Enhancing strength and ductility of Mg–12Gd–3Y–0.5Zr alloy by forming a bi-ultrafine microstructure

By means of equal channel angular pressing (ECAP) technique, an Mg–12Gd–3Y–0.5Zr alloy was processed at 300 °C for one and four passes. A bi-ultrafine (BU) microstructure of Mg-alloy, consisting of matrix grains and the second-phase particles with sizes smaller than 1 μm, was obtained after the fourth pass of ECAP. The formation of this BU microstructure originated from the complex interactions between the matrix grains and second-phase particles during the ECAP processing at elevated temperature. A simultaneous improvement of both strength and ductility was achieved in the sample with the BU microstructure, compared with the original sample. The increase in strength is resulted from the refinement of both matrix grains and second-phase particles, while the improved ductility is attributed to the considerable plasticity provided by both dislocation mechanism and profuse shear bands in the BU microstructure. An enhanced plasticity induced by the shear-band mechanism is proposed for the magnesium alloy with the BU microstructure.