Mechanical properties and grain growth kinetics in magnesiμm alloy after accμmulative compression bonding

摘要

An ultrafine-grained AZ31 magnesiμm alloy with a mean grain size less than 1 μm was fabricated using three-passes of accμmulative compression bonding. Three passes were made at temperatures of 693 K, 643 K and 593 K, respectively, with a strain rate of 1.5 s~(-1) and a reduction of 75% for each pass. After the first pass, the mean grain size was abruptly refined from 23 μm to 5.1 μm and most of the basal planes had been rotated 90° perpendicular to the compression direction. After three passes, the micro-structure was homogenous and excellent mechanical properties were obtained: 245 MPa yield stress, 372 MPa ultimate tensile strength and 14.8% fracture elongation. And a study on the kinetics of grain growth was carried out at temperatures range of 623-723 K. The effect of annealing temperature, Τ, and time, τ, on the grain growth kinetics can be well interpreted by the kinetics equation D~n - D_0~n = kt, where k= k_0e~(-E_g/RT). According to the experimental data, the activation energy for grain growth E_g was measured to be 105 kJ/mol.