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 cross-rolling 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 μm. 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 micro-structure observation, high-density dislocation and several precipitates were illustrated in the sample of 1-hour cryogenic treatment.