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In this study, we successfully developed a low RE containing Mg-3Y-2Gd-1Nd-0.5Zr (wt%) alloy with high strength-ductility synergy by combined processes of hot extrusion, hot rolling and ageing. This alloy exhibits an excellent strength-ductility balance (UTS of 345 ± 2.0 MPa, TYS of 301 ± 5.0 MPa and EL of 9.2 ± 1.9%), which is better than that of many Mg-RE wrought alloys with higher RE concentration and even comparable to that of 6061 Al wrought alloy. A long-range chain-like structure consisting of β′ phase, β H phase, β M phase and zig-zag atomic columns is observed for the first time in the studied alloy. The combined process of hot extrusion and hot rolling boosts the formation of deformed grains and low angle grain boundaries, and makes the deformed grains dominate in the alloy strengthening. Under this circumstance, the following ageing generates a novel heterogeneous structure comprising the long-range chain-like structure with broad interparticle spacing and the spacious precipitate-free zones in the deformed grains, which plays a key role in the concurrent strengthening and toughening of the alloy. The present study demonstrates that the deformed grains with long-range chain-like structures and precipitate-free zones is desirable microstructure for the low RE containing Mg alloys to achieve high strength-ductility synergy. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties of as-extruded Mg-11.5Gd-4.5Y-0.3Zr (wt%) alloy with Zn and Nd additions were investigated. The addition of Zn inhibits the dynamic recrystallization (DRX) due to the presence of the long-period stacking ordered (LPSO) phase. The addition of Nd promotes the precipitation of the Mg 5 RE (RE: rare earth) phase. The existence of the densely distributed Mg 5 RE phase before hot extrusion promotes the DRX in subsequent hot extrusion process and leads to grain refinement. The increase in the number of Mg 5 RE phase particles degrades the mechanical properties of the resultant alloy. After hot extrusion, the studied alloys exhibit a bimodal microstructure consisting of fine dynamic recrystallized (DRXed) grains of several microns and strongly textured course un-DRXed grains. The as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.3Zr alloy exhibits an excellent balance of strength and ductility (tensile yield strength of 371 ± 3.0 MPa and elongation of 7.2 ± 0.8%). The alloy strengthening is attributed to the bimodal microstructure, the Mg 5 RE and LPSO phases, and the basal texture. The tensile yield strength of the as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.3Zr alloy can be further increased to 425 ± 2.5 MPa by precipitation hardening with the T5 treatment. [ABSTRACT FROM AUTHOR]

An as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.4Zr (wt %) alloy with an excellent strength-ductility balance has been successfully developed by pre-annealing and hot extrusion. The effects of pre-annealing on microstructure and mechanical properties have been studied. Results show that the Mg 5 RE (RE: rare earth) particles, which are generated by pre-annealing treatments, are cracked during hot extrusion, and resulting Mg 5 RE fragments not only enhance the recrystallization of particle simulated nucleation (PSN), but also improve the continuous dynamic recrystallization (C-DRX) by promoting the grain subdivision. After hot extrusion, the studied alloy exhibits a bimodal microstructure consisting of fine DRXed grains with relatively random orientations and coarse un-DRXed grains with strong basal texture. Increasing the pre-annealing duration raises both the quantity of Mg 5 RE particles and the fraction of DRX, thereby decreasing the strength but increasing the ductility. With pre-annealing for 1 h the studied alloy achieves the best strength-ductility balance with tensile yield strength (TYS) of 377 ± 1.2 MPa and elongation to failure (EL) of 10.8 ± 2.0%. Further pre-annealing degrades the ductility due to the excessive Mg 5 RE particles. The alloy strengthening is attributed to the bimodal microstructure, Mg 5 RE and long-period stacking ordered (LPSO) phases, solute segregated SFs, and texture. [ABSTRACT FROM AUTHOR]

A high strength Mg-11.7Gd-4.9Y-0.3Zr (wt%) alloy with a weak tension-compression yield asymmetry has been successfully developed by pre-deformation annealing, hot extrusion and ageing. The effects of pre-deformation annealing on the microstructure evolution and mechanical properties are studied. The results reveal that pre-deformation annealing generates a large number of Mg 5 RE (RE: rare earth) phase particles and raises the fraction of dynamic recrystallization (DRX). The preformed Mg 5 RE particles not only enhance the DRX by particle simulated nucleation (PSN), but also facilitate the continuous DRX (C-DRX) by promoting the grain subdivision during hot extrusion. Without pre-deformation annealing, the as-extruded alloy exhibits a high tensile yield strength (TYS) of 376 ± 9.6 MPa but a low elongation to failure (EL) of 4.3 ± 0.1% due to the bimodal microstructure consisting of coarse un-DRXed grains with strong basal texture and fine DRXed grains with weak basal texture. After T5 treatment, the TYS further increases to 500 ± 5.5 MPa, whereas the EL reduces to 2.7 ± 0.4%. An excellent balance of strength and ductility (TYS of 343 ± 0.2 MPa and EL of 9.3 ± 0.9%) can be realized by pre-deformation annealing for 1 h due to the raised fraction of DRX and the weakened basal texture. T5 treatment further increases the TYS to 446 ± 3.8 MPa but reduces the EL to 3.0 ± 0.2%. The studied alloy exhibits good compressive performance, resulting in a weak tension-compression yield asymmetry. The grain refinement, Mg 5 RE and β ′ phases, and solute-segregated SFs contribute to the alloy strengthening. [ABSTRACT FROM AUTHOR]

Microstructure and texture evolutions during tensile and compression deformation of an as-extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy have been investigated using in-situ synchrotron radiation diffraction and subsequent microscopy. The alloy consists of 〈 10 1 ¯ 0 〉 fiber texture, { 11 2 ¯ 0 }[0001] and { 11 2 ¯ 0 }〈 10 1 ¯ 0 〉 texture components prior to deformation. The texture evolves from [0001] to 〈 10 1 ¯ 0 〉 in tension, but from 〈 10 1 ¯ 0 〉 to [0001] in compression. The evolution of texture is attributed to the activity of the tensile twinning and non-basal 〈 a 〉 type slip. The tendency of texture evolution depends on the favorable texture component for the activation of above deformation modes. The grain refinement, Mg 5 (Gd, Y, Nd) and LPSO phases, and the texture contribute to the improvement in strength. [ABSTRACT FROM AUTHOR]

A high strength Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy has been successfully fabricated via hot extrusion, cold rolling and ageing treatment. The alloy exhibits an average 0.2% proof stress (YS) of 481.6±19.9 MPa, an average ultimate tensile strength (UTS) of 517.4±27.5 MPa and an average elongation to failure of 2.0±0.4% at room temperature. The best mechanical property obtained in the present study has a YS of 502.0 MPa, an UTS of 546.8 MPa and an elongation to failure of 2.6%. The high strength of this alloy is attributed to the fine grains, stacking faults (SFs), long period stacking ordered (LPSO) phase, and precipitates of Mg 5 RE phase at grain boundaries and of β ′ phase inside the grains. Cold rolling improves the mechanical properties and enhances the ageing hardening response, but decreases the ductility. Two texture components are found simultaneously in the deformed alloy. One is the typical Mg–RE texture and another one is the unusual prismatic texture. [ABSTRACT FROM AUTHOR]

This study investigates the effects of extrusion ratio and temperature on the microstructure and mechanical properties of as-extruded Mg-11.5Gd-4.5Y-(1Nd/1.5Zn)-0.3Zr (wt %) alloys. After hot extrusion the studied alloys exhibit a bimodal microstructure consisting of fine dynamic recrystallized (DRXed) grains with relatively random orientations and coarse un-DRXed grains with strong basal texture. The increase of extrusion ratio promotes the DRX, increases the volume fraction of Mg 5 RE phase, and refines the DRXed grains, whereas the increase of extrusion temperature decreases the volume fraction of Mg 5 RE phase and coarsens the DRXed grains. The increase of extrusion temperature suppresses the DRX of Mg-11.5Gd-4.5Y-0.3Zr (GW) and Mg-11.5Gd-4.5Y-1Nd-0.3Zr (GWN) alloys, but it has a limited effect on that of Mg-11.5Gd-4.5Y-1.5Zn-0.3Zr (GWZ) alloy. The increase of extrusion ratio improves the mechanical properties of GWZ and GWN alloys, while it deteriorates the mechanical property of GW alloy. The increase of extrusion temperature leads to a decreased strength and increased ductility of the studied alloys. The change of mechanical properties is a result of the competition between the "strengthening effect" of DRXed grains and the "hardening effect" of un-DRXed grains in the changing bimodal microstructure. The Mg 5 RE phase also contributes to the alloy strengthening, but the extensive Mg 5 RE precipitates acting as the crack resources are detrimental to the ductility, especially for the GWN alloy. With the optimum extrusion condition (temperature of 450 °C and ratio of 20:1) the GWZ alloy exhibits the best mechanical performance, which is superior to that of its competitor 6000 series aluminum alloys. • The studied Mg-Gd-Y-Zn-Zr alloy has a superior strength to 6000 series Al alloys. • Both Mg5RE phase and 18R-LPSO phase enhance the DRX behaviour. • The effect of bimodal microstructure on the mechanical properties was studied. • Three Mg–Gd based alloys were extruded using different extrusion parameters. • A big database (microstructural and mechanical) was obtained by quantitative statistics. [ABSTRACT FROM AUTHOR]

Effects of 0.5 wt% cerium (Ce) addition on microstructures and mechanical properties of a wrought Mg−8Gd−1.2Zn−0.5Zr alloy were thoroughly investigated in this work. The results indicate that 0.5 wt% Ce addition has slight refinement on the as-cast grains and results in a lattice expansion of the dominant intermetallic phase Mg 3 RE. After extrusion, 0.5 wt% Ce addition leads to higher level of recrystallization and finer dynamic recrystallization (DRX) grains and non-recrystallization stripes. In addition, there are much more dynamic precipitates on the DRX grain boundaries in the alloy with Ce addition, and the crystal structure (Mg 12 RE) is different from those (Mg 5 Gd) in the alloy with free Ce addition. Under peak-aging condition, 0.5 wt% Ce addition significantly changes the precipitates in the DRX grains from basal γ′ phase to prismatic β′ phase. As a result, the as-extruded Mg−8Gd−1.2Zn−0.5Zr alloy with 0.5 wt% Ce addition owns higher strength and more obvious precipitation hardening response than the alloy with free Ce addition. [ABSTRACT FROM AUTHOR]