ENHANCEMENT OF CUMULATIVE CORROSION-FATIGUE INTERACTION LIVES OF 6061-T6 ALUMINUM ALLOY USING ULTRASONIC IMPACT PEENING PROCESS

Abstract

The fatigue behavior of 6061-T6 aluminum alloy under constant and variable amplitude loading was investigated in air for as-received and pre-corroded specimens in 3.5% NaCl corrosive solution for 77 days. The experimental results presented that the tests of fatigue life on pre-corroded samples with and without ultrasonic peening revealed a significant reduction in life related with the presence of corrosion defects before cyclic loading. In state of unpeened specimens the constant S-N fatigue strength curve was decreased by 4.5% due to immersed the specimens in corrosive 3.5% NaCl solution for 77 days, while in state of ultrasonically peened specimens for 10 sec. per line and 2.5 joul energy the reduction of S-N curve decreased to 2.2% due to the beneficial effect of this treatment for increasing the corrosion-fatigue life. The improvement of fatigue life and corrosion-fatigue life of specimens when applying of ultrasonic peening was 8.69% for dry fatigue life and 2.3% for corrosion-fatigue interaction. The results of cumulative corrosion-fatigue tests indicated that the life of corroded specimens under the effect of ultrasonic peening treatment improved to approximately (3% ـــ 2.25%) for low-high and high-low sequences.