Mechanical properties at room temperature of an Al-Zn-Mg-Cu alloy processed by equal channel angular pressing

Tensile tests were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the mechanical properties at room temperature of overaged Al 7075-O alloy. ECAP processing was performed using route B_C at different temperatures and number of passes, i.e. different processing severity conditions. The maximum load (F_max) recorded during the last pass of each ECAP path considered in this study is a very good estimation of the processing severity. The mechanical properties were studied in terms of the balance between tensile strength and ductility. In the processed Al 7075-O alloy, the grain size was reduced down to ∼150 nm. Consequently, tensile testing at room temperature revealed a significant increase in the maximum tensile strength after ECAP with respect to the as start material. In the present study, as the processing severity increases with the number of ECAP passes or with the decrease in processing temperature, there is a consistent trend of increment in ultimate tensile strength with minor decrease in uniform plastic elongation respect to the first ECAP pass at room temperature. This is in contrast to the behaviour after more severe plastic deformation conditions, where an increase in strength together with a strong decrease in elongation would be expected.     

Processing and properties of ultrafine-grain aluminium alloy 6111 sheet

The equal channel angular processing (ECAP) technique has been applied to an automotive aluminium alloy sheet (A6111). The technique utilizes a machine that was specially designed for this purpose at Monash University. It was determined that ECAP is able to refine the grain size of the sheet, diminish the detrimental as-rolled texture components in the sheet and retain an acceptable level of bi-axial ductility such as is required during the automotive forming process. Experiments were carried out on annealed, as-received sheets that were subjected to either one or two passes through the ECAP machine. For the second ECAP pass, the sheet could be processed in the same orientation as the first pass (route A) or it could be rotated 180° about the direction of feeding (route C). It was determined that route A produced marginally improved properties compared to sheet processed via route C, and that due to the frictional heating generated during the second pass, a significant amount of recovery occurred in the sheet such that an improved combination of texture and formability resulted after two passes compared to the same sheet exposed to only a single pass.     

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.     

Three Nb single crystals processed by equal-channel angular pressing—Part II: Mesoscopic bands

Three high-purity Nb single crystals with different orientations are deformed by equal-channel angular pressing (ECAP) at room temperature for one pass. Large misorientation bands (LM-bands) are observed in two single crystals, but with different appearances. An analysis of slip activity is carried out to link the primary slip systems to the observed microstructures. It is found that the LM-bands are parallel to the primary slip systems at the beginning of deformation. Further characterization of the bands shows that their end orientations tend to have a stable configuration with respect to the simple shear plane and the direction. Based on these results and comparison with earlier works, the forming process of the LM-bands during ECAP is proposed.     

室温等径转角挤压对18Ni(C-250)马氏体时效钢微观组织和拉伸性能的影响

采用等径转角挤压（ECAP）工艺在室温下对18Ni（C-250）马氏体时效钢进行单道次冷变形.对比固溶处理试样480℃时效曲线、固溶+ECAP处理试样的460和480℃时效曲线发现,一道次ECAP变形及随后的时效处理能够使马氏体时效钢的峰值时效时间明显缩短,峰值强度提高约100 MPa.结构分析表明,ECAP态实验钢的马氏体板条宽度为100—200 nm,随后的时效过程对马氏体板条宽度影响不大,而ECAP工艺对棒状δ-Ni3Mo相析出尺寸有显著影响.统计结果表明,经4 h时效处理后.固溶+480℃时效态、固溶+ECAP+480℃,460℃时效态的δ-Ni₃Mo宽度（直径）分别为4.92,12.33和3.54 nm.此外,ECAP工艺还促使18Ni马氏体钢中δ-Ni3Mo相在时效后期加速分解,使强度迅速衰减.     

ECAP工艺对TiAl_3-P/Al复合材料组织的影响

利用透射电子显微镜和光学显微镜研究了窀温下1～8道次等通道角挤压（ECAP）3工艺对TiAl3-P／Al复合材料组织的影响。结果表明,在ECAP挤压初期Al基体中的位错密度很高,在2道次后急剧降低;组织中位错墙比例在开始也呈现升高的趋势,随着应变量的增加,逐渐向小角度晶界转变;小角度晶界的出现比位错墙晚,晶内小角度晶界的比例变化趋势也是一个先增加后降低的过程,最终转变为大角晶界。ECAP过程中,TiAl3颗粒对Al基体组织变化的作用不明显。ECAP变形有效破碎了较大尺寸的TiAl3颗粒并改善了TiAl3颗粒在Al基体中分布的均匀度。板条状TiAl3在ECAP变形中不仅发生了脆性断裂,还发生了孪生变形,与基体金属的变形相互协调,使少量大尺寸TiAl3颗粒保留下来。     

12MnNb钢的ECAP变形及组织性能研究

室温下对12MnNb钢进行ECAP变形,累积等效应变达到4.通过光学显微镜、电子拉伸机等试验仪器设备,分析研究ECAP变形试样的显微组织特征及其演变规律,以及力学性能的变化规律.结果表明,C方式ECAP变形时,1道次的组织细化和强化效果最为显著,随后道次主要增加晶粒的取向差.经ECAP变形后,强度随变形道次的增加而增加,4道次后的抗拉强度达到895 MPa,并保持了较好的塑性,伸长率达到12.4%.     

ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016. Part 1: Microstructure

The microstructure evolution of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated for different processing parameters. A number of heat treatments, including F, W, O, T4, T6 and T7, were evaluated for workability required to withstand the severe plastic deformation. It was found that this aluminium alloy had limited workability at room temperature in the F, W and T4 tempers, especially at low levels of applied back pressure, while both the O and T7 tempers can be pressed to a very high strain (～1800%) without failure. Considering that the O temper has better utility for industry because of decreased preparation time, a complete study of microstructure after ECAP processing with and without back pressure was carried out for the O temper. The thermal stability of microstructure after 16 ECAP passes with 200 MPa of back pressure was also studied.     

Tensile properties and fracture characteristics of ECAP-processed Al and Al-Cu alloys

In the present paper, billets of pure Al, and cast-homogenized Al-2 wt.%, 3 wt.%, and 5 wt.% Cu alloys were successfully processed by equal channel angular pressing (ECAP) up to 10 passes without fracture at room temperature using a die with a channel angle of 110°. Giant strains imposed on workpieces lead to extreme dislocation densities, microstructural refinement, and finally ultrafine grained materials. Tensile tests were employed to examine the fracture modes and fracture surface morphologies of the ECAP-processed Al and Al-Cu alloy samples. In particular, the effects of the number of ECAP passes and the Cu content were investigated.     

等通道转角挤压变形Mg-1.5Mn-0.3Ce镁合金的组织、织构与力学性能

采用等通道转角挤压(ECAP)工艺以Bc路径在623K温度下对Mg-1.5Mn-0.3Ce镁合金进行变形,观察显微组织与织构,测试了力学性能。显微组织分析表明,镁合金经ECAP变形晶粒尺寸明显得到细化,经6道次ECAP变形后晶粒尺寸由原轧制态的约26.1μm细化至约1.2μm,且细小的第二相粒子Mg12Ce弥散分布于晶内及晶界处;同时经ECAP变形后,原始轧制织构随变形道次的增加不断减小,并开始转变为ECAP织构,织构强度不断增强;力学性能结果表明,由于晶粒细化作用大于织构软化作用,前3道次ECAP变形镁合金强度随道次的增加不断提高,与Hall?Petch关系相符,在第3道次时其抗拉强度和屈服强度达到最大值,分别为272.2和263.7MPa;在4道次之后形成较强的非基面织构,镁合金强度下降,与Hall?Petch呈相悖关系。断口分析表明,轧制态与ECAP变形镁合金的断裂方式都是沿晶断裂,由于6道次变形镁合金晶粒细化,存在更多的韧窝并获得16.8%最大室温伸长率。     

Effects of ECAP Extrusion on the Microstructure,Mechanical Properties and Biodegradability of Mg-2Zn-xGd-O.5Zr Alloys

Effects of equal channel angular pressing (ECAP) extrusion on the microstructure,mechanical properties and biodegradability of Mg-2Zn-xGd-0.5Zr (x =0,0.5,1,2 wt％) alloys were studied in this work.Microstructure analysis,tensile test at ambient temperature,immersion test and electrochemical test in Hank's solution were carried out.The results showed that Gd could further enhance the grain refinement during the ECAP extrusion.Both Gd addition and ECAP extrusion could improve the mechanical properties of the alloys,and the extrusion played the dominant role.Minor addition of Gd (0.5-1 wt％) could obviously enhance the corrosion resistance of the alloys.To some extent,ECAP extrusion improved the corrosion resistance of the alloys due to the change of second phases distribution and the refinement of grains.Further increase in extrusion pass was detrimental to the improvement of the corrosion resistance as a result of increment of the grain boundaries.     

Microstructural development in equal-channel angular pressing using a 60° die

Billets of pure aluminum and an Al–1%Mg–0.2%Sc alloy were successfully processed using equal-channel angular pressing (ECAP) with a die having an internal channel angle of 60°. Careful inspection of the microstructures after ECAP revealed excellent agreement, at both the macroscopic and the microscopic levels, with the theoretical predictions for shearing using a 60° die. The grain sizes introduced with the 60° die were slightly smaller than with a conventional 90° die; thus, the values with these two dies were ∼1.1 and ∼1.2 μm in pure Al and ∼0.30 and ∼0.36 μm in the Al–Mg–Sc alloy, respectively. Tensile testing of the pure aluminum at room temperature revealed similar strengthening after processing using either a 60° or a 90° die. In tests conducted at 673 K, the Al–Mg–Sc alloy processed with the 60° die exhibited significantly higher elongations to failure due primarily to the larger strain imposed with this die. It is shown using orientation imaging microscopy that superplastic flow in the Al–Mg–Sc alloy produces an essentially random texture and a distribution of boundary misorientations that approximates to the theoretical distribution for an array of randomly oriented grains.     

Principles of ECAP–Conform as a continuous process for achieving grain refinement: Application to an aluminum alloy

Equal-channel angular pressing (ECAP) combined with the Conform process provides a solution for the continuous production of ultrafine-grained materials. Rods of a commercial Al-6061 alloy were processed by ECAP–Conform at room temperature for up to a total of four passes. Microstructural observations showed significant grain refinement but with elongated grains after four passes with average widths of ～150 nm and lengths of ～1.2 μm when viewed on the longitudinal planes. Microhardness measurements after a single pass revealed inhomogeneities both on the cross-sectional planes and along the rod. After processing through four passes there was reasonable homogeneity throughout the rod. Measurements of the shear strengths in two orthogonal directions perpendicular to the extrusion axis showed significant strengthening after ECAP–Conform and there was no evidence for any plastic anisotropy after processing through four passes.     

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

Ultrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.     

Effects of V and Zr Additions on Microstructures and Mechanical Properties of Nb-Ti-Al-Base Alloys

Microstructures and mechanical properties of Nb-32Ti-7Al alloys containing different V and Zr contents were investigated. The microstructures were characterized using optical microscopy and scanning electron microscopy (SEM). The alloy with V and Zr presents single phase Nb solid solution (Nbss). Tensile testing was carried out at room temperature and 1373 K. The results show that these alloys have good ductility at room temperature. The strengths at room and high temperature increase with the addition of V...     

The finite element analysis of equal channel angular pressing (ECAP) considering the strain path dependence of the work hardening of metals

It is widely known that extreme grain refinement of metals can be attained through multiple passes of equal channel angular pressing (ECAP). Such processing can follow various strain paths, which correspond to different work hardening behaviors of the material being deformed. The available finite element analyses (FEA) of multiple pass ECAP do not consider this strain path effect, and employ a single stress–effective strain curve of the material for all passes. The present paper presents a FEA of a two pass ECAP processing of copper following route C. This processing route involves the shearing of the material in the same plane as in the first pass, but in a reversed shear direction. The experimental stress–strain curve of the material, considering this strain path change, was determined through reversed torsion at various strain levels associated with the strain heterogeneity in the material caused by the first ECAP pass. The consideration of the strain path effects changed the final strain distribution in the material and led to a lower punch force in the second pass, in comparison with the results from the analysis considering a single stress–strain curve for all passes.     

奥氏体不锈钢316L在ECAP过程中的组织演化及力学性能

对奥氏体不锈钢316L进行等效应变为1.02的6道次室温等通道挤压(ECAP)试验。结果表明,在ECAP挤压过程中316L发生了剪切滑移变形和孪生变形及晶粒碎化,经过4和6道次挤压后分别得到平均晶粒尺寸约80 nm和约61 nm的均匀分布的等轴晶粒。在1道次ECAP挤压后316L的抗拉强度由674 MPa增加到984 MPa, 规定塑性延伸强度则由594 MPa增加到922 MPa,维氏显微硬度由116.33 HV增加到328.31 HV,但是塑性下降严重,可以通过600 ℃后续退火处理进行改善。     

原始晶粒尺寸对ECAP变形纯钛组织性能的影响

室温下,对923 及1023 K退火1 h所得的不同原始晶粒尺寸的工业纯钛进行ECAP变形。通过TEM、EBSD、室温拉伸和显微硬度测试研究原始晶粒尺寸对ECAP变形纯钛组织性能的影响。探讨纯钛ECAP变形孪生行为和变形机制。结果表明,退火温度越高,原始晶粒尺寸越大。1道次变形后,1023 K退火纯钛的晶粒细化效果更显著。4道次变形后,923 K退火纯钛的组织更细小均匀。随着变形道次的增加,屈服强度不断增大,1道次变形后增幅最大,约为100%,且原始晶粒尺寸越大,强度增幅越大。纯钛ECAP变形机制包括位错滑移和孪生,原始晶粒尺寸越大,孪晶数量越多。     

Investigations on workability of commercial purity aluminum processed by equal channel angular pressing

Equal channel angular pressing (ECAP) is an important process for producing ultra fine grains in bulk metallic materials by means of severe plastic deformation. Workability of metals and alloys is an important parameter as it influences the fracture resistance of the material and the ease of subsequent forming by conventional techniques. In this study, the effect of various passes and processing routes of ECAP on the workability of commercially pure aluminum has been investigated. Aluminum specimens were subjected to ECAP using 90° angle ECAP die. ECAP was carried out using two processing routes for up to three passes. Microstructure characterization and mechanical property measurements were carried out. Workability was determined by means of upsetting tests on hexagonal collar specimens machined from specimens processed by ECAP. A Cockcroft fracture criterion was used to evaluate experimental results. It is observed that processing to two passes through Route C results in enhanced mechanical properties with only a slight decrease in workability.     

Evolution of precipitates of Al-Cu alloy during equal-channel angular pressing at room temperature

The evolution of precipitates and hardness changes in Al-Cu alloys during equal-channel angular pressing（ECAP） at room temperature were investigated by hardness measurement, X-ray diffraction analysis and transmission electron microscopy. The results show that with the increase of the total equivalent strain during ECAP from 0 to 8.4, the hardness of specimens with metastable θ″ phase increases first and decreases in later period. The hardness increases successively in specimens containing metastable θ′ phase and equilibrium θ phase. It is believed that the evolutions of hardness are related to the mechanism of re-dissolution of precipitates. A critical nuclei size concept is provided to express the mechanism of such re-dissolution of three precipitates in Al-Cu alloys.