DEVELOPMENT OF AGE-HARDENING TECHNOLOGY FOR ULTRAFINE-GRAINED Al-Li-Cu ALLOYS FABRICATED BY HIGH-PRESSURE TORSION

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 delta-AlLi precipitates at grain boundaries, in place of transgranular precipitation of refined delta'-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 similar to 290HV, the highest level of hardness among conventional wrought aluminum alloys. The corresponding TEM microstructures confirmed that refined delta' particles precipitate within ultrafine grains while keeping the grain size at similar to 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.