Mechanical Behavior and Microstructural Development of 6063-T1 Aluminum Alloy Processed by Equal-Channel Angular Pressing (ECAP): Pass Number Influence

Equal-channel angular pressing (ECAP) is a very interesting method for modifying the microstructure in producing ultrafine-grained materials and nanomaterials. It consists mainly of pressing test samples through a die containing two channels that are equal in cross section and intersect at a certain angle. As a result of pressing, the sample theoretically deforms by simple shear and retains the same cross-sectional area to allow repeat pressing for several cycles. A 6063-T1 aluminum alloy was investigated in this study. The specimens were processed for up to nine passes (one, three, six, and nine ECAP passes, respectively) using a die channel angle of 90°. After ECAP, the samples were cut from each specimen and prepared for metallographic analysis and mechanical testing. The microstructures of the ECAP treated and as-received material were investigated using both optical microscopy and scanning electron microscopy. All samples (ECAP processed and as-received) were mechanically investigated in compression tests. Ultimate compressive strength, yield strength, and compression modulus were obtained. Also, all ECAP processed specimens were investigated for microhardness and compared with the as-received material.     

等效应变量对等径角挤压的2A12铝合金力学性能的影响

采用内角为105°、外角为45°及内角为90°、外角为30°两套模具对2A12铝合金进行了等径角挤压实验,研究了等效应变量对其力学性能的影响。结果表明,等径角挤压可以显著改善材料的力学性能,而且等效应变量的大小与材料的力学性能密切相关。经过等径角挤压,材料所经受的累积等效应变量达到4时,材料力学性能的提高达到饱和,而且材料所经受的单次等效剪切应变量越大,材料力学性能的提高越迅速,改善越明显。     

Thermomechanical coupling simulation and experimental study in the isothermal ECAP processing of Ti-6Al-4V alloy

The thermomechanical coupling simulation of the isothermal equal channel angular pressing(ECAP) of Ti-6Al-4V alloy was conducted.The effect of processing parameters,ECAP pass number and the residual billet on the effective strain,stress and temperature distribution was investigated.Based on the coupling simulation results,it is found that the shear factor,ram speed,deformation temperature,channel intersection angle and residual billet significantly affect the ECAP deformation behaviors.Meanwhile,the experimental study of the isothermal ECAP process of Ti-6Al-4V alloy using route C,in which the repeated rotation angle around the longitudinal billet axis before reinsertion in the die was 180°,were conducted at a deformation temperature of 750°C,a ram speed of 0.3 mm·s-1,an outer arc of curvature of 60° and a channel intersection angle of 120°.Furthermore,a large amount of recrystallization occurs and some prior α phase grains grow in the post-ECAP process of Ti-6Al-4V alloy.The yield strength of post-ECAP Ti-6Al-4V alloy increases compared with that of as-received Ti-6Al-4V alloy.     

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 （Ф） of the die channel. When Ф 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 Ф is 135°, as extrusion pass increases, the weak texture forms on the scope of deviation from rotated cube （ψ=0°, θ=0°, Ф=45°＋15°） and develops to the ψ=45° fiber mainly including rotated cube. When Ф is 120°, the texture is ψ=45° fiber mainly including rotated cube that is maintained constant as extrusion pass increases.     

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.     

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.     

Effects of die angle on microstructures and mechanical properties of AZ31 magnesium alloy processed by equal channel angular pressing

1　INTRODUCTIONMagnesiumalloysarethelightestmetallicstruc turalmaterialsandhencetheyprovidegreatpotentialintheweightsavingofautomotiveandaerospacecomponents ,materialhandlingequipment ,portabletoolsandevensportinggoods[1,2 ] .Duetotheirhexago nalclose packed (HCP)crystalstructure ,magnesiumalloysperform poorformabilityandlimitedductilityatroomtemperature ,thustheirproductsaremainlyfabricatedbycasting ,inparticular ,die casting ,andtheapplicationsofwroughtmagnesiumalloysarelim ited .Nowit…     

ECAP with back pressure for optimum strength and ductility in aluminium alloy 6016. Part 2: Mechanical properties and texture

The simultaneous increase in strength and ductility of aluminium alloy 6016 processed by equal channel angular pressing (ECAP) was investigated. A complete study of microstructure, texture and mechanical properties after ECAP processing with and without back pressure was carried out for the O temper. The simultaneous increase in strength and ductility of AA6016-O with number of ECAP passes was explained by the use of back pressure during ECAP. A maximum ductility of ～100% was obtained at the temperature of 200 °C and strain rate of 10^?4 s^?1, which is a significant improvement on the ductility exhibited by AA6016 (～89%) after a conventional thermomechanical treatment at a much higher temperature of 500 °C. The mechanical behaviour was interpreted in the context of the textures developed in the material. A significant amount of texture rotation due to applied back pressure was found.     

Simulation of Aluminum Powder in Tube Compaction Using Equal Channel Angular Extrusion

Aluminum powder in tube compaction with a 25 mm front plug through equal channel angular extrusion (ECAE) at room temperature was modeled using the finite element analysis package ABAQUS. The Gurson model was used in modeling this process. 2-D simulations in a 90° angle die showed better consolidation of powder near the inner edge of the die than the outer edge after one pass of ECAE but almost full densification occurs after two passes. The effect of hydrostatic pressure on densification of the powder was investigated by using two plugs varying in length dimension. The results obtained from the simulations were also compared with experiments conducted to compact aluminum powder with mean particle diameter of 45 μm. Optical microscopy, microhardness test, and density measurements confirmed the simulations. The simulations were extended to powder compaction in a 60° and 120° angle die. It was found that one pass of ECAE is sufficient to consolidate the aluminum powder completely and uniformly in a 60° angle die, whereas the material is still porous in a 120° angle die.     

Microstructure,Texture and Mechanical Properties of Titanium Grade 2 Processed by ECAP (Route C)

In the present work the properties of titanium grade 2 after ECAP processing with original route and regimes (route C, channel angle \(\varPhi\)?=?120°, deformation temperature 300 °C, number of passes up to 8) were examined. Texture development and microstructure parameters after ECAP processing and after recrystallization were determined using electron back scatter diffraction and analysed. A significant increase of the mechanical strength accompanied by some increase of ductility was observed in the deformed samples. The kernel average misorientation and average grain orientation spread were strongly increased after deformation, which confirms the material refinement and fragmentation. The proportion of low angle boundaries increased after four ECAP passes, but after four consecutive passes high angle grain boundaries became predominant. No deformation twins were observed after four and eight ECAP passes. The material recrystallized after deformation retained a fine grain microstructure. The textures of deformed and recrystallized samples were determined. It was found that texture after 8 passes is more homogeneous that that after 4 passes, which partly explains higher ductility of this first sample.     

等通道球形转角挤压过程中工业纯铝的微观组织演变与力学性能

突破传统ECAP变形全过程通道等截面思路,提出一种耦合剪切应变和正应变于一体的新型等通道球形转角挤压(equal channel angular extrusion with spherical cavity,ECAE-SC)工艺。在自行研制的模具上对工业纯铝进行室温单道次ECAE-SC挤压实验,采用OM、EBSD和TEM等技术手段,研究了ECAE-SC变形过程中工业纯铝微观组织的演变规律,并测试了变形后试样的显微硬度。结果表明,在ECAE-SC工艺剧烈简单剪切变形诱导下,工业纯铝仅需1道次挤压变形即可获得等轴、细小、均匀的超细晶组织,平均晶粒尺寸约为400 nm;工业纯铝室温ECAE-SC变形以位错滑移为主并伴有不完全连续动态再结晶,其微观组织经历了剪切带→位错胞→小角度亚晶→大角度等轴晶粒等动态演化过程。1道次ECAE-SC变形后,工业纯铝组织以{110}001高斯织构为主,同时存在部分{111}112铜型织构;材料显微硬度值大幅提升,由初始289.4 MPa提高到565.3 MPa,增幅高达95.33%,且分布均匀性良好。     

Thermomechanicai coupling simulation and experimental study in the isothermal ECAP processing of Ti-6Al-4V alloy

The thermomechanical coupling simulation of the isothermal equal channel angular pressing(ECAP)of Ti-6Al-4V alloy was conducted.The effect of processing parameters,ECAP pass number and the residual billet on the effective strain,stress and temperature distribution was investigated.Based on the coupling simulation results,it is found that the shear factor,ram speed,deformation temperature,channel intersection angle and residual billet significantly affect the ECAP deformation behaviors.Meanwhile,the experimental study of the isothermal ECAP process of Ti-6Al-4V alloy using route C,in which the repeated rotation angle around the longitudinal billet axis before reinsertion in channel intersection angle of 120°.Furthermore,a large amount of recrystallization occurs and some prior α phase grains grow in the post-ECAP process of Ti-6Al-4V alloy.The yield strength of post-ECAP Ti-6Al-4V alloy increases compared with that of as-received Ti-6Al-4V alloy.     

工业纯钛在120°模具中的多道次ECAP室温变形组织与性能

在室温,采用通道夹角为120°的变形模具对工业纯钛(Commemial Pure Titanium,CP-Ti)以Bc方式实施四道次ECAP(EqualChannel Angular Pressing)挤压变形,成功获得表面光滑无裂纹的变形试样.文中主要研究了工业纯钛在室温下进行ECAP多道次变形的组织结构演变,并测试了变形试样的力学性能.微观结构显示工业纯钛在室温下进行多道次ECAP变形时,只在前两道次产生了大量的变形孪晶,且随道次增加变形孪晶逐渐消失.最终获得的试样晶粒平均尺寸由最初的约28μm细化到约250 nm,试样断裂强度和显微硬度分别提高到773和2486 MPa,而试样仍保持较好的延伸率(可达16.8%).     

Static mechanical properties and ductility of biomedical ultrafine-grained commercially pure titanium produced by ECAP process

Equal channel angular pressing (ECAP) is one of the most effective processes to produce ultra-fine grain (UFG) and nanocrystalline (NC) materials. Because the commercially pure titanium exhibits excellent biocompatibility properties, it has a significant potential to be utilized as an implant material. The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material. This defect can be removed by applying the ECAP process on the pure titanium. In this work, the commercially pure titanium Grade 2 (CP-Ti of Grade 2) was pressed at room temperature by the ECAP process via a channel angle of 135° for 3 passes. The microstructural analysis and mechanical tests such as tensile test, hardness test, three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through 3 passes. The microstructural evolution reveals that by applying the ECAP process, coarse grain (CG) structure develops to UFG/NC structure. Moreover, the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths, bending strength, hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.     

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.     

Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing

In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route B_C up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable η′ phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode.     

Large-scale manufacturing of aluminum alloy plate extruded from subsize billet by new porthole-equal channel angular processing technique

To manufacture plate by the combination of equal channel angular processing (ECAP) and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing (P-ECAP), was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3–5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 °C. The effective strain exhibited ascending trend in the corner of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.     

Translations: BISITS—British Industrial and Scientific International Translation Service

This paper described the mechanical properties and corrosion behaviour of new designed Mg–Gd–Nd–Zn–Zr alloy processed by equal channel angular pressing (ECAP) at 375°C. An attractive phenomenon was observed. Both strength and ductility of ultrafine grained Mg–Gd–Nd–Zn–Zr alloy were improved after multipass ECAP. The microstructure of the alloys became much finer and more homogeneous with increasing ECAP passes. The yield strength, ultimate tensile strength and elongation of the alloys under eight-pass ECAP process were over 223?MPa, 270?MPa and 36% respectively, showing desirable mechanical properties of equal channel angular pressed Mg–Gd–Nd–Zn–Zr alloy. The equal channel angular pressed alloy displayed a lower corrosion resistance immersed in Hank's solution due to the crystalline defects as well as the galvanic corrosion induced by precipitation of ultrafine β phase particles.     

Ultrafine-grained pure Ti recycled by equal channel angular pressing with high strength and good ductility

Machining chips of commercially pure Ti (ASTM grade 2) were consolidated into full density by equal channel angular pressing (ECAP) with an average grain size as low as 0.8 μm, yield strength up to 650 MPa, and ductility of ～16%. Effect of recycling condition on the microstructure and mechanical properties were investigated in terms of ECAP temperature, number of passes and chemical composition. Using electron backscatter diffraction it is evident that continuous dynamic recrystallization (however, which is purely a phenomenological terminology) plays a significant role in grain (with misorientation ≥15°) formation, whilst benefitting from high stacking fault energy, this continuous conversion of subgrain (<15°) into grain can be essentially considered as an extended recovery with a substantial presence of low angle grain boundaries in the recycled Ti. The Hall–Petch relationship is adapted to explain the strengthening of the recycled Ti. Additionally, using scanning electron microscopy fractography, the ductility was analyzed by a modified Griffith criterion. Last, superior energy efficiency of ECAP reduces environmental impact when comparing to conventional melting/casting. ECAP develops an innovative solid-state process for improving the recycling value of waste Ti.     

等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。