Thermal stability of fatigue dislocation structures in coarse-grained pure aluminum

Coarse-grained pure Al with a high stacking fault energy was first fatigued at different total strain amplitudes (Δ ξt/2) up to almost the same accumulated strain, and then annealed at different temperatures (200, 330 and 450℃) for 30 min. The fatigue dislocation structures as well as the microstructural changes resulting from subsequent annealing treatments were detected by TEM. The results show that the dislocation structures of fatigued pure Al are mainly characterized by dislocation cells. With increasing Δξt/2, the average cell size decreases, the cell walls become more densified, and the density of dislocations in cells decreases. For the coarse-grained pure Al samples fatigued and then annealed at those three temperatures for 30 min, a clear recovery of fatigue dislocation structures occurs for all samples. The only difference exists in the recovery mechanism of the samples fatigued at different strain amplitudes and then annealed at a comparatively lower temperature of 200℃ for instance, the recovery process of dislocation structures induced by fatigue at lower strain amplitude is mainly determined by the disappearance of vacancies and the annihilation of dislocations of opposite sign, while the polygonization recovery dominates at higher strain amplitudes. The results of DSC measurements on the pure Al samples fatigued at different strain amplitudes are basically consistent with the results of TEM observations. ©, 2014, Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals. All right reserved.