Low temperature super ductility and threshold stress of an ultrafine-grained Al\u2013Zn\u2013Mg\u2013Zr alloy processed by equal-channel angular pressing

Bálint Boldizsár,Péter Jenei,Anwar Q Ahmed,Ruslan Z Valiev,Maxim Yu Murashkin,Nguyen Q Chinh

doi:10.1007/s10853-021-06527-4

Abstract

Low temperature tensile and impression creep tests were carried out on an ultrafine-grained 7xxx series Al–4.8Zn–1.2 Mg–0.14Zr (wt%) alloy, which can be deformed for maximum elongation of about 200% at 150 °C. The characteristics of the deformation process, such as the strain rate sensitivity (SRS) and activation energy (Q) were determined by considering also the effect of threshold stress. Relatively high SRS of sim 0.35 and low activation energy of sim 92 kJ/mole were obtained, confirming the super ductility of the investigated ultrafine-grained alloy in the low temperature region between 140 and 160 °C.Graphical abstract

Highlights

Age-hardenable materials, such as Al–Zn–Mg alloys (7xxx series) are widely investigated due to their technological and practical importance, as these alloys are ductile at high temperatures and having high strength at low temperatures
As it has been mentioned, there is an unambiguous relationship between the ductility and the strain rate sensitivity (SRS) of the materials [16,17,18], and the total elongation of 100–200% can be expected at strain rate sensitivity higher than 0.3
Characteristics of low temperature plastic deformation of an equal-channel angular pressing (ECAP)-processed ultrafine-grained AlZnMgZr alloy were studied by tensile and impression creep tests in the low temperature region between 140 and 160 °C

Summary

Introduction

Age-hardenable materials, such as Al–Zn–Mg alloys (7xxx series) are widely investigated due to their technological and practical importance, as these alloys are ductile at high temperatures and having high strength at low temperatures. The conventional coarse-grained AlZnMg alloys have very poor ductility at low temperatures, under 0.5Tm, where Tm is the melting point. In the last two decades, by applying severe plastic deformation (SPD), such as equal-channel angular pressing (ECAP) [1,2,3,4,5,6] and high-pressure torsion (HPT) [7,8,9,10,11] techniques, several conventional Al–Zn and Al–Zn– Mg alloys have been ultrafine-grained (UFG) so that the average grain size was decreased significantly, typically down to the ultrafine region between 100 and 500 nm. The UFG structure in general, enhances both the strength of the materials by the well-known Hall–Petch effect [12, 13] and the role of the grain boundary sliding even at room temperature [6, 10, 14, 15]. For instance, the ductility and the corresponding strain rate sensitivity of some UFG Al–Zn alloys at room temperatures were significantly improved, showing the super ductility of higher than 150% and unusually high SRS above 0.25 [10, 15]

Methods

Results

Conclusion