δ′-L1<SUB>2</SUB>型規則相を含むAl-Li 2元合金の降伏応力の歪速度依存性

Abstract

The effect of strain rate on the yield stress of an Al-11.1 mol%Li alloy containing δ′-precipitates has been investigated at temperatures between 77 and 523 K and over the strain rate range from 1.77×10−4 s−1 to 1.77×10−2 s−1. At testing temperatures below 373 K, the yield stress is almost independent of strain rate at any aging stage. At testing temperatures above 373 K, the yield stress increases linearly with the logarithm of strain rate, and the strain rate dependence increases with increasing testing temperature. The yield stresses of under-aged alloy at temperatures between 373 and 473 K at high strain rates are greater than the yield stress at 77 K. For the alloy under-aged or aged nearly to its peak strength, the temperature range within which the positive temperature dependence of yield stress appears expands to the higher temperature side with increasing strain rate. The strain rate dependence of the yield stress is slightly negative at this aging stage. Within this temperature range, dislocations move in pairs cutting the δ′-L12 ordered particles. The yield stress of the over-aged alloy decreases monotonically with decreasing strain rate and with increasing testing temperature above 373 K. The modulus normalized yield stress is nearly constant at testing temperatures below 373 K at any strain rate investigated. In the over-aged alloy, dislocations by-pass the precipitates at any temperature and strain rate.