Repetitive Upsetting-extrusion Research Articles

Optimization in strength-ductility of Mg-RE-Zn alloy based on different repetitive upsetting extrusion deformation paths

This study investigated the effects of different repetitive upsetting extrusion (RUE) deformation paths on the microstructures and mechanical properties of Mg-9.32Gd-3.72Y-1.68Zn-0.72Zr (wt%) alloy. Bimodal microstructures were observed in all RUE deformed samples. Increasing the RUE ratio under the same cumulative strain enhanced the dynamic recrystallization (DRX) process, resulting in higher aspect ratios of deformed grains and dynamic precipitation of β phases. The bulk long period stacking ordered (LPSO) phases promoted the DRX process through a particle-stimulated nucleation mechanism, while the β phases hindered the growth of DRXed grains by a pinning effect during deformation. As the RUE ratios increased, the LPSO phase gradually aligned towards the extrusion direction. The R1P3 sample demonstrated the best balance between strength and ductility under small RUE ratio and multi-pass deformation, with ultimate tensile strength, tensile yield strength (TYS), and elongation reaching 382.5 ± 3.1 MPa, 302.3 ± 4.2 MPa, and 8.7 ± 0.5%, respectively. The different contributions of LPSO phases strengthening and heterogeneous deformation-induced (HDI) strengthening led to variations in TYS in different samples. Adjusting the uniformity of the deformed grain size in the bimodal microstructure based on HDI strengthening can further enhance the synergistic improvement of the alloy's strength and ductility.

Microstructure evolution and mechanical properties of industrial scale samples of Mg–Gd–Y–Zn–Zr alloy after repetitive upsetting-extrusion process

As one of the severe plastic deformation (SPD) methods, repetitive upsetting-extrusion (RUE) technique was an effective way to refine grains for large-sized billet at blank-making stage. The microstructure evolution and mechanical properties of industrial-scale Mg–9Gd–3Y–2Zn–0.4Zr (wt.%) alloys were comprehensively investigated in this paper. The experimental alloys exhibited heterogeneous microstructure in the different regions and directions due to the uneven deformation temperature and strain during the RUE deformation process. In addition, the texture and mechanical properties of the RUEed samples also exhibited obvious anisotropy. In particular, the RUEed sample in the edge region along extrusion direction (EED) showed a superior tensile strength with ultimate tensile strength (UTS) of 357 MPa, tensile yield strength (TYS) of 242 MPa and the failure elongation (FE) of 9.0%, due to the smaller average grain size (12.7 μm) and higher area fraction of the dynamic recrystallized (DRXed) grains (82.2%) than other regions. Furthermore, the results also exhibited that the enhancement of the mechanical properties of the RUEed samples were mainly attributed to Hall–Petch strengthening, Orowan strengthening and texture strengthening.

Mechanical and electrochemical behaviors assessments of Aluminum- Graphene Oxide composites fabricated by mechanical milling and repetitive upsetting extrusion

This study is aimed to fabricate the Aluminium-graphene oxide (Al-GO) composites with different concentration of GO (0.5, 1, and 2 wt. %) at 300 °C using repetitive upsetting extrusion (RUE) technique. Uniform dispersion of GO nanoplates throughout the matrix was obtained by sequence processes including the ultrasonicating, ball milling and RUE. The microstructure of composites was investigated by X-ray diffraction, scanning electron microscope and Raman analysis. The results confirmed that the Al-1GO illustrated the uniform and homogenous dispersion of GO into the Al matrix. Raman results confirm the absence of aluminum carbide phase formation during the RUE process. The mechanical properties results show the greater hardness, compressive strength and yield strength of Al-1GO than other ones. This 500% enhancement of Al-1GO in mechanical behavior may be related to desired dispersion of GO throughout the matrix. Current density of the Al matrix corrosion significantly increased from 2.65 to 15.21 (µA/cm2), when the amount of GO increased from 0 to 2 wt. % due to galvanic corrosion at the presence of the GO reinforcement.

The microstructure evolution, texture weakening mechanism and mechanical properties of AZ80 Mg alloy processed by repetitive upsetting-extrusion with reduced deformation temperature

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-Mg17Al12 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.

Effect of repetitive upsetting-extrusion on deformation uniformity and mechanical properties of Mg–Gd–Y–Zr alloy

Mg-8.3Gd-3.2Y-0.4Zr alloy underwent severe plastic deformation at 420 °C using 4-pass isothermal repetitive upsetting-extrusion (RUE) process. The deformation uniformity in different regions of the same sample after 4 passes of RUE was studied. The results showed that though there was slightly uneven deformation, the isothermal RUE process can improve uniformity. The strain in the central area is relatively small, and there are more deformed large grains. The dynamic recrystallization fraction at different positions is above 0.5, forming a more uniform microstructure, with the minimum average grain size being 10.66 μm. Discontinuous dynamic recrystallization and continuous dynamic recrystallization occur at the same time, which promotes grain refinement and improvement of microstructure uniformity. Dynamic recrystallization weakens the texture, resulting the similar texture intensity of different positions of the sample. The bottom edge position with the most uniform microstructure obtained the best tensile properties, UTS reached 323 MPa.

Microstructure, Texture and Mechanical Properties of Mg-Gd-Y-Zn-Zr Alloy during Repetitive Upsetting-Extrusion after Heat Treatment

Severe plastic deformation can be produced by repetitive upsetting-extrusion process. Using the repetitive upsetting-extrusion (RUE) process at decreasing temperature, the Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr (wt %) alloy was deformed by different RUE passes and then heat treated. The microstructure, texture and mechanical properties of the alloy were compared and analyzed. The results demonstrate that with the increase of deformation passes, the coarse grains of the alloy decreased, the dynamic recrystallization fraction increased, and the dynamic recrystallized grains phagocytized the original grains. This can promote the continuous refinement of the grains and the microstructure uniformity. The maximum texture intensity of the (0001) basal plane decreased significantly with the increase of processing passes and the dispersion degree of pole figure increased. The orientation of dynamic recrystallized grains was randomly distributed to weaken texture. Due to the refinement of microstructure and the weakening of texture, the tensile strength and yield strength of the alloy obviously increased at room temperature. The mechanical properties of the alloy reached the highest after 3 passes and heat treatment.

The evolution of long-period stacking ordered phase and its effect on dynamic recrystallization in Mg-Gd-Y-Zn-Zr alloy processed by repetitive upsetting-extrusion

Based on the repetitive upsetting-extrusion (RUE) process, the evolution of the LPSO phase and its effect on the dynamic recrystallization (DRX) of Mg-9Gd-4Y–2Zn-0.5Zr (wt%) alloy during the multi-pass deformation were studied. The results showed that with the increase of RUE processing, the DRX fraction gradually increased, the grains were effectively refined, and the texture was weakened. The lamellar LPSO phase mainly underwent mechanical crushing, bending, tearing, and kinking to become refinement. The block-shaped LPSO phases dissolved during the deformation process, forming a stripe-like structure, and its rest of the refinement mechanism was similar to the lamellar phase. The refinement of block-shaped phase was slower than that of lamellar phase. However, the block-shaped phases always promoted DRX through the PSN mechanism, while the lamellar phases with a large volume inhibited the generation of DRX. After the refinement of lamellar phases, the inhibition effect was transformed into the promotion effect, which leaded to a continuous increase in the DRX fraction. This further promoted the uniform distribution of the LPSO phases and obtained a more ideal microstructure.

Effect of variable temperature repetitive upsetting-extrusion on microstructure and texture of Mg-Gd-Y-Zr alloy

The Mg-Gd-Y-Zr alloy was subjected to the variable temperature repetitive upsetting-extrusion process, a kind of severe plastic deformation. The evolution of microstructure, texture and deformation mechanism under different passes was analysed. It is found that when the deformation temperature was relatively high at 420℃, the morphology of the grains was approximately equiaxed. Some precipitated phases were distributed at the grain boundaries and the fraction of them was relatively low. When the deformation temperature was decreased, the precipitation phases increased remarkably, playing the pinning effect and stimulate the particle stimulated nucleation (PSN) mechanism to significantly refine the grain. As the number of deformation passes increased, The grains were remarkably refined from the 80.45 μm of initial billet to 4.08 μm of 4-pass sample, gaining the more uniform microstructure. With the increase of deformation amount, the coarse grains decreased with the fraction of dynamic recrystallization increased and secondary dynamic recrystallization occurred inside the grown dynamic recrystallized grains. The (1010) fiber texture disappeared and the texture was weakened. The random of the high-temperature deformation texture was obvious due to the non-basal slip of alloy which was easier to activate.

Microstructure and texture evolution of Mg-RE-Zn alloy prepared by repetitive upsetting-extrusion under different decreasing temperature degrees

The repetitive upsetting-extrusion (RUE) experiments of Mg-RE-Zn alloy were carried out to study the grain refinement and texture evolution under different decreasing temperature degrees during the deformation process. The results showed that during the RUE processing, the samples underwent dynamic recrystallization (DRX) and exhibited the similar bimodal microstructure comprising coarse deformed grains and fine dynamic recrystallized grains around. The continuous dynamic recrystallization (CDRX) process and the discontinuous dynamic recrystallization (DDRX) process occurred simultaneously, promoting grain refinement. The particles and the second phases precipitated, which effectively induced DRX to occur through the particle-stimulated nucleation (PSN). As the degree of decreasing temperature and the initial deformation temperature increased, the average grain size and texture intensity of the alloy decreased because the volume fraction of DRXed grains with small grain size and weak texture increased.

Mechanical Response and Microstructure Evolution of a Repetitive Upsetting Extrusion Processed AZ61 Magnesium Alloy in Semi‐Solid Compression

Semi‐solid billets of an AZ61 magnesium alloy are prepared by a repetitive upsetting‐extrusion (RUE)‐based strain induced melt activation (SIMA) method. Mechanical response and microstructure evolution in compression of the semi‐solid slurry with high solid fraction are investigated. The results reveal that the SIMA‐processed thixotropic structure comprises of globular solid particles and liquid films. True stress–true strain curves experience a rapid increase to the peak within a small strain, a slow decline, and the final steady‐state flow. Three regions of the dense deformation region, the severe deformation region, and the free deformation region are detected in the compressed specimen with reference to microstructure observation. Liquid segregation is found in the free deformation region due to the exudation of the liquid phase. The compression of the semi‐solid slurry is achieved by the coordination of the solid particles’ rearrangement and the liquid flow. The initial deformation stage is governed by the sliding or rotating of the solid particles. Mechanisms of the sliding between solid particles and the plastic deformation of the solid particles are responsible for the second and the final deformation stages, and their relative contribution is closely related to the solid fraction and deformation strain.

Effects of Repetitive Upsetting Extrusion on the Microstructure and Texture of GWZK124 Alloy under Different Starting Temperatures.

The effects of repetitive upsetting extrusion under different starting temperatures on the microstructure and texture of GWZK124 alloy were investigated. The results clearly showed that the particles and second phases induced dynamic recrystallization (DRX), which can be explained by the particle-stimulated nucleation (PSN) mechanism. It was shown that grain refinement during repetitive upsetting extrusion (RUE) is dominated by a complicated combination of continuous dynamic recrystallization and discontinuous dynamic recrystallization. The RUEed alloys under different starting temperatures exhibited a bimodal microstructure comprising fine DRXed grains with weak texture and coarse deformed grains with strong texture. The DRXed grains could weaken the texture. As the RUE starting temperature decreased, the average grain size increased and the volume fraction of DRXed grains decreased.

Effects of repetitive upsetting-extrusion parameters on microstructure and texture evolution of Mg–Gd–Y–Zn–Zr alloy

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- Mg5(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.

Effect of Isothermal Repetitive Upsetting Extrusion on the Microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr Alloy.

Repetitive upsetting extrusion (RUE) was applied to the as-homogenized Mg-12.0Gd-4.5Y-2Zn-0.4Zr (wt %) alloy at 773 K. The microstructure evolution of the alloy during RUE was investigated. The results indicated that almost all Mg5(Gd,Y,Zn) phases and fine-lamellar long-period stacking-ordered (LPSO) phases were dissolved into the matrix after homogenization treatment at 793 K for 16 h. After one RUE pass, dynamic recrystallization (DRX) occurred. During subsequent RUE passes (from one to three passes), average volume fractions of DRXed grains increased from 43.9% to 65.8%, and that of fine-lamellar and block-shaped LPSO phases gradually decreased. All samples exhibited a typical bimodal microstructure consisting of some initial grains containing fine-lamellar LPSO phases, but consisting mostly of fine-DRXed grains with a mean grain size of 6 μm. Because of an increase in the accumulated strains, the coarse grains were substituted with fine-DRXed grains, the grains were gradually refined, and the microstructure distribution became more homogeneous.

Grain Refinement and Texture Evolution of Mg-Gd-Y-Zn-Zr Alloy Processed by Repetitive Usetting-extrusion at Decreasing Temperature

A homogenized Mg-13Gd-4Y-2Zn-0.5Zr (wt%) alloy was subjected to a repetitive upsetting-extrusion (RUE) process at decreasing temperature from 480 °C to 370 °C. The microstructure and texture development of the alloy during the RUE process was investigated. The results show that average grain size decreases with increasing cumulative strain and decreasing temperature. Uniform ultrafine-grain structure with an average grain size of 3.4 μm is achieved after 6 passes, i.e., cumulative strain of 8.4. Grain refinement is induced by a complicated combination of discontinuous dynamic recrystallization(DDRX) and continuous dynamic recrystallization(CDRX). Kink of lamellar long period stacking order (LPSO) phases play an important role in the grain refinement through subdividing the coarse grains by inducing recrystallization evolved in the kink bands. After 1 pass of RUE, a strong basal texture is obtained. With increasing RUE passes, the texture is gradually weakened, which results from cooperative effect of dynamic recrystallization(DRX) and the alternative change of loading directions (axial and radial) during RUE processing.

Constitutive behavior of a SIMA processed magnesium alloy by employing repetitive upsetting-extrusion (RUE)

Thixotropic compression tests were carried out on a repetitive upsetting-extrusion (RUE) processed AZ91D magnesium alloy at temperatures ranging from 500 °C to 550 °C by using a Gleeble-1500 thermal-mechanical simulator. Semi-solid stress-strain data were obtained. A modified constitutive model was established to describe the thixotropic behavior of the RUE strained alloys. The results revealed that three stages of elastic-like deformation, strain hardening deformation and rheological viscoplastic deformation were involved in the thixoforming process. Furthermore, the compressed microstructures in semi-solid state were investigated with referring to microstructure observation. Dominant deformation mechanisms during the thixotropic compression were considered as the slipping or rotating mechanism of the solid particles along the liquid films, the slipping mechanism between the solid particles, the plastic deformation mechanism of the solid particles and the DRX behavior of the solid particles, whose function varied with the change of temperature and strain rate.

Nano grain refinement and strengthening of copper under room temperature RUE process

In this investigation repetitive upsetting-extrusion (RUE) process was used to investigate the effect of severe plastic deformation on the microstructural changes and flow behavior of commercial pure copper. Initial material together with two passes, four passes and eight passes of RUE in annealed and non-annealed condition were studied. Results show that grain refinement, in the scale of nano meter, has mostly been achieved only after two passes of RUE which is essentially a combination of one upsetting and one extrusion path. Increasing the number of passes after four passes of RUE did not have discernible effect on the grain refinement. Such a behavior is explained to be due to saturation of dislocations and the formation of high angle grain boundaries after only two passes of RUE. The grains after eight passes of RUE process even became slightly larger than the two and the four passes of RUE. This was related to restoration phenomena occurring during high number of passes of RUE. Flow strength of the material after different passes substantially increased, though the rate at which the flow stress increased declined by increasing the number of passes. ETMB model were used to explain the deformation behavior of the RUE samples.

Thixoforming of semi-solid AZ91D alloy with high solid fraction prepared by the RUE-based SIMA process

In the present study, semi-solid billets of AZ91D magnesium alloy were prepared by employing the repetitive upsetting-extrusion (RUE) based strain induced melt activation (SIMA) process. Thixoforming experiments were performed using semi-solid alloys experiencing various RUE temperatures and semi-solid reheating temperatures. The microstructure characterization and microhardness of the thixoformed products were investigated. Microstructure examination results indicated that semi-solid globular microstructure ensuring good thixotropic filling performance was prepared by applying the RUE-based SIMA method. Thixoformed components with good surface quality were obtained. Compared with the original as-cast alloy, significant grain refinement and microhardness improvement occurred in the thixoformed components. And the mean grain sizes and microhardness values were measured to be in the ranges of 11.81–23.84 μm and Hv80.67–Hv90.65, respectively. By means of further comparison of microstructure and microhardness, the grain coarsening and microhardness reduction of the thixoformed components were verified by elevating the RUE deformation temperature and semi-solid remelting temperature. Furthermore, strengthening mechanisms during thixoforming involving the application of the RUE-based SIMA route were discussed in detail. The results showed that the comprehensive effect of fine grain strengthening, dispersion strengthening, and solid solubility strengthening should be responsible for microhardness improvement.

Microstructure evolution of an AZ91D magnesium alloy subjected to intense plastic straining

In the present study, repetitive upsetting-extrusion (RUE) process was employed to induce severe plastic deformation (SPD) for an AZ91D magnesium alloy at temperatures ranging from 285 °C to 380 °C. Finite element method (FEM) and technical experiment were performed to reveal the non-uniform behavior during the RUE process. The results from the finite element analysis showed that effective strain was unevenly distributed in one-cycle strained sample and the non-uniformity would exist permanently with increasing deformation cycles. The microstructure evolution of the RUE processed alloys was characterized by optical microscopy, which clarified the microstructural development from heterogeneous and coarse as-cast structure, heterogeneous and refined structure to final homogeneous and fine-grained structure of the 340 °C and eight-cycle processed sample. In addition, a critical strain was suggested from the metallographic observation results. It was proposed that α-Mg grain structure was sufficiently refined by imposing accumulated strain beyond the critical value and the invariability of grain sizes was illustrated. A homogeneous structure with mean grain size of ∼3.04 μm was obtained after 285 °C and three-cycle RUE process, corresponding to an accumulated true strain of about 3.75. Furthermore, the fragmentation and dispersed distribution of the β-Mg17Al12 phase induced by shearing was confirmed by referring to scanning electron microscope (SEM) examination. Moreover, refining mechanisms responsible for grain structure were discussed in detail with reference to the transmission electron microscope (TEM) analysis results.

Microstructure evolution of a SIMA processed AZ91D magnesium alloy based on repetitive upsetting-extrusion (RUE) process

Repetitive upsetting-extrusion (RUE) was introduced into the strain induced melt activation (SIMA) process. The semi-solid feedstock of AZ91D magnesium alloy with superior thixotropic features was successfully prepared by the modified SIMA process. Prior to partial remelting, the process involving the application of RUE pre-deformation to as-cast alloy was conducted. Consequently, a severely strained structure consisting of fine α-Mg grains and highly fragmented β-Mg17Al12 particles was obtained. During the subsequent isothermal treatment between the solidus and the liquidus, the microstructure evolution of the RUE processed alloys subjected to various deformation cycles and temperatures was investigated at the temperature range of 550–580°C for various durations. The results indicated that the RUE-based SIMA process was a valid route for preparing high-quality thixotropic materials, and the isothermally treated microstructure consisted of fine solid globules surrounded by uniform liquid films. The microstructure evolution model for the modified SIMA process was proposed with reference to the micrograph examination. And the mechanisms responsible for the spheroidization and coarsening of the globular structure were discussed in detail. Further study on effective parameters clarified that the thixotropic features of semi-solid slurry were affected by the parameters of RUE process as well as the isothermal treatment process. And the desirable globular structure, featured by fine, homogeneous and well globularized solid grains and continuous liquid films, was obtained by three-cycle RUE process at 285°C followed by isothermal treatment at 560°C for 15min.

RUE-based semi-solid processing: Microstructure evolution and effective parameters

In this paper, repetitive upsetting-extrusion (RUE) was used for the semi-solid processing of 7075 Al alloy for the first time. Specimens of 7075 alloy were subjected to different RUE cycles at 250°C, and the semi-solid treatment was carried out at a range of 580 to 620°C for 2–35min. The results indicated that the semi-solid slurry's microstructure is fine and spheroidal, and is superior to that produced by the conventional strain induced melt activation (SIMA) process. The effect of inhomogeneous strain distribution across the cross section of the pre-deformed sample on the thixotropic microstructural features was investigated using the finite element method (FEM). Increasing the number of RUE cycles accelerates the recrystallization rate, reduces the average grain size and improves the degree of spheroidization. The Lifshitz–Slyozov–Wagner (LSW) theory was used to describe the coarsening process of the semi-solid slurry in the new RUE-based modified SIMA process. The effect of the number of RUE cycles on the coarsening kinetics of the solid particles was discussed.