Effect Of Nd Addition On Microstructures And Mechanical Properties Of Magnesium Alloy

During the last few decades, the world has seen considerable attention in magnesium-based alloys. Magnesium alloys, as the lightest constructive metals, are attractive candidates for a number of wide applications such as 3C applications and aerospace industries. Compared with other competing structural materials such as aluminum alloys and steels, the wide-scale commercialization of magnesium alloys are hindered by their low strength and poor ductility due to their hexagonal close-packed crystal structure, which results in an insufficient number of operative slip and twinning systems. Element alloying is an effective way to improve mechanical performance of magnesium alloys, while thermo-mechanical process can enhance the formability of magnesium by grain refinement from the technical point of view. Therefore, we should further enhance the mechanical properties of magnesium alloys, it is necessary to research the regular and corresponding mechanism of the effect of alloying on microstructure and mechanical properties for Mg alloys in order to promote the integration of function and structure, enhance the value and expand the application of Mg alloy.The study reported different Nd addition in Mg-Y-Zr alloys and Mg-Al-Ca alloys for obtaining the good mechanical properties. The microstructure and mechanical properties of these alloys were investigated by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction( XRD), tensile and compressive testing in this work.Several results can be concluded as follows:(1) Nd-free alloy included ?-Mg and Mg24Y5 phase, in which Mg24Y5 has a body-center cubic structure. While adding Nd leads to form a new second phase, namely ?(Mg12YNd2). After hot extrusion, there was more and more broken particles of Mg24Y5 and ? phase dispersing in matrix which promoted the nucleation of dynamic recrystallization, the volume fraction of recrystallization advanced, and the average grain size of recrystallization could be refined from 4.58? m to 1.28? m. The tensile strength and yield strength of extruded alloy increased with increment of Nd, the maximum values of them were 285 MPa and 233 MPa respectively. Nd-free alloy exhibited a high elongation of 29.1%. The elongation decreased to 4.7% with increasing Nd content.(2) After rolling process, dynamical recrystallization(DRX) process happened in the rolled Mg-Y-Zr-Nd alloy, the grains were elongated along the rolling direction, the second phase was broken during the rolling process and also distributed along the rolling direction. The texture type after rolling process is basal texture and the texture intensity decreased with the increase of Nd content. Annealing cannot change the type of basal texture of the sheet, but can effectively weaken the intensity of basal texture. The yield strength and ultimate tensile strength of roll-annealed Mg-Y-Zr-Nd alloy sheets decreased while the fracture elongation increased after annealed at both temperature. In this study, Mg-Y-Zr-Nd alloy prepared by extrusion, rolling and annealing treatment exhibit high performance, the mechanical properties significantly better than current commercial magnesium alloy sheets. The Mg-Y-Zr-Nd alloy sheet has the potential of engineering application.(3) Nd-free Mg-Al-Ca alloy included ?-Mg and Mg17Al12 and Al2 Ca phase, the Nd atoms adding to the Mg-Al-Ca alloys combined with Al to form two new intermetallic compounds, namely Al11Nd3 and Al2 Nd phase, and the amounts of Al2 Nd and Al11Nd3 phases increase with the increase of Nd addition. As increasing Nd addition, the average grain size of Mg-Al-Ca alloy could be refined from 4.80? m to 2.39?m, and the intensity of basal texture could be weaken from 5.3 to 2.8.The tensile strength and yield strength of extruded alloy increased with increment of Nd at 150?, while the elongation decreased slightly. The strengths at 150? are improved due to the grain refinement strengthening and precipitation strengthening and solution strengthening. The extruded bar with 1.76 wt.% Nd presented higher yield strength(159MPa), ultimate tensile strength(229MPa) and relatively high elongation(?=39.3%). These alloys have better mechanical properties than wrought WE43 magnesium at 150°, and their cost is lower than wrought WE43 magnesium alloys. At room temperature, the mechanical properties of these four alloys present tha same trend as 150?.