Reciprocating Extrusion Process Research Articles

The microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy during the reciprocating extrusion process (REP)

In this paper, the microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy fabricated by reciprocating extrusion process (REP) at 340 ℃ for 2–8 passes is characterized by optical microscopy (OM), Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD).The results show that the microstructure was refined significantly, dynamic recrystallization (DRX), fragmentation of the second Mg2Si phase and precipitation of the Mg2Sn phase occurred during REP. With the increase of the REP passes, the fraction of low angle grain boundaries (LAGBs) showed a decreasing trend and the secondary phases distribution became more and more homogeneous and the degree of DRX was increased. At the same time, the initial extruded fiber basal texture was gradually weakened and became random as the REP passes increases. The hardness of the alloy also shown an increasing trend with the increase of REP passes. The grain refinement mechanism, texture evolution and increase of hardness were mainly related to the dynamic recrystallization and the particle stimulation nucleation (PSN) effect of the second phases.

Preparation of tritium breeding Li2TiO3 ceramic pebbles via newly developed piezoelectric micro‐droplet jetting

AbstractWet methods as an emerging technique for the preparation of millimeter‐sized tritium breeding ceramic pebbles, but the imposed air pressure as the driving forces to extrude slurry droplets are fluctuating during the reciprocating extrusion process, which caused a slight inconsistency in pebble sizes. In this study, a piezoelectric micro‐droplet jetting approach was proposed by introducing a piezo‐driven valve and modifying the slurry barrel mechanism to realize the air pressure invariable. A self‐developed piezoelectric micro‐droplet jetting device was successfully utilized to prepare Li2TiO3 green pebbles with coefficients of variation being lower than 2.7%. The size of the green pebbles could be precisely controlled in the range of 0.88–1.37 mm by manipulating the nozzle diameter, the air pressure, and the jetting time. The pebbles sintered at 1000°C for 3 h possessed a small grain size of ∼5.9 μm, a satisfied relative density of ∼84.8% T.D., and a high crush load of ∼25.7 N, implying the prepared pebbles could be used as a promising solid tritium breeding material in fusion reactors. These findings are anticipated to provide new opportunities for the highly efficient preparation of size‐controllable tritium breeding ceramic pebbles.

The Microstructure and Texture Evolution of Mg-5sn-1si-0.8y Alloy During the Reciprocating Extrusion Process (Rep)

The Microstructure and Texture Evolution of Mg-5sn-1si-0.8y Alloy During the Reciprocating Extrusion Process (Rep)

Tool wear analysis of C-shaped equal channel reciprocating extrusion process of AISI-H13 steel die using finite element method

Tool wear analysis of C-shaped equal channel reciprocating extrusion process of AISI-H13 steel die using finite element method

Effect of reciprocating extrusion temperature and passes on the microstructural evolution of Mg-5Sn-1Si-0.8Y alloy

AbstractIn this study, a reciprocating extrusion process (REP) was employed on Mg-5Sn-1Si-0.8Y magnesium alloy and the effect of the REP temperature (in the range of 340 °C to 400 °C) and number of REP passes (in the range of 2 to 8 at 340 °C) on the microstructural evolution of the alloy were investigated. The results show that the microstructure observed varied from edge to centre on the cross and longitudinal sections of the specimen. Upon increasing the extrusion temperature from 340 °C to 400 °C, the grain size distribution became uneven; the Mg2Si phase was concentrated at the grain boundaries, and the amount of Mg2Sn precipitated was reduced. In comparison with changing temperature, increasing the number of REP passes was more effective for improving the homogeneity of the alloy. With an increasing number of extrusion passes, the distributions for the grain size and second phases became increasingly uniform. In this study, an alloy subject to 8-REP passes and extrusion at 340 °C showed the finest and most homogeneous microstructure. Finally, a quantitative relationship between the REPed grain size and the Zener–Hollomon parameter was obtained.

The Influences of Reciprocating Extrusion Passes on the Microstructure Properties of Al 6061/SiC Composites

The present study discusses the microstructure properties of Al–SiC composites. Certain deformation processes such as reciprocating extrusion (RE) were found to be applicable to strengthen the metal matrix composites (MMCs) and to refine the grains of the matrix. In line with this argument, reciprocating extrusions were implemented by applying up to five passes. The RE process was employed in fabricating a homogenous dispersion of SiCp and a fine-grain composite structure. The composites in question were studied in terms of their behaviors and microstructures on the basis of the RE process.

Bulk Nanomaterials and Powders Consolidation Produced by Cyclic Extrusion Compression

The Cyclic Extrusion – Compression - reciprocating extrusion process (CEC) is one of severe plastic deformation methods (SPD), which allow to produce bulk nanomaterials without changing the initial shape of deformed samples. The results are presented showing that the average grains size and microbands thickness in aluminium alloys decrease below 100 nm. The investigations revealed that the average grains size is about 250 nm and 200 nm in polycrystalline and monocrystalline copper, respectively.The Cyclic Extrusion Compression method is also used to produce bulk materials by powder consolidation. The subgrains/nanograins inside the silver powder particles after the consolidation processes achieved the mean size of about 100 nm. Moreover, it has been found that inside structure observed by TEM, the consolidated powder granules consisted from nanometric twins of about 10 – 20 nm. This silver based powder consolidated by CEC method were extruded by hydrostatic extrusion method. The final product were the wires with a diameter of 3 mm, which were used to electrical contacts production.

Effects of reciprocating extrusion process on mechanical properties of AA 6061/SiC composites

A reciprocating extrusion (RE) process was used to improve the mechanical properties of Al-based composite manufactured using cast and powder metallurgy (PM). AA 6063 cast and AA 6061 powders were used as the matrix materials, and the matrix was reinforced by 5% SiC (volume fraction) particles. The hardness and grain size of extruded samples decrease with increasing the number of extrusion pass, while the toughness and ductility increase. As the tensile strength of the samples decreases, the elongation of the extruded samples increases. Consequently, reciprocating extrusion is an effective method for improving the mechanical properties of metal matrix composites (MMC).

The effects of a reciprocating extrusion process on the friction and wear behaviors of AA 6061/SiC composites

Abstract

Investigation on effects of reciprocating extrusion process on microstructure of AA 6061 based composites

The reciprocating extrusion (RE) method was developed to fabricate the fine grain AA 6061 and AA 6063 alloys and to obtain their optimum mechanical properties. While 6061/72 μm aluminium alloy powder and AA 6063 bar material were used as a matrix material separately, SiC/20 μm ceramic particles were used as reinforcement. Billets were produced from AA 6061 powders and AA 6063 materials mixed with SiC ceramic particles by sintering and stir casting method respectively. Using the RE process, which was performed at 573 K for one, five and nine passes, the billets were extruded again to investigate the microcharacterisation of the products. The hardness, microstructure, grain size and distribution of the extruded samples were examined and analysed using an SEM. High resolution electron backscatter diffraction and TEM methods were also applied for grain analysis. The manufacturing method of the billets to be extruded reciprocatively affects the hardness that occurs after the deformation. The hardnesses of all samples increase first and then decrease with pass number. After extrusion passes, the longer or larger silicon particles were broken into finer particles and microstructures were changed from the initial to a new structure. A homogeneous distribution of SiCp and refined grain structure of the test materials were obtained by RE. However, the process temperature applied during the process has a greater effect on the change in grain size than that of the occurring deformation.

MICROSTRUCTURE AND WEAR RESISTANCE OF A COMPOSITE Gr/Al2O3/Al PRODUCED BY RECIPROCATING EXTRUSION

A reciprocating extrusion process was used to produce graphite and alumina reinforced pure aluminium composite. The graphite particles (0~5vol%), alumina particles (10 vol%) and pure aluminium particles (balanced) were dehydrated separately at 70°C in vacuum for 3 hours, and then mixed together. A round billet with 50 mm in diameter was prepared by hot pressing at 350°C with the mixed particles and then extruded to a fully-consolidated goblet-like sample at 480°C and 430MPa by reciprocating extrusion. The results showed that all reinforced particles were refined and uniformly distributed in the matrix by reciprocation extrusion severe plastic deformation. The presence of graphite particles caused the reduction in the friction coefficient and wear rate of the Gr / Al 2 O 3/ Al composite. Compared with the composite prepared only by alumina particles (10 vol%) and pure aluminium particles, the friction coefficient and wear rate of the Gr / Al 2 O 3/ Al composite, which contains 5vol% graphite and 10vol% alumina particles, decreased 45.3% and 33.5%, respectively, and thereafter it displays an excellent combination of low friction coefficient (0.37) and wear rate (2.2×10-7mm3/(N.m)), and appears to be more promising.

Al<sub>2</sub>O<sub>3</sub>/Al Composites Consolidated from Alumina and Aluminum Particulates by Reciprocating Extrusion

MMCs can be usually fabricated by powder metallurgy, stir casting and spray co-deposition, etc. Al2O3/Al composites were produced by means of reciprocating extrusion with alumina and pure aluminum particulates in the present study. The microstructure was analyzed by scanning electronic microscope, and the mechanical properties were measured by hardness tester and universal testing machine, respectively. The results showed that Al2O3/Al composites with as high as 20 vol.% alumina can be successfully produced by reciprocating extrusion. During reciprocating extrusion process, the reinforced alumina particles can be fragmentized and uniformly distributed in the aluminum matrix. The tensile strength and hardness of the composites increase as volume fraction of alumina particles increases, whereas the elongation decreases. Compared with the pure aluminum compact, the tensile strength and hardness of the composite with 20 vol.% alumina particles is 29.3% and 93.5% higher, respectively; whereas the elongation decreases 66.6%, and the fracture mechanism of the composites is attributed to ductile rupture.

Study of 6061-Al2O3p composites produced by reciprocating extrusion

A reciprocating extrusion process was developed to consolidate 6061-Al2O3p composites from mixed powders. The 6061 alloy powder was first dehydrated in a vacuum chamber at 450 °C and then mixed with 12.5 µm Al2O3 powder in various volume fractions: 0, 5, 10, 20, and 30 pct. The mixed powders were hot pressed at 300 °C under a pressure of 300 MPa and finally extruded reciprocatingly 14 times at 460 °C. The results show that the composites were fully densified, with no sign of pores or oxide layers observable in the optical microscope. The Al2O3 particles were distributed uniformly in the matrix. As compared with 6061 alloys, the composites demonstrated a smaller precipitation hardening and elongation, but exhibited a higher Young’s modulus and a larger work hardening capacity. The degradation of precipitation hardening was due to the loss of Mg, which reacts with Al2O3 to form MgAl2O4. The large work-hardening capacity is attributable to the incompatibility between Al2O3 and the matrix, which possibly generates more dislocations to harden the matrix. The composites had much higher friction coefficients and greater wear resistances than the 6061 alloy against steel disc surface. The friction coefficient of the 6061-30 vol pct Al2O3p composite was double that of the 6061 alloy and the wear resistance was 100-fold. As compared with similar composites reported previously, these composites possessed much higher elongation at the same strength level. A 30 vol pct Al2O3p still displayed an elongation of 9.8 pct in the T6 condition. All of these improvements are attributed to the merits, including full densification of the bulk, uniform dispersion of the Al2O3 particles in the matrix, and strong binding between the Al2O3 particles and the matrix resulting from reciprocating extrusion.

An in situ composite of Al (graphite, Al4C3) produced by reciprocating extrusion

A reciprocating extrusion process was used to produce an in situ composite of Al (graphite, Al4C3). 6061 Al alloy powder was first dehydrated at 450°C in vacuum, and then mixed with graphite powder in various volume fractions up to 20%. The mixed powder was hot pressed as a billet and finally consolidated by a reciprocating extrusion machine. Each billet was extruded through the die 15 times. The results show that all the graphite particles were greatly refined and uniformly distributed in the matrix. The graphite in-situ reacted with the Al matrix to form fine dispersed Al4C3 particles both during reciprocating extrusion and subsequent solution treatment. The higher the volume fraction of graphite added to the matrix, and the longer the solution treatment, the harder the composite. The 6061Al-20% (graphite, Al4C3) composite that was solution-treated for 24 h, and then peak aged, could attain a hardness level of 7075-T6 alloy. As for the wear rate, this initially increased due to the presence of the graphite particles; but with higher graphite content and prolonged solution treatment the wear rate subsequently decreased. This phenomenon is attributed to the fact that although the graphite could soften the composites, the Al4C3 strengthened the composites during prolonged solution-treatment time. The wear test demonstrated that composite containing 20% (graphite, Al4C3) which has been solution-treated for 24 h can exhibit an excellent combination of coefficient frictional and wear rates, ∼50 and 70%, respectively, of those of 6061 alloy.

Synthesis of fine Pb–50 vol.-%Sn alloys by a new process of reciprocating extrusion

A reciprocating extrusion process has been developed for producing Pb–50 vol.-%Sn bulk alloys with fine and uniform microstructures. Two starting materials were used. One was made up of alternately stacked layers of pure Pb and Sn, and the other was cast billets with the same composition. The microstructural evolution as a function of the number of extrusions for these starting materials was investigated and compared. As the number of extrusions increased, the mixing and refining were found to start from the container wall side and die side, and then extended towards the inner core and ram side. The characteristic widths of the Pb and the Sn phases in both starting materials decreased rapidly in the first few passes and then approached the same value. Furthermore, both cases had a similar phase size limit and morphology in which the Pb and the Sn phases formed mutually intervening skeletons beside some isolated islands. The limiting phase width could be explained by the grain boundary sliding mechanism which has been used to explain the high strain rate superplasticity.

Improved Microstructures and Mechanical Properties of 2024 Aluminum Alloy Produced by a Reciprocating Extrusion Method

A reciprocating extrusion process was used to work the 2024 aluminum alloy ingots at 723 K so that refined microstructures and improved mechanical properties could be obtained. The number of extrusion passes was monitored to see their effect upon microstructure and properties. As the number of extrusion passes was increased, the grains became finer but after 5 passes a limiting grain size of about 2 μm was approached. On the other hand, the dispersoids and inclusions became smaller and more equiaxed, and more uniform in the matrix up to 20 passes. Grain refinement results from the repeated partial recrystallization and the increased number of inclusions and dispersoids to enhance recrystallization during reciprocating extrusion. The refinement of dispersoids And inclusions was attributable to three possible cracking mechanisms: bending mechanism, short-fiber loading mechanism and shear mechanism depending on the shape of a particle. Redistribution of particles is driven by the cyclic plastic flows of extrusion and compression during reciprocating extrusion. In the first 5 passes, yield strength and ultimate tensile strength showed a small decrease but elongation increased much. After more passes, their variations became small. The overall loss of strength is about 10% and the increase of elongation is about 54%. The combination of strength and elongation is still significantly improved. The decrease in strength is mainly due to the coarseness of S' precipitates which is related to the loss of quenched vacancies. The large improvement of elongation is mainly attributable to the refinement of inclusions.

A reciprocating extrusion process for producing hypereutectic Al–20wt.% Si wrought alloys

A reciprocating extrusion process has been developed for producing hypereutectic Al–20wt.% Si alloys with fine and uniform microstructures and superior properties. Rapidly-solidified layers and cast billets are used as the starting materials. The results show that the interfaces between the layers of the rapidly-solidified alloys could be fully eliminated, and strength and ductility are both improved as the number of extrusion passes increases. For the ingot-processed alloys, the plate-like Si phase in the eutectic and enormous primary Si crystals are refined to a large extent and thus both strength and ductility are increased by 9 and 67%, respectively. Because of having finer Si particles, the rapidly-solidified alloys exhibit a superior combination of mechanical properties to that of the ingot-processed alloys. Fractography demonstrates that the larger Si particles in the ingot-processed material increased the amount of cleavage failure processes.