Discrete Dislocation Dynamics Study of Precipitation Strengthening during Laser Peening of A7075 Alloy

To elucidate the surface modification mechanism of the A7075 alloy via laser peening (LP), discrete dislocation dynamics (DDD) analysis of the LP process under ultra-high strain rates was conducted, specifically focusing on this precipitation-strengthened alloy. Using a model incorporating a low volume fraction of precipitates, we captured the dislocation evolution and the intricate dislocation-precipitate interactions during the process, demonstrating the formation of a mesh-like dislocation network that subsequently evolves into dislocation cells. The stress-strain response indicated that precipitates enhance the alloy strength, with the strengthening increment becoming larger as the precipitate volume fraction increased. Furthermore, the analysis demonstrated that dislocation-precipitate interactions increase the number of junctions, promote the formation of the dislocation network, and effectively elevate the dislocation density during plastic deformation, thereby contributing to work hardening. Notably, under the present simulation conditions, cross-slip-induced dislocation rearrangement was found to play a key role in the formation of the dislocation network; indeed, simulations in which cross-slip was artificially suppressed showed that the precipitate-induced strengthening increment was substantially reduced.