Effect of Microstructure Evolution on Corrosion Behavior of Friction Stir Welded Joint for 2195-T8 Alloy

Corrosion behavior of friction stir welded 2195-T8 Al-Cu-Li alloy has been studied. Immersion and electrochemical open-circuit potential (OCP) test were applied. The microstructure and precipitates evolution in different zones were investigated by scanning electron microscopy, stereoscope, and transmission electron microscopy. The corrosion tests showed that the sequence of corrosion resistance of each area of the joint is: welding nugget zone (WNZ) > base metal > heat affected zone (HAZ). The WNZ showed highest corrosion resistance due to the fine recrystallized grains, the dissolution of T₁(Al₂CuLi) phase, and the refined and evenly-distributed particles in this area. However, the HAZ had the lowest corrosion resistance due to the intergranular precipitates, deleterious precipitate-free zone (PFZ), S′ (Al₂CuMg) phase, and the galvanic corrosion couples formed among T₁, θ′, and PFZ.