ECAP-processed Material Research Articles

Ignition-resistant Mg‐2Y‐2Gd‐1Ca alloy for aviation applications

Novel Mg‐2Y‐2Gd‐1Ca alloy was processed by extrusion or equal channel angular pressing (ECAP) to analyse the effect of the microstructure on ignition temperature, mechanical properties and corrosion resistance. The ignition temperature measured by a linear heating experiment in the electric furnace was found to be ≈ 950 °C, regardless of the microstructure of processed materials. The ignition temperature of the alloy is 300 °C higher than that of as-cast magnesium, thanks to the presence of alloying elements and the formation of the stable oxide. Thermogravimetry analysis and differential thermal analysis revealed that the onset of the oxidation process is ≈ 50 °C below this temperature. Partially recrystallised microstructure after extrusion led to a good combination of strength and ductility of the studied alloy. On the other hand, ECAP-processed material is characterised by a higher strength but lower ductility. Initial corrosion attack is significantly affected by the processing technique, but the difference diminishes within the first day of immersion in 3.5% NaCl solution, and the corrosion rate is comparable after one week of immersion. The only difference is in the distribution of the corrosion attack, which is more localised in extruded samples because of the occurrence of larger Mg2Ca particles compared to the ECAP-processed one.

Comparison of the effect of ECAP and SSE on microstructure, texture, and mechanical properties of magnesium

Microstructure, crystallographic texture, and mechanical properties of pure Mg, as a model hcp metal, were compared after processing by the two severe plastic deformation (SPD) techniques of equal channel angular pressing (ECAP) and simple shear extrusion (SSE). Both processes were performed on extruded bars at 250 °C for up to four passes, where the minimum grain sizes of 13.7 and 9.8 µm were achieved in the ECAP and SSE processes, respectively. The fraction of dynamically recrystallized (DRX) grains, high angle grain boundaries (HAGBs), and the evolution of dislocation density with equivalent strain experienced the same trend in both processes with higher values after ECAP. The textural evolutions were completely different during ECAP and SSE despite their similar deformation modes. A conventional shear texture was developed after ECAP, while after SSE basal planes were aligned parallel to the processing direction. In the ECAP-processed material, texture softening and lower dislocation density counterbalanced the strengthening effect of grain refinement, resulting in a decrease in shear yield stress (SYS) and ultimate shear strength (USS), while in SSE the shear strength increased constantly with increasing number of passes. It can be deduced from the experimental results that SSE was more effective in achieving a fine-grained homogenous microstructure with high shear strengths as compared to ECAP. • Compare microstructure, and strengths after simple shear extrusion (SSE) and equal channel angular pressing (ECAP) of Mg. • SSE was found more efficient in grain refinement compared to ECAP. • Higher fractions of DRX and high angle grain boundaries (HAGBs) were achieved in ECAP than in SSE. • Develop different shear texture components after ECAP and SSE despite having similar deformation modes. • In contrast to ECAP, the shear strengths after SSE increases by increasing the number of passes.

Thermal stability and superplastic behaviour of an Al-Mg-Sc alloy processed by ECAP and HPT at different temperatures

An Al-3%Mg-0.2%Sc alloy was processed by ECAP and HPT at different temperatures. Afterwards, samples subjected to 10 turns of HPT at 300 and 450 K, 8 passes of ECAP at 300 K and 10 passes of ECAP at 600 K were annealed for 1 hour at 523 K and their mechanical properties and microstructure were examined using microhardness measurements and EBSD analysis. In addition, tensile specimens with similar dimensions were machined from the HPT and ECAP-processed materials and further tensile tested at 523 K. The results demonstrate that the Al alloy processed by HPT at 450 K exhibits higher microhardness values (~138 Hv) and a smaller average grain size (~0.28 µm) after annealing at 523 K among all SPD processing conditions. Accordingly, the material subjected to HPT at an elevated temperature displays superior superplastic properties such that an elongation of ~1020 % was attained after testing at 523 K at 1.0 × 10−3 s−1. Furthermore, detailed EBSD analysis revealed a significant fraction of low-angle grain boundaries (LAGBs > 33 %) in the ECAP-processed material after annealing which may be responsible for the inferior superplastic behaviour by comparison with the HPT-processed samples (LAGBs < 13 %) tested at 523 K.

Effect of soft Bi particles on grain refinement during severe plastic deformation

Two aluminum alloys, Al–8Zn and Al–6Bi–8Zn were subjected to equal channel angular pressing (ECAP) up to 5 passes at room temperature. The microstructural evolution and the grain refinement behavior of these alloys were systematically studied by electron backscatter diffraction (EBSD). After 5 passes of ECAP, ultrafine grained microstructures formed in both alloys. However, the grain structure in the Al–6Bi–8Zn alloy is much finer than that of Al–8Zn alloy, showing that the soft Bi particles have a strong influence on enhancing the grain refinement during ECAP. The strengths of the ECAP-processed materials were measured by hardness test and it showed that after 5 passes of ECAP, the hardness of the Al–6Bi–8Zn alloy was higher than that of the Al–8Zn alloy. The effects of soft Bi particles on the deformation behavior during ECAP and the final strength of the Al–6Bi–8Zn alloy were discussed.

Neutron diffraction and finite element analysis of the residual stress distribution of copper processed by equal-channel angular pressing

Residual stress remaining after plastic deformation significantly affects the physical and chemical behaviors of materials. In this work, the residual stress distribution in Cu after single-pass equal-channel angular pressing (ECAP) was evaluated using neutron diffraction and the finite element method (FEM). The residual stress distributions simulated using the FEM are in good agreement with the experimental results measured using the neutron diffraction method. The workpiece had non-uniform distribution of residual stresses from bottom to top region of a rod specimen with circular cross-section. The axial residual stress in the top region of the workpiece was highly tensile; while it was only slightly tensile in the bottom region. On the other hand, the radial and hoop residual stresses were tensile in the bottom region, whereas they were compressive in the top region. Despite such non-uniformity of residual stresses, the middle region of the workpiece had relatively homogeneous tensile residual stresses. This investigation on the residual stress distribution in the ECAP-processed material provides a new window from which engineering problems in related with residual stress can be issued and solved.

Enhancement effect of inter-pass annealing during equal channel angular pressing on grain refinement and ductility of 9Cr1Mo steel

To obtain enhanced mechanical property in both the strength and the ductility, 9Cr1Mo steel (T91) was severely deformed by equal channel angular pressing (ECAP) combined with an additional inter-pass annealing. Tensile results show that the additional inter-pass annealing can significantly improve the ductility (i.e. 18% of the total elongation after four-pass extrusion with the inter-pass annealing) but slightly decrease the tensile strength comparing with the case without the inter-pass annealing (i.e. 10% of the total elongation after four-pass ECAP processing). The average grain size of the two passes ECAP-processed materials with the inter-pass annealing (~0.8µm) is smaller than that of the sample without inter-pass annealing (~2µm), and the fraction of the high angle grain boundaries in the samples with the inter-pass annealing (~40%) is higher than that of ~34% (two-pass ECAP) without the inter-pass annealing based on electron backscattering diffraction analysis. The crystallite size and dislocation density were evaluated by means of the modified Williamson-Hall plot based on X-ray diffraction analysis. The microstructural analysis indicates that the enhanced ductility of the ECAP processed and inter-pass annealed materials can be attributed to the relatively smaller grain sizes, larger crystallite sizes and lower dislocation densities.

Design, simulation and manufacturing of a connecting rod from ultra-fine grained material and isothermal forging

In this research work, a study on the mechanical properties of isothermal forging for connecting rods is made from previously ECAP (Equal Channel Angular Pressing)-processed AA1050 and AA5083 aluminium alloys. This severe plastic deformation (SPD) process is used in order to achieve a starting material with a submicrometric structure, thus improving the mechanical properties of the part. In this study, the design and the experimentation process is shown, where this involves the design stage by finite element simulations, the experimental tests and the use of metallographic techniques for the required properties to be analysed. It is observed that there is an improvement in the mechanical properties when the starting material is ECAP-processed before carrying out the isothermal forging. This improvement consists in an increase of 20% in the hardness of the final connecting rod which also possesses a microstructure grain size of 500nm. To come to these conclusions, the results obtained with the connecting rods manufactured by isothermal forging from previously ECAP-processed material are compared with those conventionally manufactured. Therefore, the feasibility and the advantages of the industrial manufacturing of mechanical components by isothermal forging from ECAP-processed material are demonstrated here as mechanical properties are achieved, as well as a better flow of the material and at a lower forging temperature. In the existing bibliography, there are no research works dealing with the manufacturing of connecting rods from ultra-fine grained material and that is the reason why this present study is considered to be of scientific and technological interest, and therefore, it may be considered to be at the frontline of current knowledge.

Mechanical Properties Analysis of an Al-Mg Alloy Connecting Rod with Submicrometric Structure

Over these last few years, there has been a growing interest in developing mechanical components from submicrometric materials due to the significant improvement that these materials present compared to their original state. This present research work deals with the study of the mechanical properties of a connecting rod isothermally forged from different starting materials. These materials are as follows: annealed aluminum alloy (AA) 5754, the same alloy previously deformed through equal channel angular pressing (ECAP) and a third case where the previously ECAP-processed material is subjected to a recovery heat treatment. A comparison is made between finite volume (FV) simulations and experimental tests with respect to hardness, plastic strain and forging force. Furthermore, the improvement in the mechanical properties of the connecting rod forged from predeformed material is evaluated in comparison to the connecting rod forged with annealed material. The microstructure of both cases is also compared at the end of the manufacturing process.

Grain boundary misorientation and positron annihilation characteristics in steel Eurofer processed by equal channel angular pressing

Electron back-scattered diffraction and positron annihilation lifetime measurements were performed on the ferritic–martensitic 9 %Cr Eurofer steel processed by equal channel angular pressing (ECAP) at 550 °C. The orientation imaging mapping images reveal ECAP-induced changes toward a more stable texture via rotation around 〈111〉 and 〈110〉 axes. These are accompanied by transformation of martensite into ferrite and a remarkable change in the bimodal distribution of grain misorientations with reduction of the fraction of high-angle grain boundaries. The positron annihilation measurements evidence the release of vacancies retained in the ECAP-processed material and their clustering into nanovoids in samples heat treated at T ≥ 500 °C. It is found that tensile strain applied at 600 °C can inhibit this void formation in the ECAP-deformed material for 1 and 2 passes, but not in the case of 4 passes. A model for accounting the results is proposed.

Design and mechanical property analysis of ultrafine grained gears from AA5083 previously processed by equal channel angular pressing and isothermal forging

In this present study, the isothermal forging of two different gears is carried out from material previously deformed by the severe plastic deformation (SPD) process known as Equal Channel Angular Pressing (ECAP). At present, there are only a few studies which use this material predeformed that exhibits improved mechanical properties as a result of the SPD process for use in subsequent processes or applications. The design and optimization of the die geometry required for the isothermal forging of gears are shown and both microhardness and microstructure are compared when these forged gears are obtained from annealed material (N0) and ECAP-processed material (N2). With this present research work, it is demonstrated that there is an improvement in forgeability and microhardness as well as a decrease in the grain size of the material predeformed by SPD.

Prediction of Surface Fracture of 6061 Al Processed by Equal-Channel Angular Pressing

Improving the efficiency of equal-channel angular pressing (ECAP) necessitates predicting the location of fracture and the number of ECAP passes required when fracture is formed. However, the damage mechanism in ECAP-processed materials remains insufficiently understood. Surface fracture formation during the ECAP of 6061 Al-T4 alloy was investigated by finite element simulation and experimentation. The simulation of damage distribution in the sample was based on the Cockcroft and Latham criterion. Fracture formed in the upper and lower surfaces of the sample, a finding that is in good agreement with the simulation results for damage factor. A critical damage factor, calculated from the experimental data, accurately predicted the number of ECAP passes required when surface fracture is formed. Tensile stress was caused by various strain rates in different parts of the sample cross-section as the sample was pressed through the bend channel; this stress was the main driver of damage formation.

Electrochemical Properties of AL-6060 Alloy After Industrial-Scale ECAP

The equal-channel angular pressing (ECAP), as the most famous method of severe plastic deformation, has the potential for upscaling from the laboratory to industrial scale. Thus, it is important to examine the practice-relevant properties of large billets deformed by this process. Mechanical properties and corrosion resistance significantly affect the service life of the structural components. The mechanical properties of Al-6060 alloy after industrial-scale ECAP (the cross-sectional sizes of the billets were 50 × 50 mm2) were analyzed by P. Frint. In the present work, we investigate the effect of one pass of the in-dustrial-scale ECAP on the electrochemical properties of Al-6060 alloy by means of potentiodynamic polarization tests in a 0.1 M NaCl solution. The corroded surfaces were analyzed by means of optical microscopy and scanning-electron microscopy. In order to characterize the homogeneity of the corrosion behavior of the ECAP-processed material, all analyses were taken in different zones perpendicular to the extrusion axis. The results indicate that one pass of ECAP does not deteriorate the electrochemical behavior of Al-6060 alloy.

Analyses of route Bc equal channel angular pressing and post-equal channel angular pressing behavior by the finite element method

Equal channel angular pressing (ECAP) process provides an efficient procedure for achieving ultrafine grained microstructures with excellent mechanical properties in metallic materials. In this article, a simulation scheme for predicting the mechanical behavior during and after ECAP was proposed. The proposed scheme was applied for interstitial-free (IF) steels, which are widely used for the automobile body applications. Plastic deformation behavior during several passes of ECAP in route Bc, including such aspect as deformed geometry, corner gap, forming load and strain uniformity, was predicted. Tensile testing responses of the ECAP-processed IF steel, including strain hardening, onset of necking, and post-necking behavior, were analyzed using the finite element method and compared with the experimental results. The predicted tensile curves, ultimate tensile strength, and elongation varying with the number of ECAP passes were in good agreement with experimental results. The computational scheme developed was demonstrated to successfully predict not only the plastic deformation behavior during ECAP but also the mechanical properties of the ECAP-processed material.

Assessment of tensile strength using small punch test for transversely isotropic aluminum 2024 alloy produced by equal channel angular pressing

The microstructures of metallic materials become extremely refined and their mechanical strengths exhibit considerable anisotropy when subjected to severe plastic deformation by equal channel angular pressing (ECAP). The small punch (SP) testing method was employed as a substitute for the standard tension test to assess the anisotropic tensile strength of materials produced by ECAP. SP testing is a viable alternative to standard tension tests because ECAP samples are usually limited to approximately 10 mm in length in the transverse direction perpendicular to the extrusion (longitudinal) direction of the ECAP process and the dimensions of the SP test specimen are 10 mm × 10 mm × 0.5 mm. The SP tests were performed using specimens of over-aged aluminum 2024 alloy subjected to three ECAP passes at 150 °C and extracted by wire cutting along the longitudinal and transverse axes. The failure surfaces of SP specimens after testing showed that failure was caused by shear deformation and that ECAP-processed materials displayed anisotropic strength. Based on these results, a method is proposed to assess tensile strength along both the transverse and the longitudinal axes of ECAP materials exhibiting anisotropic strength. The validity of the proposed method was verified through a comparison of its performance evaluating plastic flow strength with measurements obtained by tension tests along the longitudinal axis.

The influence of nano-scale surface roughness on bacterial adhesion to ultrafine-grained titanium

We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, Grade-2) on bacterial attachment to the mechano-chemically polished surfaces of the material. The ultrafine crystallinity of the bulk was achieved by severe plastic deformation by means of equal channel angular pressing (ECAP). The chemical composition, wettability, surface topography and roughness of titanium surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements, as well as atomic force microscopy (AFM) with 3D interactive visualization of the titanium surface morphology. It was found that physico-chemical surface characteristics of the as-received and the ECAP-modified CP titanium did not differ in any significant way, while the surface roughness at the nano-scale did. Optical profilometry performed on large scanning areas of approximately 225 μm × 300 μm showed that there was no significant difference between the roughness parameters R a and R q for surfaces in the two conditions, the overall level of roughness being lower for the ECAP-processed one. By contrast, topographic profile analysis at the nano-scale by AFM did reveal a difference in these parameters. This difference was sensitive to the size of the scanned surface area. A further two surface roughness parameters, skewness ( R skw) and kurtosis ( R kur), were also used to describe the morphology of titanium surfaces. It was found that the bacterial strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 65.8 and Pseudomonas aeruginosa ATCC 9025, showed preference for surfaces of ECAP-processed titanium. S. aureus cells were found to have a greater propensity for attachment to surfaces of ECAP-modified titanium, while the attachment of P. aeruginosa, while also showing some preference for the ECAP-processed material, was less sensitive to the ECAP processing.

Mechanical properties and microstructure of a Mg alloy AZ31 prepared by equal-channel angular pressing

A squeeze cast magnesium–aluminium–zinc alloy AZ31 was subjected to equal-channel angular pressing (ECAP) at 200 °C up to four passes following route B c. The grain size was reduced by a factor of about 100–200 through ECAP processing. The mechanical properties of as cast (non-pressed) and the ECAP-processed material were examined using compression tests from room temperature to 300 °C. ECAP pressing resulted in a significant increase of the room temperature yield strength of the alloy. At elevated temperatures (200 and 300 °C) an inverse dependence was found, i.e. the yield stress in the ECAP-processed specimens was lower than in the cast material. A recrystallized structure was formed only after four passes of ECAP. Dynamic recrystallization occurred during the deformation at elevated temperatures (300 °C). Coarser recrystallized grains were formed in the specimen that had undergone four passes of ECAP. The strain imposed by ECAP influences the heterogeneity of the final microstructure of specimens after compression tests.

A comparison of the properties of SPD-processed AA-6061 by equal-channel angular pressing, multi-axial compressions/forgings and accumulative roll bonding

Commercially available AA-6061 in the annealed condition was subject to severe plastic deformation (SPD) processing by equal-channel angular pressing (ECAP), multi-axial compression/forgings (MAC/F) and accumulative roll bonding (ARB) at room temperature to approximately the same accumulated strain (∼4). Micro-hardness testing showed that materials processed by ECAP, MAC/F and ARB followed the same trend. The tensile properties of MAC/F- and ARB-processed materials were compared with those of the ECAP-processed material from the literature. MAC/F material exhibited high strain rate sensitivity in the temperature range of 300–350 °C. The SPD technique used, whether ECAP, MAC/F or ARB, did not significantly affect the flow behavior of AA-6061.

Superplasticity and internal friction in microcrystalline AZ91 and ZK60 magnesium alloys processed by equal-channel angular pressing

Low-temperature superplasticity (LTSP) and internal friction in microcrystalline ZK60 and AZ91 magnesium alloys processed by equal-channel angular pressing (ECAP) are reported. Excellent low-temperature superplasticity (<300 °C) was observed in ECAP-processed materials: elongations to failure are 810 and 570% in ZK60 and AZ91 alloys, respectively, at a strain rate of 3×10 −3 s −1. Internal friction can be practically used to determine the optimum temperature for superplasticity.

Low-temperature superplasticity and internal friction in microcrystalline Mg alloys processed by ECAP

Excellent low-temperature superplasticity (<300 °C) was observed in the ECAP-processed materials: elongations to failure are 810% and 570% at a strain rate of 3 × 10 −3 s −1 for ZK60 and AZ91 alloys, respectively. Internal friction can be practically used to determine the optimum temperature for superplasticity.