Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation

Abstract

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.

Damage and Fracture Behaviours in Aged Austenitic Materials during High-Temperature Slow Strain Rate Testing

“…There are differences between the strain rates regarding precipitation, both AISI 304 and Alloy 617 using a strain rate of 10 -6 /s at 700°C shows more and larger intergranular precipitates and a possible DRX structure. This means that the larger intergranular precipitates is formed during SSRT at elevated temperature and can be due to a combination of the longer deformation time at elevated temperature and the presences of dislocations junctions, possibly assisted by pinning of dislocations from the DSA process, that simplify the nucleation of precipitates in GB [9]. The intergranular precipitates cause GB embrittlement when Cr and C atoms diffuse to the GB to form carbides that often cracks between GB and the precipitate.…”

A Set of Tests for Studying the Effect of the Stress State on Ultimate Metal Plasticity at High Temperature

“…The work in [36] suggests using experiments of simple cyclic loading at different temperatures (-20, 20 and 60 °С) and different methods of preliminary heat treatment of specimens to study the effects of strain aging on behaviour of aluminium alloys. Some part of specimens has been prepared to have a maximum preliminary aging at high temperatures, when solute atoms create discretely distributed particles of the secondary phase.…”

“…However, these tests are very difficult technically for the purposes of studying the plasticity of metal materials under hot deformation. The studies described in the works [32][33][34][35][36][37][38] can be given as few examples of performance of tests in the high pressure chamber at high temperatures.…”