[en] An aluminum-copper alloy (Al-2024) was successfully subjected to high-pressure torsion (HPT) up to five turns at room temperature under an applied pressure of 6.0 GPa. The Al-2024 alloy is used as a fuselage structural material in the aerospace sector. Mechanical properties of the HPT-processed Al-2024 alloy were evaluated using the automated ball indentation technique. This test is based on multiple cycles of loading and unloading where a spherical indenter is used. After two and five turns of HPT, the Al-2024 alloy exhibited a UTS value of ∼1014 MPa and ∼1160 MPa respectively, at the edge of the samples. The microhardness was measured from edges to centers for all HPT samples. These results clearly demonstrate that processing by HPT gives a very significant increase in tensile properties and the microhardness values increase symmetrically from the centers to the edges. Following HPT, TEM examination of the five-turn HPT sample revealed the formation of high-angle grain boundaries and a large dislocation density with a reduced average grain size of ∼80 nm. These results also demonstrate that high-pressure torsion is a processing tool for developing nanostructures in the Al-2024 alloy with enhanced mechanical properties

[en] Research highlights: → Al₃Sc precipitates in Al-2% Si alloy lead to higher strength and smaller grains. → After 5 turns in high-pressure torsion, grain size is ∼0.15 μm and strength ∼375 MPa. → Ball indentation is effective for measuring the mechanical properties. - Abstract: High-pressure torsion (HPT) was used to process Al-2% Si and Al-2% Si-0.25% Sc alloys for up to five turns and the mechanical properties of the processed materials were evaluated using the ball indentation technique (BIT). The results show that the presence of Al₃Sc precipitates is effective in producing higher strength levels and greater grain refinement in the Al-2% Si-0.25% Sc alloy. The introduction of scandium reduces the grain size of the Al-2% Si alloy from ∼0.38 to ∼0.15 μm after 5 turns of HPT and the corresponding maximum tensile strength is increased from ∼325 to ∼375 MPa. The grain and substructure formation in the Al-2% Si alloy is similar to aluminum with dislocation cell formation and a reasonably recovered microstructure whereas in the Al-2% Si-0.25% Sc alloy it is non-homogeneous with arrays of non-equilibrium boundaries and dislocation tangles within the grains.

[en] Disks of an Al-6061 metal matrix composite, reinforced with 10 vol.% Al₂O₃ particles, were processed by high-pressure torsion (HPT) at room temperature for 1/4, 1/2, 1, 5 and 10 turns under an applied pressure of 6.0 GPa. The evolution of microstructure was investigated using optical microscopy and scanning electron microscopy. During HPT processing the average grain size within the aluminum matrix decreased from ∼ 35 μm in the unprocessed condition to ∼ 170 nm after processing through 10 turns but there was no significant effect on the size and distribution of the alumina particulate clusters. The values of the Vickers microhardness were recorded across the surface of each disk and then plotted as two-dimensional and three-dimensional color-coded contour maps. The results show the hardness increases from ∼ 56 Hv in the initial condition to ∼ 165 Hv after HPT for 10 turns. The results demonstrate that, as in many unreinforced metallic alloys, the evolution of hardness with strain exhibits strain hardening without any significant recovery. - Highlights: •The average grain size of the Al matrix was ~ 170 nm after processing for 10 turns. •No significant effect of HPT on the size and distribution of the Al₂O₃ particles. •The evolution of microhardness demonstrates strain hardening without recovery. •The microhardness at low strains increases linearly from the center to the edge. •The microhardness at high strains becomes homogeneous with a saturation of ~ 170 Hv.

[en] Aluminum of commercial purity was processed by equal-channel angular pressing (ECAP) through two, four and eight passes at room temperature. A series of [1 1 4] convergent-beam electron diffraction (CBED) zone axis patterns were obtained using an electron probe with a diameter of 20 nm. Observations were recorded both immediately adjacent to the grain boundaries and in the grain interiors. Symmetry breaking of the higher-order Laue zone (HOLZ) lines was observed adjacent to the boundaries after two and four passes but not in the grain interiors. Pattern simulation of the CBED patterns taken from the two- and four-pass samples adjacent to the boundaries revealed a homogeneous strain with compressive and shear components. The presence of these homogeneous strains demonstrates that the internal stresses associated with the deformation of aluminum at room temperature are localized in the close vicinity, to within ∼20 nm, of the grain boundaries.