Understanding the Effect of Acoustoplasticity on the Microstructural Evolution and Hardness of Aluminum 2024 Alloy

Acoustoplasticity has been used to join thin layers of metallic materials and therefore it is considered to be a welding technique. In this work, acoustoplastic deformation was performed on 6mm thick Al 2024 plates. Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and Vickers hardness characterization were performed on the plates to evaluate the effects of the acoustoplastic conditions on the surface residual stresses. The acoustoplastic conditions ranged from 1000W to 2500W at 20 kHz frequency. The rolled Al 2024 baseline microstructure exhibited elongated grains larger than 1mm in length and on the order of 10-20um in width. The hardness values did not vary significantly for the near surface compared to the depths up to 600um from the surface; i.e Al 2024 2000W sample HV values ranged between 96-165. However, the near-surface regions were affected by the acoustoplasticity, which appeared to induce some subgrain formation and texturing and this appeared to affect the residual stress, which was measured both parallel and perpendicular to the elongated grains. Residual stress was measured using a novel low power X-Ray diffraction-based technique that collects the entire diffraction cone and computes the stress. The results suggest that prior to acoustic deformation, the stress was tensile due to rolling, and post acoustic deformation, a compressive stress was induced. This technique presents as a great tool for severe plastic deformation with microstructure and stress control. The variations in the residual stress measurements as a function of the microstructure will be discussed.