Abstract
Magnesium alloys are now being increasingly used as a structural material wherever the 'lightness' is the major criterion. This is attributed to their inherent superior properties, such as very low density, high specific strength, excellent castability & machinability, good damping capacity, high dent resistance and so on. But due to low corrosion resistance, structural applications of magnesium alloys are still limited, since many mechanically-loaded parts are often subjected to prolonged cyclic stresses in an active medium. In the present work, fatigue behavior of extruded AZ61 magnesium alloy has been evaluated under three different kinds of corrosive environments: (a) high humidity environment (80% relative humidity) (b) 5 wt. % NaCl environment, and (c) 5 wt. % CaCl_2 environment. Fatigue tests were conducted under axial loading at stress ratio of -1 and at a frequency of 20 Hz. Extruded AZ61 indicated a fatigue limit of 135 MPa under low humidity of 35-40 %RH, while a clear effect of humidity was seen under high humidity of 80 %RH at stress amplitudes below the fatigue limit. In NaCl and CaCl_2 environments, the fatigue strengths were drastically reduced. The reduction rate of fatigue strength due to corrosive environment was 0.22 under high humidity condition, 0.85 under NaCl environment, and 0.77 under CaCl_2 environment. This remarkable reduction of fatigue strength in corrosive environments was attributed to the formation of corrosion pit, which was enhanced under cyclic loading.
