Low cycle fatigue of Al-4.5wt.%Cu polycrystalline alloy was studied. Six different sets of specimens were heat treated at different times and/or temperatures to investigate the effect of tempering, grain size, and aging on the fatigue properties of polycrystalline Al-4.5wt.%Cu alloy. Strain-controlled low cycle fatigue testing with a strain rate of 10E-04 sec−1 was conducted at room temperature. The fatigue response of the alloy was evaluated microscopically in terms of appearance of cyclic slip bands, and macroscopically in terms of cyclic stress strain response.;The effect of tempering was studied using, two sets subjected to 0-temper heat treatment, and another four sets subjected to T6-temper heat treatment. It was found that the cyclic stress strain response of 0-tempered Al-4.5wt.%Cu alloy exhibited an increase in saturation stress with plastic strain, and also exhibited precipitate free zones (PFZ's) in the microstructure. On the other hand, the cyclic stress strain response of T6-tempered Al4.5wt.%Cu alloy exhibited a definite plateau region where the saturation stress remained constant with plastic strain. PFZ's were observed in the 0-tempered alloy; however, they were not observed on T6-tempered alloy. Slip bands and PSB's were observed extending across the grain at 45° orientations from the grain boundary in the T6-temper.;The effect of grain size in T6-tempered Al-4.5wt.%Cu alloy was investigated using two different heat treatment. In addition, the effect of second phase also investigated using two different aging times. It was found that the smaller the grain size the lower the saturation stress and the larger the grain size the higher the saturation stress. It was also found that second phase of one day aged has higher saturation stress than second phase of three days aged.
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