The impression creep behavior and microstructure evolution of cast and cast-then-extruded Mg-10Gd-3Y-0.5Zr (wt%)

The impression creep behavior of Mg-10Gd-3Y-0.5Zr (wt%, GW103) was investigated by flat cylindrical indenter experiments at temperatures ranging from 200 degrees C to 325 degrees C. The punching stresses, which were calculated based on the indenter dimensions, varied from 50 MPa to 505 MPa. Samples were examined in the peak-aged cast condition (cast-T6) and in the cast-then-extruded plus peak-aged condition (ex-T5). Using a power-law relationship, the creep stress exponent (n) varied from 1.4 to 5.1 for the cast-T6 alloy, where lower values were obtained at lower temperatures and stresses. The creep activation energy (Q) increased from 87 to 191 KJ/mol with increasing stress. For the ex-T5 alloy, the n values were 2.2, 3.4 and 3.4 at 200 degrees C, 250 and 300 degrees C, respectively. The Q value increased from 121 to 165 kJ/mol with increasing stress. However, by using a hyperbolic sine relationship, single activation energies of 93 and 134 KJ/mol were obtained for the cast-T6 and ex-T5 alloy, respectively. The zone at the edges of the indenter underwent the largest stress and strain, resulting in broken grain boundaries. Extension twinning occurred both in the zone at the edges of the indenter and underneath the indenter face for the cast alloy, while no twinning was observed for the extruded alloy. Intergranular cracking was observed in the zone at the edges of the indenter for the tests under high temperature and high stress. (C) 2015 Elsevier B.V. All rights reserved.