The effects of testing temperature and strain rate on the yield stress of an aged Al-Li-Cu-Mg-Zr alloy have been investigated at temperatures between 77 K and 523 K and over the strain rate range of 1.77 × 10-4s-1 to 1.77 × 10-2s-1. The deformation-induced dislocation structure was examined by transmission electron microscopy. In the specimens as quenched, under-aged or aged nearly to the peak strength, dislocations move as pairs when the alloy is deformed at 290 K. In the over-aged specimens, dislocations move as single dislocations and tangle during deformation. For the alloy under-aged or aged nearly to its peak strength, the yield stress decreases with increasing testing temperature from 77 K to 290 K, and the positive temperature dependence of yield stress is observed in the temperature range from 290 K to 450 K. Within this temperature range, dislocations move in pairs cutting the δ'-L12 ordered particles. The yield stress decreases with increasing testing temperature above 450 K, and dislocations move as single dislocations. The serrated yielding characteristic is observed for specimens as quenched, under-aged and aged nearly to the peak strength. At testing temperatures below 423 K, the yield stress is almost independent of strain rate at peak-aged and over-aged stages. For the under-aged stage, the strain rate dependence of the yield stress is negative at the temperature range within which the positive temperature dependence of yield stress appears. At testing temperatures above 473 K, the yield stress increases linearly with the logarithm of strain rate at any aging stage, and the strain rate dependence increases with increasing testing temperature.
(Received March 13, 1987)
Keywords: aluminum-lithium-copper-magnesium-zirconium alloy, ordered precipitate, precipitation hardening, solid-solution hardening, serrated stress-strain curve, mechanical property, temperature dependence, strain-rate dependence, super-dislocation, transmission electron microscopy
* This paper was originally published in Japanese in J. Japan Inst. Metals, 50 (1986), 961.
** Department of Technology, Faculty of Education, Fukuoka University of Education, Munakata 811-41,Japan.
*** Department of Metallurgy, Faculty of Engineering, Kyushu University, Fukuoka 812, Japan.