Warm Equal Channel Angular Pressing Research Articles

Microstructure and properties of ZrB2-reinforced aluminum matrix composites consolidated by ECAP process

In this research work, the effects of mechanical alloying and subsequent compaction by ECAP on the microstructural, physical, and mechanical properties of Al-ZrB2 metal matrix composites (MMCs) were evaluated. To prepare composite powders, a mixture of Al and ZrB2 particles was mechanically alloyed at various times of 1, 6, 12, 18 and 24 h. SEM micrographs indicate that the size of the obtained particles decreases by increasing the time of mechanical alloying up to 18 h. However, after this time, increasing the time of mechanical alloying has led to an increase in the size of the particles. By means of mechanical alloying for 18 h, the average size of fine particles reached 823 nm, while coarse particles were 8 μm. The calculation via the use of XRD examination implies that the mean crystallite size of powder decreased from about 68 nm to 31 nm and 26.8 nm, for Al and Al-5%ZrB2 samples, respectively, while lattice strain increased from 0.25% to 0.64% and from 0.3% to 0.73% after 1 h to 24 h milling of same samples, respectively. However, the rate of crystallite size reduction after 12 h of mechanical alloying is gradually reduced, and that is reached its lowest level after 18 h. After that, increasing the time of mechanical alloying has led to a saturation in the lattice strain. In continue, the resulting composite powder was heated, consolidated and turned into bulk material by warm equal channel angular pressing (ECAP) at the temperature of 250 °C. The resultant optimum composite has been characterized by EDS elemental mapping. Microhardness measurements and shear punch tests were performed to evaluate the mechanical properties of the unreinforced and composite samples after the ECAP process. The Al-ZrB2 MMC bulk samples subjected to ECAP, with a ZrB2 amount of 5 wt%, had a relative density, hardness, and ultimate shear strength of 99.3%, 170 HV, and 151 MPa, respectively, using powders which have been mechanically alloyed up to 24 h.

High-strain-rate superplasticity and microstructural evolution in ECAP-processed Mg–6.5Y–1.2Er–1.6Zn–0.5Ag alloy

A warm equal-channel angular pressing (ECAP) procedure was applied to a new Mg–6.5Y–1.2Er–1.6Zn (WEZ612)–0.5Ag alloy with a long-period stacking ordered (LPSO) phase. The microstructure, superplasticity, and deformation mechanism of the WEZ612–0.5Ag alloy were then systematically investigated. Three different precipitation phases formed in the alloy with trace Ag addition, namely LPSO, γ, and nanoprecipitate phases. A remarkable elongation of 726% was attained at 623 K and a strain rate of 0.01 s−1. The strain rate sensitivity index (m) and activation energy (Q) under these deformation conditions were 0.461 and 133.08 kJ mol−1, respectively. These m and Q values confirm that the primary deformation mechanism of the WEZ612–0.5Ag alloy at 623 K was grain boundary sliding assisted by lattice diffusion. The highly stable LPSO phases, γ precipitates, and nanoprecipitates synergistically improved the superplasticity of the alloy by retarding crack propagation and grain growth and by promoting the basal plane slip.

Improving microstructure and corrosion resistance of LPSO-containing Mg–Y–Zn–Mn alloy through ECAP integrated with prior solution treatment

Unique Mg-RE (rare earth) alloys with long-period stacking ordered (LPSO) structures have attracted extensive attention for their excellent mechanical properties and bright prospects. Thus it is urgent to improve their corrosion resistance simultaneously. The present work focused on the improvement of microstructure and corrosion behaviours in new Mg-2.2Y-1.1Zn-0.4Mn (wt. %) alloys with mixed LPSO phases through warm equal-channel angular pressing (ECAP) integrated with prior solution treatment (ST). The results show that the multi-pass ECAP process optimizes the grain size and distribution of mixed LPSO phases, which improves the corrosion resistance of the alloy. During the integrated ECAP processing, the massive 18 R phase was broken from 100 μm (as-cast) to 5–8 μm (12 passes), and the precipitated 14H phase was more uniformly distributed in the fined α-Mg matrix. Accordingly, the corrosion resistance of the LPSO-containing samples from 0 to 8 ECAP passes increased for a more uniform and more refined structure. In contrast, the corrosion resistance improvement of the 12-pass ECAP one was reduced slightly for weakened 18 R barriers.

Cooperative Effect of Li Content and Equal-Channel Angular Pressing on Microstructure and Mechanical Properties of Al-Mg-Li Alloy

This paper investigated the cooperative effects of Li addition and warm Equal Channel Angular Pressing (ECAP) on improving the mechanical properties of an Al-Mg-Li alloy for further weight reduction. The results showed that more Li addition could obviously refine the grains of the as-cast alloy and reduce its density value to only 2.37 g/cm3 when Li content reached 2.5% (about 12.6% lighter than commercial Al alloys). It also had a pronounced influence on the precipitations in the Al-5.5Mg-xLi-0.1Zr alloy, i.e., the number density and size of Al2MgLi and δ’-Al3Li phases. The yield strength of the as-cast alloy was increased with increasing Li, but the elongation deteriorated due to primary network intergranular Al2MgLi and more δ’ particles in the high Li-containing alloy. The warm multi-pass ECAP process was found to simultaneously improve the strength and ductility of the Al-Mg-Li alloys, and greatly alleviate the detrimental effect of Li addition on the elongation, thereby making the ultrafine-grained (UFG) alloys, a good combination of lightweight and high performance, very attractive for aerospace applications for much higher specific strength than both Al matrix composites and Mg alloys.

Effect of warm equal channel angular pressing on the structure and mechanical properties of Ti0.16Pd0.14Fe (wt%) alloy

Abstract Here we analyze the microstructure and phase composition of a Ti alloy with 0.16Pd and 0.14Fe (wt%) alloy exposed to warm equal channel angular pressing (ECAP) at 648 K. The analysis shows that after four ECAP passes, the material assumes a submicrocrystalline structure with an average grain size of 0.28 μm, as against its initial value 10 μm, and that the α phase dominates in the alloy both before and after ECAP. The initial alloy reveals a high content of Fe and Pd atoms near grain boundaries compared to central grain regions. Such near-boundary zones contain orthorhombic α′′ martensite in addition to the α phase, and β or α + β particles are found directly at the grain boundaries. These features of the phase composition are inherited after ECAP. The yield strength of the ECAP treated alloy is 500 MPa, being greater than the initial strength 350 MPa, and its margin of plasticity is rather high. The torsional strain up to fracture in the initial and in the ECAP treated alloy is 70% and 50%, respectively.

High Performance Fine-Grained Biodegradable Mg-Zn-Ca Alloys Processed by Severe Plastic Deformation

The tensile strength, fatigue, and corrosion fatigue performance of the magnesium alloy ZX40 benefit strongly from hybrid deformation processing involving warm equal-channel angular pressing (ECAP) at the first step and room temperature rotary swaging at the second. The general corrosion resistance improved as well, though to a lesser extent. The observed strengthening is associated with a combined effect of substantial microstructure refinement down to the nanoscale, reducing deformation twinning activity, dislocation accumulation, and texture transformation. The ultimate tensile strength and the endurance limit in the ultrafine-grained material reached or exceeded 380 and 120 MPa, respectively, which are remarkable values for this nominally low strength alloy.

Effect of equal channel angular pressing (ECAP) on the evolution of texture, microstructure and mechanical properties in the Al-Cu-Li alloy AA2195

In this study, one of the severe plastic deformation (SPD) techniques, Equal Channel Angular Pressing (ECAP) has been successfully applied to the Al-Cu-Li alloy AA2195 at 250 °C and the development of microstructure, texture and mechanical properties has been studied. A systematic analysis has been carried out by using EBSD and TEM to understand the microstructural features, and the nature of different precipitates presence in the alloy AA2195. Microstructural features indicate considerable grain refinement leading to an average grain size of 2.8 ± 0.7 μm after 4 ECAP passes. Continuous dynamic recrystallization (CDRX) has been identified as the mechanism that leads to the formation of fine grain structure in the alloy AA2195 during the warm ECAP process. TEM results confirm the distribution of strengthening precipitates δ′(Al3Li), β(Al3Zr) and T1(Al2CuLi) in the alloy. The overall texture has become weak after ECAP processing and has been simulated using Visco-plastic self-consistent simulation (VPSC). The evaluation of mechanical properties indicates a substantial increment in hardness, strength properties with a minor reduction of ductility after 4 passes. Low mechanical property anisotropy is expected in the processed AA2195 alloy due to its weak texture.

Effect of equal-channel angular pressing and post-aging on impact toughness of Al-Li alloys

Overcoming the toughness inadequacy of Al-Li alloys is in urgent need for developing new low-density and high-performance aerospace aluminum alloys. In this research, continuous equal-channel angular pressing (ECAP) and post-aging were developed to significantly enhance the impact toughness of 1420 Al-Li alloy. The effects of the processes on microstructure evolution, impact absorbed energy and fracture surfaces of 1420 alloy were investigated. The results demonstrated that the impact toughness of ultrafine-grained (UFG) 1420 alloy after 8 ECAP passes at 573 K reached up to 26.6 J/cm2 at room temperature and increased sixfold compared with that of the coarse-grained sample, but the post-aging reduced the beneficial effect. The remarkable improvement after the warm ECAP was mainly due to the UFG microstructure, certain amount of dislocations, and the fine precipitates with uniform distribution, thereby making UFG 1420 alloys more attractive in aerospace applications.

Mechanical Properties and Microstructure of an Al-Zn-Mg-Sc-Zr Alloy Processed by Warm Equal Channel Angular Pressing and Subsequent Aging

An ultrafine-grained Al-Zn-Mg-0.1Sc-0.1Zr alloy was obtained by warm equal channel angular pressing (ECAP) and cold rolling. The microstructure evolution of the alloy during deformation and after subsequent aging was investigated by transmission electron microscopy. The results showed that the alloy grains were remarkably refined and that the dislocation density considerably increased after serve deformation. Tensile tests revealed that the yield strength (YS), ultimate tensile strength (UTS) and elongation of the cold-rolled Al-Zn-Mg-Sc-Zr alloy were ~ 456 MPa, ~ 469 MPa and 16.7%, respectively. After 16 ECAP passes, higher strength (YS: ~ 526 MPa, UTS: ~ 589 MPa) was achieved, with the elongation decreasing to ~ 11.7%. After optimal aging, the YS and UTS of the sample subjected to 16 ECAP passes increased to ~ 594 MPa and ~ 606 MPa, respectively, maintaining an appropriate elongation of ~ 10%. The main strengthening mechanisms and microstructure evolution during ECAP and subsequent aging was discussed.

Improvement in formability of semi-solid cast hypoeutectic Al-Si alloys by equal-channel angular pressing

Microstructure of Al-Si alloys are characterized by brittle eutectic Si particles. It is known that morphological change of Si particles from coarse acicular flake to fine fiber improves strength and ductility at once. To control the morphology without alloying, combined effects of semi-solid casting and severe plastic deformation were investigated in this study. The authors prepared a semi-solid JIS AC4CH cast alloy (Al-7.14%Si-0.41%Mg) with fine Si particles and a conventional cast alloy with coarse Si particles. The both alloys were processed through warm equal-channel angular pressing (ECAP) under several thermo-mechanical histories. Microstructure evolution by ECAP was evaluated in relation to deformation behavior.ECAP process was not able to refine Si particles of the conventional cast alloy as fine as those of the semi-solid cast alloy. Submicron Si particles in the semi-solid cast AC4CH slightly coarsened by warm ECAP. Combination of semi-solid casting and ECAP process provided refinement of Si particles, grain refinement of primary phase, and decrease of hardness difference between primary phase and eutectic. Controlling ECAP processing conditions improved strength and/or ductility and enabled flexible design of mechanical properties of semi-solid AC4CH.

Prior thermo-mechanical processing to modify structure and properties of severely deformed low carbon steel

The article focuses on the severe plastic deformation (SPD) of low carbon steel AISI 1010 performed at increased temperature. The grain refinement of ferrite structure is monitored and described with respect to different initial steel structure modified by thermal and thermomechanical (TM) treatment (TM) prior severe plastic deformation. The refinement of coarse initial ferrite structure with grain size in range of 30 – 50 gm resulted from solutioning was conducted then in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process and quite uniform ferrite structure with grain size of the order of gm was obtained. The further grain refinement steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP ϕ = 120°) at 300°C, introducing different strain in range of εef = 2.6 -4. The change of microstructure in dependence of the effective strain was evaluated by SEM and TEM study of thin foils. The high straining of steel resulted in extensive deformation of ferrite grains and formation of mixture of submicron grains structure in banded deformed structure with dense dislocation network and subgrains. The dynamic polygonization process, due to increased ECAP temperature, modified the submicrocrystalline structure formation. There was only indistinctive difference observed in structure refinement when considering different initial structure of steel. The tensile behaviour was characterized by strength increase followed by softening. None work hardening phenomenon appeared at tensile deformation of deformed bars.

Structure Refinement of Medium Carbon Steel and Deformation Properties Respond

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour.

Effect of two-step severe plastic deformation on the microstructure and mechanical properties of commercial purity titanium

The present work investigates the microstructural and mechanical properties of commercial purity titanium after processing by a two-step severe plastic deformation procedure entailing warm equal channel angular pressing (ECAP) followed by cold rolling at liquid nitrogen temperature (LNT). The effect of subsequent cold rolling at room temperature is also investigated for comparison. After 10 passes of ECAP, an ultrafine-grained structure with average grain size of 213 nm was achieved. Subsequent cold rolling at LNT led to further refinement and decreased the grain size to 114 nm. Under these conditions, the material displayed high tensile strength of 995 MPa and high elongation to failure of 23%. These promising mechanical properties were interpreted in terms of characteristics of the microstructure: grain refinement, increased dislocation density, and a high fraction of high angle grain boundaries.

Grain Refinement and Deformation Behaviour of Medium Carbon Steel Processed by ECAP

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour.

Prior Structure Modification on Grain Refinement and Deformation Behavior of Medium Carbon Steel Processed by ECAP

The present work, deals with grain refinement of medium carbon steel AISI 1045 (0.45% C), having different initial ferrite–pearlite microstructure resulted from thermal and thermomechanical treatment (TM). The purpose of TM steel processing was to refine ferrite and modify pearlite lamellae structure. The final grain refinement of steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route, in dependence of the applied effective strain ϵef, resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. When applying higher shear stress (ϵef = 4) the mixed structure of subgrains and ultrafine grains was formed within ferrite phase, regardless the initial steel structure morphology. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting, and breaking was found efficient as straining increased. Processes of dynamic polygonization and recrystallization in deformed structure also contributed to submicrocrystalline grains formation in deformed structure. Comparing results the course of lamellae cementite spheroidization was then more efficient in prior TM treated steel. The tensile deformation results confirmed the strength increase, however deformation behavior and strain hardening generally for different initial structural conditions of steel, showed diversity.

Fabrication of Al-based composites reinforced with Al2O3-Tib2 ceramic composite particulates using vortex-casting method

Vortex casting is one of the simplest methods of producing metal matrix composites (MMCs). However, this simple method does have some drawbacks, which reduce the mechanical properties of the produced composites. In this study, we tried to modify the process of composite production before, during, and after the casting procedure. Low-cost Al2O3-TiB2 ceramic composite particles, which produced after combustion synthesis, were used as reinforcement. These powders, which are thermodynamically stable with molten aluminum below 900?C, were mixed with aluminum and magnesium powders before casting using ball milling and the mixed powders were injected into the molten metal (pure Al). This process was applied to enhance the wettability of ceramic particles with molten aluminum. After casting, warm equal channel angular pressing (ECAP) and hot extrusion processes were applied to investigate their effects on the mechanical properties of the final composites. It was revealed that both warm ECAP and hot extrusion have a strong influence on increasing the mechanical properties mainly due to decreasing the amount of porosities.

Production of Ti–6Al–4V billet through compaction of blended elemental powders by equal-channel angular pressing

Abstract In this work, compaction by warm equal-channel angular pressing (ECAP) with back pressure was used to produce Ti–6Al–4V billets from both commercially pure (CP) titanium and titanium hydride (TiH 2 ) powders, which were mixed with pulverised binary Al–V master alloys of two distinct Al/V ratios and with elemental aluminium powder to arrive at the nominal alloy composition. It was demonstrated that the right combination of temperature, high hydrostatic pressure and plastic shear deformation permits consolidation of the powder mixture to maximum green densities of 99.26%. Moreover, after direct compaction of blended elemental powders by equal-channel angular pressing (ECAP) with back pressure, the sintering temperature required for chemical and microstructural homogenisation of the compacts could be reduced by 150–250 °C. This was possible due to high green density, increased contact area between powder particles and the formation of fast diffusion paths associated with grain refinement by severe plastic deformation. The sintered Ti–6Al–4V billets exhibited a maximum density of 99.88%, Vickers hardness of 409–445 HV1 and ultimate tensile strength in the range of 1000–1080 MPa. In contrast to findings of other authors, the use of TiH 2 powders in conjunction with ECAP processing did not bring any benefits with regard to the production of the Ti–6Al–4V alloy.

Effect of Preliminary Treatment on Grain Refinement of Medium Carbon Steel Using ECAP at Increased Temperature

By application of thermomechanical controlled rolling and accelerated cooling, the carbon steel grain refinement is limited to levels of ~ 5 μm in steels. The strain assisted or strain induced transformation could be considered for the refining process. The present work, likewise, deals with grain refinement of medium carbon steel containing 0.45 wt pct carbon having different initial microstructure modified by either thermal and/or thermomechanical treatment (TM) prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain of 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The steel samples of different initial structure were then subjected to six ECAP pressing passes through die channel angle of 120°. The microstructure development was analyzed in dependence of effective strain introduced (εef ~ 2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. As straining increases the dynamic polygonization and recrystallization became active to form mixture of polygonized subgrains and submicrocrystalline grains having high angle boundaries. The straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The lamellae cementite spheroidization was more extensive in TM treated steel samples. The tensile behavior was characterized by strength increase for both structural steel states; however the work hardening behavior was modified in steel where preliminary TM treatment was introduced to modified coarse ferrite-pearlite structure.

Ultrafine grained structure development in steel with different initial structure by severe plastic deformation

The present work deals with grain refinement of medium carbon steel, having different initial microstructure, modified by either thermal and/or thermomechanical treatment (TM) prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain of 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced (εef ~2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. The straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The cementite lamellae spheroidization was more extensive in TM treated steel samples. The tensile behavior was characterized by strength increase for both structural steel states; however the work hardening behavior was modified in steel where preliminary TM treatment was introduced to modified coarse ferrite-pearlite structure.

Workability Limits of Commercial Purity Titanium Subjected to Equal Channel Angular Pressing

Commercial purity Ti is an important candidate material for orthopedic and dental implants because of its high specific strength, good corrosion resistance and excellent biocompatibility. However, for biomedical applications as a replacement for Ti-6Al-4V alloy that is currently used, improvement in strength of CP Ti is necessary. This can be achieved by using severe plastic deformation (SPD) processes like equal channel angular pressing (ECAP) at warm working temperatures followed by conventional processing at room temperatures. This requires adequate workability after ECAP. In this study, the workability of CP Ti after warm ECAP has been investigated. Specimens of CP Ti, 17 mm in diameter, were extruded using processing route Bc through an ECAP die with an angle of 120◦ between the two intersecting channels and at a temperature of approximately 400oC. Workability testing was carried out using collar type compression specimens by upsetting the specimens between flat platens till the onset of cracking. Workability diagrams have been plotted as a function of axial and hoop strains at failure. The results show that processing by ECAP lead to only minor reductions in workability of CP Ti. The tensile strength is enhanced considerably by this process.