Search Results (5)

Strengthening Mg alloys with rare earth elements has been a research focus for several decades. To minimize the usage of rare earth elements while enhancing mechanical properties, we adopted the strategy of alloying with multiple rare earth elements, namely Gd, Y, Nd, and Sm. Additionally, to promote the precipitation of basal precipitate, Ag and Zn doping was also induced. Thus, we designed a new cast Mg-2Gd-2Y-2Nd-2Sm-1Ag-1Zn-0.5Zr (wt.%) alloy. The microstructure of the alloy and its relevance to mechanical properties in various heat treatment conditions were investigated. After undergoing a heat treatment process, the alloy demonstrated exceptional mechanical properties, with a yield strength of 228 MPa and an ultimate tensile strength of 330 MPa achieved through peak-aging for 72 h at 200 °C. The excellent tensile properties are due to the synergistic effect of basal γ″ precipitate and prismatic β′ precipitate. In its as-cast state, its primary mode of fracture is inter-granular, whereas in the solid-solution and peak-aging conditions, the predominant mode of fracture is a mixture of trans-granular and inter-granular fractures. Full article

Enhancing the mechanical properties of magnesium alloys to meet the urgent need for their lightweight applications in the aerospace field has always been a great challenge. Herein, the effect of Ag on the microstructure and tensile properties of the Mg−2.5Nd−1.0Sm−0.4Zn−0.1Ca−0.5Zr (EK30) alloy prepared by integrated extrusion and equal-channel angular pressing is studied. The microstructure of as-extruded alloys consists of α-Mg grains and the β phase. The addition of Ag increases the β-phase content. The β phase can promote dynamic recrystallization by inducing a particle-stimulated nucleation mechanism and inhibiting grain growth, which leads to grain refinement and texture weakening. At 250 °C, the ultimate tensile strength of the EK30–2.0Ag alloy (225.9 MPa) increased by 13.8% compared to the Ag-free alloy (198.4 MPa). When the tensile temperature increased from 25 °C to 250 °C, the ultimate tensile strength of the EK30–2.0Ag alloy decreased by 14.3%, from 263.7 MPa to 225.9 MPa. Notably, the addition of Ag slightly reduced the elongation of the alloy at 250 °C; the elongations of the EK30–2.0Ag alloy and the EK30 alloy are 41.5% and 37.0%, respectively. The elongation of the EK30–2.0Ag alloy increased from 22.7% at 25 °C to 52.7% at 275 °C. All alloy tensile fractures exhibited typical plastic fracture characteristics. This study provides an effective way to enhance the high-temperature mechanical properties of magnesium alloys by Ag alloying and a special severe plastic deformation method. Full article

Achieving magnesium-rare earth alloys with excellent mechanical properties remains a challenging goal in the aerospace industry. The integrated extrusion and equal channel angular pressing were employed to refine grain and improve the mechanical properties of Mg-xNd-2.0Sm-0.4Zn-0.4Zr alloys. The effect of Nd element on microstructure and mechanical properties of the extruded and subsequently aged alloys were carried out by varying the amount of the Nd element from 0 wt.% to 2.5 wt.%. The optical microscopy results indicated that the grain size was remarkably refined by the addition of Nd element. The grain size decreased from 29.7 μm to 10.9 μm with increasing of the Nd element from 0 wt.% to 2.5 wt.%. The transmission electron microscopy results showed that the nano-scaled basal lamellar precipitates, prismatic lamellar precipitates and granular precipitates were formed in α-Mg matrix. The amount of the precipitates increased significantly by the addition of Nd. Moreover, the strength of the alloys significantly improved with Nd. Superior strength and considerable plasticity were obtained as the content of Nd element reached 2.0 wt.%, while the tensile strength of the Mg-2.0Nd-Sm-Zn-Zr alloy (315 ± 5 MPa) increased by 35.8% with respect to the Nd-free alloy (232 ± 3 MPa). Full article

The effect of solution treatment time on the microstructure and mechanical properties of aged the Mg-2.0Nd-2.0Sm-0.4Zn-0.4Zr (wt.%) alloy were investigated to give full play to the performance of the alloy. As the solution treatment time increased from 2 h to 12 h at 788 K, the grain size of the solution-treated alloy significantly increased, and the network-like β-Mg₁₂(Nd, Sm, Zn) phase gradually dissolved into the α-Mg matrix. It should be noted that no obvious residual β phase can be observed when the solution treatment time was more than 8 h. After the solution-treated alloy was further aged at 473 K for 18 h, a large number of nanoscale precipitates were observed in the α-Mg matrix. The solution treatment time was 2 h, the α-Mg matrix mainly consisted of spherical-shaped and basal plate-shaped precipitates. Upon the increase of solution treatment time to 8 h, the key strengthening phases transformed from spherical-shaped precipitates and basal plate-shaped precipitates to prismatic plate-shaped β′ precipitates. The orientation relationship between β′ precipitates and α-Mg matrix was ($\overline{1}$10)_β′ // (1$\overline{1}$00)_α and [112]_β′ // the [22$\overline{4}$3]_α. Further increasing of solution treatment time from 8 h to 12 h, the key strengthening phases mainly were still β′ precipitates. The solution treatment of aged alloy was carried out at 788 K for 8 h, which achieved optimal ultimate tensile strength (UTS) of 261 ± 4.1 MPa, yield strength (YS) of 154 ± 1.5 MPa, and elongation of 5.8 ± 0.1%, respectively. Full article

In this work, the generalized stacking fault energies (GSFEs) of {10-11}<11-23> slip system in a wide range of Mg-X (X = Ag, Al, Bi, Ca, Dy, Er, Gd, Ho, Li, Lu, Mn, Nd, Pb, Sc, Sm, Sn, Y, Yb, Zn and Zr) binary alloys has been studied. The doping concentration in the doping plane and the Mg-X system is 12.5 at.% and 1.79 at.%, respectively. Two slip modes (slip mode I and II) were considered. For pure magnesium, these two slip modes are equivalent to each other. However, substituting a solute atom into the magnesium matrix will cause different effects on these two slip modes. Based on the calculated GSFEs, two design maps were constructed to predict solute effects on the behavior of the {10-11}<11-23> dislocations. The design maps suggest that the addition of Ag, Al, Ca, Dy, Er, Gd, Ho, Lu, Nd, Sm, Y, Yb and Zn could facilitate the {10-11}<11-23> dislocations. Full article