Development of Age-Hardening Technology for Ultrafine-Grained Al-Li-Cu Alloys Fabricated by High-Pressure Torsion

Abstract

The age-hardening behavior and precipitation microstructures with high dislocation density and ultrafine grains have been studied for cold-rolled and severely deformed 2091 Al-Li-Cu alloy. The age-hardenability at 463K was reduced by high-pressure torsion (HPT) due to the accelerated formation of larger 8-AlLi precipitates at grain boundaries, in place of transgranular precipitation of refined δ’-Al₃Li particles that are predominantly observable in the no-deformed and 10%-rolled specimens. When aged at 373K, however, it was successfully achieved for the HPT specimen to increase the hardness up to ~290HV, the highest level of hardness among conventional wrought aluminum alloys. The corresponding TEM microstructures confirmed that refined δ’ particles precipitate within ultrafine grains while keeping the grain size at ~206nm. This result suggests that the combined processing of severe plastic deformation with age-hardening technique enables the fabrication of novel aluminum alloys concurrently strengthened by ultrafine-grained and precipitation hardenings.