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The Mg-Al-RE series heat-resistant magnesium alloys are applied in automotive engine and transmission system components due to their high-temperature performance. However, after serving at a high temperature for a long time, the Al11RE3 phase coarsened and even decomposed, while the Mg17Al12 phase grew and dissolved, which limits the service temperature of Mg-Al-RE series heat-resistant magnesium alloys to a maximum of 175 °C. In this study, a new preparation method for in situ AlN particles was presented. The AlN/Mg-4Al-4La-0.3Mn composites were prepared by a master alloy and casting method. The effects of various contents of AlN (0.5–3.0 wt.%) on the microstructure and mechanical properties of the Mg-4Al-4La-0.3Mn (AE44) alloy at room (25 °C) and high temperatures (150–250 °C) were investigated. Microstructure analysis revealed that the inclusion of AlN led to a reduction in both the grain size and second phase size in the AE44 alloy, while also improving the distribution of the second phase. The average grain size, Al11La3 phase, Al2La phase, and Al3La phase of the 2.0 wt.% AlN/AE44 composite were 135.7, 9.6, 1.9, and 12.6 μm, respectively, which were significantly lower than those of the AE44 matrix alloy (179.8, 12.6, 3.3, 17.8 μm). The refinement was attributed to the ability of AlN particles to serve as heterogeneous nucleation cores for α-Mg and, at the same time, impede the growth of the solid–liquid interface, eventually leading to grain refinement. With the increase in the AlN content, the mechanical properties of composites initially exhibited an increase at both room and high temperatures, followed by a subsequent decrease. When the AlN content was 2.0 wt.%, the composite exhibited optimal strength and plasticity matching. At room temperature, the TYS, UTS, and EL values of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite were 96 MPa, 175 MPa, and 7.0%, respectively, which were increased by 26 MPa, 27 MPa, and 0.7% when compared with the base alloy. The TYS of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite at 150 °C, 200 °C, and 250 °C were 17 MPa, 14 MPa, and 22 MPa higher than those of the matrix alloy, respectively. The main strengthening mechanisms were second phase strengthening, load transfer strengthening, and thermal mismatch strengthening. At elevated temperatures, AlN particles effectively pinned the grain boundaries, inhibiting their migration, and hindered dislocation climbing, resulting in excellent mechanical properties of the composites at high temperatures. This study contributes to the advancement of in situ AlN particle preparation methods and the exploration of effects of AlN on the properties and microstructure of Mg-Al-RE alloys at high temperatures (150–250 °C). [ABSTRACT FROM AUTHOR]

Micro-alloying of Ca in Mg–1Zn-0.3Nd (wt.%) alloy is found to significantly improve tensile strength and process high ductility simultaneously. It closely correlates with grain refinement and the increased coherent nano Mg 2 Ca and (Mg, Zn) 3 Nd precipitates. Ca addition enhances alloying elements co-segregation at grain boundary and promotes grain refinement. Furthermore, nano Mg 2 Ca particles induced by Ca addition can significantly promote the precipitation of (Mg, Zn) 3 Nd phase via the heterogeneous nucleation mechanism owing to their excellent coherency relationship and ultimately lead to the pronounced strengthening effect. In addition, both fine grains and the coherent characteristics between Mg 2 Ca, (Mg, Zn) 3 Nd, and Mg matrix facilitate strain coordination during deformation and yield relatively high ductility. • Micro-alloying Ca in Mg–Zn-Nd alloy significantly increases tensile strength while keeping high ductility. • Ca addition enhances the co-segregation of alloying elements at grain boundary and refines grain size. • Nano Mg 2 Ca particles and the induced (Mg, Zn) 3 Nd precipitates with excellent coherency relationship lead to the pronounced strengthening effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nd promotes the co-segregation of Zn and Nd at grain boundary combination with the nanoscale (Mg, Zn) 3 Nd precipitates significantly refine the grain size. • Ce significantly enhances the co-segregation of Zn and Ce at the grain boundary and yields a noticeable solute drag effect on the mobility of the grain boundary. • A noticeable improvement in strength and ductility is achieved by Ce addition in Mg-Zn alloy. The role of alloying element segregation at grain boundary on the microstructure and mechanical properties is investigated in the case of Ca, Ce, and Nd addition in Mg-1Zn (wt.%) alloy. Segregation of alloying elements at grain boundary is demonstrated in all the designed ternary alloys, leading to a strong solute drag effect on the mobility of grain boundaries and ultimately the grain size. While the co-segregation of Zn and Ce is revealed in the Mg-Zn-Ce alloy, only the segregation of Zn is observed in the Mg-Zn-Ca alloy. The co-segregation of Zn and Nd in Mg-Zn-Nd alloy is demonstrated to lead to the relatively large solute drag pressure at grain boundary, which in combination with the Zener pressure emerging from nanoscale (Mg, Zn) 3 Nd precipitates significantly refines the grain size. The grain refinement in combination with the bimodal microstructure significantly contributes to the increased strength of the designed ternary alloys. Furthermore, the addition of Ca and Ce are found to simultaneously improve the strength and ductility, which is closely correlated with the segregation of alloying elements at the grain boundary. Among the considered alloying species, Ce is shown to efficiently improve the mechanical properties of Mg-Zn alloy. [ABSTRACT FROM AUTHOR]

The effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-2Al-0.5Ca-xZn (x = 0, 0.3, 0.6, 0.9 wt.%) alloys were investigated in this work. The results showed that the extruded sheets exhibited a completely dynamically recrystallized microstructure, the grain size was refined, and texture weakening was achieved with Zn addition because of the segregation of Zn atoms on grain boundaries, which suppresses the growth of dynamic recrystallized grains. The addition of 0.6 wt.% Zn improved both the tensile strength and ductility of the as-extruded Mg-2Al-0.5Ca alloy. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed a 0.2% proof stress of 145 MPa, an ultimate tensile strength of 317 MPa, and an elongation of 30.0% along the extruded direction. The simultaneous improvement of strength and ductility was mainly due to the fine and homogeneous grain microstructure and the weakened extrude direction (ED)-tilted texture. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed little in-plane anisotropic tensile properties, with a 0.2% proof stress, ultimate tensile strength, and elongation in the 45° direction of 148 MPa, 299 MPa, and 25.0%, and those in the transverse direction of 148 MPa, 269 MPa, and 16.8%, respectively. [ABSTRACT FROM AUTHOR]

The micro addition of Ca is demonstrated to noticeably increase the strength and ductility of Mg–Zn–Ce alloy, which is closely correlated with the enhanced alloying segregation at grain boundary. Addition of Ca is found to yield the enhanced Zn segregation and co-segregation of Zn, Ce, and Ca. The mechanism behind is that Ca decreases the segregation energy while promoting the diffusion process of Zn, ultimately accelerating the thermodynamic and kinetic process of segregation. The enhanced alloying segregation induced by Ca effectively stabilizes grain boundary, which contributes to the refined grain size, retardant mobility of dislocation and ultimately improved strength. Furthermore, the intergranular fracture energy can be noticeably increased by Ca owing to the promoted alloying element segregation at grain boundary, which contributes to the improved grain boundary cohesion and ductility. The controllable segregation at grain boundary via alloying is intended to contribute to the development of advanced magnesium alloys. • The micro Ca addition noticeably increases the strength and ductility of Mg–Zn–Ce alloy. • Ca decreases the segregation energy while increasing the diffusion rate of Zn, yielding the enhanced alloying element segregation. • The enhanced alloying segregation stabilizes grain boundary and increases the intergranular fracture energy. [ABSTRACT FROM AUTHOR]

The mechanical properties of as-extruded Mg-11Gd-5Y-2Zn-0.7Zr (GWZ1152) alloy were systematically studied with respect to their microstructures at room and high temperatures. It exhibited excellent ultimate tensile strength (UTS) of 365 MPa at room temperature (RT), while it maintained relatively high UTS as the temperatures increased to 250 °C (342 MPa), 300 °C (337 MPa) and 350 °C (278 MPa) with a strain rate of 1.85 × 10−3 s−1. The microstructural characterizations revealed that such outstanding heat resistance is mainly attributed to (i) the fine dynamic recrystallized (DRXed) grains and strongly textured un-DRXed grains, (ii) the block-shaped LPSO phase and the nano-scale β precipitates, (iii) the nano-spaced basal LPSO/SFs. Compared to other heat-resistant Mg alloys, our intrinsic chemistry properties contribute to the superior high-temperature mechanical properties of GWZ1152 alloy. For the deformation modes at RT, the dislocations were mainly generated and accumulated on the block-shaped LPSO, followed by cracking and propagation. At 250 °C and 300 °C, non-basal slip inside the coarse un-DRXed was generated, the cracks and fractures were initiated along the slip trace. The main deformation mechanism of GWZ1152 alloy at 350 °C was grain boundary sliding, cracks usually occurred at grain boundaries. • Mg-11Gd-5Y-2Zn-0.7Zr alloy exhibited excellent ultimate tensile strength at 25 °C, 250 °C, 300 °C and 350 °C. • The deformation modes of the alloys were systematically studied at different temperatures. • The relationship between the deformation modes and mechanical properties were discussed at room and high temperatures. [ABSTRACT FROM AUTHOR]

In this study, a novel alloy designing concept, refining grain size and depressing intergranular deformation (inter-GD) simultaneously, is put forward to prepare the Mg alloy with preeminent strength-ductility synergy. A basic alloy, Mg–1Sb–1Mn (SM11), is extruded at 220 °C to attain ultrafine microstructure. Thereafter, the co-addition of Sn and Zn is conducted to inhibit the inter-GD which is the softening mechanism of the ultrafine-grained SM11 alloy. Compared with SM11 alloy, the tensile yield strength, ultimate tensile strength and compressive yield strength of Mg–1Sb–1Mn–1Sn-0.2Zn (SMTZ1110) alloy increases from 196 MPa, 245 MPa and 193 MPa–301 MPa, 361 MPa and 273 MPa MPa respectively, without the loss of tensile elongation. With the co-addition of Sn and Zn, the grain size is refined from 1.07 μm to 0.82 μm. The narrower network spacing of Mg 3 Sb 2 in the as-cast SMTZ1110 alloy promotes particle-stimulation nucleation during extrusion, resulting in finer grains of the extruded SMTZ1110 alloy. The in-situ experiments unveil that the deformation mechanisms in the SM11 alloy are mixed inter-GD and intragranular deformation, while the deformation mechanisms of the SMTZ1110 alloy shift to the modes predominated by intragranular deformation. The transmission electron microscope results show the segregations of Sn and Zn which pin and stabilize grain boundaries and further depress the inter-GD. Under the combining effects of depressing inter-GD and fine-grain strengthening, the strength of the extruded SMTZ1110 alloy is significantly improved. This study provides new insight into the development of Mg alloy with an excellent balance between strength and ductility. [ABSTRACT FROM AUTHOR]