Compared microstructure and properties of an AlZnMgCu alloy processed by high pressure sliding and high-pressure torsion

Abstract

Achieving high yield strength via submicrometer grain size and nanoscaled precipitation has been reached in 7### aluminum alloys thanks to severe plastic deformation (SPD) by High Pressure Torsion (HPT) process. Unfortunately, this technique has inherently strong limitations since only small parts can be processed and the plastic strain is not homogeneous. These limitations prevent large scale production of Ultra Fine Grain (UFG) materials for potential applications. A recent severe plastic deformation process, High Pressure Sliding (HPS) developed by Fujioka and Horita, allows to homogeneously deform large scale sheets by shear at higher speed. In this work, the competition between precipitation, grain growth and recrystallization during heat treatments after SPD was studied in depth for an AlZnMgCu alloys deformed by HPS with two deformation levels (γ ≈ 15 and γ ≈ 20) in order to investigate if the high mechanical properties obtained by HPT can be reached by HPS. Microstructures analyses after deformation and ageing were carried out by transmission electron microscopy and in situ small angle X ray scattering and then related to the mechanical behavior evaluated by tensile tests. Experimental data show very similar microstructures after HPS and HPT, with a good thermal stability thanks to the competition between precipitation, recrystallization and recovery. The obtained microstructural features lead to exceptional yield strength (>800 MPa) as compared to the classical aluminum alloys. This study is therefore very promising towards the aim of obtaining very high yield strength aluminum alloys suitable for applications.