Origin of the serrated flow and anomalous strength evolution in the severe plastic deformed 2195 Al–Li alloy

This work investigates room-temperature serrated flow and anomalous strength variations in forged 2195 Al–Li alloys as functions of forging temperature, focusing particularly on dense dynamic strain precipitation of intragranular icosahedral quasicrystalline phases T₂. To achieve this, 2195 Al–Li alloys were forged at temperatures ranging from 180 to 460 °C, reaching a maximum cumulative strain of 2.4, thereby ensuring comparable microstructure and microtexture while varying dynamic precipitation behaviors. The study reveals that forging between 220 and 380 °C significantly promotes dynamic strain precipitation of intragranular, globular icosahedral quasicrystalline phases T₂ (Al₆CuLi₃) due to the high-density, strain-induced crystal defects, which provide enhanced diffusion pathways and sufficient energy to surpass nucleation barriers. The size and average spacing of T₂ particles increase with higher forging temperatures, extending the dislocation arrest duration at these precipitates. Consequently, alloys forged within 300–380 °C exhibit intensified serrated flow and severe strain localization during room-temperature tensile tests, resulting in substantially lower tensile elongation compared to alloys forged above 420 °C. The tensile strength initially decreases and then sharply rises with forging temperatures from 300 to 460 °C, reaching a minimum at approximately 380 °C, coinciding with the precipitation or absence of T₂ phases. This work paves the way for the designation of high-performance 2195 Al–Li alloys by hot deformation.