Microstructure and mechanical properties of Mg-Nd-Zn-Zr alloy processed by integrated extrusion and equal channel angular pressing

The ultrafine-grained Mg-Nd-Zn-Zr alloy was obtained by an integrated extrusion and equal channel angular pressing at 350 degrees C with one pass. Microstructural observations showed a significant refinement of grain structure after a single pass extrusion. The average grain size was reduced to around 500 nm. Numerous beta(1) phases and GP zones were observed in the extruded and subsequently aged alloy. A weak fiber texture with <10<(1)over bar>0> tilting angle of similar to 30 degrees from normal direction towards extrusion direction was found in the extruded alloy. The extruded and subsequently aged alloy presented similar texture to that of the extruded alloy. The extruded alloy exhibited the yield strength (YS), ultimate tensile strength (UTS) and elongation of 248 MPa, 288 MPa and 14.4%, respectively. The extruded alloy after aging treatment achieved higher strength and slightly lower ductility with the YS, UTS and elongation of 264 MPa, 307 MPa and 12.9%, respectively. Compared to the as-cast alloy, the mechanical properties of the extruded and subsequently aged alloy increased 158%, 65% and 34% in YS, UTS and elongation, respectively. The increase in the strength of the extruded and subsequently aged alloy was attributed to both the grain refinement and the precipitation strengthening. The fracture surfaces of the extruded alloy were composed of a lot of small dimples and some cleavage planes. After the aging treatment, the cleavage planes were increased resulting in a decline in the ductility. (C) 2017 Elsevier B.V. All rights reserved.