Influence of equal channel angular pressing on the evolution of microstructures, aging behavior and mechanical properties of as-quenched Al-6.6Zn-1.25Mg alloy

Abstract

In the present study, the microstructural evolution and mechanical properties of AA7046 aluminum alloy (Al-6.60Zn-1.25 Mg-0.20Cu-0.15Zr, Wt%) processed by 1–4 passes equal channel angular pressing (ECAP) at room temperature were revealed. The results reveal the formation and evolution of substructures, such as dislocation tangles, dislocation cells, and shear bands, during ECAP processing. High-resolution X-Ray diffraction results show that the dislocation density increases to ~2.56 × 1014 m−2 after 3 passes of ECAP. The average grain size was refined from 6.9 μm (before ECAP) to 0.86 μm after 4 passes of ECAP. The initial strong texture developed in hot extrusion process evolves into {112} 〈8 10 1〉 orientation. The yield strength and ultimate tensile strength before ECAP are 156 MPa and 282 MPa, respectively, and the corresponding values increase to 370 MPa and 432 MPa after 4 passes of ECAP. A significant increase of strength mainly originates from dislocation strengthening and fine grain strengthening effects. When the deformed alloy aging at 120 °C, the microhardness of the alloy decreased slightly at the early stage (0.5 h) and then increased to a peak hardness at 18 h. The time to obtain the peak hardness was advanced, compared to conventional T6 aging. This phenomenon mainly results from the recovery of dislocations; moreover, the dense dislocations accelerate the precipitation of the η phase. Dislocation strengthening and precipitation strengthening synergistically contribute to the strength of the ECAP deformed alloy during the aging process.