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Based on the deforming technique of severe plastic deformation (SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion (RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 °C and decreasing by 10 °C for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent. [ABSTRACT FROM AUTHOR]

Gleeble-3500 thermal simulator was applied to realize the rotary backward extrusion forming of Mg-13Gd-4Y-2Zn-0.5Zr (wt%) alloy at different circumferential strain rate from 0.009 s−1 to 0.027 s−1 at 400°C and the dynamic recrystallization mechanism and texture evolution were studied. The results show that the grain size of the alloy was obviously refined after rotary backward extrusion. As the circumferential strain rate increased, the dynamic recrystallization fraction gradually increased causing the grain size decreased and the distribution of microstructure became more uniform. At the same time, the texture of {0001}, {10-10}, {11-20} was weakened and the grain orientation distribution became more random. With the increase of circumferential strain rate, the discontinuous dynamic recrystallization mechanism became dominant, which promoted the weakening of texture and grain refinement of the alloy. [ABSTRACT FROM AUTHOR]

• A new deformation method of RFE was proposed. • RFE can increase strain and significantly refine grains compared with FE method. • Microstructure and texture evolution of N = 0 and N = 100 were studied for comparison. This study proposed an effective plastic deformation technique, rotating forward extrusion (RFE) for producing rare-earth (RE) Mg alloy bars. The results showed that the equivalent strain increased significantly and the equivalent stress continuously decreased with increasing rotation revolutions. The metal streamline of the edge of the sample was along the extrusion direction (ED), and the center part was perpendicular to the ED. The grains were obviously refined, complete dynamic recrystallization (DRX) behavior was achieved, and the basal texture was weakened with increasing rotation revolutions during the RFE process. [ABSTRACT FROM AUTHOR]

The decreasing temperature reciprocating upsetting-extrusion (RUE) deformation experiment was carried out on Mg-Gd-Y-Zr alloy to study RUE deformation on the influence of microstructure of the alloy. This work showed that with the gradual increase of RUE deformation passes, the continuous dynamic recrystallization (CDRX) process and the discontinuous dynamic recrystallization (DDRX) process occurred at the same time, and the grain refinement effect was obvious. Particulate precipitation induced the generation of DRX through particle-stimulated nucleation (PSN). In addition, after one pass of RUE deformation, the alloy produced a strong basal texture. As the RUE experiment proceeded, the basal texture intensity decreased. The weakening of the texture was due to the combined effect of DRX and alternating loading forces in the axial and radial directions. After four RUE passes, the mechanical properties of the alloy had been significantly improved, which was the result of the combined effect of dislocation strengthening, fine grain strengthening, and second phase strengthening. [ABSTRACT FROM AUTHOR]

• A rotary extrusion forming process for cylindrical tubular parts is proposed. • The deformation behavior of rare-earth magnesium alloy under direct extrusion and rotary extrusion was compared. • The flow stress of the rotary extrusion is significantly lower than that of the direct backward extrusion. • The cup-shaped parts formed via rotary extrusion exhibits a typical gradient structure. • The width of refinement becomes wider as the rotations number increases. Rotary extrusion is a technique to produce workpieces with a very large strain and a weak texture. In this work, deformation behavior and microstructure evolution of magnesium alloys via rotary extrusion were investigated. The results show that the flow stress of the rotary extrusion is significantly lower than that of the direct backward extrusion. The equivalent stress decreases upon the increase of the rotations number. The cup-shaped parts formed via rotary extrusion exhibits a typical gradient structure, which expands from its center to the borders. The basal texture of the sample is smaller than that produced by direct backward extrusion. Moreover, it further decreases upon the increase of the rotation number. [ABSTRACT FROM AUTHOR]

Mg–13Gd–4Y–2Zn–0.5Zr alloy was subjected to compression–torsion deformation at 450 °C with a strain rate of 0.001–0.5 s−1 using a Gleeble 3500 torsion unit. The effects of compression–torsion deformation on the microstructure and texture were studied, and the results showed that with the decrease of strain rate, the texture strength decreased, the number of dynamic precipitated particles increased, the degree of recrystallization increased, and the dynamic recrystallization mechanism changed from a continuous dynamic recrystallization mechanism to a continuous and discontinuous dynamic recrystallization mechanism. Along the direction of increasing radius, the degree of dynamic recrystallized grain (DRX) increased, the number of dynamic precipitated particles increased, and the texture strength slightly increased. [ABSTRACT FROM AUTHOR]

Abstract Repetitive upsetting-extrusion (RUE), a severe plastic deformation, was performed on the Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr (wt %) alloy at different deformation temperatures in the range of 693–773 K for 1, 2 and 3 passes. The study was aimed to determine the effects of deformation temperatures and processing passes of RUE on the microstructure and texture evolution of the RUEed alloy. It is found that dynamic recrystallization (DRX) occurred in the alloy and β- Mg 5 (Gd,Y,Zn) phase particles precipitated at grain boundaries during the RUE processing. The microstructure was refined remarkably during RUE, the microstructure distribution became more homogeneous and the degree of DRX was increased with the number of the processing passes increasing. The grain refinement was mainly caused by DRX, and the LPSO phases stimulated the DRX around the grain boundaries via particle stimulation nucleation mechanism. The microstructure and texture evolution were mainly depended on the RUE processing parameters, such as processing passes and deformation temperatures. The basal texture was gradually weakened during more processing passes and higher deformation temperatures of RUE processing. The microstructure and texture evolution of the alloy were affected more by processing passes than deformation temperatures during RUE. After 3 RUE passes, some (0001) basal planes were perpendicular to the ED and that also were parallel to the ED in some grains, which is different from that observed in both extruded alloys and other plastically deformed counterparts. The number fraction of low angle grain boundaries tended to decrease while the average misorientation angles tended to increase with the processing passes and deformation temperatures of the RUE increasing. Highlights • The Mg-Gd-Y-Zn-Zr alloy was processed by RUE under different conditions. • The microstructure and texture evolution during RUE were investigated. • The DRX occurred in the alloy during the RUE. • The microstructure and texture were affected more by passes than temperatures. [ABSTRACT FROM AUTHOR]

• One pass repetitive upsetting-extrusion(RUE) apply to process AZ80 Mg bars under different deformation parameters. • A weaker fiber texture is developed via RUE of extruded bars due to the application of interactive stress state. • Deformation parameters affect microstructure evolution, acting on strength, plasticity and anisotropy of extruded bars. • The tensile yield anisotropy of extruded bars is greatly reduced due to texture dispersion and grain refinement. [Display omitted] Repetitive upsetting-extrusion (RUE) is known as a processing method that effectively improves the properties of a billet without changing its initial shape. In this paper, one pass RUE with reduced deformation temperature (re-upsetting at 360 °C and secondary extrusion at 340 °C) and different extrusion speeds (0.5 and 1 mm/s) is implemented to improve the strength and toughness of AZ80 Mg rods, and simultaneous reduction in tensile anisotropy is achieved. Influences of one pass RUE method on the resulting microstructure and texture evolution of the alloy are investigated alongside their correlated impact on its mechanical properties. After RUE processing, the grain structure of AZ80 alloy is characterized by numerous fine dynamic recrystallized (DRXed) grains, combined with large unDRXed grains obtained at high extrusion speed or coarse DRXed grain bands obtained at low extrusion speed. Besides, β-Mg 17 Al 12 particles dynamically precipitated during deformation, acting as strong barrier against grain boundary migration through pinning effect. Through introduction of an interactive stress state, the RUE process promotes dispersion of the fiber texture that typically develops during the extrusion process. The key factor that promotes weakening of the fiber texture is derived from the refinement of basal orientated deformed grains, which form during upsetting deformation, into numerous non-basal orientated DRXed grains during early-stage extrusion. Compared with coarse deformed grains, these fine DRXed grains delay transformation of texture into the typical [10-10]–[11-20] fiber component. Grain refinement is implicated as the most significant factor with respect to simultaneous improvement of strength and toughness in the extruded rods, while tensile yield anisotropy in response to loading along the ED and TD is attributed to unDRXed grains with [10-10] fiber orientation. Compared to the as-cast state, extruded rods demonstrate increases in yield strength, ultimate tension strength, and elongation maximally up to ~2.6, ~2.2, and ~4.9 times, respectively. And when complete DRX structure is nearly achieved, the tensile yield anisotropy of extruded bar is effectively eliminated because the refined grains with relatively dispersed orientation inhibit the nucleation of tension twin and simultaneous enhance the Hall-Petch effect. [ABSTRACT FROM AUTHOR]