Cyclic Extrusion Compression Research Articles

Microstructure and mechanical properties of AM60B magnesium alloy prepared by cyclic extrusion compression

The cyclic extrusion compression (CEC) process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.

Microstructure evolution and grain coarsening behaviour during partial remelting of cyclic extrusion compression formed AZ61 magnesium alloy

The effects of CEC passes, isothermal holding time and reheating temperature on the microstructure evolution and grain coarsening behaviour of AZ61 magnesium alloy produced by the recrystallisation and partialmelting (RAP) process were investigated. Before partial remelting, as-cast AZ61 alloy was deformed by cyclic extrusion compression (CEC) with one pass and two pass at 330 °C. After CEC, the microstructure consisted of unrecrystallized grains and deformed eutectic compounds. Increasing isothermal holding time resulted in the formation of spheroidal grains surrounded by liquid films. With increasing the isothermal holding time, the solid grain size increased and the degree of spheroidization was improved. With increasing the reheating temperature, namely increasing liquid fraction, the solid grain size obviously decreased during the period from 560 °C to 570 °C and then slightly increased after 570 °C, while the shape factor increased monotonously. During partial remelting, increasing reheating temperature can properly short the isothermal holding time to obtain fine structure. Moreover, increasing the numbers of CEC passes could produce finer semi-solid microstructure. The coarsening behavior of solid grains in the semi-solid state obeys Ostwald ripening and grain coalescence mechanisms. The coarsening rate constant, K, was 80 µm3·s−1 for samples partially remelted at 595 °C. After CEC plus partial remelting, the ideal and fine semi-solid state structure can be obtained, which was suitable for thixoforming.

The Effect of Reciprocating Extrusion (Cec) on the Consolidated Silver Powders Microstructure / Wpływ Dwustronnego Wyciskania (Cws) Na Mikrostrukture Konsolidowanych Proszków Srebra

The microstructure and properties investigations silver powders consolidated by cyclic extrusion compression (CEC) were performed. The AgSnBi and AgNi powders using for electrical contacts were investigated. The observation by using optical microscopy (MO) and transmission electron microscopy (TEM) were apply. The strong diminishing of microstructure inside the consolidated granules were found. This phenomenon cause microhardness increase, restricted by material porosity.

Effect of Hot Extrusion and Cyclic Extrusion Compression Progress on the Microstructures and Properties of Mg-Zn-Y-Nd Alloy

Magnesium alloys are promising candidate materials for cardiovascular stents due to their good biocompatibility and degradation property in human body. However, in vivo tests also show that improvement in mechanical property and corrosion resistance is necessary for wide application. In this study, hot extrusion and cyclic extrusion compression (CEC) were used on Mg-Zn-Y-Nd alloy, the effects of hot extrusion and CEC process on the microstructures, mechanical properties and corrosion properties of alloy were studied. The results showed that the microstructures of CEC treated Mg-Zn-Y-Nd alloy became finer and more homogenous, some nanoparticles which came from the cluster phase uniformly precipitated inside grains, alloy had good mechanical properties and corrosion resistance. The immersion test results in SBF solution at 37 for 24h showed that the alloy after CEC treatment is uniform corrosion.

Spheroidal microstructure formation and thixoforming of AM60B magnesium alloy prepared by SIMA process

The microstructure development in the semi-solid state of AM60B magnesium alloy prepared by strain induced melt activation (SIMA) was described. In the SIMA route, cyclic extrusion compression (CEC) and conventional compression were used to predeform as-cast AM60B, respectively. Partial remelting and thixoforming were also carried out within the semi-solid zone. The results showed that coarse-grained structure disappeared and a fine-grained structure resulted in the CEC formed alloy. However, coarse grains and recrystallized grains co-existed in the compression formed alloy. During partial remelting, the alloy treated by CEC exhibited ideal, fine microstructure, in which completely spheroidized grains contain little entrapped liquid. Polygonal grains were spheroidized to some extent but the previous irregular shape was still obvious in the compression formed alloy. The mechanical properties of the thixoformed AM60B produced by CEC plus partial remelting were better than those of the thixoformed alloy produced by compression plus partial remelting.

Microstructural refinement and homogenization of Mg–SiC nanocomposites by cyclic extrusion compression

An as-extruded Mg–1wt%SiC nanocomposite was processed by cyclic extrusion compression (CEC) at 350°C. The homogeneity of grain and SiC nanoparticle (∼50nm average diameter) distribution during the processing was investigated. With the increasing number of CEC passes, a finer grain size and more uniform particle distribution are obtained along with significant improvement in hardness. The matrix grain size is reduced remarkably from ∼27.6μm to ∼6.5μm after 8 passes of CEC. Nanoparticle declustering occurs through a mechanism of kneading caused by the intense turbulent flow of the Mg matrix during CEC, and the SiC nanoparticles are dispersed into the original particle-free regions. The property improvement is mainly attributed to Orowan strengthening and the Hall–Petch effect.

Microstructure of AgNi and AgSnBi Powders Consolidated by CEC

Powder metallurgy is widely used to the production of AgNi and AgSnBi powders employed for electrical contacts. In the work AgNi and AgSnBi powders were consolidated by the cyclic extrusion compression (CEC) method enabling cyclic unlimited deformation. In the initial stage the AgNi powder contained the two phases Ag and Ni, recognized by the EDX technique using scanning electron microscopy (SEM). The investigations shown that the Ni phase is distributed in the form of small granules around larger Ag granules. In the AgSnBi powder phases Ag + Bi + Ag3Sn (ξ) were distributed uniformly. It was found that after the CEC consolidation phases were excellently joined without cavities and cracks. Detailed observations of microstructure have been performed by the transmission electron microscopy (TEM) and revealed inside the consolidated granules nanometric grains with the nanometric twins inside.

The microstructure and properties of cyclic extrusion compression treated Mg–Zn–Y–Nd alloy for vascular stent application

Magnesium alloys are promising candidate materials for cardiovascular stents due to their good biocompatibility and degradation properties in the human body. However, in vivo tests also show that improvement in their mechanical properties and corrosion resistance is necessary before wide application. In this study, cyclic extrusion compression (CEC) was used to enhance the mechanical properties and corrosion resistance of Mg–Zn–Y–Nd alloy. The results show that the grain size was greatly refined to 1 μm after CEC treatment. The second phase distributed along the grain boundaries with grid shape and nano-sized particles uniformly distributed in grains. The elongation (δ), ultimate tensile strength (UTS) and yield strength (YS) of the CEC treatment samples were 30.2%, 303 MPa and 185 MPa respectively. The CEC treated samples showed homogeneous corrosion because of the grain refinement and the homogeneous distribution of nano-sized second phase. The corrosion current density of the alloy decreased from 2.8×10−4 A/cm2 to 6.6×10−5 A/cm2 after CEC treatment. Therefore, improved mechanical properties, uniform corrosion and reduced corrosion rate could be achieved by CEC.

Cyclic expansion-extrusion (CEE): A modified counterpart of cyclic extrusion-compression (CEC)

Abstract A new method of severe plastic deformation, cyclic expansion-extrusion (CEE), is introduced; CEE is considered as a substitute for the well-known, cyclic extrusion-compression (CEC), by implementing its advantage which is processing samples for the desired number of passes with no need to remove them from the die until the whole number of passes are accomplished. In addition, no external back-pressure system is needed which is the main advantage of this process compared to CEC. This modified process was performed experimentally on aluminum alloy 1050 and was also investigated by finite element analysis. Results reveal that, performing CEE makes it possible to impose large strain values per pass while maintaining a homogeneous hardness distribution in the sample's cross section as well.

Experimental and FEM Analysis of the AA 6082 Processed by Equal Channel Angular Extrusion

Recent studies have shown that severe plastic deformation processes (SPD) improve the mechanical properties of the processed parts. Some of the most outstanding SPD processes are as follows: High Pressure Torsion (HPT), Repetitive Corrugation and Straightening (RCS), Cyclic Extrusion Compression (CEC), Accumulative Roll Bonding (ARB), Conform and Continuous Combined Drawing and Rolling (CCDR), among others, but the most well-known is Equal Channel Angular Extrusion or Pressure (ECAE/ECAP). The aim of these processes is to introduce high values of deformation inside the parts in order to reduce the grain size and thus to improve the mechanical properties of the starting material. The study of the damage imparted to an AA-6082 alloy is made in the present work. This alloy is received as cast and it is quenched at a temperature of 530 °C during 4 hours in order to be processed by ECAE at room temperature using different geometries of the dies. The imparted damage is also studied by using FEM simulations.

Microstructure, Thermal and Electrical Properties of Ultrafine Aluminium

In article the influence of large effective deformation on microstructure, thermal diffusivity and electrical conductivity is described. The tested material was monocrystalline aluminum deformed by the cyclic extrusion compression (CEC) method. The evolution of misorientation distribution, sub(grain) size was determined by using electron back scattered diffraction (EBSD) technique. The second part of the study was to evaluation of thermal diffusivity by using the laser-flash method. The LFA 427 laser-flash facility were applied. The electrical properties as electrical impedance was made by impedance bridge RLC type. The obtained results show that with increase of deformation the insignificant decrease in thermal diffusivity and electrical conductivity occurred.

Recycling of Aluminum Scrap by Severe Plastic Deformation

The production of primary aluminum is an energy costly process. With the global warming being of concern, the secondary aluminum stream is becoming an even more important component of aluminum production and is attractive due to its economic and environmental benefits. Recycling of aluminum by new solid state recycling techniques instead of conventional remelting and subsequent refining processing can result in significant energy savings. Severe Plastic Deformation (SPD) techniques have been applied for consolidating nano particles into fully dense materials with good mechanical properties. However, solid state recycling of scraps by SPD is only in the beginning. In the present study, degreasing of aluminum chips from the machine workshop was investigated by a thermal method and chemical treatment. Thereafter, the decoated chips were recycled by Cyclic Extrusion Compression (CEC) at deformation temperatures between 400 and 500 °C. The microstructure and mechanical properties of the recycled aluminum scrap processed by SPD were subsequently investigated. The results show that SPD technology provides a promising alternative for recycling of aluminum scrap. Thermal degreasing of aluminum scrap resulted in more oxidization of aluminum scrap particles. Visible interfaces between chips were observed even at a low magnification.

Structural Stability of Cu Processed by Severe Plastic Deformation Method

The annealing behaviour of monocrystaline Cu processed by Cyclic Extrusion Compression (CEC) was investigated. The effect of the CEC strain on the annealing behaviour of submicrometer grained structure was studied by examination of the microstructural changes of the samples processed by two different CEC strains, 4.8 and 13.9 during annealing at 300oC for the time in the range from 1sec to 120 min. The results show that microstructure is stable up to an annealing time of 15 min. At a higher time of annealing (above 15 min), a gradual grain growth occurs.

Microstructure Formation in Austenitic Steel after Compression with Oscillatory Torsion Test

Different techniques have been used to introduce large strains into metals, for example torsion under pressure (HPT), cyclic extrusion compression (CEC), equal channel angular extrusion (ECAE), or accumulative roll bonding (ARB). Recent investigations are focused on analyzing new and alternative techniques for introducing severe plastic deformation (SPD) and to compare SPD techniques in terms of grain refinement and enhancement of properties. Compression with oscillatory torsion was applied to 0H18N9 austenitic steel to achieve a large strains. The microstructure was characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Formation of deformation twins and shear bands are responsible for the structure refinement in materials with low stacking fault energies (SFEs) such as austenitic steel. The investigations revealed, that nano-sized grains of 0H18N9 steel after processing by compression with oscillatory torsion are found in three different types of regions.

Consolidation behavior of Mg–10Gd–2Y–0.5Zr chips during solid-state recycling

Unlike that of sintering of fine powders, chips are consolidated by hot deformation in the solid-state recycling. In this work, conventional extrusion (CE) and cyclic extrusion compression (CEC) are used to investigate single and multi-passes shear deformation on the consolidation of chips during solid-state recycling. The results show that utilization of Mg chips with smaller specific surface area (i.e. coarser powder) contributes to easier solid-state bonding because of the decrease in specific surface area which promotes suppression of oxide contamination in the recycled specimens. Enhanced consolidation of chips is not only ascribed to the physical mechanisms caused by plastic deformation, but also to atom diffusion between chips triggered by shear plastic deformation at elevated temperatures. Multi-passes shear deformation breaks the oxide films easier into small particles which are dispersed within the grains or at grain boundaries. It is postulated that the shear deformation of chips is responsible for the better consolidation of chips by high-temperature deformation.

Microstructure evolution of AZ series magnesium alloys during cyclic extrusion compression

Electron Backscatter Diffraction (EBSD), transmission electron microscopy (TEM) and optical microscopy (OM) are employed to characterize the microstructure evolution of AZ31, AZ61 and AZ91 Mg alloys during cyclic extrusion compression (CEC). The results show that CEC is an efficient grain refinement method for magnesium alloys. The most effective CEC pass is the first pass. There exists a critical CEC pass for three Mg alloys and beyond this critical pass the grain size and the homogeneity of microstructure retains almost constant. With increasing CEC passes, the fraction of low angle grain boundaries (LAGBs) tends to decrease and the average misorientation angle increases. Typical network shape structure of fine grains is obtained in the microstructure of AZ31 Mg alloy with fewer Mg 17Al 12 particles after CEC 7 passes. The microstructure of the different Mg alloys at the same number of passes becomes more homogeneous as Mg 17Al 12 particles increase from AZ31, AZ61 to AZ91. The Mg 17Al 12 particles promote increases of the fraction of high angle grain boundaries (HAGBs), the dislocation density, the refinement process of coarse grains at initial CEC pass, and the texture randomization and delay the formation of network shape structures.

Microstructure and mechanical properties of Mg–10Gd–2Y–0.5Zr alloy recycled by cyclic extrusion compression

Cyclic extrusion compression (CEC) as a new solid-recycling processing was applied to recycle the Mg–10Gd–2Y–0.5Zr alloy. The microstructure and mechanical properties of the recycled alloy were studied. Results showed that after 6-passes CEC processing at 673 K, equiaxed grains of <5 μm were obtained. Meanwhile, deep cracks caused by interfaces decohesion between chips were almost vanished. More second phase particles were observed in the recycled specimens than ingot-processed ones. High temperature CEC of the recycled specimens can accelerate the precipitation of the second phase particles. Ductility of the recycled alloy mainly depended on the degree of elimination of the interfaces between the chips. After 4-passes CEC processing at 723 K, the recycled alloy exhibited a combination of high strength and excellent ductility, and this strength can be ascribed to the grain refinement, uniform distribution of oxide and the precipitation of Mg 24(Gd,Y) 5, as the second phase particles.

Effect of the Second Phase on the Microstructure of Magnesium Alloys during Cyclic Extrusion Compression

Cyclic extrusion compression (CEC) is an effective severe plastic deformation (SPD) process which can be used for fabricating ultrafine grained light materials such as magnesium alloys. This method introduces three-dimensional compression and shear stresses and the process can be repeated for a certain number of passes until the desired accumulated strain has been introduced. In order to reveal the effect of second phases on the microstructure developed in magnesium alloys during CEC, three different alloys (AZ31, AZ31-1wt.%Si and AZ91) were investigated after CEC 7 passes performed at 225°C. The experimental results show that the CEC process can effectively refine the microstructures of these alloys and the mean grain size achieved is 1.3µm, 1.5µm and 1.4µm, respectively. It is revealed that the grain size, grain shape and grain boundary structures are little affected by coarse phase Mg2Si but strongly affected by the fine phase Mg17Al12. The fine phase Mg17Al12 seems to increase the relative grain misorientations, hence enhancing the formation of high angle grain boundaries (HAGBs). It is expected that such changes are improving mechanical properties, subsequent forming behavior and surface quality.

New possibilities for intense plastic deformation of aluminium alloys on a special CEC press

The new machine for deformation of metals and alloys by Cyclic Extrusion Compression method has been presented. The special, 600 kN capacity press was designed and build to deform materials by the CEC way. The press is equipped by microprocessor control system for hydraulic steering and measurement of the forces exerted by tools. The microstructure of AlMgSi (6082) samples deformed by new CEC press showed the nanometric features such as dimension of grains below 100 nm and large disorientation between nanograins. The nanostructure was found after the 24 cycles of the CEC (ϕ = 16). The simulation of plastic flow in CEC process was performed by a DEFORM software. The process has been modelled in relation to the technically pure aluminium and 6082 aluminium alloys deformed with the reduction of sample diameter from 10 to 8.5 mm and next increase from 8.5 to 10 mm in a single CEC cycle. It was found that at suitably selected values of counterforce the tensile circumferential stresses occurred behind the matrix where radial extrusion took place. Increasing the level of hydrostatic pressure it was possible to prevent an increase of the dangerous tensile stresses. Based on the data from numerical simulation of the CEC processes a special diagram has been prepared, which facilitates suitable choice of the counterforce level.

Network-shaped fine-grained microstructure and high ductility of magnesium alloy fabricated by cyclic extrusion compression

An extraordinary microstructure with mean grain size of 1.77 μm accompanying fine grains of 150 ± 50 nm was obtained for magnesium alloy AZ31 by cyclic extrusion compression (CEC). The ductility improved 2.2 times while yield strength decreased 50 MPa after CEC 7 passes compared with as-extruded alloy. A compound grain-refining mechanism was proposed to explain the microstructure evolution during CEC. Dislocation density, texture and grain-boundary structure were employed to clarify the relationship between microstructure and mechanical properties of AZ31 alloy after CEC.