Investigation of the de-alloying behaviour of θ-phase (Al2Cu) in AA2024-T351 aluminium alloy

For multi-phase intermetallic particles consisting of both θ-and S-phase, de-alloying occurred preferentially at S-phase and the de-alloying of θ-phase initiated in the regions surrounding S-phase. The selective dissolution of Al from θ-phase resulted in porous copper-rich θ-phase remnant, comprised of randomly oriented copper metallic particles and copper oxides with sizes of 10–50 nm. Banding structure developed during the de-alloying of θ-phase particles that contain stacking faults. The de-alloying of θ-phase could preferentially occur from beneath the alloy surface, associated with the local low pH environment generated by trenching of the alloy matrix in the periphery θ-phase particles.