Route Bc Research Articles

Effect of heat treatment and severe plastic deformation on microstructure and texture evolution of 7075 alloy

Present work described the effects of heat treatment and severe plastic deformation on microstructural, texture and mechanical properties for EN AW 7075 alloy. The dendritic structure and eutectic phases attained after casting were almost dissolved after 96 h of homogenisation treatment. The homogenised alloys were further processed by equal channel angular pressing (ECAP) by BC route at room temperature and consequently carried the signature of refined microstructure, higher hardness, yield strength, and tensile strength after two consecutive ECAP passes. The main observation of the present investigation includes the formation of random texture in as-cast and homogenised conditions and changing to Cθ and A*2θ components after the first pass and strong Bθ,B-θ and A-θ components along with weaker A*2θ, Cθ components after the second pass.

Enhanced Precipitation and Recrystallization in a Mg-Zn Alloy During Low-Temperature Extrusion

Lightweight magnesium (Mg) alloys have great potential to be used in a variety of structural applications. However, Mg’s hexagonal crystal lattice and the limited number of deformation slip systems create fundamental challenges during forming. Furthermore, the selection and amounts of alloying additions can lead to complex phases and transformations or location-sensitive precipitate reactions (i.e., in grain or grain boundary regions). Mg-Zn alloys are promising candidates for applications requiring high strength due to their high hardening response. In this study, we processed solution treated Mg-3Zn (wt.%) using equal channel angular extrusion (ECAE) along the Bc route at 150 oC. The microstructure of the extruded material showed two distinct regions. The grain interior showed a dense distribution of nano precipitates. The grain boundary region contains recrystallized ultrafine grains with some reprecipitation occurring inside them. We employed the Lukác-Balík strain hardening model to estimate the dislocation density evolution during the processing, and we linked these dislocations to the high density of precipitates seen in the grain interiors.

Microstructure, mechanical properties, and degradation of Mg-Ag alloy after equal-channel angular pressing.

Enhancing the strength of Mg-based biodegradable alloys without decreasing their corrosion resistance is a major engineering challenge. In addition, the growing demand for effective reduction of infections and inflammation after implant placement motivates the design of alloys with appropriate compositions or coatings. One promising alloying element is silver, whose antibacterial effect has long been known. Therefore, a Mg-4% Ag alloy was selected for this study. The alloy was investigated under three conditions: as-cast, after T4 treatment, and after T4 treatment with subsequent equal-channel angular pressing (ECAP) using a newly developed double-ECAP die, which offers an equivalent strain per pass of 1.6. The first pass through the double-ECAP die was conducted at 370 °C and the second at 330 °C using route BC. The microstructure of the as-cast Mg-4% Ag consisted of large grains (several hundred microns) and a dendritic structure with micron-sized Mg54Ag17 precipitates. T4 heat treatment caused dissolution of the dendrites and formation of a solid solution without changing the grain size. Consequently, the ultimate compressive strength (UCS) was increased by approximately 30%, and the compressive strain at fracture reached approximately 23%. The compressive yield strength (CYS) remained nearly constant at approximately 30 MPa. Subsequent ECAP led to strong grain refinement (from 350 μm to 38 μm after one pass and 15 μm after two passes) and further increases in the CYS and UCS, to 45 and 300 MPa after the first pass and 62 and 325 MPa after the second pass, respectively. The as-cast alloy exhibited a very high degradation rate in a simulated body fluid at approximately 36 °C. The degradation rate of the alloy after T4 treatment was much lower. Subsequent ECAP had no significant effect on the degradation properties. Thus, it can be concluded that grain refinement has little effect on the degradation rate.

Development of homogeneity in a Cu-Mg-Ca alloy processed by equal channel angular pressing

A Cu-0.41Mg-0.06Ca (wt.%) alloy was processed by equal channel angular pressing (ECAP) for up to 12 passes via Bc route at room temperature, and its homogeneity was evaluated from three aspects of hardness, microstructure and crystallographic texture. The hardness was measured in detail on the whole transverse planes, and the microstructure and the crystallographic texture in the central and bottom regions on the transverse planes were investigated by electron backscatter diffraction (EBSD) technique. After 1 ECAP pass, the hardness in the central region was 9.4% higher than that in the bottom region; the microstructure in the central region consisted of the elongated grains, while that in the bottom region was composed of the slightly distorted grains; the crystallographic texture in the central region followed the ideal orientations of the ECAP crystallographic texture, nevertheless the crystallographic texture in the bottom region obviously deviated from any ideal orientation of the ECAP crystallographic texture. Then, with the increase of ECAP passes, the hardness and microstructure differences between in the two regions gradually weakened, and the deviation of the crystallographic texture in the bottom region gradually decreased. After 8 ECAP passes, the both regions showed the same hardness, the similar ultrafine-grained microstructure and the similar crystallographic texture. The difference formation should be attributed to the non-uniform strain caused by the friction between the sample and the die wall, rather than caused by the corner gap. The difference weakening should be attributed to the strain hardening behavior of metals. The strength calculation showed that the Cu-Mg-Ca alloy after 8 ECAP passes had almost the same yield strengths where 593 MPa for the central region and 583 MPa for the bottom region, showing only 1.7% difference.

Discontinuous grain growth in an equal-channel angular pressing processed Fe-9Cr steel with a heterogeneous microstructure

A particle-containing Fe-9Cr steel was processed by six passes of equal-channel angular pressing (ECAP) using route Bc to produce an ultrafine-grained (UFG) microstructure with a heterogeneous distribution of high-angle boundaries (HABs) and low-angle boundaries (LABs). Annealing was carried out on the ECAP-processed Fe-9Cr from 500 to 700 °C, for up to 48 h. It was found that the UFG microstructure was stable up to 550 °C. Discontinuous grain growth was first observed in the sample annealed at 600 °C, accompanied by an increase in LAB fraction. The discontinuous grain growth became evident during high temperature annealing (650–700 °C), leading to a reduction in LAB fraction and a significant increase in grain size. Grain growth was the main reason for the decline in hardness. It is proposed that in the current heterogeneous microstructure, grain growth initially occurs in regions of dominantly HABs, and subsequently takes place in regions that mainly consist of LABs, thereby forming a bimodal microstructure. Textures of the annealed structure were shown to be similar to those of the ECAP processed structure. No differences in textures were found between abnormal grains and the matrix in the annealed structure in current case.

Influence of temperature of ECAP processing on the microstructure and microhardness of as-cast AX41 alloy

The influence of the temperature of ECAP processing on the microstructure and mechanical properties of commercial as-cast AX41 magnesium was investigated. ECAP processing was conducted at temperatures of 220 °C and 250 °C up to N = 8 passes via route Bc. The original grain size of 200 μm was found to decrease with increasing number of passes at both temperatures. After 8 passes, the grain size of 1.4 μm and 2.6 μm was obtained at 220 °C and 250 °C, respectively. This difference was attributed to the suppressed dynamic recrystallization for N > 2 caused by substantial decrease in dislocation density of $$ \left\{ {10\bar{1}0} \right\}11\bar{2}0 $$ prismatic and $$ \left\{ {10\bar{1}1} \right\}11\bar{2}3 $$ pyramidal -type edge dislocations and more pronounced high-temperature grain growth at 250 °C. Despite the different grain sizes, similar crystallographic textures and dislocation densities were observed at both temperatures after 8 passes. The microhardness values increased up to 4 passes at both temperatures in accordance with the variation of the grain size, indicating the dominance of Hall–Petch strengthening.

Microstructure and electrochemical study of equal channel angular pressed Al-Zn alloys

This research focuses on the effect of severe plastic deformation (SPD) on microstructure and properties of Al and Al-Zn (in 1, 2, 3, 4, 5 wt%) anodes of Al-air battery. The Al-Zn alloys with a diameter of 12.5 mm and 62.5 mm long were pressed in an ECAP die (press angle $=90°, XP=20°), using route Bc with 2, 4, 6, 8 passes at room temperature. Microstructural characterization was carried out using scanning electron microscope (SEM). The cast samples were solutionized at 450 °C for 1 hr after pressing. Grain size of the as-ECAP samples decreased with an increase of ECAP passes. The smaller grain size resulted in strengthening of Al-Zn. An decrease in grain size was due to significant change in the microstructure from an intensive shear stress after ECAP. Polarization test in a 3.5wt% NaCl solution were used to study electrochemical behaviours of the as-cast and ECAP Al-Zn alloys. The conclusion from the research will be used as a platform to develop Al anodes for Al-air battery in the future.

Effect of Back Pressure on the Consolidation Behaviour of Titanium Sponge Particles Processed by ECAP

Titanium is a hard metal with good mechanical properties, corrosion resistant and biocompatibility which makes it have a wide range of applications (biomedical and aerospace). Severe plastic deformation (SPD) is employed to produce Ultrafine Grained (UFG) structures. UFG structures have better mechanical properties due to their compaction. Equal Channel Angular Pressing (ECAP) is adapted to produce a UFG structure in Titanium. In this process, titanium sponge powder is filled in the aluminium shell by intermediate tapping to fill the volume of the shell. The shell is then closed with an Al cap and ECAP is done with continuous back pressure at 300°C. The test specimen has undergone four passes in route BC at different back pressure (50, 100 and 150 MPa) where titanium is consolidated without any crack. Titanium showed decreased grain size and porosity with increasing backpressure. In particular, it is seen that the sample ECAPed by 100 MPa backpressure showed a relative density of about 98% with a hardness of 37 HRC. It is seen that ECAP is more economical and the product obtained by the ECAP process has better properties.

Analysis of the Tribological Properties of Commercial Pure (CP) Aluminum Developed by Chip Consolidation through Equal Channel Angular Pressing (ECAP)

The goal of this research work is to study the role of equal channel angular pressing on consolidation behavior of machined chips of CP Al through ECAP. The chips are collected by orthogonal cutting with cutting edge angle 75° and depth of cut 0.2 mm. The ECAP die with Φ = 90° (channel angle) and Ψ = 20° (corner angle) is used for consolidation of machined chips. The consolidation is done by pre-heating the chips at 200°C upto four passes through processing route BC. The maximum density of 99% and hardness of 94 HV was obtained after 4 ECAP passes. Tribological properties is evaluated by Pin-on-disc dry wear testing for three different loads at a constant sliding speed 750 RPM and distance of 5 kms. Chip consolidated CP Al is inferior in wear resistance with as-received CP Al owed to localised debonding of chips with the sliding disc.

Microstructural evolution of equal channel angular drawn purity titanium at room temperature

Thin commercial-purity titanium (CP–Ti) wire was successfully acquired by equal channel angular drawing (ECAD) at room temperature with route Bc using a 90° die at a relatively high drawing speed of 10 mm s−1. The as-drawn CP–Ti wires were of good quality free of cracks and segmentation on their surface. The grain size of CP–Ti was reduced from ∼32 μm for the as-annealed wire to ∼700 nm for 12-passes equal channel angular drawn wire. The grain experienced transition from microband to thin lath and to equiaxed subgrains with the increment in drawing passes. Face-centered cubic (FCC) phase was triggered obviously to accommodate the large shear strain induced by ECAD at the drawing rate of 20 mms−1. The thickness of the FCC phase increased with an increase in drawing passes, and no equiaxed subgrains were formed in CP–Ti. Accordingly, the drawing speed significantly affects the deformation mode and microstructural evolution of CP–Ti during ECAD. A lower drawing speed provides a longer time for the structure recovery, thus resulting in the occurrence of dynamic recovery when ECAD was performed at room temperature. Additionally, {101¯2} tension twinning and {112¯2} compression twinning occurred simultaneously to accommodate ECAD shear deformation. The success in processing CP–Ti rods at room temperature through multiple passes of ECAD provides a new perspective to efficiently fabricate ultrafine grained small-sized materials continuously.

An Investigation on Microstructure Evolution, Mechanical Properties, and Strain Aging of Mg-1.8Zn-0.7Si-0.4Ca Biomedical Alloy Processed by Equal Channel Angular Pressing

The influence of equal channel angular pressing (ECAP) on microstructure and mechanical behavior, as well as, strain aging during ECAP and post-ECAP of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy was examined. The alloy in solid solution heat-treated condition was processed by ECAP with route BC at 350 and 400 °C. The specimens ECAPed at 350 °C were aged at 125 and 150 °C for different times. The hardness and shear punch test results indicated that performing ECAP at 350 °C for 4 passes increases the hardness and shear strength of the alloy from 48 HV and 110 MPa to 71 HV and 188 MPa, respectively. It was revealed that the average grain size of the alloy decreases from 78 µm to about 3 µm after 4 passes of ECAP. Three precipitates of CaMgSi, Ca2Mg6Zn3, and Mg2Si were detected in the solid solution specimen. After 4 passes of ECAP at 350 °C, Ca2Mg6Zn3 was completely dissolved and the morphology of Mg2Si changed from Chinese script to fiber-shaped particles. Dynamic strain aging occurred at high-temperature ECAP, and the specimens were overaged during post-ECAP aging. Small MgZn particles were detected in the overaged sample.

Influence of Grain Refinement by ECAP on Mechanical and Erosion Corrosion Properties of AISI 4130 Steel: Experimental and Prediction Approach

Sever plastic deformation (SPD) is widely employed to make ultrafine-grained structure (UFGS) materials that satisfy desired properties such as high strength, good tribological properties, and lightweight. Equal channel angular pressing (ECAP) is one of the most important SPD techniques. The current work studies the effect of ECAP passes on mechanical properties, microstructure, and the erosion–corrosion (E–C) resistance of AISI 4130 steel. ECAP at high temperature according to Bc route (billet rotation 90 deg counterclockwise after every pass) was applied and UFGS AISI 4130 specimens with an average grain size of 500 nm were obtained after four ECAP passes. Consequently, the effects of ECAP on the tensile, hardness, and impact properties were investigated. The E–C resistance of unECAPed and ECAPed specimens was evaluated by using seawater slurry with specified sand concentrations. Various microscopes were employed to investigate the microstructure and surface changes due to ECAP and E–C. The results showed that the AISI 4130 steel processed by ECAP has enhanced mechanical and E–C properties. The main mechanisms of E–C are plastic deformation, craters, and small pits. A predication model based on an artificial neural network (ANN) was developed to predict the E–C behavior of both unECAPed and ECAPed materials. The model is able to estimate the weight loss without the need to perform extra experiments. A good agreement between the predicted values and the experimental results was achieved.

Investigation on the Creep Behavior of AZ91 Magnesium Alloy Processed by Severe Plastic Deformation

This paper describes the grain refinement due to equal-channel angular pressing (ECAP) and the creep properties of the ECAP-processed AZ91 magnesium alloy. The resulting microstructure and creep properties were examined by scanning electron microscope and impression creep test method. Microstructural evolution reveals that the grains were refined to 14 µm after four ECAP passes at 628 K, following route Bc. The creep tests were carried out under stresses in the range of 35 to 95 MPa at temperatures in the range of 538 to 583 K. Based on a power law between the impression rate and stress, the stress exponents were about 2 and the activation energies were about 129 kJ/mol, which are close to that for lattice diffusion of magnesium. Considering the obtained results, it can be stated that the grain boundary sliding is the dominant creep mechanism at low stresses and high temperatures. Deformation mechanism is grain boundary sliding (GBS) during creep of the AZ91 alloy at low stresses and high temperature and deformation behavior can be determined from:$$\upvarepsilon^{\cdot } = 7.25\left({\frac{{\text{b}}}{{\text{d}}}} \right)^{2} \left({\frac{{\text{Gb}}}{{\text{kT}}}} \right)\left( {\frac{\upsigma}{{\text{G}}}} \right)^{{2.02}} {\text{D}}_{L}$$

Thermal Stability and Mechanical Behaviour of Equal Channel Angular Pressed Structural Steel IS2062

The annealing behaviours of the equal channel angular pressed (ECAP) structural steel (hypoeutectoid) were investigated. The sample was processed up to four pass-through routes Bc in 120° angle die at ambient condition. Due to the effect of ECAP process, mechanical properties significantly improved, whereas the ductility drastically decreased in the material. The microstructural and mechanical characterization illustrates that the recovery process occurred at an annealed temperature of 500–525 °C and the recrystallization process occurred when the sample was annealed at 550 °C. When the annealing temperature was 600 °C, the grain growth process occured in the ECAPed sample and the strength, hardness and ductility were almost equivalent to the as-received material. The microstructural analysis was revealed in the TEM micrography. According to the microstructural and mechanical property analysis, the intermediate annealing temperature of 525 °C to 550 °C was suitable for this material to optimize the strength and ductility.

Texture evolution and strengthening mechanism of single crystal copper during ECAP

For finding a process for improving the strength of single crystal Cu while still maintaining good plasticity and electrical conductivity, the die with an internal angle (Ф) = 105° and an outer curvature angle (ψ) = 37°was used to prepare the equal channel angular pressing (ECAP) deformation by route Bc. The deformation behavior of single crystal copper during ECAP was investigated through electron backscatter diffraction (EBSD), optical microscope (OM) and X-ray diffraction (XRD). The mechanical properties and electronic conductivity after deformation were tested. The results show that the texture evolution is {111}<112> (intital)→ {111}<110>→ {111}<112>→ {112}<110> during 4 passes deformation. The tensile strength and the hardness of single crystal copper increased 123% and 115% respectively after four passes, the electrical conductivity has no obvious decrease. This result indicates that ECAP method can significantly improve the strength of single crystal copper, simultaneously, the plasticity and conductivity of the material remains at an excellent level.

The Effect of ECAP Temperature on the Microstructure and Properties of a Rolled Rare Earth Magnesium Alloy.

Deformation of an as-rolled rare earth Mg-2Y-0.6Nd-0.6Zr alloy, at different temperatures, was carried out along the BC (90° anticlockwise rotation of the samples after each ECAP pass) route by equal channel angular pressing (ECAP). The effects of the deformation temperature and the predeformation on the microstructure of the magnesium alloy were determined by the microstructure examination. The slip systems and texture change of the Mg-2Y-0.6Nd-0.6Zr alloy were investigated by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD), after equal channel angular deformation. The results showed that after seven passes of rolling, the grain size in the Mg-2Y-0.6Nd-0.6Zr alloy was refined to approximately 22 µm and the slip occurred mainly by a cylindrical slip and a pyramidal slip. After one pass of ECAP at 340 °C, the internal average grain size was significantly reduced to 11 µm, the cylindrical diffraction intensity clearly weakened, and the pyramidal diffraction intensity increased. EBSD pole figure analysis revealed that the base texture of the rolled Mg-2Y-0.6Nd-0.6Zr alloy weakened from 24.31 to 11.34 after ECAP. The mechanical properties indicated that the tensile strength and elongation of the rolled Mg-2Y-0.6Nd-0.6Zr alloy reached maximum values, when the deformation temperature was 340 °C.

Effect of Equal Channel Angular Pressing Processing Routes on Corrosion Resistance and Hardness of Heat Treated A356 Alloy

Equal channel angular pressing (ECAP) via routes A and Bc was used to process heat treated A356 alloy. The samples produced a range of microstructures in order to investigate the effect of straining on its corrosion behavior in 3.5 wt. % NaCl solution and hardness. The ECAP was conducted at room temperature in a mold with channel angle of 120°. The results show that brittle coarse silicon particles were effectively fragmented into smaller size in the Al-rich matrix after the processing. The hardness and corrosion resistance test showed improvement after T5 and T6 heat treatment, preferably to T6 due to wholly changed in silicon particles morphology than T5. The hardness increased with ECAP processing from 60.66 Hv to 1133.47, 124.91 Hv after three passes route Bc and four passes route A, respectively. The evaluation of corrosion resistance of the alloy showed improvement from 0.0424 to 0.00173, 0.00149 mmy-1 after three passes route Bc and four passes route A, respectively. In this research, both strength and corrosion resistance are improved by ECAP processing of A356 alloy using both routes.

A constitutive model to describe high temperature flow behavior of AZ31B magnesium alloy processed by equal-channel angular pressing

Equal channel angular pressing (ECAP) is a well-known process for developing an ultrafine-grained microstructure in metals and alloys. In this study, the hot deformation behavior of an AZ31B Mg alloy has been evaluated as a function of ECAP passes and processing routes. Specimens were subjected to three passes of ECAP using a die angle of 120° using processing routes BC and C. Isothermal hot compression testing at strain rate ranging from 0.01 to 10 s−1 and temperatures ranging from 250 to 400 °C were conducted and flow curves generated. The flow curve data generated were fitted to standard constitutive equations used to describe hot working behavior and the activation energies were determined. It was observed that the activation energies for hot deformation decreased after ECAP and this can be related to the grain refinement due to the ECAP process. Activation energy decreased from 161.6 kJ/mol in the annealed condition (grain size: 29 μm) to 145.3 kJ/mol for route 3BC (grain size: 4.7 μm) and 132.3 kJ/mol for route 3C (grain size: 4.9 μm). Equations for predicting the peak flow stress for various ECAP passes has been generated using the Zener Hollomon parameter and these are in agreement with the experimentally observed values.

Effective grain refinement of pure Cu processed by new route of equal channel angular pressing

Microstructures and mechanical properties of pure Cu processed by equal-channel angular pressing (ECAP) at room temperature (RT) were investigated. Samples were subjected to eight passes using routes BC, A and X. A new route which is called route X was proposed in this paper. Route X has a specific rotation angle of the sample between consecutive passes to maintain the angle between the shear plane (SP) and grain elongation plane (EP) equal to the angle between adjacent faces of {111} slip plane in each pass. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were utilized to investigate the deformed microstructure. The ultrafine grained (UFG) bulk pure Cu was fabricated by three different routes for eight passes. The TEM and XRD results revealed that dislocation density and grain size are both lower using route X after eight passes. The results of the tensile tests at RT showed that route X has better strength and elongation than routes A and BC processed samples, which is attributed to the lower dislocation density and smaller grain size with mostly high angle grain boundaries using route X. Furthermore, the fracture mechanism of ECAPed samples was discussed.

Can zinc alloys be strengthened by grain refinement? A critical evaluation of the processing of low-alloyed binary zinc alloys using ECAP

In this work, the effect of equal channel angular pressing (ECAP) on the microstructure and mechanical properties of zinc and zinc alloys with Ag, Cu, and Mn additions (0.5 at%) was investigated. Four passes of ECAP Route BC was performed at room temperature for each material. Properties of investigated materials after ECAP were compared to their coarse grained counterparts obtained via indirect hot extrusion at 300 °C. Highest strengthening effect was observed for alloy containing the Mn addition. Grain refinement in materials after ECAP was obtained, mean grain diameter is equal to 20 µm in the case of pure zinc, and less than 3.2 µm for alloys. Strain rate dependent plasticity increase was observed for all fine grained materials, with maximum elongation of 510% measured for Zn-Cu alloy after ECAP. Grain refinement did not result in increased yield and ultimate tensile strength of alloys after ECAP. In all investigated materials tensile properties after ECAP were 20 ~ 60% lower than in hot extruded samples. Based on the tensile properties, microstructure and texture analysis, the changes in the main deformation mechanisms were considered. It was presented that the crystallographic texture and grain size are the main factors affecting twinning, slip and non-slip deformation mechanisms resulting in large differences in observed mechanical properties.