Effect of heat treatment on elevated temperature tensile and creep properties of the extruded Mg-6Gd-4Y-Nd-0.7Zr alloy

The light and heavy rare earth elements are added to the magnesium alloys to improve the strengths and the creep resistance. The age hardening behaviors of the extruded Mg-6Gd-4Y-Nd-0.7Zr alloy aged at 200, 225 and 250 °C were investigated. Tensile tests and creep tests of the extruded and extruded-T5 Mg-6Gd-4Y-Nd-0.7Zr were carried out at 150-300 °C. The relationship between the microstructure and the properties of the extruded-T5 Mg-6Gd-4Y-Nd-0.7Zr alloy was studied. The result shows that the extruded Mg-6Gd-4Y-Nd-0.7Zr (contained less than 10 wt% Gd) peak aged at 225 °C for 72 h has the excellent creep resistance and high strengths with the UTS more than 350 MPa from room temperature to 200 °C, which are correlative with the precipitates. The high dense and uniform distribution of β′ phase with good heat stability precipitates inhibiting the dislocation motion contributes to age hardening, accelerates the ageing hardening response and increases the creep resistance. The artificially aged (T5) at low temperature further creep tested and tensile tested at higher temperatures decreases the resistance to the dislocation motion and the grain boundary sliding, resulting in the reduction in creep properties and strengths of the extruded-T5 Mg-6Gd-4Y-Nd-0.7Zr alloy above 225 °C.