Prediction of Exfoliation and Stress Corrosion Performance of 7178-T76 and 7075-T76 Aluminum Alloy Sheet and Plate

In solutions of methyl alcohol and carbon tetrachloride, an abrupt change of several hundred millivolts occurs in the solution potential of 2000 series and copper-bearing 7000 series aluminum alloys after a certain amount of aging at elevated temperature. The specific aging time at which this change occurs can be varied by adjusting the solution composition or by changing the type or amount of chemical conditioner added to the solution. For aluminum alloys in which a desired property, such as resistance to exfoliation or stress corrosion cracking, is a function of the extent of aging, this potential change shows promise of being a simple and easily interpretable quality control test for assuring that sufficient aging is achieved. A previous paper described the application of this measurement for assuring the stress corrosion resistance of T8 type tempers of alloy 2219.²  The present paper indicates that the technique can be extended to the T76 type tempers of alloys 7075 and 7178.