Controlling the high temperature mechanical behavior of Al alloys by precipitation and severe straining

Abstract

The aim of this work was to investigate the influence of the precipitate distribution on the microstructure and on the room and high temperature mechanical properties of an age-hardenable aluminium AA6082 alloy following severe straining by high-pressure torsion (HPT). With this goal, specimens in the as-cast and T6 peak-aged conditions were processed by HPT using 0.5, 1 and 5 turns at room temperature. At high strain levels (J>100), similar saturation grain sizes (~250 nm), high-angle boundary fractions (~80%) and hardness values (Hv~160) were obtained for both initial conditions. Grain refinement led to significant strengthening and to good ductility values at room temperature. Analysis by TEM and EDS elemental mapping revealed that HPT processing of the as-cast condition led to fracture of the stable E-phase into many small precipitates located preferentially along grain boundaries and triple junctions. By contrast, HPT processing of the T6 peak-aged specimens revealed a partial dissolution of the needle-shaped nanoprecipitates. The different evolutions of the precipitate distributions following straining in the as-cast and peak-aged conditions gave rise to dramatic differences in the mechanical properties and the operative deformation mechanisms at warm temperatures. These results provide evidence that the high temperature mechanical behavior of age-hardenable Al alloys may be conveniently controlled by altering the precipitate distribution followed by severe straining.

Texture evolution in high-pressure torsion processing

“…It is interesting to note that the compilation in Table 2 demonstrates that the texture evolution after high shear strains is also affected by the value of the γ SFE . For example, the texture of Al-based alloys becomes weak after high shear strains [116][117][118][119][120][121]129] while the texture of Ni and Cu-based alloys appear to be reasonably stable [72,123,127,128]. This difference is related to the hardening and grain refinement behaviors in high and low γ SFE alloys.…”

“…The effect of a preliminary heat treatment on the texture evolution was investigated for the Al-0.6Mg-0.4Si (wt.%), commercial AA6082 and Cu-0.86Cr (at.%) alloys [119,120,130]. Figure 8 presents the evolution of the texture of the Al-0.6Mg-0.4Si alloy under different initial conditions (solid solution treatment at 813 K for 2 h and quenched to RT, aged for 5 minutes at 473 and 523 K, respectively) [119].…”

“…In order to confirm any correlation, Table 5 was developed based on the fundamental microstructural parameters of grain size and fraction of HAGBs, the microhardness and the texture evolutions reported for AA6082 [120] and Cu-0.86Cr [130] alloys during HPT processing. It is evident that the effect of precipitate particles on the microstructural parameters, microhardness and texture evolution depend strongly on the amount of shear strain.…”

Influence of Grain Coarsening on the Creep Parameters During the Superplastic Deformation of a Severely Friction Stir Processed Al-Zn-Mg-Cu Alloy

“…Bulk nanostructured materials usually present good superplastic response at high strain rates and relatively low temperatures due to their exceptional microstructures in the form of highly misorientated ultrafine grains [1][2][3][4][5][6]. In this regard, friction stir processing (FSP) is a severe plastic deformation (SPD) technique based on the concepts of friction stir welding (FSW) [7] capable of producing ultrafine grain sizes (< 1 µm) using appropriate parameters [8][9][10][11][12].…”