The effect of tempering on low cycle fatigue behavior of Al-2024

A low cycle fatigue study on Al-2024 polycrystalline alloy was conducted under symmetric tension-compression at room temperature, using a servo-hydraulic testing machine, to investigate the effect of tempering on cyclic deformation. The tests were conducted at constant frequency for O-temper condition and a constant strain rate for T6-temper condition. The fatigue response of the alloy was evaluated macroscopically in terms of cyclic stress strain response and microscopically in terms of appearance of cyclic slip bands. It was found that the cyclic stress strain response of O-tempered alloy exhibited an increase in saturation stress with plastic strain whereas the cyclic stress strain response of T6-tempered alloy exhibited a definite plateau region where the saturation stress remained constant with plastic strain. The T6-temper alloy showed the presence of persistent slip bands (PSBs), which were extending across the grain at 45° orientations from the grain boundary. No (PSBs) were observed in the microstructure of the O-temper alloy; however, precipitate free zone (PFZ) was observed adjacent to the grain boundaries. Needle-like precipitates were also observed within the grains with two different orientations and the angle between them was 65° in the O-tempered alloy.