The effect of ultrasonic surface rolling on microstructure and corrosion behaviour of selective laser melting-fabricated 2099 aluminium‑lithium alloy

Selective laser melting (SLM)-fabricated aluminium‑lithium alloys exhibit substantial potential in aerospace applications owing to structure-function integrated characteristics. However, their high chemical activity can increase their corrosion susceptibility and limit service reliability. In this study, ultrasonic surface rolling (USR) is applied to an SLM-fabricated 2099 aluminium‑lithium alloy, revealing the effects of USR on its electrochemical-corrosion behaviour. The USR treatment decreased the surface roughness by 94.76 % and formed a plastic-deformation region of ∼200 μm. In the deformed region, a compressive residual stress was introduced, reaching up to −274 MPa, and the average grain size decreased by 35.16 %. Moreover, in the surface region of the deformed layer, submicron ultrafine equiaxed grains were formed, and a large amount of precipitated θ′ (Al₂Cu) phases were also dissolved and dispersed. The USR-induced corrosion-resistant surface reduced the corrosion current density by ∼16.01 % and increased the polarisation resistance by ∼476.36 %. This improvement can be attributed to the combined effects of USR on the surface-roughness reduction, introduction of compressive residual stress, grain refinement, and θ′ (Al₂Cu) phase dissolution. These findings provide valuable insights into the microstructure evolution induced by USR and its role in enhancing the corrosion resistance of the SLM-fabricated 2099 aluminium‑lithium alloy.