Tensile creep behavior and microstructure evolution of Mg-11Gd-2Y-0.5Zr alloy

Mg-11Gd-2Y-0.5Zr(wt.%, the same below) alloy was prepared by vacuum induction furnace. The creep behavior of the alloy at 200-270 degrees C/110-150 MPa was studied. Constitutive equation of steady state creep rate was constructed. The evolution of precipitated phases in alpha-Mg matrix and grain boundary before and after creep was analyzed by high resolution transmission electron microscopy (HRTEM). The results show that Mg-11Gd-2Y-0.5Zr alloy has excellent creep resistance. The steady state creep rate increases with the increase of stress and temperature. The steady state creep rate is only 7.75 x 10(-9) s(-1) at 270 degrees C/130 MPa. The average stress exponent and creep activation energy are 3.62 and 40.3420607 kJ/mol, respectively, at 200-270 degrees C/110-150 MPa. The creep mechanism is mainly dislocation slip and grain boundary slip. The fine beta' phase in the alpha-Mg matrix coarsens gradually and becomes elliptical, triangular distribution and interconnection. The beta' at grain boundary evolves into the equilibrium phase beta. There is precipitation free zone (PFZ) on the side of grain boundary due to the sliding of grain boundary.