Remarkable Near-Surface Microstructure Of Nanoparticles And Oxide Film In Laser Shock Peened Al-Zn-Mg-Cu Alloy

The near-surface microstructure in an Al-Zn-Mg-Cu (7075-T6) alloy after Laser Shock Peening without Coating (LSPwC) was characterized by advanced electron microscopy methods. A remarkable microstructure composed of a similar to 2 mu m wide newly solidified matrix recast surface layer embedded with O-rich Al nanoparticles (NPs) with the close-packed orientation relationship (OR) as the surrounding Al matrix has been discovered, together with a nano-scale aluminum oxide layer formed on the outermost surface. The formation mechanism is associated with high-pressure surface ablation leading to melting, vaporization and shock-assisted rapid solidification during the LSPwC process. The close-packed OR between NPs and matrix is believed to be due to surface energy minimization. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.