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The microstructure, chemical composition and phase constitution of the surface film formed on molten Mg-2.82Nd-0.45Zn-0.32Zr alloy in an open melting furnace under a protective gas mixture of 3% SO 2 and 97% CO 2 at temperatures 983–1053 K were investigated, using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) techniques. Based on the test results and thermodynamic calculations, the protection mechanism was presented in this paper. The gas mixture provided an effective protection for the Mg alloy melt through forming a continuous and dense surface film of MgO, MgSO 4 , Nd 2 O 3 and ZrO 2 . While the formation of surface Nd 2 O 3 and MgSO 4 film provided protection to the melt at low temperatures (about 983 K), and the surface C and ZrO 2 coupled with inner enrichment of Nd improved the protective effect of the film at high temperatures (around 1053 K). [ABSTRACT FROM AUTHOR]

Highlights: [•] A modified WE43 alloy, free of heavy rare earth elements, has been assessed. [•] The new alloy, Mg–4Y–3Nd–0.5Zr (wt.%), is stronger than WE43 up to 573K. [•] The new alloy is more creep resistant than WE43 alloy at 473K under 40–80MPa. [•] It is promising to use neodymium to replace heavy rare earth elements in WE43. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study has been made of the effect of grain size on the tensile and creep properties of Mg–2.6Nd–0.35Zn–xZr (in wt%) alloys (ML10 or ZM6) at 250°C, the maximum long-service temperature for these alloys. Grain sizes ranging from 102 to 920μm were produced in the T6 state after grain refinement with Zr. The sand cast Mg–2.6Nd–0.35Zn alloy solidified as largely columnar grains (900±430μm). An addition of 1.8% Zr reduced the grain size to 84μm but most grains were still irregular rather than equiaxed. The grain size increased linearly with 1/Q (Q: growth restriction factor) calculated from the soluble Zr content only. Significant grain hexagonalization occurred during solid solution treatment at 530°C (720min). Both the yield strength and ultimate tensile strength at 250°C followed the Hall–Petch relationship while the ductility increased linearly with decreasing grain size. The steady-state creep rate at 250°C increased significantly with decreasing grain size but followed the general power law at each stress level evaluated (50–90MPa). The effect of grain size on creep is related to the applied stress where the grain size effect exponent p showed a linear dependency on applied stress. To satisfy the requirements for both the tensile and creep properties at 250°C, the T6 grain size of these alloys should be limited to about 174μm. However, when the T6 grain size is <100μm, it may result in a significant increase in the steady-state creep rate. [Copyright &y& Elsevier]

Abstract: The effects of Nd addition on the microstructures and mechanical properties at elevated temperatures of a Mg–0.3Zn–0.32Zr alloy were investigated in this study. The grain sizes of Mg–0.3Zn–0.32Zr alloys were decreased from 120μm to 76μm and grain morphologies were changed from hexahedron to rosette-like by increasing Nd addition from 0.21% to 2.65%. Both Nd and Zn are fully dissolved into the Mg matrix when Nd addition is less than 0.84% and the as-cast structure consists of only α-Mg. Increasing Nd concentration over 1.62%, intermetalitics Mg12(Nd,Zn) phase confirmed by X-ray diffractometer (XRD) occurs at the grain boundaries and triple grain boundaries. The heat treatment results in the Nd fully dissolved and then re-precipitated as Mg12(Nd,Zn), distributing as cluster within the grains and along the grain boundaries. The heat treatment also results in some grain coarsening, and Nd acts as effective barriers for the grain agglomeration. The existing of Mg12(Nd,Zn) phase within the grains and along the grain boundaries for the alloys containing high Nd acts to lock the grain boundaries and reduce grain boundary and dislocation sliding, leading to obvious improvements both in tensile strength and yield strength as well as a slight decrease in elongation at elevated temperatures. [Copyright &y& Elsevier]