Microstructure and mechanical properties of Mg-Ni-Gd alloy synthesised by powder metallurgy

The hexagonal close-packed structure renders magnesium weak at room and high temperatures for structural applications despite its low density. Inducing thermally stable and coherent second phases would enhance/retain the strength of Mg-based alloys even at high temperatures. This paper aims to develop a high-strength Mg-based nanocomposite. A master alloy composed of Ni and Gd was cast and the composition of Mg97.56Ni1.22Gd1.22 (at.-%) was prepared using ball milling for 150 h. XRD plots of the as-milled powder having nano-size crystallites confirm the partial dissolution of the master alloy. Consolidation through sintering with 5, 7 and 9 h of exposure at 550 degrees C and extrusion at 500 degrees C resulted in the formation of Mg5Gd, Mg2Ni, Gd2O3 and MgO phases. The extruded samples possessed a high strength of 804 MPa, which can be attributed to ultra-fine grains and dispersoid strengthening by homogeneously distributed second-phase particles in the 100-200 nm range.