Development of surface modified Mg-2Gd-2Yb alloy through friction stir processing: corrosion behaviour and short-term anodic performance

This study investigates the influence of friction stir processing (FSP) on the microstructural evolution, corrosion behaviour and electrochemical performance of Mg–2Gd–2Yb alloy shows potential for further evaluation in short-duration cathodic-protection applications. The as-cast base material (BM) was processed using two FSP conditions: FSP02 (2 passes, 33 mm/min, 1400 rpm) and FSP04 (4 passes, 33 mm/min, 1400 rpm). FSP significantly refined the coarse-grain structure of the BM from approximately 808 µm to 8–10 µm, producing a homogeneous and defect-minimized microstructure. FSP02 exhibited the most effective grain refinement, while FSP04 showed slight grain coarsening due to cumulative heat input during multiple passes. Transmission electron microscopy revealed improved particle dispersion and strong particle matrix interactions in the processed specimens. Corrosion behaviour was evaluated under thermo-static (− 20 to 80 °C) and thermo-cyclic conditions. The BM exhibited severe localized corrosion characterized by pitting, cracking, and unstable corrosion product layers. In contrast, FSP specimens developed more uniform corrosion morphologies owing to refined grains and enhanced elemental distribution. At elevated temperatures, corrosion mechanisms shifted from chloride-assisted attack to the formation of protective MgO/Mg(OH) 2 -rich surface layers. Rare-earth elements (Gd and Yb) promoted surface film stability and reduced chloride penetration. Corrosion performance varied according to temperature, in that BM had the minimum corrosion rate at − 20 °C, while FSP02 had the minimum corrosion rate between 0 to 40 °C and FSP04 had the minimum corrosion rate at 60 and 80 °C. However, FSP02 was found to perform better than BM in electrochemical polarization and making it a promising candidate for short-duration cathodic-protection applications.