Search

This study investigated the microstructure and mechanical properties of Mg-(7-x)Y-xNd-2Al (x = 0, 2, 4, 6) alloys with rare earth (RE) element Nd instead of Y. The results reveal that the substitution of Nd for Y promotes the formation of the Al-RE phase and Mg-RE eutectic phase in the as-cast alloy. Furthermore, after solution treatment, all eutectic phases dissolve into the α-Mg matrix, while the Al-RE phase (Al2RE phase) does not dissolve. Additionally, the lamellar Al2RE phase precipitates in the grains of the Nd-containing alloy. The age-hardening curve indicates that when Nd is substituted for Y, the peak-aging time is reduced and the peak hardness increases. Moreover, Nd promotes the precipitation of the nanometer β″ phase during aging, which improves the mechanical properties of the alloy. The best peak-aging yield strength, tensile strength, and elongation of the 4% Nd alloy are 182, 285 MPa, and 7.4%, respectively. [ABSTRACT FROM AUTHOR]

The effect of niobium (Nb) on the microstructure and mechanical properties of ductile iron was investigated by metallographic analysis and mechanical tests. The analysis of precipitates by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) reveals that the precipitated phase with a size less than 5 µm is composed of Nb, Mo and C. The phase diagram obtained by thermodynamic calculation and cooling curve analysis shows the precipitation of NbC during the solidification. The microstructure analysis indicates that the addition of Nb deteriorates the morphology of graphite and promotes the formation of pearlite. The mechanical properties analysis shows that the addition of Nb in ductile iron increases the hardness and strength, but decreases the elongation and impact toughness. The optimum value of ultimate tensile strength and yield strength is achieved at the Nb content of 0.14%. With the Nb addition of 0.14%, the hardness, ultimate tensile strength, yield strength, elongation and impact toughness are 182.3 HBW, 530.6 MPa, 405.2 MPa, 16.6% and 91.5 J/cm2, respectively. [ABSTRACT FROM AUTHOR]

In order to improve the effects of grain refinement, modification and refined degassing of Al-Si alloy synchronously, and to solve the problems of their mutual restrictions, the new type of composite refining modifier (K2TiF6, KBF4, NaCl and KCl) was used to tailor the microstructure of AlSi10Mg alloy. Through varying the content of K2TiF6 and KBF4, the effects of the composite refining modifier on microstructure and mechanical properties of AlSi10Mg alloy were investigated compared with the conventional C2Cl6 refining agent. The experimental results indicate that TiB2 is formed in situ by K2TiF6 and KBF4 at 800 °C. TiB2 distributed in the melt acts as nucleation substrates for the primary Al (α-Al), which promotes the refinement transition of α-Al. The Na and K in the composite refining modifier jointly modify the eutectic Si. At the same time, the reaction products can remove gases and oxidized inclusions from the melt and play a critical role in refined degassing. Excellent mechanical properties can be obtained when K2TiF6 and KBF4 account for 3.5 wt.% of the melt, with an increase in tensile strength and elongation of 33.1 and 126.9%, respectively, compared with adding 1.6 wt.% of C2Cl6 to the melt. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Gd/Y on the microstructure and mechanical properties of Mg-13(Gd, Y)-1Zn-1Al was investigated by different material characterization methods. The results showed microstructure of Mg-13(Gd, Y)-1Zn-1Al (GY58, GY76, GY94, GY112) consisted of α-Mg, granular Al2RE, lamellar LPSO, acicular Al2RE and block-shaped eutectic Mg-RE phases. The eutectic Mg-RE phase was Mg24(Zn, RE)5 in GY58 and GY76, while Mg3(Zn, RE) in GY94 and GY112. As Gd/Y increased, the content of second phases decreased gradually. The contents of granular Al2RE, LPSO and eutectic phase decreased, while the content of acicular Al2RE increased. As Gd/Y increased, the grain size of α-Mg increased. GY58 had the smallest grain size, which was only 26.5 μm. When Gd/Y increased from 5/8 to 11/2, the grain size increased 9%, reaching 28.9 μm. As Gd/Y increased, the size of granular Al2RE decreased gradually, while that of acicular Al2RE increased. When Gd/Y was 9/4, the comprehensive mechanical properties were the best and the ultimate tensile strength, yield strength and elongation reached 232.7 MPa, 162 MPa and 9.1%, respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of Al contents (0, 0.5, 1.0 and 1.5 wt.%) on the microstructure evolution, texture and mechanical properties of Mg-4Y-3Nd alloys rolled sheets were investigated. The results showed that the Al2RE phase was formed when Al was added into the as-cast alloys, which could refine the microstructure of the alloys. After homogenization treatment, the Al2RE phase was insoluble, and the Al2RE phase at the grain boundaries could pin the grain boundaries to prevent grain growth. The Al-containing alloys had good grain thermal stability. The Al2RE phase promoted dynamic recrystallization (DRX) through the particle-stimulated nucleation (PSN) mechanism and refined recrystallized grains during the rolling process. Al refinement will affect the texture type and strength of the alloy. The addition of 0.5 wt.% Al could improve the texture intensity, and a further increase in Al would reduce the texture intensity. When the Al content was 1.5 wt.%, the alloy had the smallest recrystallized grains, the weakest texture intensity, and the best mechanical properties. The tensile strength, yield strength and elongation were 264.4, 225.3 MPa and 9.4%, respectively. [ABSTRACT FROM AUTHOR]

In recent years, the utilization of Al as a grain refiner in Mg–RE alloys has gained widespread attention because of its advantages such as low cost. In this study, Mg–5Y–4Sm–xAl (x = 0, 0.6, 1.2 and 1.8 wt.%) alloys were fabricated, and high grain refinement efficiency of Al addition was obtained. Subsequently, the effect of different Al addition on the grain refinement was investigated and the refinement mechanism was discussed deeply in two major aspects. Firstly, Al2RE particles were formed in the solidification process and acted as the nucleation sites of α-Mg. The numerical density and diameter of those particles were obviously increased by increasing Al addition. Secondly, the addition of Al reduced the solute elements content in the α-Mg melt, resulting in a decrease in the grain growth restriction factor (Q value). Furthermore, the synergistic effect of solute elements and nucleation particles on grain refinement was described by the interdependent theory. Finally, the Al addition is beneficial to improve the mechanical properties of alloy. When the Al addition was 1.8%, the room temperature tensile strength of the alloy reached a maximum of 221 MPa and the maximum elongation was 9.2%. When the Al addition was 1.2%, the yield strength of the alloy reached a maximum of 142 MPa. [ABSTRACT FROM AUTHOR]

The development of magnesium alloys with superior plasticity and favorable strength is still challenging in aerospace industry. Herein, hot extruded Mg-xNd-2.0Sm-0.4Zn-0.4Zr alloys (x = 0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) were rationally designed and easily prepared in order to implement the favorable combination of strength and plasticity. The effects of Nd element addition on the microstructure and mechanical properties of the hot extruded alloys were systematically investigated by optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The OM results indicated that the grain size of the hot extruded alloys decreased from 27.1 to 14.1 μm with increasing Nd addition from 0 to 2.5 wt.%. Some coarse β phases existed at the grain boundary when the addition of Nd element increased to 2.0 wt.%. The TEM results showed that the nanoscaled basal lamellar precipitates, granular precipitates and prismatic lamellar precipitates formed in α-Mg matrix. And the amount of precipitated phase increased obviously with the increase of Nd element addition. The ultimate tensile strength increased significantly from 203 ± 3.0 to 237 ± 2.5 MPa, and the elongation decreased from 30.5 to 21.2 % when the Nd elements increased from 0 to 2.5 wt.%. The fractographs of the hot extruded alloys could be classified as ductile fracture. [ABSTRACT FROM AUTHOR]

In the present paper, the effect of initial microstructure on the hot extruded Mg-6Nd-2Al alloy was carried out by microstructural observation and mechanical property testing. The results show that there are short rod-shaped Al11Nd3 phase, strip-shaped Mg12Nd phase and granular Al2Nd phase in the as-cast Mg-6Nd-2Al alloy after hot extrusion. The as-cast alloy is treated by solid solution and then hot extrusion, the granular Al2Nd phase can still be observed in the alloy, and the needle-shaped Al2Nd phase precipitates inside the α-Mg matrix. A typical (0001) texture and {01-10} prismatic surface texture appear in the as-cast alloy after hot extrusion, while in the solid-solution alloy after hot extrusion does not form an obvious preferred orientation. The ultimate tensile strength and the yield strength of the as-cast alloy after hot extrusion are higher, which are 271.2MPa and 247.8MPa, respectively. However, the elongation of the as-cast alloy after hot extrusion is lower, which is 15.3%. [ABSTRACT FROM AUTHOR]

In the present paper, the Mg-11Gd-2Y-1Zn alloys with different Al addition were fabricated by the gravity permanent mold method. The effect of Al content on microstructure evolution and mechanical properties of as-cast Mg-11Gd-2Y-1Zn alloy was studied by metallographic microscope, scanning electron microscope, XRD and tensile testing. The experimental results showed that the microstructure of as-cast Mg-11Gd-2Y-1Zn alloy consisted of α-Mg phase and island-shaped Mg3 (RE, Zn) phase. When Al element was added, Al2RE phase and lamellar Mg12REZn (LPSO) phase were formed in the Mg-11Gd-2Y-1Zn alloy. With increasing Al content, LPSO phase and Mg3 (RE, Zn) phase gradually decreased, while Al2RE phase gradually increased. There were only α-Mg and Al2RE phases in the Mg-11Gd-2Y-1Zn-5Al alloy. With the increase of Al content, the grain size decreased firstly and then increased. When the Al content was 1 wt.%, the grain size of the alloy was the minimum value (28.9 μm). The ultimate tensile strength and elongation increased firstly and then decreased with increasing Al addition. And the fracture mode changed from intergranular fracture to transgranular fracture with increasing addition. When Al addition was 1 wt.%, the maximum ultimate tensile strength reached 225.6 MPa, and the elongation was 7.8%. When the content of Al element was 3 wt.%, the maximum elongation reached 10.2% and the ultimate tensile strength was 207.7 MPa. [ABSTRACT FROM AUTHOR]

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 ( 1 ¯ 10)β′ // (1 1 ¯ 00)α and [112]β′ // the [22 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. [ABSTRACT FROM AUTHOR]

In order to broaden applications of magnesium rare earth alloys in aerospace fields, the microstructure and mechanical properties of as-cast Mg-6Gd-2Y-Nd-0.4Zn-0.5Zr alloys can be improved by Ag alloying, and the elevated temperature strengthening mechanism is revealed. The microstructure analysis shows that the as-cast alloys mainly consist of α-Mg equiaxed grain and network-like β-Mg5(Gd,Y,Nd,Ag,Zn) phase. The addition of the Ag exhibits a strong grain refinement effect and promotes the formation of the second phase in the as-cast alloys. It is noteworthy that the content of Ag exceeds 1.5 wt%, and a small amount of Mg17Ag2(Gd,Y,Nd,Zn) phase is formed at grain boundaries. The results of tensile test reveal that the as-cast Mg-6Gd-2Y-Nd-1.5Ag-0.4Zn-0.4Zr alloy has excellent mechanical properties. Compared with the Mg-6Gd-2Y-Nd-0.4Zn-0.4Zr alloy, the ultimate tensile strength is 220 MPa at 25 °C and 225 MPa at 250 °C, which are improved by 15.7 and 11.3%, respectively. [ABSTRACT FROM AUTHOR]

• The addition of Al can promote the formation of equiaxed grains in WAAM Mg-RE alloy. • Al 2 RE phase can act as heterogeneous nucleation particles to refine WAAM Mg-RE alloy. • WAAM Mg-4Y-3Nd-1.5Al alloy has isotropic mechanical properties. The effects of adding 1.5% Al on the microstructure and mechanical properties of Mg-4Y-3Nd (WN43) alloy prepared by wire arc additive manufacturing (WAAM) were investigated. The addition of Al inhibits the formation of eutectic, promotes the formation of Al 2 RE phases, resulting in the formation of fine equiaxed grains (34 ± 1.1 μm). Consequently, the anisotropy of mechanical properties decreased significantly, and the mechanical properties were improved. The tensile strength, yield strength, and elongation of the alloy were measured as 244 MPa, 142 MPa, and 17.9%, respectively. These findings suggest that Al shows promise as an effective grain refiner for WAAM-produced magnesium rare-earth alloys. [ABSTRACT FROM AUTHOR]