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

Abstract

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.