Investigating ion release using inline ICP during in situ scratch testing of an Mg-Li(-Al-Y-Zr) alloy

An electrochemical flow cell was constructed to permit the application of a mechanical scratch to the exposed material while monitoring the open circuit dissolution rates of the elemental alloy components. Elemental dissolution rates were determined where measured downstream using inductively coupled plasma atomic emission spectrometry (ICP-AES). The technique is demonstrated with Mg-Li(-Al-Y-Zr) alloy exposed to 0.01 M NaCl. A mechanical scratch was applied manually using a non-conductive and non-contaminating sapphire lancet without interrupting the on-line measurement. The ion dissolution rate from the newly exposed surface was significantly higher than the dissolution rate from the remaining surface area, corresponding to a high local current density. Notably, the increase in the dissolution rate from the scratched area occurred gradually after the scratch; then subsided within 200 s after the scratch, indicating that this particular Mg-alloy can repassivate by the formation of a surface film after a scratch was applied. This is the first reported use of an in situ scratch cell coupled with ICP-AES.