LAUSR

Ultrafine‐grained (UFG) aluminum alloys produced by severe plastic deformation demonstrate high mechanical properties but low thermal stability, which can negatively affect their service characteristics. Herein, the thermal stability of structure and S‐phase (Al2LiMg) evolution in UFG Al−5.5Mg−2.2Li−0.12Zr alloy produced by equal‐channel angular pressing (ECAP) are studied during heating and direct annealing. It is found that the UFG structure with an average grain size of about 1 μm formed by ECAP is preserved at up to 410 °C (≈0.7 T m), with a significant decrease in dislocation density (from 5 × 109 to 3 × 108 cm−2) and the fraction of low‐angle grain boundaries (from 20% to 5%) at 380 °C. The dissolution of metastable semicoherent SI‐phase particles located within grains at 330 °C is accompanied by a corresponding increase in Mg content in solid solution. The transfer of Mg atoms from solid solution to grain boundaries at 380 °C with subsequent coalescent growth of SII particles leads to an increase in the volume fraction (from 3% to 12%) and size of the particles and to recrystallization in UFG Al−Mg−Li alloy at 415 °C.