Amelioration of Mechanical Properties of Rolled Mg-4.5Al-2.5Zn Alloy by Cryogenic Cycling Treatment

In this study, cryogenic cycling treatment was used to process the hot-rolled Mg-4.5Al-2.5Zn alloy sheets to research the influence on mechanical properties and microstructure. Optical microscopy, electron back-scatter diffraction and transmission electron microscopy were applied to characterize the microstructures and analyze the mechanisms. The consequences indicate that the cryogenic cycling treatment has significantly influence on improving the mechanical properties. With the cycle of cryogenic cycling treatment increasing to 5 cycles, the sample processed by 3 cycles presents the highest ductility (~ 18.6%), while the 4-cycle one shows the highest strength (~ 311.8 MPa). The improvement can be attributed to fine grains, introduced high-density dislocation, 9.8%-fraction low-angle grain boundaries (LAGBs), the precipitation of Mg₁₇Al₁₂ phase and the texture with the intensity of 17.5. Although the average grain sizes of the samples processed by cryogenic cycling treatment have no obvious difference, internal stress variations induced by cryogenic cycling treatment significantly influence LAGBs, the basal texture evolution, and the prismatic < a > slip, pyramidal < c > slip and pyramidal < c + a > slip activation.