Repetitive Upsetting-extrusion Process Research Articles

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.

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.

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.

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.

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.

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.

Microstructure and mechanical properties of AZ61 magnesium alloy prepared by repetitive upsetting-extrusion

The process of repetitive upsetting-extrusion (RUE) was used to achieve severe plastic deformation (SPD) for an as-cast AZ61 magnesium alloy in temperature range of 285−380 °C. The microstructure and mechanical properties of the as-cast and RUE processed AZ61 alloys were investigated. The results indicated that homogeneous fine-grained structure with mean grain size of 3.5 μm was obtained as the accumulated true strain in the axial direction increased to 4.28 after three RUE passes at 285 °C. The dominant reason of grain refinement was considered the dynamic recrystallization induced by strain localization. It was also found that the microstructural evolution was affected by temperature and accumulated deformation. The mechanical properties of RUE processed AZ61 alloys were significantly improved owing to grain refinement. Furthermore, the relationship between deformation parameters and mechanical properties of AZ61 alloy prepared by RUE processing was revealed by tensile tests carried out at room temperature.

Repetitive upsetting extrusion process and microstructure evolution of AZ61 magnesium alloy

The rigid plastic finite element method was used to simulate the repetitive upsetting extrusion (RUE) process of an AZ61 magnesium alloy. Flow nets, field variables and the influence of initial blank temperature and RUE passes on the RUE process were analysed systematically. The results showed that large accumulated strain induced by multi-pass operation could be obtained by RUE process. The applied load versus displacement curves were obtained by RUE process test and the forming principle was revealed. Microstructure evolution during RUE process was demonstrated by microstructure observation, which revealed that the RUE strain induced process has a pronounced effect on grain refinement. Under the conditions of 340°C and 1 mm s−1, the initial cast structure with average grain size of 95 μm evolved to fine and uniform DRX grains with average grain size of 6·9 μm after three RUE passes.

Deformation behaviour of bulk materials during repetitive upsetting-extrusion (RUE)

Repetitive upsetting-extrusion (RUE) that was originally invented to process powder materials for bulk mechanical alloying is currently being used to process bulk materials. Bulk materials are subjected to severe plastic deformation using the same die design that was used to process powder materials. As the deformation behaviour of powder and bulk materials are quite different, it has to be evaluated whether a single die design is suitable to process both these materials. Further, information on the deformation behaviour and strain homogeneity that can be achieved by subjecting bulk materials to RUE process are also currently not available. To address these issues, both numerical analysis and actual experiments on commercial pure copper has been carried out. The results obtained are presented and discussed here

Ultrafine grained structure and mechanical properties of a LY12 Al alloy prepared by repetitive upsetting-extrusion

The process of repetitive upsetting-extrusion (RUE) was used to achieve severe plastic deformation, and its validity in preparing bulk ultrafine-grained materials was demonstrated by experimental investigation on a LY12 Al alloy. The results showed that the microstructure evolution of the alloy due to RUE processing was of a three-step character. With the increase of the RUE processing passes, i.e., the increase of the accumulated true strain, the grain size of the alloy gradually decreased, while the compressive yield stress, σ 0.2, and the micro-hardness, H v, increased correspondingly. In particular, after 10 passes of RUE processing corresponding to an approximate accumulated true strain of 8.926, an equiaxed ultrafine microstructure with an average grain size of about 200 nm was obtained. As a consequence, the σ 0.2 and H v of the alloy were enhanced from the starting 318.5 MPa and 112.3 H v to 513.6 MPa and 176.5 H v, respectively. The results also showed that the Hall–Petch relationship persists for the RUE-processed LY12 Al alloy with ultrafine grains down to 200 nm.