Influence of Decreased Temperature of Tensile Testing on the Annealing-Induced Hardening and Deformation-Induced Softening Effects in Ultrafine-Grained Al–0.4Zr Alloy

Abstract

The influence of decreased temperature of tensile testing on annealing-induced hardening (AIH) and deformation-induced softening (DIS) effects has been studied in an ultrafine-grained (UFG) Al–Zr alloy produced by high-pressure torsion. We show that the UFG Al–Zr alloy demonstrates a DIS effect accompanied by a substantial increase in the elongation to failure δ (up to δ ≈ 30%) depending on the value of additional straining. Both the AIH and DIS effects weaken with a decrease in the tensile test temperature. The critical deformation temperatures were revealed at which the AIH and DIS effects are suppressed. The activation energy Q of plastic flow has been estimated for the UFG Al–Zr alloy in the as-processed, subsequently annealed and additionally strained states. It was shown that the annealing decreases the Q-value from ~80 kJ/mol to 23–28 kJ/mol, while the subsequent additional straining restores the initial Q-value. Alloying with Zr results in the expansion of the temperature range of the AIH effect manifestation to lower temperatures and results in the change in the Q-value in all of the studied states compared to the HPT-processed Al. The obtained Q-values and underlying flow mechanisms are discussed in correlation with specific microstructural features and in comparison to the UFG Al.

Effects of Hardening by Annealing and Softening by Additional Plastic Deformation in Ultrafine-Grained Al and Al-Based Alloys: Brief Review

“…The DIS effect accompanied by a significant increase in ductility was reported in Ref. [24] for the UFG Al-0.4Zr (wt.%) alloy structured by HPT. Additional HPT to 0.25 turns led to a decrease in the UTS and YS values, while the magnitudes of elongation to failure and the uniform elongation substantially increased to the values typical for the HPT state (Fig.…”

“…Similar to the case of HPT-processed Al, both the AIH and DIS effects weaken with a decrease in the tensile test temperature in the HPT-processed Al-0.4Zr alloy [24]. Alloying with Zr expands the temperature range of the AIH effect manifestation to lower temperatures as compared to the similar effect in CP Al.…”

“…Adapted from Ref. [24]. (a) Stress-strain curves of Al-1.5Cu (wt.%) alloy in the initial coarse-grained state (curve 1), after HPT processing (curve 2), after annealing at 125 °C, 1 h (curve 3), after annealing at 180 °C, 1 h (curve 4).…”

“…The influence of tensile test temperature (deformation temperature def T ) on the AIH and DIS effects was investigated for UFG Al (99.6 wt.%) [28], UFG Al-0.4Zr (wt.%) [24], and UFG Al-1.47Cu-0.34Zr [27]. The UFG structures in all studied systems were formed by HPT processing at 6 GPa to 10 turns.…”

“…Recently, two new phenomena have been reported for commercially pure (CP) aluminum (Al) with UFG structure. It was shown that annealing can cause hardening, and the subsequent small severe plastic deformation (SPD) can lead to softening in UFG Al and some UFG Al-based alloys structured by SPD [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. These phenomena are called annealing-induced hardening (AIH) and deformation-induced softening (DIS), respectively.…”