Conventional Backward Extrusion Research Articles

High elongation heterostructure rare earth magnesium alloy based on rotating backward extrusion process

In this paper, Mg-9.5Gd-4Y–2Zn-0.5Zr cylindrical parts were prepared by the conventional backward extrusion (CBE) process and rotating backward extrusion (RBE) process. The effects of the two processes on the microstructure and mechanical properties of different orientation regions of rare earth magnesium alloy were analyzed and compared. The RBE process introduces a torsional shear quantity based on the CBE process. By changing the direction of plastic flow, has a positive effect on the elongation (EL) of the alloy. It was found that dynamic recrystallization (DRX) occurred in both CBE and RBE processes. With the transition of deformation, the strain continues to accumulate, and the DRX mechanism changes from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX). Compared with the CBE process, the grain refinement of the RBE process is more significant. After deformation, a more significant heterostructure is obtained in the RBE-45° region, and the average grain size reaches 24.7 μm. The ultimate tensile strength (UTS), yield strength (YS), and EL of the alloy in this region are 292.5 ± 7.7 MPa, 226.6 ± 7.4 MPa, and 21.5 ± 1.3 %, respectively. Although the strength is slightly lower than that of CBE alloy, better plasticity is obtained. The excellent strength-toughness synergy is attributed to the synergistic effect between heterogeneous regions of non-uniform microstructure. This study provides some theoretical guidance for the industrial production of large-size magnesium alloy cylindrical parts and subsequent applications.

The Deformation Characteristics and Effect of Processing Parameters on the Microstructure of 7075 Al Shell Part Manufactured by Rotating Backward Extrusion

Rotating backward extrusion (RBE) is known as a new severe plastic deformation technology that effectively combines the features of conventional backward extrusion (CBE) and torsion deformation. In this study, 7075 Al alloy shell parts were successfully prepared by CBE and RBE with a different number of revolutions (N = 5, 10, 15, 25, 50) at 410 °C. The effects of the RBE process on the grain refinement, precipitates and properties of extruded parts were revealed, and the deformation characteristics were compared with CBE. The results showed that the RBE process could greatly eliminate the dead deformation zone at the bottom of the CBE section and significantly improved the comprehensive strain level of the material due to the addition of severe torsional deformation via an open punch. The grain refinement feature of RBE parts showed a gradient distribution that continuously weakened from the inner wall to the outer wall with decreasing compressive and torsional stress. Increasing the number of revolutions significantly promoted the level of grain refinement, the grain refinement range, and effectively broke down and refined the coarse insoluble Fe-rich phases of the extruded parts. It was revealed that the finest grain size of approximately 1.3 μm could be obtained in the inner wall region when N was increased to 25, which was linked to the comprehensive effects of continuous dynamic recrystallization and geometric dynamic recrystallization. RBE greatly promoted an improvement in properties of the extruded parts. After T6 treatment, the microhardness of the fine-grained region of the RBE (25 N) part increased to ~192–197 HV, compared with ~180 HV in the initial T6-extruded state.

The evolution of microstructure and texture of AZ80 Mg alloy cup-shaped pieces processed by rotating backward extrusion

This study proposed an effective plastic deformation technique, rotating backward extrusion (RBE), for producing high performance AZ80 magnesium alloy cup-shaped pieces. The RBE process was carried on the Gleeble-3500 test machine at 653 K, and the conventional backward extrusion (CBE) was also conducted for comparison. A detailed microstructure analysis was performed using the optical microscopy (OM) and electron back-scatter diffraction (EBSD). The results shown that the equivalent strain and deformation uniformity of the cup pieces could be substantially increased by the RBE process compared with the CBE process. Furthermore, the RBE process could significantly improve the grain refining capacity and the proportion of dynamic recrystallization (DRX), of which the maximum reduction of grain size was 88.60%, and the maximum increase of DRX proportion was 55.30% in the cup bottom. The main deformation mechanism of the RBE process was the discontinuous DRX (DDRX), while the continuous DRX (CDRX) was also occurred in the cup transition. Compared with the CBE sample, the texture of the cup bottom was weakened for the RBE sample. The microhardness value of the RBE sample was higher than that of the CBE sample, which can be attributed to the grain refinement strengthening.

Optimization of Die Parameters in Annular Channel Angular Extrusion Based on Strain Distribution Uniformity

In this paper, a recently developed backward extrusion method enforcing severe plastic deformation is modified for processing cup-shaped part with homogeneity strain. Variation of channel angles (Φ) and corner angles (Ψ) have been employed to obtain a better strain distribution. The performance is analyzed using finite element modeling Deform 3D commercially available software. To verify the simulation results, the experiment was carried out for AZ80 magnesium alloy. The present work investigates effective strain distribution behavior, analyzed by several strain regions during the forming process. Furthermore, the influence of different channel and corner angles on the strain distribution uniformity of the wall in the formed part is especially evaluated. The best strain homogeneity is obtained with Φ=75° and Ψ=60°. Particularly worth mentioning is that the strain uniformity achieved by this novel method is better than that obtained in the conventional backward extrusion. While the smaller corner angle (Ψ) can develop gradient effective strain distribution, adversely affecting the strain homogeneity.

An Investigation on the Microstructure and Texture of an AZ80 Cup-Shaped Piece Processed by Rotating Backward Extrusion.

The rotating backward extrusion (RBE) process, as a new severe plastic deformation (SPD) process, is based on conventional backward extrusion and rotation, which meets the requirement of modern industrial development with its high performance and production efficiency. However, there is little research on the microstructure evolution and texture modification of the RBE process. Thus, in this study, the effect of different rotating revolutions, e.g., n = 5, n = 10, and n = 50, on the microstructure and texture development for the RBE process based on the AZ80 magnesium (Mg) alloy were investigated at 653 K. The results disclose that the rotating revolution is an influencing processing parameter on the deformation of the RBE process. The grain refining ability is enhanced with the increase of the rotating revolutions, and the minimum grain size of the cup bottom, shearing zone, and cup wall can reach to 16.7 μm, 15.6 μm, and 13.0 μm, respectively, under the condition of n = 50. Furthermore, with the increase in the rotating revolutions, the microstructure of the alloy becomes more uniform and the proportion of dynamic recrystallization (DRX) is also increased. The maximum DRX fractions of the sample for the cup bottom and cup wall are 95.4% and 86.8%, respectively, at n = 50. The DRX mechanism of the RBE process is determined by the continuous DRX and discontinuous DRX. In addition, the texture can be significant weakened during the RBE process, especially at the cup bottom, where the maximum pole intensity can be reduced from 17.6 at n = 10 to 6.5 at n = 50, which can be attributed to the higher proportion of new DRXed grains whose orientations are more random compared with the deformed grains.

The effect of processing parameters on the microstructure and texture evolution of a cup-shaped AZ80 Mg alloy sample manufactured by the rotating backward extrusion

The rotating backward extrusion (RBE) process is of great potential for producing the high qualitative cup-shaped AZ80 magnesium (Mg) alloy pieces based on the severe plastic deformation (SPD). However, researches on RBE process involving the microstructure and texture development are still pretty limited. Thus, in this work, the RBE process of AZ80 Mg alloy cup-shaped pieces was performed at three temperatures of 573, 613 and 653 K combining with three different rotating revolutions of 5, 50 and 100. Furthermore, the conventional backward extrusion (CBE), i.e. N = 0 in the rotating revolution, was also conducted for comparison. The effects of rotating revolution and processing temperature on the microstructure and texture evolution were studied in detail. The results showed that a relatively refined and homogeneous microstructure could be achieved by the RBE process compared with the CBE process. With the increasing rotating revolutions, the average grain size of the sample was decreased and the dynamical recrystallization (DRX) fraction was increased gradually. As the temperature increasing, the grain size of the cup-shaped samples was gradually increased, and the DRX fraction was also gradually increased for N = 0 and N = 5 samples, while it was almost unchanged for N = 50 and N = 100 samples. The smallest grain size of 3.9 μm and the largest DRX fraction of 99.2% were both obtained at 573 K with N = 100. The grain refinement during the RBE process was mainly caused by the DRX, which was determined by the deformation mechanism including the continuous DRX (CDRX) and discontinuous DRX (DDRX). Decreasing the deformation temperature could promote the generation of dynamic precipitates (DP), increasing rotating revolutions could reduce the size of the DP and make the undissolved eutectic phase (EP) more fragmented. In addition, the strong texture exhibited in the CBE samples could be effectively weakened by increasing the rotating revolution or temperature during the RBE process, owing to the higher proportion of new DRXed grains whose orientations were more random compared to the deformed grains.

Comparisons of microstructure homogeneity, texture and mechanical properties of AZ80 magnesium alloy fabricated by annular channel angular extrusion and backward extrusion

Abstract This paper provided an efficient single pass severe plastic deformation (SPD) method, annular channel angular extrusion (ACAE), for fabricating AZ80 magnesium alloy shell part. The effect of ACAE process on the microstructure homogeneity, texture, and mechanical properties of extruded part was experimentally investigated. For comparison, conventional backward extrusion (BE) was also conducted on processing AZ80 part with same specification. The results showed that ACAE process has a better capacity to refine the microstructure and dramatic improve the deformation homogeneity of the extruded part than BE process. Due to two strong shear deformations were implemented, ACAE process could also concurrently modify the basal texture more notably than BE process. In particular, a bimodal texture was found in ACAE extruded part, which was greatly related to the enhanced synergetic action of basal slip and secondary slip caused by the effective shear stress. More uniform and superior hardness along the thickness and height of part were achieved via ACAE process. Further surveying of tensile tests also showed that the part fabricated by ACAE process exhibited significantly higher and far more homogeneous tensile properties with an excellent balance of strength and ductility. The remarkable enhanced tensile properties of ACAE extruded part could be primarily attributed to the significant grain refinement, which provided a powerful grain boundary strengthening effect and meaningfully suppressed the development of twin-sized cracks during tensile deformation. It was established that ACAE process seemed to be a very promising single pass SPD method for manufacturing Mg-based alloy shell parts with more homogeneous microstructure and superior performance.

Refining the microstructure and modifying the texture of the AZ80 alloy cylindrical tube by the rotating backward extrusion with different rotating revolutions

Abstract This study proposed a novel severe plastic deformation technique, rotating backward extrusion (RBE), for producing high performance AZ80 alloy cylindrical tubes. Three different rotating revolutions were chosen and entitled as N = 5, N = 50 and N = 100 in terms of the total revolutions, respectively. The effect of the different revolutions of the RBE process on the microstructure and texture evolution of AZ80 tubes was investigated at the 573 K. The conventional backward extrusion (CBE) entitled as N = 0 was also conducted for comparison. The microstructure observation of the tube bottom (region A) and inner wall (region B) indicated that the average grain size was decreased and the proportion of dynamic recrystallization (DRX) was increased gradually with the increasing rotating revolutions. Particularly, the N = 100 sample obtained the finest grain size of 1.23 μm and the largest DRX proportion of 99. 09% at the region B. The deformation mechanisms of the N = 5 sample were twin-induced recrystallization (TDRX) and continuous DRX (CDRX), while only discontinuous DRX (DDRX) was occurred in the N = 50 sample. In addition, the preferred orientation of [10-10] fiber texture existed in the CBE sample was replaced by the [10-10]-[2-1-10] double fiber texture of the RBE samples in the region A, which would be attributed to the activation of prismatic slip systems in the unDRXed region and the formation of the CDRXed grains with 30° [0001] grain boundaries. After the deformation, the [10-10]-[2-1-10] fiber texture was still existed in the N = 5 and N = 50 samples, but the N = 100 sample had became a non-fiber texture. Furthermore, with increasing rotating revolutions, the basal pole intensity of the studied alloys exhibited a trend of first decreasing and then increasing in both region A and B, which indicated that the texture could be weakened during the RBE process.

Numerical and Experimental Analysis of Rotating Backward Extrusion as a New SPD Process

Rotating backward extrusion (RBE) as a new severe plastic deformation technique is a continuous process to produce cylindrical tubes with fine grains and superior properties. In this study, the RBE process with an open punch was applied to the AZ80 alloy at 653 K, and the deformation mechanisms and the microstructure evolution were examined by the finite element method (FEM) and thermal simulation experiment. The results showed that the effective strain of the RBE process was higher than that of the conventional backward extrusion (CBE) process, and the strain increased with revolutions increasing. The strain improvement of the RBE process was related to the large cumulative plastic deformation imposed by the continuous rotation of the open punch. Furthermore, the extrusion load was reduced significantly in the RBE process comparing with the CBE process, due to the change of friction stress and stress state of the materials. And the maximum load reduction of the FEM and experiment was 47.33% and 31.6%, respectively. The average grain size of the RBE sample could be reduced by up to 90% in the region A at 30 N compared with the CBE sample. The maximum increase in microhardness of the RBE sample relative to the CBE sample was 23% at 30 N in the region A. Therefore, the grain refinement and mechanical properties of the materials can be substantially improved by the RBE process.

Development of a novel high straining backward extrusion process

In this study, a new method of backward extrusion is proposed. In this new process, a punch with a movable mandrel was designed. A hollow billet was firstly backward extruded and subsequently upset with the use of the punch after the mandrel returned. The extrusion and upsetting processes were successively executed in order for a higher effective strain to be imposed and a fibrous tissue flow direction to be controlled. In order for the capability of this process to be investigated, experimental and finite element (FE) methods were used. The effective strain of the final part prepared by both the conventional and the new process were compared along the bottom radial and wall axial direction respectively. In the results, it is shown that the plastic strain applied through the processed sample was approximately higher in twice the value of the sample processed via conventional backward extrusion. Consequently, this may improve the mechanical properties and anisotropy of the final products. The difference of the UTS and the TYS between radial and tangential at the bottom was less than 3%.This new process has proven to be promising for parts with a central hole at the bottom production in order for the parts low performance to be improved.

A novel backward extrusion process through rotating die and open punch

Abstract In this study, a new method of backward extrusion through rotating die and open punch, named rotating backward extrusion (RBE), is proposed. In this new process, a torque is imposed on the die that drives billet rotating. The rotating billet was backward extruded with the use of the punch with end face groove. To investigate the capability of this process, the experiment and finite element (FE) analysis were carried out for AZ80 magnesium alloy used as experimental material. The effects of rotating speed on the effective strain and process load were analyzed. The effective strain of the final part and process load were compared for cup extrusion by both the conventional and the new process respectively. The results showed that the average effective strain through the processed sample was approximately higher in 3 times the value of the sample processed via the conventional backward extrusion. The reduction of process load is about 20% in maximum in comparison with the conventional backward extrusion process. This new process has proven to be promising for the hollow parts production because of lower process force and imposing higher effective strain. The potential for grain refinement and mechanical properties improvement are required to fully evaluate for the new process.

Development of a novel bulk plastic deformation method: hydrostatic backward extrusion

This paper aimed to propose a novel bulk plastic deformation method entitled hydrostatic backward extrusion process that is an implementation of the benefits of hydrostatic extrusion to the backward extrusion process. The applicability of the process was investigated using experimental tests and finite element analysis. The results showed that the produced tube by hydrostatic backward extrusion exhibits higher effective plastic strain while needing lower process load (elimination of friction force). The maximum process load in hydrostatic backward extrusion was obtained 55 kN that was 61.1 and 264.6 kN in the novel method of backward extrusion and conventional backward extrusion processes, respectively. This new method is promising for processing of high-strength ultrafine-grained tubes and hard-to-deform materials because of the nature of the processing by hydrostatic pressure.

Development of a novel method for the backward extrusion

In this study, a new method of backward extrusion using small diameter billet is proposed. In this new process, the die setup consists of three main parts of the fix-punch, the moveable punch and the matrix. The fix-punch has been used to decrease the cross section of applied billet and finally reducing the total force of the process. To investigate the capability of this process, experimental and finite element (FE) methods were used. The results showed that the first advantageous of the new process is that the load is reduced to about less than a quarter in comparison with the conventional backward extrusion process. This higher reduction in the required force is due to reduce of the cross section of the initial billet. EF results showed that while needing lower loads, the applied plastic strain through the processed sample is about two times higher than that in the sample processed via conventional backward extrusion. This is the second advantageous of the process. Eventually, the most important advantages of the novel method of backward extrusion are the lower process force, imposing higher effective strain and a better strain homogeneity through the tube length. This new process is also very promising for producing ultra fine grained (UFG) samples because the higher level of shear strains.

Upper bound analysis of torsional backward extrusion process

In this paper, backward extrusion process with low die rotation was studied to improve the problems of conventional backward extrusion process: the requirement of large forming machine, the difficulty in selecting the die material caused by high surface pressure, high cost of forming machine caused by improvement of noise and vibration, etc. In this experiment, model material, plasticine, was used as specimen. The result of torsional and conventional backward extrusions experiment were analyzed and compared by two methods. One is upper bound technique computing velocity field, and another is FEM simulation with DEFORM-3D. In the upper bound analysis, the velocity fields were derived using the dual stream functions. The use of stream functions in formulating upper bound solutions has some advantages. The number of unknown is reduced and incompressibility condition is satisfied. These result show that the torsional backward extrusion is a very useful process because this process yields the homogeneous deformations and lower forming load (decrease about 30%). In this paper, the most proper angular velocity of container is found to be around 0.16 rev/s. But, if the angular velocity was over 0.18 rev/s, deformation pattern was non-uniform and forming load was increased. Due to the decrease in forming load, die life can be improved and it is possible to use a press of relatively low capacity. Also this process can reduce corner cavity and improve the initial cast structure, owing to the high deformation and uniform strain distribution. Additionally, this process might be useful for powder compacting.