FATIGUE BEHAVIOR OF A COMMERCIAL ALUMINUM-ALLOY IN SEA-WATER AT DIFFERENT TEMPERATURES

Fatigue tests of a commercial aluminium alloy are conducted in sea water at different temperatures using a specially designed experimental environmental chamber installed on a standard rotating bending fatigue testing machine. The tests are carried out in air at 20-degrees-C to establish the sigma-N curve for this alloy as a reference curve, while tests in sea water are at 20, 30, 50 and 80-degrees-C to investigate the role of temperature on the fatigue behaviour. Changing the medium from air to sea water during fatigue results in a significant decrease in the fatigue endurance limit. Increasing the temperature from 20 to 80-degrees-C reduces the endurance limit from 0.58 to 0.3 sigma(y). In a generalized empirical estimation formula, the present study suggests an incorporation of an environmental factor (C(E)) which depends on both the working medium and the temperature. Fracture surface examination on the scanning electron microscope indicates a great dependence of the pitting and/or intergranular corrosion fatigue cracks on the testing temperature and the applied cyclic stress levels.