A Stress Corrosion Cracking Model.
CORNELL AERONAUTICAL LAB INC BUFFALO N Y
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The characteristic susceptibility to stress-corrosion cracking exhibited by certain titanium and many aluminum alloys was studied. Mechanisms germane to establishing the conditions for stress-corrosion cracking in heat-treatable alloys during precipitation hardening are covered. A 7075 A1 alloy and an A1-Zn-Mg ternary alloy were used in construction of a stress-corrosion model. The model showed that the stress corrosion cracking susceptibility of A1 alloys becomes reduced if one or more of the following can be realized 1 elimination of the precipitation-free zone, PFZ, through proper heat treatment 2 inducement of the formation of primary precipitates in the PFZ to enhance hardening 3 inducement of the segregation of solute atoms to produce sufficient grain boundary hardening into the PFZ 4 reduction of the PFZ width to a practical minimum and 5 addition of an additive such as Cd, Sn and In to initiate precipitation of CuAl2 in the PFZ during initial aging. The resistance to stress-corrosion cracking will be increased because of 1 the virtual elimination of the difference in mechanical properties between the PFZ and the train interior due to differences in thermal history, and 2 due to the presence of Cd, the reduction of the anodic effect at the grain boundaries. Author
- Properties of Metals and Alloys