Mechanical properties and grain growth kinetics in magnesium alloy after accumulative compression bonding

An ultrafine-grained AZ31 magnesium alloy with a mean grain size less than 1μm was fabricated using three-passes of accumulative compression bonding. Three passes were made at temperatures of 693K, 643K and 593K, respectively, with a strain rate of 1.5s-1 and a reduction of 75% for each pass. After the first pass, the mean grain size was abruptly refined from 23μm to 5.1μm and most of the basal planes had been rotated 90° perpendicular to the compression direction. After three passes, the microstructure was homogenous and excellent mechanical properties were obtained: 245MPa yield stress, 372MPa ultimate tensile strength and 14.8% fracture elongation. And a study on the kinetics of grain growth was carried out at temperatures range of 623-723K. The effect of annealing temperature, T, and time, t, on the grain growth kinetics can be well interpreted by the kinetics equation Dn-D0n=kt, where k=k0e(-Eg/RT). According to the experimental data, the activation energy for grain growth Eg was measured to be 105kJ/mol. © 2012.