Significant effect of mechanical polishing on the surface corrosion behavior of different aged 2A97 Al-Li alloy

To improve surface appearance, mechanical polishing is often applied on Al alloy workpieces. Interestingly, the surface mechanical polishing has a pronounced influence on the corrosion behavior of the 2A97 Al-Li alloy because it alters the surface microstructure and residual stress under different aging conditions. There are ultra-fine sub-grains and high-density dislocations in the surface deformation layer (DSL) caused by mechanical polishing. The δ′, T₁, and θ' phases that were originally aging and precipitated were sheared, broken, and dissolved during the polishing. Solute elements are concentrated on the sub-grain boundaries and dislocations, and the Cu-rich second phase is precipitated and grown in the surface deformation layer. The combined effects of the DSL and residual stress play an important role in governing corrosion behavior. The refined subgrains in the DSL facilitate the initiation of pitting and intergranular corrosion. Overall, the corrosion resistance of 2A97 alloy after mechanical polishing is higher than that of the unpolished alloy under the same aging condition. Under identical polishing conditions, the corrosion resistance of the alloy follows the order: over-aged > peak-aged > under-aged. In the over-aged condition, the alloy exhibits an I_corr of 1.05 × 10^–6 (A·cm⁻²) and a residual compressive stress of only 17.4 MPa, both of which are significantly lower than those of the solid solution state alloy.