Influence of cryogenic treatment time on the mechanical properties of AZ31 magnesium alloy sheets after cross-rolling

To investigate the influence of cryogenic treatment time on the mechanical properties and the microstructure of the AZ31 Mg alloy sheets, the different times of cryogenic treatment after two -pass cross -rolling were carried out at air-cooling, 1 hour, 3 hours and 6 hours. The consequences of the tensile experiment illustrated that the crossrolling Mg alloy with 1 -hour cryogenic treatment showed the highest ultimate tensile strength (343 MPa), which was 9.6%, 9.6% and 11.7% higher than air-cooling, 3 -hour cryogenic and 6 -hour cryogenic samples. The primary reasons for this include fine-grained strengthening, twin strengthening, low -angle grain boundaries (LAGBs) strengthening, dislocation strengthening and precipitation strengthening. The internal grain of the magnesium alloy sheet after 1 hour of cryogenic treatment was refined to 5.2 mu m. The {10-11} contraction twin, {10-12} extension twin and {10-12}-{10-11} double twin were surveyed according to the electron backscatter diffraction (EBSD) results. On the <11-20> axis, all the four samples exhibited the {0001} basal texture. And the sample of 1 -hour cryogenic treatment exhibited the highest basal texture intensity. According to the microstructure observation, high -density dislocation and several precipitates were illustrated in the sample of 1hour cryogenic treatment.