帶輪的沖壓工藝與模具設(shè)計(jì)【三維UG工件圖】
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Materials Science and Engineering A 493 (2008) 130140Scale up and application of equal-channel angular extrusionfor the electronics and aerospace industriesStephane Ferrassea, V.M. Segalb, Frank Alforda,Janine Kardokusa, Susan StrothersaaHoneywell Electronic Materials, 15128 E. Euclid Avenue, Spokane, WA 99216, USAbEPM, 11228 Lemen Rd-Suite A, Whitmore Lake, MI 48198, USAReceived 9 February 2007; received in revised form 12 April 2007; accepted 25 April 2007AbstractTwo areas are critical to promote equal-channel angular extrusion beyond the stage of a laboratory curiosity: (i) tool/processing design and scaleup;(ii)developmentofnewsubmicrometer-grainedproducts.BothgoalsarepursuedatHoneywell.Thefirstcaseisthesuccessfulcommercializationof ECAE for the production of sputtering targets from single phase alloys in the electronic industry. Blank dimensions are significantly larger thanthose reported in the literature. Other described applications are targeted to the increase of tensile strength, high-cycle fatigue and toughness inmedium-to-heavily alloyed Al materials used in aerospace. In these alloys, the optimal properties can be reached with better understanding of theinterplay between plastic deformation and precipitation mechanisms. 2007 Elsevier B.V. All rights reserved.Keywords: ECAE; Submicrocrystalline materials; Flat products; Sputtering; Fatigue; Toughness1. IntroductionFor the past 10 years, severe plastic deformation (SPD) tech-niques have been the focus of intense research because theycan produce metallic materials with submicrometer grain sizesranging from 50 to 500nm 1,2. One promising SPD methodis equal-channel angular extrusion (ECAE) 3. It can pro-duce bulk pieces of submicrocrystalline materials induced byintense plastic straining by simple shear. Till now, researchhas made steady progress on the characterization of the tex-ture,structureandmechanicalpropertiesofsubmicrocrystallinematerials and the effect of main ECAE parameters and post-deformation annealing 429. However, despite the abundantliterature, problems of engineering and commercialization werediscussed only recently 3032 and very few practical appli-cations are reported. The overwhelming majority of researcherscontinue to work with small long cylindrical or square billets.A few attempts to scale up the billet size are known 3235 butthere is no report of successful commercialization.This paper reviews the efforts in die design, scale up andcommercialization of ECAE for flat billets conducted at Honey-Corresponding author. Tel.: +1 509 2522118; fax: +1 509 2528743.E-mail address: Stephane.F (S. Ferrasse).well 36,37. Selected examples show that this technology canpenetrate a market in one or more of the following ways: (i)provide an overall cost reduction versus the standard manufac-turing or design, (ii) provide superior product performance and(iii)answeranunmetneed.OneexampleinvolvesthefirstECAEproductswithsubmicrometerormicrometergrainsizesforhighpurity Al, Cu and Ti sputtering targets used in the fabricationof logic and memory components. Two other examples concernmedium and heavily alloyed Al materials used in aerospace andtransportation. Special attention is paid to the effects of ECAEon the structures and properties of single phase Cu and, espe-cially, Al when the amount of alloying composition increasesfrom a very low level (as in sputtering targets) to a higher level(as in commercial alloys for aerospace). It is argued that newmechanisms and, therefore, additional opportunities for appli-cations arise as the alloying level increases because of the newinterplay between plastic deformation and phase transformationduring a thermo-mechanical treatment.2. Process scale up and designHoneywells focus has been, historically, the ECAE of flatproducts, which was first introduced in Ref. 38. In that case(Fig. 1), a typical billet shape is characterized by thickness a,0921-5093/$ see front matter 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.msea.2007.04.133李瑜S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140131width b and length c with c, b?a 30,3840. Usually, dimen-sions c and b are equal to allow the use of the same tool formulti-passprocessing(with90rotationbetweenpasses).Theprocessing characteristics of one pass ECAE for flat and longbilletsaresimilar.However,usually,forflatbillets,theaxisofthepermissible90billetrotationisperpendiculartotheextrusionaxis (axis Z in Fig. 1) whereas, for long products, it is parallel totheextrusionaxis.Duringscaleup,twoconsiderationscomeintoplay:(i)tooldesign,and(ii)optimizationofECAEdeformationmode.2.1. Tool designFrom a production perspective, the major drivers for tooldesign include safety, cost and productivity.2.1.1. Safety and costThe biggest issue is the potential breakage/buckling of thepunch if conventional low cost tool steels are used. For a givenmaterial, the punch pressure p1must be significantly less thanthe yield strength of the punch material. The punch pressure is30p12k=p2k+mF2A(1)wherepisthepressureattheexitoffirstchannel,kisthematerialshearflowstress,mistheplasticfrictioncoefficient,Fistheareaof stationary die walls and A is the billet cross-sectional area.For the tool itself, the maximum pressures on the punch p1and channel wall nact at the end of the entrance channel. Asshown in 30, for a low friction case (m0.25)p12k 1 +m(cb + ca)ba(2)n2km(cb + ca)ba(3)Therefore, the preferable ways for reducing die/punch pres-sures are (i) to limit the ratio c/a610 and (ii) to minimizefriction in both channels. Two corresponding strategies are thechoice of effective lubricants and movable channel walls. A sig-nificant advantage of flat ECAE billets versus long billets interms of equipment and design is that movable walls along theFig. 1. Principle of the ECAE technique for flat billets.entrancechannelarenotneededforflatproducts.Thisisbecausea?b for flat products whereas a=b for long products. There-fore p1and nare lower for flat products and formulae (2) and(3) can be approximately reduced top12k 1 +mca(4)n2kmca(5)A movable bottom wall at the exit channel is recommendedhowever for both flat and long products because lubricant isatomically removed along the bottom of exit channel.2.1.2. ProductivityThe two important factors are processing speed and billetejection. For reasonably ductile materials, the processing speedisnotalimitingfactorandmaybesufficientlyhigh(510mm/s).The billet ejection presents a more complex problem, especiallyfor long cylindrical billets. In the case of flat billets, a mov-able bottom wall of the exit channel operated by an additionalhydraulic cylinder provides an effective and simple solution.2.2. Optimization of ECAETherearetwolevelsofoptimizationforsingleandmulti-passECAE.2.2.1. Single passA level of simple shear straining should be as high as possi-ble for an effective refinement of microstructures 11. This ismostly controlled by the conditions of friction and the chan-nel geometry which has in turn two critical parameters: (i)the angle 2 between the two channels and (ii) the shape ofthe channel intersection. Usually, channels are performed withsharp (no radius) or round corner intersections. Slip line solu-tions 18,30,41 and finite element modeling 43 reveal theexistence of a fan-like deformation zone in cases of noticeablefrictionand/orroundcornerchannels.Insuchcases,simpleshearis redistributed along three different directions 41. Moreovereven for frictionless conditions and sharp corners, a dead metalzone exists at the channel corner for 2 90. Therefore, toolangle 2 =90, sharp corner channels and near frictionless con-ditions are the optimum characteristics to realize the effectivesimple shear of =2 along one direction. The most importantproblem is the elimination of the friction along the bottom walloftheoutletchannelwherehighcompressivepressureandinten-sive slip act simultaneously. With the movable bottom wall,the fan angle can be minimized as shown by slip line analy-sis 30,41. The Honeywell dies operate under those conditionsowing to advanced die design and lubricants.2.2.2. Multi-pass processingThe two major parameters are the deformation route (asequence of billet rotation after each pass) and the total numberof passes (accumulated strains). For flat billets, the definition ofthe four fundamental routes A, B (or BA), C and D (or Bc) 38132S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140Fig. 2. Production ECAE die with 4000tonnes press capacity.remains similar to long billets except for the axis of rotation asdescribed earlier.2.3. Scale-up effortsBased on the above considerations, Honeywell started thescale-up efforts of ECAE in 1997 with the construction of thefirst production die. Today, several large-scale die sets for a fewstandard billet sizes are in normal operation for Al, Cu and,occasionally, pure Ti using presses with 1000 and 4000tonnescapacity (Fig. 2). Most of these dies have been in use on aweekly basis for 6 years. The mass of the largest ECAE bil-let is 32.7kg for Al alloys 36 and, most recently, 110kg forCu and Cu alloys. As a comparison, the largest reported ECAEprocessed Al billet obtained with a die channel angle of 10534,35hasamassof6.7kgwhereasthemassofthemosttypical10mm10mm60mmAlbilletusedforresearchis0.016kg.Thereisnoreportofascale-upattemptoftheECAEprocessforCu.Importantly,theeffectsofECAEonmicrostructures,textureand properties have been verified at the various industrial scalesas will be shown in the Section 2. In the authors view, the expe-rience attained on the production floor demonstrates that ECAEis scalable and opens up the era of its industrialization.3. ECAE of sputtering targetsECAE is particularly interesting for high-purity materialsbecause grain refinement is the only available mechanism thateffectively enhances strength and retains good ductility (Hall-Petch hardening) whereas the other hardening mechanismsare either ineffective (precipitation and solution hardening) ordetrimental to ductility (dislocation hardening). For specificmaterialsandcrystalstructures,ECAEcanalsoactivateandcon-trol texture hardening. This approach remains valid for dopedor low-alloyed materials such as high-purity Cu, Ti and Almaterials with or without doping and low alloying used in themanufacture of sputtering targets. In this section, we use abbre-viations of the electronic industry where 6N and 5N5 puritymeans 99.9999% and 99.9995% purity, respectively.3.1. Microstructures of targets after ECAEMulti-pass ECAE of high-purity materials results in a fewmain effects: (i) development of either submicrocrystalline orveryfine(usually20?m)microstructuresindependentlyofthestarting grain size; (ii) enhanced structure uniformity; (iii) tex-ture control via the number of passes, route and post-processingheat treatment 39; (iv) elimination of large phases and pre-cipitates by solution heat treatment before ECAE. Grain size,uniformityandabsenceoflargeparticlesarethemostinfluentialfor sputtering performance. The critical factor for choosing par-ticular structure is the thermal stability during target fabricationor service. Here are some examples:Fig. 3. EBSD of ECAE processed 6N Cu with a grain size of 5?m: (a) grain size and texture map; (b) distribution of boundary misorientation angles.S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140133Fig. 4. Grain size evolution as a function of accumulated strains for ECAE or rolling alone of 5N5 (99.9995%) Al and 5N5 (99.9995%) Al+30ppm Si.(i) For high-purity materials with low melting temperatures(Tm1?m) grain size as a function of annealing temperature (1h) for ECAE six pass route D or rolling alone of 5N5 Al, 6N Cu and 6NCu+0.5% Sn. For 5N5 Al+30ppm Si, only the ECAE case is displayed.134S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140Fig. 6. Evolution of the recrystallization temperature (after 1h heat treatment)as a function of the amount and nature of a few dopants/alloying elements forECAE 6N Cu.equiaxial grain morphology, low mobility of twin bound-aries,structureuniformityandnearrandomtexture(Fig.3).Fig. 5 compares the evolution of the grain size versus theannealing time for both ECAE and standard 5N5 Al, 6NCu 37 and Cu alloys. For example, for ECAE 6N Cu,full static recrystallization occurs at 225C for 1h andresultsinauniformgrainsizeof58?m,whichgrowsonlyslightly to 15?m after additional annealing at 300C, 1h.The structure remains uniform without abnormal grains.In comparison, the grain size of 6N Cu after standard pro-cessing (85% rolling) increases from 35 up to 65?m afterannealing at 225C, 1h and 300C, 1h, respectively.(ii) For high purity Al and Cu, doping (defined here as up to2000ppm of a foreign element) is a powerful technique torefine further the fine micrometer ECAE grain sizes and/orimprove the thermal stability of both the fine microme-ter and submicrometer ECAE microstructures to elevatedtemperatures. A notable example is 5N5 Al doped with2030ppm Si. The size of ultra fine grains decreases from60 to 25?m and is far smaller than the as rolled structureafter a similar strain level (Fig. 4). The simple shear defor-mation mode of ECAE and non monotonic loading pathof route D(Bc) are believed to play a critical role in thisremarkable difference in grain size between the as ECAEandasrolledstructures41,42.Fig.6displaysthedramaticinfluence of the nature and quantity of dopants on temper-atures of static recrystallization after six ECAE passes viaroute D for submicrocrystalline 6N Cu. A near logarith-mic dependence is obtained. In particular, Ag, Sn and Tihave such a strong influence that a doping level is enoughto produce submicron-grained structures that are stable forsputtering.(iii) In pure Al and Cu with a sufficient amount of dopingoralloyingcomponents,submicrocrystallinestructuresarestable for sputtering applications during a target life. Anexample of a submicrometer-grained structure in ECAEprocessed Al0.5Cu alloy is shown in Fig. 7 36,37. Trans-mission electron microscopy (TEM) reveals a uniform andFig.7. TEMofmicrostructureofmonolithicECAEAl0.5Cutargetwith0.5?mgrain size.equiaxed submicrometer grain size of 0.30.5?m (Fig. 7)that corresponds to a refinement factor of 100 comparedto conventional processes. Very fine dispersions (less than50nm) of second phase material are present.3.2. Sputtering performanceECAE targets exhibit superior sputtering performance (fordetails see Refs. 36,37) that includes: (i) reduction of arcing;(ii) low level of particles and splat defects on the wafer; (iii)improved film thickness uniformity and consistent film perfor-mance; (iv) improved step coverage due to the superior beamcollimation of the submicron-grained structures.3.3. Mechanical properties and target designFig. 8 shows data on yield strength (YS) and ultimate tensilestrength (UTS) for ECAE processed 6N Cu and doped 6N Cu,5N5 Al0.5Cu and 4N5 Ni at room temperature. Compared toconventional processing YS and UTS is from 4 to 10 times and2to3timeshigher,respectively.TheeffectismostsignificantonYS, which is a critical property for target applications becauseit governs the onset of permanent plastic deformation and mayresult in target warping during sputtering. In the case of 6N Cu,dopinghasanoticeablestrengtheningeffectinadditiontoECAE(Fig. 8). The tensile elongation also remains high: above 20%forsubmicrocrystallineAl0.5Cuand3540%forsubmicrocrys-talline 6N Cu. The high strength of pure submicron-grainedmaterialspermitstheuseofamonolithicdesign,wheretheentiretargetisamono-block(Fig.9).Thisisauniquedesigncomparedto that of traditional targets, which consists of a target materialbonded or soldered to a backing plate made from strong materi-als like Al 6061 or CuCr. The main advantages of a monolithicdesign are An increased target lifetime up to 50% in comparison withdiffusionbondeddesignsbecausesputteringisnolongerlim-ited by the diffusion bond line 36,37. A direct consequenceis the increase in throughput (number of processed wafersper target) and lifetime of other chamber components and thereduction of downtime.S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140135Fig. 8. UTS and YS for the submicrocrystalline (ECAE) and conventional sputtering target microstructures of 5N5 Al0.5Cu, 6N Cu, 6N Cu0.15Ag, 6N Cu0.2Snand 4N5 Ni. Simplified manufacturing by elimination of the costly, multi-step and risky diffusion bonding operation. Due to the highductility, deformation by conventional means (rolling, draw-ing)canbeperformedafterECAEtoobtainthefinalproducts.Recent developments of ECAE Al and Cu targets are thehollow cathode magnetron (HCM) target. These targetsrequireforminganECAEblankintoacomplexcup-likeshapewith a final diameter of about 393.7mm, a height of 381mmand a thickness of 12.725.4mm.4. ECAE of Al alloys for aerospace and transportationAs alloying goes up, the number of second phases (eithersoluble or insoluble) increases, which results in two otherpotentially available strengthening mechanisms: (i) solutionand (ii) precipitation hardening. The effects of ECAE thermo-mechanicalprocessingonmicrostructureandpropertiesbecomemorevariedandmoredifficulttopredict.Fornon-heat-treatablealloys, grain refinement during ECAE remains the dominantstrengthening mechanism 2,12. More interesting cases canbe developed for heat-treatable alloys. For a medium level ofalloying, precipitation hardening is usually as powerful as grainrefinement and the goal is to optimize processing to combineboth these effects 13,2024. One example described below isECAE of Al 2618 alloy, which is used in turbocharger compo-nents for the aerospace and transportation industries. For heavyalloying,theeffectofmicrostructurerefinementbyECAEonthematerial strength can become minor compared to other harden-ing mechanisms. Nonetheless, other important characteristicssuch as toughness 2529 can be greatly enhanced by usingECAE as shown below for a spray-cast Al alloy for landing gearcomponents.4.1. ECAE of Al 2618 for turbocharger components4.1.1. ProcessingThree cases of the pre-ECAE material conditions were stud-ied:(I) Solutionizing at 529C, 24h with immediate waterquenching to dissolve all soluble phases.Fig. 9. (a) Flat 300mm monolithic ECAE Al0.5Cu target with AMAT design and overall dimensions diameter 523.8mm25.4mm thickness sputtered up to2738kWh (+52% life increase); (b) non-flat and non-sputtered 300mm monolithic ECAE 6N Cu with HCM Novellus design and overall dimensions diameter393.7mm25.4mm thickness381mm height.136S. Ferrasse et al. / Materials Science and Engineering A 493 (2008) 130140Table 1Mechanical properties of A2618 after ECAE process for three initial conditions (cases I, II, and III) and comparison with standard propertiesConditionProcessYS (MPa)UTS (MPa)Elongation (%)CaseIOne ECAE pass (as deformed)499.9544.713One ECAE pass+150C, 10h558.558614Two ECAE pass (as deformed)56660111Four ECAE pass (as deformed)407.5477.1314Case IIFour ECAE pass (as deformed)393.7455.812Case IIIFour ECAE pass (as deformed)312.3332.410StandardAl 2618 T61 (at 25C)370.3435.110Al 2618 T31 (at 25C)248.2358.517Al 2618 O (at 25C)75.8172.418(II) Solutionizing at 526C, 20h followed by quenching inboiling water and peak aging at 200C, 20h in air. ThisT6conditionprovidedanequilibriumsolidsolutionmatrixwith 0.050.1?m CuMgAl2precipitates and hardnessHB=115.(III) Solutionizingat529C,24hfollowedbywaterquenchingand overaging at 385C, 4h in air to provide large precip-itates, low strength and hardness HB=47.5 (O condition).In this case, the strengthening effect of ECAE alone canbe evaluated.In all cases, ECAE was conducted for one, two, four and sixpasses at die temperatures between 150 and 200C via routeD (rotation +90) as was described in Section 3. The effect ofpost-ECAE isochronal annealing was also studied.4.1.2. Tensile propertiesTable 1 shows the effect of ECAE on the hardness, yieldstrength, ultimate tensile strength and elongation. The majorf
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