Corrosion Behaviour and Residual Stress State of Laser-Welded Ti6Al4V/AA7075 Joints with a Ag Interlayer

In this study, the corrosion performance and near-surface residual stress state of laser-welded Ti6Al4V/AA7075 dissimilar joints produced with a silver (Ag) interlayer are investigated. Potentiodynamic polarization, cyclic polarization, and electrochemical impedance spectroscopy (EIS) were carried out on Ti6Al4V base alloy (BA), AA7075 BA, and the fusion zone (FZ) containing the Ag interlayer. The Ag interlayer FZ exhibits an intermediate but clearly improved corrosion response compared with AA7075 BA, with a corrosion potential E_corr ≈ 0.260 V, corrosion current density i_corr ≈ 4.55 × 10⁻⁶ A cm⁻², and polarization resistance Rp ≈ 7.08 kΩ cm². EIS fitting further indicates a charge-transfer resistance of R_ct ≈ 3.7 × 10⁴ Ω cm² and a moderate oxide film resistance, consistent with a more stable electrochemical interface than AA7075 BA in 3.5 wt.% NaCl. Additionally, the residual stress measurements reveal that the Ag interlayer joint develops a predominantly compressive residual stress field on both sides of the weld. This compressive state is beneficial for delaying pit-to-crack transition and enhancing durability under corrosive loading. A brief comparison with our previously published Ti6Al4V/AA7075 welds produced using a Cu interlayer under the same laser welding parameters and joint configuration as the present study shows that the Ag interlayer provides more favourable compressive residual stresses and a more noble, higher-resistance electrochemical response.