Effect of multiple laser shock peening on microstructure, crystallographic texture and pitting corrosion of Aluminum-Lithium alloy 2060-T8

This study investigated the influence of multiple laser shock peening on microstructure, crystallographic texture, and pitting corrosion behavior of Aluminum-Lithium alloy 2060-T8 (in 3.5% NaCl) using EBSD, SEM and XPS techniques. Results show that microstructure and crystallographic texture were noticeably influenced by the peening passes. At single peening, plastic strain accommodation was homogenous, resulting in higher fraction of low Sigma CSL boundaries, and significant crystallographic texture transformation from fibre (unpeened) into Cube {001}< 100 > component (corresponding to dynamic recovery as plastic deformation mode) was induced. In contrast, repetitive peening (3 & 5 passes) induced heterogeneous plastic strain accommodation, developed random and low angle grain boundaries, and texture transformation from fibre to Goss {011}< 100 >, implying recrystallization as corresponding plastic deformation mode. As a result of dense atomic structured microstructures/textures, pitting corrosion after single peening was significantly lowered than that of multiple peening. Major reason for the improved corrosion behavior at single peening pass was the formation of dense and uniform alpha-Al2O3 type oxide film, which significantly lowered the materials dissolution. Whereas, multiple peening led to the formation of porous gamma-Al2O3 , theta-Al2O3 oxides and Cu-rich regions, which activated the deeper and wider pitting. Besides, the effect of precipitates (Al2CuLi, theta' (Al2Cu) and beta' (Al-3 Zr)) on pitting corrosion is quantitatively examined.