HOT DEFORMATION MECHANISMS OF A SOLUTION-TREATED AL-LI-CU-MG-ZR ALLOY

Solution-treated 8090 and 8091 Al-based alloys vv ere subjected to hot torsion testing in the temperature range of 300 degrees C through 500 degrees C at strain rates of 0.1 to 5 s(-1), up to an equivalent stra in of 4. The flow stresses for alloys 8090 (8091) were found to depend on strain rate through a sinh function with exponent 3.95 (2.37) and on temperature through an Arrhenius behavior with activation energy of about 287 (282) kJ/mol. Studies using transmission electron microscop y (TEM) have been performed with the aim of understanding the differen ce in deformation mechanisms at 500 degrees C, 400 degrees C, and 300 degrees C. During hot processing, the mechanism of dynamic recovery is operative, The change in average subgrain size (d) with-the condition s of deformation, i.e., Zener-Hollomon parameter and steady-stale now stress (sigma(s)), was quantitatively characterized. Heat treatment at 550 degrees C induced the precipitation of Al3Zr particles which are resistant to dislocation shear. Furthermore, electron microscopic anal yses have revealed a large number of helical dislocations, prismatic l oops, and some Orowan loop formation after deformation at 500 degrees C and 400 degrees C. The density of these defects depends an the tempe rature of deformation and strain rate, At 300 degrees C, dynamic preci pitation of T-2 (Al6CuLi3) and T-1 (Al2CuLi) phases strongly affected hot deformation behavior. In all cases, the microstructural analyses w ere consistent with a dual-slope description of the mechanical behavio r during hot deformation.