CORROSION-FATIGUE BEHAVIOR OF 7050-ALUMINUM-ALLOY IN DIFFERENT TEMPERS

Corrosion fatigue (CF) experiments, including both high-cycle axial fa tigue (S-N curve) and fatigue crack growth (FCG), have been performed on 7050 aluminum alloys in a 3.5 wt% NaCl solution as a function of ag ing treatment. The results of these environmental tests were compared with those obtained in laboratory air to characterize the effect of ag ing treatment on CF susceptibility. Fatigue resistance in both peak ag ed (T6) and overaged (T73) tempers was dramatically reduced by the aqu eous chloride environment. The FCG rates for T73 condition were lower than the counterparts for T6 condition in both air and saline solution . 7050-T73 alloy exhibited longer fatigue lives in air but shorter one s in the corrosive environment as compared to the T6 temper. This may be attributed to the formation of more extensive and larger corrosion pits acting as crack nuclei to facilitate crack initiation, in the T73 tempered condition. Comparison of CF and stress corrosion cracking (S CC) results reveals that overaging treatments used to improve grain bo undary characteristics and increase the intergranular SCC resistance m ight not guarantee an equivalent improvement in the resistance to tran sgranular CF cracking. (C) 1998 Elsevier Science Ltd. All rights reser ved.