Origin of Prestrain-Induced Cyclic-Strain Hardening: Multi-Scale Experimental Characterizations and Simulations of 7075 Aluminum Alloy

Abstract

The influence of prefabricated dislocation features on the post-cyclic process in 7075 aluminum alloy exhibits significant variations, which are of great importance in terms of concerns, designs, and discoveries. To emphasize the impact of strain rate on subsequent dislocation slip, predeformation was controlled under a constant microplastic stress of 240 MPa, with strain rates ranging from 10-4s-1 to 10-1s-1. The maximum cyclic stress in the post-cyclic stage was maintained at the same level as the prestress, with two different stress amplitudes: 40±200 MPa and 20±220 MPa, respectively. It was observed that, under different microplastic cyclic stress amplitudes, the effect of rate-dependent prestrain on post-cyclic stability was not constant but rather exhibited an exact opposite behavior. Through experimental mechanism analysis, as well as verification through molecular dynamics and crystal plasticity simulations, it was determined that dislocation aggregations at grain boundaries or phase interfaces, induced by rate-related prestrain, provided structural self-regulation and sustainable sources for dislocation development in the post-cyclic stage. These findings offer new insights for the optimization of microstructural design through dislocation engineering.

Keywords: 7075 aluminum alloy, Cyclic stability, Rate dependent prestrain, Crystal plasticity, Molecular dynamics