Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

AbstractMagnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 °C, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy

Effect of rare earth elements on the structures and mechanical properties of magnesium alloys

By means of first-principles calculations, we have investigated the effects of rare earth elements (REEs) on the structures and mechanical properties of magnesium. The lattice parameters, elastic constants, bulk moduli, shear moduli, Young's moduli and anisotropic parameter of these solid solutions have been calculated and analyzed. The nearest-neighbor distance between Mg and the REEs is also analyzed to explore the correlation with the bulk moduli. The results show that the 4f-electrons and atomic radii play an important role in the strengthening process. The anomalies of the lattice parameters and mechanical properties at Eu and Yb are due to the half-filled and full-filled 4f-electron orbital states. Finally, the increase of directional bonding character near the alloying elements may account for the anisotropy and brittleness of these magnesium alloys

Achieving High-Strength and Toughness in a Mg-Gd-Y Alloy Using Multidirectional Impact Forging

High strength and toughness are achieved in the Mg-4.96Gd-2.44Y-0.43Zr alloy by multidirectional impact forging (MDIF). The forged sample has a fine-grained microstructure with an average grain size of ~5.7 µm and a weak non-basal texture, and it was characterized by an optical microscope (OM), scanning electron microscope (SEM), and electron back-scattering diffraction (EBSD). Tensile results exhibit the tensile yield strength (TYS) and static toughness (ST) of as-homogenized alloy dramatically increased after forging and aging, i.e., the TYS increased from 135−5+4 MPa to 337−2+2 MPa, and the ST enhanced from 22.0−0.5+0.3 MJ/m3 to 50.4−5.4+5.3 MJ/m3. Specifically, the forged Mg-Gd-Y-Zr alloy owns higher TYS than that of commercial rolled WE54 (Mg-5.25Y-3.5Nd-0.5Zr) and WE43 (Mg-4.0Y-3.0Nd-0.5Zr) alloys

Twin evolution in cast Mg-Gd-Y alloys and its dependence on aging heat treatment

Effects of rare-earth (RE) and precipitates on twin evolution in cast Mg-10Gd-3Y-0.5Zr (wt.%) (GW103) alloys of solid solution (T4) and aged (T6) states are investigated performing quasi-static room temperature compression tests and microstructural characterization. It is found that both {10–12} and {11–21} extension twins (ET1 and ET2) can appear in the T4 and T6 states but with different emergence sequences. As the aging heat treatment leads to consumption of RE solutes which could inhibit atomic shuffling required for nucleation of ET1 but not ET2, ET2 occurs prior to ET1 in the T4 state, and ET1 emerges before ET2 in the T6 state. The extension twins here mainly coordinate the plastic deformation through the non-Schmid effect. Our results shed light on the influence of RE elements on twin evolution in magnesium alloys and have implications in developing high-performance Mg-RE alloys

Tension-compression asymmetry of temperature dependencies in Mg rare-earth alloys

To reveal the tension-compression asymmetry of temperature-dependency in Mg-RE alloys, uniaxial tensile and compression tests followed by microstructural characterizations were performed on a cast Mg-10Gd-3Y-0.5Zr (wt.%) alloy under various temperatures. The results show that this alloy exhibits anomalous temperature effects on mechanical properties (such as tensile strength and plasticity) during tension, while they are not observed during compression tests, demonstrating that the anomalous temperature effects exhibit loading path dependence. The tension-compression asymmetry of the anomalous temperature-dependency associated with variations in twinning. It is believed that these variations in twinning result from the interplay between the inhibitory effect of rare earth elements on twinning and the promoting effects of elevated temperature or a change in the loading path from tension to compression, with the loading path having a stronger promoting influence than the deformation temperature

Radiative Transfer Model Simulations for Ground-Based Microwave Radiometers in North China

Ground-based microwave radiometer profilers (MWRPs) are widely used to provide high-temporal resolution atmospheric temperature and humidity profiles. The quality of the observed brightness temperature (TB) from MWRPs is key for retrieving accurate atmospheric profiles. In this study, TB simulations derived from a radiative transfer model (RTM) were used to assess the quality of TB observations. Two types of atmospheric profile data (conventional radiosonde and ERA5 reanalysis) were combined with the RTM to obtain TB simulations, then compared with corresponding observations from three MWRPs located in different places in North China to investigate the influence of input atmospheric profiles on TB simulations and evaluate the quality of TB observations from the three MWRPs. The comparisons of the matching samples under clear-sky conditions showed that TB simulations derived from both radiosonde and ERA5 profiles were very close to the TB observations from most of the MWRP channels; however, the correlation was lower and the bias was obvious at 51.26 GHz and 52.28 GHz, which indicates that the oxygen absorption component in the RTM needs to be improved for lower-frequency temperature channels. The difference in location of the radiosonde and MWRP sites affected the TB simulations for the water vapor channels, but had little impact on temperature channels that are insensitive to humidity. Comparisons of both simulations (ERA5 and Radiosonde) and the corresponding TB observations from the three sites indicated that the water vapor channels observation quality for the MWRP located in southern Beijing needs improvement. For the two types of profile data, ERA5 profiles have a more positive effect on TB simulations in the water vapor channels, such as enhanced consistence, reduced bias and standard deviation between simulations and observations for those MWRPs located away from the radiosonde station. Therefore, hourly ERA5 data are an optimal option in terms of compensating for limited radiosonde measurements and enhancing the monitoring quality of MWRP observations within 24 h

Electronic origin of the anomalous solid solution hardening of Y and Gd in Mg: A first-principles study

National Basic Research Program of China [2007CB613704]; National Natural Science Foundation of China [50874100]Y and Gd demonstrate anomalous solid solution hardening efficiency, which cannot be understood using the elastic impurity-dislocation interaction theory. We performed first-principles calculations to investigate the effect of different alloying elements such as Al, Zn, Y, and Gd on the chemical bonding of Mg solid solutions. The present calculations clearly show that the anomalous solid solution hardening of Y and Gd in Mg may be understood based on the increased bonding strength of both Mg-Y (Gd) and Mg-Mg

First-principles calculations of the beta'-Mg7Gd precipitate in Mg-Gd binary alloys

National Basic Research Program of China [2007CB613704]; National Natural Science Foundation of China [50874100]The metastable beta' phase is often the most effective hardening precipitate in Mg-Gd based alloys. In this paper, the structural, elastic and electronic properties of the recently identified beta'-Mg7Gd precipitate in Mg-Gd binary alloys were investigated using first-principles calculations based on density functional theory. The lattice mismatches between the coherent beta'-Mg7Gd precipitate and alpha-Mg matrix are discussed and used to rationalize the experimentally observed morphology of the precipitate. The mechanical properties were investigated through analysis of the single-crystal elastic constants and the polycrystalline elastic moduli. It is found that beta'-Mg7Gd is brittle in nature. Strong covalent bonding in beta'-Mg7Gd, as inferred from its electronic structure, further explains its mechanical properties. Our theoretical results show good agreement with experimental measurements