Deformation driven enhancement of strength-ductility synergy of a PM AA6061-10Cu hybrid material

Abstract

A powder metallurgy (PM) AA6061-10Cu hybrid material was fabricated by a thermomechanical consolidation technique involving hot extrusion of the compact of an AA6061 aluminum alloy and Cu powder blend. By increasing the extrusion ratio from 9:1 to 25:1, both the yield strength (YS), ultimate tensile strength (UTS) and elongation to fracture (EL) of the material all increased significantly from 122 MPa, 207 MPa and 6.8 % to 155 MPa, 256 MPa and 8.9 %. This clearly signifies the deformation driven enhancement of strength-ductility synergy of the PM hybrid material. After a tailored T6 heat treatment, the superior tensile properties associated with increased deformation were maintained, with the YS and UTS increasing from 189 to 253 MPa to 246 and 297 MPa, while maintaining the EL at 5.8 %. In both states, the improvement of strength is attributed to nano-precipitate strengthening from the high volume fractions of Al₂Cu, Al-(Fe, Cr, Si) and Al-(Fe, Cr) precipitates, grain boundary strengthening due to the refinement and increased volume fraction of recrystallized grains, and dislocation strengthening within the Cu particles. The significant improvement in ductility of the as-extruded hybrid material is attributed to the promotion of coordinated deformation facilitated by the high density geometrically necessary dislocations (GNDs) resulting from the pronounced size disparity between dynamic recrystallized (DRXed) and deformed grains in the matrix, as well as the substantial increase in the volume fraction of DRXed grains, which provides strong support for grain boundary sliding and rotation within the grain layer, positively influencing strain continuity at the AA6061/Cu interface. These findings offer new insights for hybrid material design to achieve superior mechanical performance.