 5456-H321 at 6,000 

 feet. The maximum pit depths were deeper at depth than at the surface 

 for the following alloys: 1100-H14 at 6,000 feet; 2219-T81 at 2,500 

 feet; 3003-H14 at 2,500 feet; Alclad 3003-H12 at both 2,500 and 6,000 

 feet; 5086-H34 at 2,500 feet; 5456-H321 at 2,500 feet; and 6061-T6 at 

 2,500 feet. 



Except for the 2024-0 alloy, crevice corrosion was more severe at 

 depth than at the surface. 



Intergranular corrosion was present in alloys 2219-T81, 5083-H113, 

 5086-H32, 5086-H34 and 6061-T6. 



There was an overall increase in the corrosion rates of alloys 

 1100-H14, 5052-0, 3003, Alclad 3003, 6061-T6 and 5456-H321 with a de- 

 crease in the concentration of the oxygen content of sea water as 

 shown in Figure 2. There was an overall decrease in the corrosion 

 rates of alloys 2024-0, 2219-T81 and 5086-H34 with a decrease in the 

 concentration of the oxygen content of sea water as shown in Figure 3. 



The changes in the mechanical properties due to exposure after 

 surface immersion for 6 months in the Pacific Ocean are given in Table 

 4. Only the mechanical properties of alloy 2219-T81 were impaired. 



Analyses of the corrosion data and mechanical property data sup- 

 ports the conclusion that, in general, sea water at depths of 2,500 

 and 6,000 feet in the Pacific Ocean is more aggressive than at the 

 surface after 6 months of exposure. 



