Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

Superplastic behavior of a fine-grained Mg-Gd-Y-Ag alloy processed by equal channel angular pressing

An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 μm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization(DRX). This microstructure contained fine grains with an average size of 1.3 μm, a high fraction of high angle grain boundaries(HAGBs), and nano-sized Mg_(5)Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy(TEM). High-temperature shear punch testing(SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity(SRS) index(m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively,delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol^(-1) and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding(GBS) assisted by grain boundary diffusion.

EFFECT OF EQUAL-CHANNEL ANGULAR PRESSING ON STRUCTURE OF Al ALLOY 2024

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The effect of Equal Channel Angular Pressing process on the microstructure of AZ31 Mg alloy strip shaped specimens

Equal Channel Angular Pressing(ECAP)is one of the most applicable Sever Plastic Deformation(SPD)processes which leads to strength and ductility improvement through the grain refining and development of a suitable texture.In this study,after designing and manufacturing a suitable die,4 pass ECAP process at route C is done on strip shaped specimens of AZ31 magnesium alloy in order to achieve desirable microstructural and mechanical properties.Microstructure then got studied through the optical microscopy.Results show that mean grain size is decreased and grain size distribution got close to normal distribution state by increasing the pass number.However,the grain size is reduced by increasing of ECAP temperature.

Microstructure evolution and mechanical behavior of AZ31 Mg alloy processed by equal-channel angular pressing

AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).

Reducing the tension-compression yield asymmetry of extruded Mg-Zn-Ca alloy via equal channel angular pressing

The influence of equal channel angular pressing on the tension-compression yield asymmetry of extruded Mg-5.3 Zn-0.6 Ca(weight percent)alloy has been investigated.The microstructure was obviously refined by the large strain during the equal channel angular pressing,accompanied with very fine Ca_(2)Mg_(6)Zn_(3) phases with average diameter of 70 nm.The weak tension-compression yield asymmetry after equal channel angular pressing is mainly attributed to the reduced volume fraction of extension twinning during the compression,because the slope(k)of twinning in Hall-Petch relationship is higher than that of dislocation slip,and the twinning deformation is difficult to take place with decreasing grain size.The basal slip is more active in the alloy after equal channel angular pressing,due to the non-basal texture components,which hinders the twinning activation and reduces the yield asymmetry.Furthermore,the presence of fine precipitate restricts the twinning activation,which also contributes to the reduction of yield asymmetry.

Effect of Y content and equal channel angular pressing on the microstructure, texture and mechanical property of extruded Mg-Y alloys

The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.

Microstructure and mechanical property of a high-strength Mg-10Gd-6Y-1.5Zn-0.5Zr alloy prepared by multi-pass equal channel angular pressing

In this work,a high-strength Mg–10Gd–6Y–1.5Zn–0.5Zr(wt.%)alloy was fabricated by successive multi-pass equal channel angular pressing(ECAP).The microstructure and mechanical property of as-cast and ECAP alloys were systematically researched by X-ray diffractometer,scanning electron microscopy,transmission electron microscopy and compression test.The results show that the microstructure of as-cast alloy consists ofα-Mg grains,Mg24Y5 networks,18R blocks,fine 14H lamellas,and fewY-rich particles.After 8 passes ECAP,dynamic recrystallization ofα-Mg is developed and their average grain size decreases to about 1μm.The network Mg_(24)Y_(5) phase at grain boundaries is broken into small particles with average diameter lower than 0.5μm.Moreover,18R blocks are kinked and delaminated,or broken into small particles and blended with Mg24Y5 particles.14H lamellas grow gradually or are dynamically precipitated within certainα-Mg grains.Compression tests indicate that 8p ECAP alloy exhibits excellent mechanical property with compressive strength of 537 MPa and fracture strain of 17.0%.The significant improvement for both strength and ductility of deformed alloy could be ascribed to DRX grains,refined Mg24Y5 particles,18R kinking and dynamical precipitation of 14H.

Friction stir welding of AZ31 magnesium alloys processed by equal channel angular pressing

Equal channel angular pressing （ECAP） is an effective thermo-mechanical process to make ultrafine grains. An investigation was carried out on the friction stir welding （FSW） of ECAPed AZ31 magnesium alloys with a thickness of 15 mm. For different process parameters, the optimum FSW conditions of ECAPed AZ31 magnesium alloys were examined. The basic characterization of weld formation and the mechanical properties of the joints were discussed. The results show that the effect of welding parameters on welding quality was evident and welding quality was sensitive to welding speed. Sound joints could be obtained when the welding speed was 37.5 mm/min and the rotation speed of the stir tool was 750 r/min. The maximum tensile strength （270 MPa） of FSW was 91% that of the base materials. The value of microhardness varied between advancing side and retreating side because of the speed field near the pin of the stir tool, which weakened the deformed stress field. The value of microhardness of the welding zone was lower than that of the base materials. The maximum value was located near the heat-affected zone （HAZ）. Remarkable ductile character was observed from the fracture morphologies of welded joints.

Microstructure and mechanical properties of ZE10 magnesium alloy prepared by equal channel angular pressing

ZE10 magnesium alloy was subjected to equal-channel angular pressing （ECAP） up to 12 passes in a die with an angle of 120° between the two channels at 250-300℃. An inhomogeneous microstructure of bimodal grains including fine grains of 1-2 μm as well as coarse grains of about 20μm was obtained after the initial 1-4 ECAP passes. The grain size became increasingly homogeneous with further ECAP processing and the grains were significantly refined to 1-2 ktm after 8 passes and further refined to 0.5-1 μm after 12 passes. The alloy＇s yield strength changed slightly but the ductility improved greatly initially up to 4-6 passes corresponding to the bimodal grain microstructure. And after the subsequent pressing of more than 8 passes, the tensile strength including yield strength improved while the elongation decreased gradually.

Mechanical responses, texture and microstructural evolution of high purity aluminum deformed by equal channel angular pressing

Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.

Observation of macroscopic shear band in aluminum-based alloy during equal-channel angular pressing

Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pressing passes reach 2, and the severe macroscopic shear band extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and over 60% of sample volume is occupied by macroscopic shear band when the ECAP reaches 4 passes.

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl3 and also by surface analysis.Anodizing was conducted for 20 min at 200 and 400 A/m2 in a solution containing 1.53 mol/L H2SO4 and 0.018 5 mol/L Al2(SO4)3·16H2O at 20 ℃.Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films.The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without,indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy.Second phase precipitates such as Si,Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP.Al-Cu-Mg intermetallic compounds are dissolved during anodization,whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al.FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds,since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates.The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates,which act as origins of pitting corrosion.

Microstructure and tensile properties of ultrafine grained copper processed by equal-channel angular pressing

Equal-channel angular pressing （ECAP） process was applied to a 12 mm ×12 mm ×80 mm billet of pure copper （99.98 wt.%） at room temperature. The shear deformation characteristics, microstructure evolution, and tensile properties were investigated. A combination of high strength （-420 MPa） and high elongation to failure （-25%） was achieved after eight ECAP passes at room temperature. The mixing of ultrafme grains （-0.2 μm） with nanocrystalline grains （-80 nm） resulted in high tensile strength and ductility.

Microstructural Evolution and Thermal Stability of Ultra-fine Grained Al-4Mg Alloy by Equal Channel Angular Pressing

Experiments were conducted to evaluate the grain refinement and thermal stability of ultra-fine grained Al-4Mgalloy introduced by equal-channel angular pressing (ECAP) at 473 K. The results show that the intensities of X-ray(111/222) and (200/400) peaks for the alloy processed by ECAP decrease significantly and the peak widths of halfheight become broadening compared with the corresponding value in the annealed alloy. The microstructure of 2passes ECAPed alloy consists of both elongated and equiaxed subgrains. The residual strain in the alloy increaseswith increasing passes numbers, that appears as increasing dislocation density and lattice constant of matrix. Anequiaxed ultra-fine grained structure of～0.2μm is obtained in the present alloy after 8 passes. The ultra-fine grainsare stable below 523 K, because the alloy retains extremely fine grain size of～1μm after static annealing at 523 Kfor 1 h.

Deformation mechanism at impact test of Al-11% Si alloy processed by equal-channel angular pressing with rotary die

Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.

On the cold rolling of AZ31 Mg alloy after Equal Channel Angular Pressing

Among the various Severe Plastic Deformation(SPD)processes,Equal Channel Angular Pressing(ECAP)is one of the most applicable one which improves strength and ductility due to grain refinement and suitable texture development.In this study,cold rolling were carried out on the 4 pass ECAPed(in route A and C)strip shaped specimens of AZ31 magnesium alloy to investigate the ECAP effects on the roll-ability.Results showed that reduction in area which can be concerned as an index for roll-ability increased after ECAP.It was also seen that ECAP in route C enhanced roll-ability more than route A.

In vitro and in vivo studies on pure Mg, Mg-1Ca and Mg-2Sr alloys processed by equal channel angular pressing

In the present work,the biomedical as-cast pure Mg,Mg–1 Ca and Mg–2 Sr alloys were processed with equal channel angular pressing(ECAP)technique to develop ultrafine microstructure within the materials,and their microstructures,mechanical properties,degradation behavior,cytocompatibility in vitro and biocompatibility in vivo were studied comprehensively.Finer-gained microstructures and improved mechanical properties of these three materials after ECAP were confirmed compared to their as-cast counterparts.Moreover,after ECAP the degradation rate of pure Mg was increased while that of Mg–1 Ca or Mg–2 Sr alloys decreased compared to the ascast counterparts.Additionally,good in vitro cytocompatibility and in vivo biocompatibility of these three materials were revealed by cell cultural tests using osteoblastic MC3 T3-E1 and human mesenchymal stem cells(h MSC)and in vivo animal tests at the lateral epicondyle of SD-rats’femur.This study offers an alternative powerful avenue to achieve good comprehensive properties of magnesium-based biodegradable metals.It might also help to extend the applied range of magnesium-based biodegradable metals in orthopedic field.

Deformed texture of copper processed by equal channel angular pressing via different angle routes

The commercially pure copper with dimension of 80 mm×20 mm×4 mm was used for equal channel angular pressing (ECAP), of which their outward appearance coordinate is corresponded with that of rolling deformation modes. Cold-deformed texture was investigated. The results show that the texture character in pure copper processed by ECAP is related with intersection angle (Φ) of the die channel. When Φ is 90° and the sample is extruded for one pass, its texture consists of α and β orientation lines including mainly C, B, S and Goss components, moreover a little rotated cube is found. When Φ is 135°, as extrusion pass increases, the weak texture forms on the scope of deviation from rotated cube (ψ=0°, θ=0°,φ=450°±150°) and develops to the ψ=45° fiber mainly including rotated cube. When Φ is 120°, the texture is ψ=45° fiber mainly including rotated cube that is maintained constant as extrusion pass increases.

Tensile properties of 2024 Al alloy processed by enhanced solid-solution and equal-channel angular pressing

Equal-channel angular pressing(ECAP) of an enhanced solid-solution treated 2024 Al alloy was successfully performed at room temperature, with an imposed equivalent normal strain of about 0.5. A very high hardness about HV191 and yield strength about 610 MPa (30% higher than those of the unECAPed 2024 Al alloy) in terms of commercial aluminum alloys were observed for the ECAPed 2024 Al alloy. In addition to the strengthening, this process allows the ECAPed 2024 Al alloy have a moderate level of tensile ductility (about 12.7%) and a significant strain hardening capability up to tensile failure. After aged at 373 K for 48 h, the ECAPed alloy increases its hardness (about HV201) and tensile ductility (about 14 %) further. The TEM results show that the ECAPed 2024 Al alloy presents a plate structure (about 50-100 nm) with high density of dislocation and additional thin plate (approximately <10 nm= inside. The XRD results show that the ECAP processing decreases the texture and increases the dislocation density of the alloy considerably. The theoretical calculations show that the increase of dislocation density resulting from ECAP processing makes a considerable contribution about 55.2 % for the improvement of yield strength.