Size-dependent role of S phase in pitting initiation of 2024Al alloy

Size-dependent electrochemical role of the S phase at the initial corrosion stage of 2024Al alloy has been elucidated by transmission electron microscopy technique. A critical size of about 10 nm is identified below which S phases are out of electrochemical function at the initial corrosion stage, when Al20Cu2Mn3 dispersoids play a crucial role. The electrochemical function of S phases becomes remarkable and triggers the local dissolution of the Al matrix with increasing the size. Moreover, the mechanism of the size effect has been discussed in detail.