Microstructural Characterization of Homogenised and Aged Mg-Gd-Nd-Zn-Y-Zr Alloys

Abstract

The microstructure of the Mg—6%Gd-3.7%Nd-0.3%Zn-0.18%Y-0.15%Zr (%wt) alloy has been investigated after solution treatment at 540°C for 24hr followed by isothermal aging at 175°C up to 32 days by using of Vickers hardness, optical microscopy, scanning electron microscopy equipped with EDS, X-ray diffraction and transmission electron microscopy. It was observed that the homogenized alloy contained primary α-Mg solid solution, eutectic structures, cuboid shaped phases and Zr-rich clusters. The eutectic structures were the products of a ‘quasibinary eutectic reaction’ L→α-Mg+β-Mg₅RE. The eutectic phase was characterized to be of Mg₅Gd prototype with the composition Mg₅(Gd_xNd_1-x, x≈0.2). The cuboid shaped phases, with the composition Gd₄(Nd_xY_1-x, x≈0.5), grew during aging and reached ~3μm average size. Precipitation of β" and β' phases during aging was observed. The maximum microhardness was achieved after 16 days of aging.