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Title: Fatigue-Property Enhancements of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing (ECAP)

Abstract

The fatigue behavior of magnesium-alloy, AZ31B, pre-strained by Equal-Channel-Angular Pressing (ECAP) was studied as a function of the accumulated plastic-strain level and the orientation of the samples (along and parallel to the ECAP pressing direction). The material was processed via route BC, at 200 oC, for 1, 2, and 8 passes, with and without a back-pressure applied on the billet during ECAP. The low-cycle fatigue behavior of the AZ31B alloy is shown to be anisotropic and texture-dependent. Due to the initial texture orientation, the specimens loaded parallel to the ECAP pressing direction have a longer fatigue life than the samples loaded perpendicular to it. The low-cycle fatigue life of the AZ31B alloy is enhanced by ECAP. The fatigue-property improvement is discussed in the light of the grain-size refinement, enhanced ductility, and texture evolution.

Authors:
 [1];  [2];  [2];  [3];  [1];  [1];  [1];  [4];  [2]
  1. ORNL
  2. University of Tennessee, Knoxville (UTK)
  3. University of Virginia
  4. Shenyang University of Technology
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); High Temperature Materials Laboratory
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
931658
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Metallurgical and Materials Transactions A; Journal Volume: 38A; Journal Issue: 13
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALLOYS; DUCTILITY; GRAIN SIZE; MAGNESIUM ALLOYS; ORIENTATION; PRESSING; TEXTURE; Magnesium alloy; AZ31B; Equal-Channel-Angular Pressing (ECAP); Fatigue

Citation Formats

Wu, Liang, Stoica, G. M., Liao, Hao Hsiang, Agnew, Sean R, Payzant, E Andrew, Wang, Gongyao, Fielden, Douglas, Chen, Lijia, and Liaw, Peter K. Fatigue-Property Enhancements of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing (ECAP). United States: N. p., 2007. Web. doi:10.1007/s11661-007-9123-8.
Wu, Liang, Stoica, G. M., Liao, Hao Hsiang, Agnew, Sean R, Payzant, E Andrew, Wang, Gongyao, Fielden, Douglas, Chen, Lijia, & Liaw, Peter K. Fatigue-Property Enhancements of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing (ECAP). United States. doi:10.1007/s11661-007-9123-8.
Wu, Liang, Stoica, G. M., Liao, Hao Hsiang, Agnew, Sean R, Payzant, E Andrew, Wang, Gongyao, Fielden, Douglas, Chen, Lijia, and Liaw, Peter K. Mon . "Fatigue-Property Enhancements of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing (ECAP)". United States. doi:10.1007/s11661-007-9123-8.
@article{osti_931658,
title = {Fatigue-Property Enhancements of Magnesium Alloy, AZ31B, through Equal-Channel-Angular Pressing (ECAP)},
author = {Wu, Liang and Stoica, G. M. and Liao, Hao Hsiang and Agnew, Sean R and Payzant, E Andrew and Wang, Gongyao and Fielden, Douglas and Chen, Lijia and Liaw, Peter K},
abstractNote = {The fatigue behavior of magnesium-alloy, AZ31B, pre-strained by Equal-Channel-Angular Pressing (ECAP) was studied as a function of the accumulated plastic-strain level and the orientation of the samples (along and parallel to the ECAP pressing direction). The material was processed via route BC, at 200 oC, for 1, 2, and 8 passes, with and without a back-pressure applied on the billet during ECAP. The low-cycle fatigue behavior of the AZ31B alloy is shown to be anisotropic and texture-dependent. Due to the initial texture orientation, the specimens loaded parallel to the ECAP pressing direction have a longer fatigue life than the samples loaded perpendicular to it. The low-cycle fatigue life of the AZ31B alloy is enhanced by ECAP. The fatigue-property improvement is discussed in the light of the grain-size refinement, enhanced ductility, and texture evolution.},
doi = {10.1007/s11661-007-9123-8},
journal = {Metallurgical and Materials Transactions A},
number = 13,
volume = 38A,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Thermal stability of the ultra-fine grained (UFG) microstructure of magnesium AZ31 alloy was investigated. UFG microstructure was achieved by a combined two-step severe plastic deformation process: the extrusion (EX) and subsequent equal-channel angular pressing (ECAP). This combined process leads to refined microstructure and enhanced microhardness. Specimens with UFG microstructure were annealed isochronally at temperatures 150–500 °C for 1 h. The evolution of microstructure, mechanical properties and dislocation density was studied by electron backscatter diffraction (EBSD), microhardness measurements and positron annihilation spectroscopy (PAS). The coarsening of the fine-grained structure at higher temperatures was accompanied by a gradual decrease of the microhardnessmore » and decrease of dislocation density. Mechanism of grain growth was studied by general equation for grain growth and Arrhenius equation. Activation energies for grain growth were calculated to be 115, 33 and 164 kJ/mol in temperature ranges of 170–210 °C, 210–400 °C and 400–500 °C (443–483 K, 483–673 K and 673–773 K), respectively. - Highlights: • Microhardness of UFG AZ31 alloy decreases with increasing annealing temperature. • This fact has two reasons: dislocation annihilations and/or grain growth. • The activation energies for grain growth were calculated for all temperature ranges.« less
  • Microstructure of a metal can be considerably changed by severe plastic deformation techniques such as high pressure torsion, extrusion and equal-channel angular pressing (ECAP). Among these methods, ECAP is particularly attractive because it has a potential for introducing significant grain refinement and homogeneous microstructure into bulk materials. Typically, it reduces the grain size to the submicrometer level or even nanometer range and thus produces materials that are capable of exhibiting unusual mechanical properties. In the present study, a test unites for equal channel angular pressing was constructed and this system was used for Al-Zn-Mg-Cu alloy. After the optimization tests, itmore » was seen that the most effective lubricant for the dies was MoS{sub 2}, the pressing pressure was around 25-35 ton and the pressing speed was 2 mm/s. By using these parameters, the Al-Zn-Mg-Cu alloy was successfully ECAPed up to 14 passes at 200 deg. C using route C. After ECAP tests, the specimens were characterized by transmission electron microscope (TEM), hardness and macrostructural investigations. It was seen that the plastic deformation in the ECAPed specimens occurred from edge to the centre like whirlpool. In addition, the deformation intensity increased with increasing pass number. The grain size of the specimens effectively also decreased with increasing pass number. That is, while the grain size of unECAPed specimen was 10 {mu}m, this value decreased to 300 nm after 14 passes. At the beginning, while there was a banding tendency in the grains toward deformation direction, homogeneous and equiaxed grains were formed with increasing pass number. This grain refinement was as a result of an interaction between shear strain and thermal recovery during ECAP processing. Hardness measurements showed that the hardness values increased up to 4 passes, decreased effectively at 6th pass, again increased at 8th pass and after this pass, the hardness again decreased due to dynamic recrystallization.« less
  • Commercial purity Al was severely deformed by equal channel angular pressing (ECAP) up to eight passes using route B{sub C}. The deformation microstructure was characterized quantitatively by electron-backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural homogeneity was investigated by EBSD at various locations from center to surface of the samples on a longitudinal section parallel to the pressing direction. Structural parameters including mean boundary spacing, boundary misorientation angle and fraction of high angle grain boundaries were measured and characterized through the section of the ECAP samples. EBSD scans revealed a homogeneous ultrafine grained microstructure after 8 passes. Themore » analysis showed that the fraction of high angle grain boundaries was more than 70% at most locations of the sample section. Also, an average boundary spacing of 380 nm was obtained by the linear intercept method. TEM analysis was used for more detailed characterization of the microstructure, such as low angle boundaries with misorientation angles smaller than 2 deg. Using the structural parameters-flow stress relationship, the flow stress was estimated based on the EBSD and TEM/Kikuchi-line analyses and compared with measured values.« less
  • In this work we were interested in doing simulation using finite elements analysis (FEA) to study the equal channel angular pressing process (ECAP), which is currently one of the most popular methods of severe plastic deformation Processes (SPD). for fabricating Ultra-Fine Grained (UFG) materials, because it allows very high strains to be imposed leading to extreme work hardening and microstructural refinement. The main object of this study is to establish the influence of main parameters which effect ECAP process which are magnitude of the die angle and the friction coefficient. The angle studied between (90-135°) degree, and magnitude of themore » friction coefficient μ between (0.12-0.6), and number of pass. The samples were made from aluminum alloy at room temperature with (15X 15) mm cross section and 150 mm length. The simulation result shows that normal elastic strain, shears elastic strain, and max. shear elastic strain increased, when changing the angle from 90° to 100°. and decrease between the angle 110° to 135°. Also the total deformation increased when we change die angle from 90° to 135°. By studding the friction effect on the die and sample we noted that increasing the friction coefficient from 0.12 to 0.6, normal elastic strain, and shear elastic strain increased and increasing the friction coefficient from 0.1 to 0.6 decrease the normal and shear stress.« less
  • Processing through the application of equal-channel angular pressing (ECAP) is recognized as one of the attractive severe plastic deformation techniques where the processed bulk metals generally achieve ultrafine-grained microstructure leading to improved physical characteristics and mechanical properties. Magnesium has received much attention to date for its lightweight, high strength and excellent elasticity. Mg alloys with addition of CaO is reported to provide the successful casting procedure without usage of greenhouse gas, SF{sub 6}, whereas it is generally used for preventing the oxidation of Mg during casting. In the present investigation, a CaO added AZ31 (AZ31-CaO) magnesium alloy was processed bymore » ECAP at elevated temepratures with a few steps of reduction which result in significant grain refinement to ~ 1.5 μm after 6 passes. Compression testing at room temperature demonstrated the AZ31-CaO alloy after ECAP showed enhanced yield strength more than the as-processed commercial AZ31 alloy while both alloys maintained ductility in spite of significant reduction in grain size. The improved strength in the AZ31-CaO alloy was attributed to the formation of fine Al{sub 2}Ca precipitates which experience breaking-up through ECAP and accelerate the microstructural refinement. Moreover, the preservation of ductility was attributed to the enhancement of strain hardening capability in the AZ31 alloy at room temperature. This study discusses the feasibility of using ECAP to improve both strength and ductility on magnesium alloys by applying the diagram describing the paradox of strength and ductility. - Highlights: • AZ31 and AZ31-CaO magnesium alloys were processed by ECAP up to 6 passes. • AZ31-CaO alloy after ECAP showed improved yield strength without losing ductility. • CaO in AZ31 forms fine Al{sub 2}Ca accelerating microstructural refinement during ECAP. • Feasibility of using ECAP was shown to improve both strength and ductility in Mg.« less