Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation

Paper in proceeding, 2010

The effects of dynamic strain ageing (DSA) and dynamic precipitation (DP) on the stress-strain response during low-cycle fatigue of naturally aged (NA) and peak-aged (PA) AA7030 alloy at different temperatures was investigated. The results show that the PA temper is largely unaffected by DSA/DP, and the cyclic deformation behavior is controlled by the accumulation of dislocations and strain localization due to repeated shearing of precipitates. In the NA temper, on the other hand, the effect of temperature on DSA and DP is the main mechanism controlling the stress-strain response. At temperature above room temperature, DP in the intense slip bands inhibits cyclic softening and the samples harden until the on-set of crack growth. At lower temperatures, the rate of DP is too slow to compensate for the softening in the slip bands and the stress amplitude saturates or decreases. The stress amplitude development is shown to primarily be a result of the evolution of the effective stress associated with dislocation-precipitate interactions.