On the Equilibrium Intermetallic Phase in Mg-Nd-Ag Alloys

Abstract

The equilibrium intermetallic phase in Mg-Nd-Ag alloys has not been well understood. In this work, intermetallic particles in the solution-treated microstructure of commercial magnesium alloy QE22 (Mg-2.5Ag-2.0Nd-0.7Zr, wt pct) have been investigated using scanning electron microscopy, electron diffraction, atomic-resolution imaging and mapping techniques of scanning transmission electron microscopy (STEM) and thermodynamic modelling. The intermetallic particles are distributed in the inter-dendritic regions. They have coarse irregular shape and share the same crystal structure. The intermetallic phase (designated δ) is determined to have an orthorhombic structure (space group Cmcm, a = 1.02 nm, b = 1.18 nm, c = 1.00 nm) and a composition of NdAgMg11, which are different from those reported previously. An atomic model is proposed for the δ phase based on atomicresolution STEM images and atomic-scale energy-dispersive X-ray spectroscopy maps. The δ lattice is structurally related to that of Mg12Nd phase in binary Mg-Nd alloys. The Gibbs energy of formation of NdAgMg11 is determined from the equilibrium study at 793 K (520 °C), including the entropy of formation using the present experimental phase analysis data obtained at lower temperature.Implications to the formation temperature range and thermal stability of this phase and alloy solidification are discussed based on the calculated Mg-Nd-Ag phase diagram and Scheil solidification paths of alloys.

Dynamic recrystallization and deformation constitutive analysis of Mg–Zn-Nd-Zr alloys during hot rolling

“…At present, the research on thermal deformation of Nd containing magnesium alloys mainly focused on magnesium alloys with high content of Y, Zr, Ag and Zn, mainly due to the mechanical strengthening of these alloying elements. However, studies on thermal deformation behavior of multi-component Mg-Zn-Nd-Zr alloys have not been widely reported [17,18,19,20,21,22,23,24,25,26]. The common characteristic of these alloys with trace alloying elements is that the microstructure changes significantly after thermal deformation.…”

Effect of homogenization on microstructure evolution and mechanical properties of aged Mg-Nd-Sm-Zn-Zr alloy

“…Magnesium (Mg) -rare earth (RE) alloys have been greatly developed in the past decades due to their low density, good corrosion resistance and potential for energy saving [1][2][3][4][5]. Hence, the Mg-RE alloys are widely applied in aerospace, electronic communication and automobile applications [6].…”

Microstructure evaluation and thermal deformation behaviours of wrought magnesium alloys

“…However, studies on the thermal deformation behaviour of multi-component Mg-Zn-Nd-Zr alloys have not been widely reported [16][17][18][19][20][21][22][23][24]. In a recent study report, the high-pressure torsion (HPT) deformation characteristics of the Mg-Nd alloys were studied [25].…”