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The paper focuses on producing of ultrafine-grained (UFG) structure in the Al 6061 alloy by a new severe plastic deformation (SPD) technique, developed recently in our laboratory, namely equal channel angular pressing with parallel channels (ECAP-PC). The evolution of microstructure at ECAP-PC was examined and was proved that the alloy becomes of a homogenous UFG structure after 4 passes. Such a structure increases essentially the alloy's mechanical properties, specifically strength and ductility. The advantages of this new technique in producing of UFG alloys over conventional ECAP are considered and discussed as well.

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Three different Al-Zn alloys (2, 10, 30 wt% Zn) have been processed by severe plastic deformation (SPD) in the solutionized state to investigate the concomitant mechanisms of grain refinement and phase separation. The data of high resolution analytical transmission electron microscopy clearly reveal the key role of grain boundaries that promote Zn segregation and fast diffusion. Surprisingly, it is also shown that SPD carried out at 150°C could give rise to a finer multiphase structure comparing to room temperature processing. Our observations seem to indicate that it resulted from a competition between the classical discontinuous precipitation of Zn and SPD-induced dynamic precipitation.

Cite this article as: Nguyen Q. Chinh, Péter Jenei, Jenő Gubicza, Elena V. Bobruk, Ruslan Z. Valiev and Terence G. Langdon, Influence of Zn content on the microstructure and mechanical performance of ultrafine-grained Al-Zn alloys processed by high-pressure torsion, Materials Letters, http://dx.doi.org/10.1016Letters, http://dx.doi.org/10. /j.matlet.2016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Keywords: Al-Zn alloys, grain boundaries, indentation, micro-pillars, strain rate sensitivity, ultrafine grains Abstract: Al-Zn alloys were processed by high-pressure torsion (HPT) to produce ultrafine-grained (UFG) materials. For low Zn contents, HPT gave strengthening due to grain refinement while for the highest Zn concentration the decomposition of the microstructure yielded an abnormal softening at room temperature. The microstructure decomposition led also to the formation of a Zn-rich phase which wet the Al/Al grain boundaries and enhanced the role of grain boundary sliding with unusually high strain rate sensitivity. The occurrence of intensive sliding in these UFG alloys is demonstrated by deforming micro-pillars.

This paper investigates a dynamic aging effect induced by severe plastic deformation (SPD) and subsequent artificial aging on structure and mechanical properties of aluminum Al-Mg-Si alloys. Application of optimal processing parameters of SPD via equal-channel angular pressing with parallel channels and subsequent artificial aging ensures simultaneous enhancement of strength and ductility in the processed alloys. Ultrafine-grained microstructures with strengthening metastable b 0 and b 00 precipitates generated during SPD processing and subsequent artificial aging provide enhanced strength due to significant grain boundary hardening and precipitation hardening.

The important benefits of ultrafine-grained (UFG) alloys for various applications stem from their enhanced superplastic properties. However, decreasing the temperature of superplasticity and providing superplastic forming at lower temperatures and higher strain rates is still a priority. Here, we disclose, for the first time, the mechanism by which grain boundary sliding and rotation are enhanced, when UFG materials have grain boundary segregation of specific alloying elements. Such an approach enables achieving superplasticity in commercial Al alloys at ultralow homologous temperatures below 0.5 (i.e. below 200°C), which is important for developing new efficient technologies for manufacturing complex-shaped metallic parts with enhanced service properties. IMPACT STATEMENTFor the first time, ultralow-temperature superplasticity is found in commercial 7xxx Al alloy. This discovery enables the development of new technologies for the superplastic forming of complexshaped products with enhanced service properties.