Contributions to yield strength in an ultrafine grained 1050 aluminum alloy after DC current annealing

Abstract

The ultrafine grained (UFG) 1050 aluminum alloy was prepared by equal channel angular pressing at cryogenic temperature (cryoECAP). The evolution of the yield strength and microstructures of UFG 1050 aluminum alloy after direct electric current (DC current) annealing at 150–400°C for 1h were investigated by tensile test, electron back scattering diffraction pattern (EBSD) and transmission electron microscopy (TEM). For the cryoECAPed and annealed samples at 150–250°C, the predominant boundaries are high angle boundaries (HABs) (>60%), many dislocations accumulate at subgrain and/or grain boundaries, the yield strength (126–159MPa) mainly comes from the dislocation and grain boundary strengthening contributions. While an unusual increase in the yield strength (by 8.1–11.2%) observed in samples annealed at 150–200°C is attributed to an additional strengthening contribution from the more HABs having stable structures which can act as effective barriers to dislocation motion during tensile deformation. When annealing at 300–400°C, the microstructures are free of dislocations, the yield strength (29–45MPa) comes from the grain boundary strengthening contribution. With the application of DC current, the larger grain size, lower dislocation density and higher fraction of LABs having misorientation angle between 3−7° in samples annealed at 150–250°C result in the lower yield strength, while the smaller average grain sizes in samples annealed at 300–400°C cause the higher yield strength.