Low temperature super ductility and threshold stress of an ultrafine-grained Al–Zn–Mg–Zr alloy processed by equal-channel angular pressing

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

Effect of the Equal Channel Angular Pressing on the Microstructure and Phase Composition of a 7xxx Series Al-Zn-Mg-Zr Alloy

“…This reduction is presented as the mentioned drop of activation energy, Q p from 147.4 kJ/mol to 117.7 kJ/mol for the ECAP-processed sample compared to the un-deformed sample, as demonstrated in Figure 8. Although further investigations are needed to clarify better the details of thermally activated processes-both the dissolution and precipitation-during DSC measurements, the present results are important for understanding the unusually high-plastic behavior of this UFG alloy after ECAP processing [12] which will soon be examined. On the whole, the grain-refining, strengthening, as well as precipitation-facilitating effects from equal channel angular pressing as a useful severe plastic deformation process are an exciting field in today's materials science.…”

“…These alloys are widely studied due to their technological and practical importance in the manufacture of automobiles, aircraft, and other construction materials [1][2][3][4][5]. It is well-established that the 7xxx materials have high mechanical properties [6][7][8][9][10] due to the fact that their microstructure can be changed on a very wide scale from the supersaturated solid solution state by applying different heat treatments [6,7] and/or severe plastic deformation techniques [11,12]. In general, if the supersaturated alloy is artificially aged under different conditions, various metastable and stable precipitates can be formed.…”

“…When a pre-deformation becomes severe plastic deformation (SPD), both the grain structure and precipitate structure of an AlZnMg alloy may change significantly [13]. In the last twenty-five years, the SPD technique using equal channel angular pressing (ECAP) was widely applied to refine the average grain size, resulting in an ultrafine-grained (UFG) microstructure, improving the mechanical properties of metal alloys via the Hall-Petch effect [11,12,[14][15][16]. Also, some recent works show that the precipitation of dispersed second phases in the form of interlayers or segregations at grain boundaries and in grain interiors plays an important role in achieving simultaneously strength, ductility, stress corrosion, fatigue, superplasticity at lower temperatures, and thermal and deformation stability in UFG or nanostructured Al alloys [17][18][19][20][21][22][23][24].…”

Microstructure Evolution during High-Pressure Torsion in a 7xxx AlZnMgZr Alloy

“…Despite extensive investigations [26][27][28][29][30], the effect of the shear strain in a wide range of deformation imposed in HPT processes on the microstructure and on the subsequent mechanical properties of several AlZnMg alloys has not been clarified in detail.…”