

Semisolid metal forming by novel sloping plate process
- 期刊名字:中国有色金属学会会刊(英文版)
- 文件大小:819kb
- 论文作者:GUAN Ren-guo,WANG Chao,SHANG J
- 作者单位:College of Materials and Metallurgy
- 更新时间:2020-11-10
- 下载次数:次
Available online at www.sciencedirect.com●CIENCE@oInerTransactions ofNonferrous Metals骂PSociety of ChinaScienceTrans. Nonferrous Met. Soc. China 16(2006) s1265-s1269Presswww.csu.edu.cn/ysxb/Semisolid metal forming by. novel sloping plate processGUAN Ren-guo(管仁国), WANG Chao(王超), SHANG Jian-hong(尚剑洪), XING Zhen-huan(邢振环)College of Materials and Metallurgy, Northeastern University, Shenyang 110004, ChinaReceived 28 July 2006; accepted 15 September 2006Abstract: Semisolid metal forming by a novel sloping plate process was studied. A sloping plate with wavelike surface was used toprepare semisolid alloy. Semisolid billets and slurries with good microstructures and excellent property were prepared by cooling orpreheating the sloping plate. During preparing semisolid alloy by the proposed process, the co-action of burst nucleation and dendritefragmentation causes fine spherical microstructure formation, and casting temperature, cooling strength and sloping angle are themain factors influencing the alloy microstructure. Under the current experimental conditions, in order to prepare good qualitysemisolid billets, proper casting temperature ranges of 660-690 Cfor AlMg3 alloy and 660 -680 C for AISi6Mg2 alloy aresuggested. A small car hub wheel of AISi6Mg2 alloy was thixoformed, and its pattem and inner microstructure are fine. Thereasonable technological conditions for preparing AlSi6Mg2 slurry are also proposed: the sloping plate preheating temperature is 300C, and the casting temperature is 680 C.Key words: AlMg3; AISi6Mg2; sloping plate; semisolid; forming; microstructure; propertynew convenient process for preparing semisolid alloy. It1 Introductionis also called the cooling slope method and has alreadybeen used to manufacture rheo-rolling plate of aluminumSemisolid metal forming is applied in many fieldsalloy [6- 7]. This process has some advantages:uch as automobile, aviation, electronic industry. Manyconvenience and low cost, which are favorable forstructural parts are manufactured every year in developedindustrial application. It can be used to prepare semisolidcountries [1-4]. However, its application is not verymaterials of steel, AI- and Mg- based alloys. Manyextensive in other countries. One of the reasons is thatreports have described the effect of a flat cooling plate onthe parameters, such as temperature, solid fraction, andalloy microstructures [5- 7]. In recent years, newmould preheating temperature should be controlledrheocasting is also highlighted, in this process, thestrictly during the forming process. A short process routecasting temperature is required very low, and sometimesis favorable for industrial application, so many scientiststhe sloping plate is also used for cooling the alloy. Up totry to shorten and simplify the forming process, andnow, there is no study of the use of a wavelike slopingsome near-net- shape technologies have been developedplate or of preheating the plate for preparing semisolid[2- -9]. Semisolid metal forming process includes twoalloy. In order to further improve the quality of preparedtypical forming routes. One is thixforming and the othersemisolid alloy, in this paper, the flat cooling plate wasis rheoforming. In the first forming route, the semisolidmodified to a wavelike patterm, as shown in Fig.1. Hence,illet prepared beforehand is cut and remelted to apreparing semisolid billets and slurries by cooling or thesemisolid temperature, and then it is formed at thepreheating the proposed sloping plate were studied.semisolid state. In the rheoforming, the slurry is directlyformed at the semisolid state, so it needs no remelting. A2 Experimentalsloping plate process has ever been developed to preparefine grain materials. As a new semisolid forming process,Experiments were performed using an in- houseit was proposed several years ago and is regarded as adesigned setup中国煤化工sloping plateFoundation ite: Proece(5060400) spported by the National Natural Science Foundation of ChinaCNMH G:turmee Foundationof Educational Ministry and Natrual Science Foundation of Liaoning Province, ChinaCorresponding author: GUAN Ren-guo; Tel: +86 24-83681463; E mail:uanrg@smm.ncu.edu. cns1266GUAN Ren guo, et al/Trans. Nonferrous Met. Soc. China 16(2006)Liquid alloyCoolingwaterHeating- Sloping plateelementSlopingangleSemisolid billetRhoeformingFig.,1 Schematic diagram of novel sloping plate processmade from copper was designed with a wavelike surfaceFig.2 Semisolid billetand can be cooled by the cooling water or be heated bythe heating element. The plate length was set at 640 mm.The experimental materials were self-prepared AlMg3,AlSi6Mg2 alloy, and they all have a wide semisolidtemperature range of 600 640 C and 557-615 C,respectively. The smelting temperatures for these alloyare 720, 740 and 750 C respectively, and the castingtemperatures is set at 640 -750 °C. When the meltedalloy is poured on the wavelike sloping plate, the alloy isstirred and cooled by the sloping plate and evolves tosemisolid alloy gradually, finally, it is collected by awater-cooling copper mould. Two different sloping plateconditions were studied, namely, it was either cooled orpreheated. The first method was performed to preparesemisolid billet for thixoforming, and the latter wasapplied to prepare the slury for rheoforming. AlSi6Mg2alloy was thixoformed at the semisolid state. Thetechnological parameters, such as casting temperature,sloping angle and plate preheating temperature wereoptimized by experiments. Semisolid bllts prepared bycooling the plate were remelted at semisolid temperatureand were quenched at different holding times formicrostructure observation. Semisolid billet of AlMg3100umalloy was compressed at semisolid region orGleeble1500 thermal simulation machine to analyse theFig.3 Microstructures of semisolid billets of AISi6Mg2 alloyforming property. Microstructure observation wasprepared at different casting temperatures: (a) 660 C; (b) 680performed on the Olympus microscope.3 Results and discussioncan be prepared by cooling the wavelike sloping plate.Under proper casting temperatures, the microstructures3.1 Preparation of semisolid billetsof the semisolid billets of AISi6Mg2 alloy are composedFig.2 shows the semisolid billet obtained in theof spherical grains and a small amount of rosettecopper mould. Its microstructures of AlSi6Mg2 alloystructures, and the grain size is 10- -50 um, the averageprepared at 660 C and 680 C are shown in Fig.3. Thegrain size is very fine, as shown in Fig.3. The remeltedmicrostructures of remelted semisolid billets (semisolid billets中国煤化Ipherical grainsAlSi6Mg2 alloyprepareddifferent castingand remnant 1体=stess and truetemperatures are shown in Fig.4, and those of AlMg3strain curves 0THCNMH(.1let of AlMg3alloy prepared at 660 C are shown in Fig.5.alloy at semisolid temperature region. It can be seen thatThe results show that high quality semisolid billetnot only deformation force is small, but also the curveGUAN Ren-guo, et a/Trans. Nonferrous Met. Soc. China 16(2006)s126732 r28 t610 C, 3 min24-2016H5 12615 C, 3 min80.10.20.4(6)Fig.6 True stress- true strain curves of compressing semisolidbillet of AIMg3 alloy(e =0.1s ")exponent of stress and strain is negative. The stresssharply reaches the first peak, followed by a litledecrease and a stable deformation stage. At the secondstage, semisolid alloy exhibits a good thixo-deformationproperty. Many literatures agree that this behaviorderives from spherical grain slipping and liquid100umdeformation. Slipping mainly happens along grainboundaries and in the liquids, and the deformation forceFig4 Microstructures of remnelted semisolid bilts ofincludes liquid flow resistance and grain boundaryAISi6Mg2 aloy: (a) 660 C casting, 610 C, 20 min; (b) 680 Cfriction. Because spherical grains can constantly adjustcasting, 600 C, 30 mintheir position during slipping, deformation became easyto proceed, associated with a negative curve exponent.So during compressing semisolid alloy, liquids can take alubrication function. Aggregation, welding and workhardening will not take place until the strain reaches acertain value. While conventional casting is usuallycomposed of big dendrites. Even it is preheated, it cannot evolve to spherical structures. Fig.7 shows themicrostructure of re-melted dendritic casting 0AlSi6Mg2 alloy prepared by conventional casting. Thealloy is composed of large dendritic network and liquids,and obviously different from spherical structures, whichwill easily cause work hardening and fracture, so it is not中国煤化工, 200 um0HCNMH G100 um 'Fig.5 Microtructures of re-melted semisolid billets of AIMg3alloy prepared at 660 C: (向) 620 C, 90 min; (b) 620 C,120Fig.7 Microstructure of re melted dendritic casting bllet ofAISi6Mg2 alloy芳分数据s1268GUAN Ren-guo, et al/Trans. Nonferrous Met. Soc. China 16(2006)suitable for semisolid forming.was thixoformed at the semisolid state. Fig.9 shows theproduct pattern and its inner microstructure of the sample.3.2 Preparation of semisolid slurryIt is shown that the thixoformability of the billet isThe semisolid slurries prepared at differentexcellent and: its product is also fine. The innertemperatures were collected by the cooling copper mould.microstructure of the product is mainly composed ofThe mould has a strong cooling ability, so thsmall spherical grains. The average grain size is smallersolidification microstructures of the slury in the mouldthan 60 μum.can partly exhibit the original microstructures of theprepared slurry. Fig.8 shows the microstructures of theslurry of AISi6Mg2 alloy prepared at 680 C bypreheating the sloping plate. It can be seen that the slurryis mainly composed of fine spherical or rosette grainsand remnant liquids. Especially, when the sloping plate ispreheated at 300 C, the slurry cast at 680 C has goodmicrostructure and is suitable for theoforming, as isshown in three dimensions in Fig.8. It should be declaredthat due to the cooling ability of the copper mould is notas strong as that of direct quenching by water or oil, theslurry still has a lttle time to solidify in the mould, and29 9:35AMdendrites may grow during this period. So the actualmicrostructures of the original slurry should be moreexcellent than that shown in Fig.8.100umFig.9 Product pattern and its inner microstructure3.4 Microstructure formation and influence factorsSome researchers discussed the microstructure700 umformation mechanism during preparing semisolid alloyby the flat sloping plate. It was considered that a largeFig.8 Slurry microstructure of AISi6Mg2 alloy in threequantity of crystal nuclei forming on the sloping platedimensional directions prepared by preheating sloping plate atcauses fine microstructure formation [5]. Thi300 Cpresumption can be ascribed to burst nucleationmechanismt explained in detail elsewhere [4- -5] and canThe experimental results indicate that the proposedexplain how the microstructure refines, but obviously, itprocess can prepare not only semisolid billet foris not enough to prospect the structure evolution. Therethixoforming but also the slurry for rheoforming. Forare some questions that have to be discussed. 1) Thepreparing semisolid billet, the sloping plate should bebove explanation is simple and has no experimentalcooled, while it needs preheating to prepare slurry.evidence. 2) Microstructure formation is closely relatedThrough a great deal of experiments, the appropriateto the moving patterm of the alloy. Collision and shearconditions for preparing AlSi6Mg2 alloy slurry werecaused by中国煤化工dendrite armsuggested: the preheating temperature of the slopingfragmentation,pherica grainCNMH GEplate is 300 C, and the casting temperature is 680 C.formation, so n is sollual WUidiuui not only thethermodynamic factors but also the metal flow for3.3 Thixoforming of AISi6Mg2 alloystudying microstructure formation. 3) Burst nucleationThe prepared semisolid billet of AISi6Mg2 alloymechanism can not explain the phenomenon that theGUAN Ren-guo, et al/Trans. Nonferrous Met. Soc. China 16(2006)s1269spherical structure can form even when the sloping plateplate quickly, the microstructure can not be adequatelywas preheated. Generally, burst nucleation often happensmodified. Experimental results show that the properin the case of low temperature casting. Only enough lowangle range should be 40*- -60" [5 -8].casting temperature can provide adequate undercoolingfor innumerable crystal nucleus formation. In terms of4 Conclusionsthis theory, preheated sloping plate can not meet theconditions for burst nucleation and can not lead to fine1) Semisolid billets and slurries with goodspherical structures. But the current experiments showmicrostructures have been prepared by cooling orthe contrary results. Fine spherical microstructures werepreheating the novel sloping plate. A small car hub wheelobtained by preheating the sloping plate, as shown inof AISi6Mg2 alloy was thixoformed, and its patterm andFig.8. It is considered that the coaction of burstinner microstructure are fine.nucleation in the whole melt and the dendrite fracture2) During preparation of semisolid alloy by thecauses the formation of fine spherical microstructures.proposed process, the co-action of burst nucleation andDendrite fragmentation induced by metal flow is thedendrite fragmentation causes fine sphericaldominant factor resulting in fine spherical structuremicrostructure formation, and casting temperature,formation, which was ilustrated in some related studiescooling strength and sloping angle are the main factors[8 -9].influencing the alloy microstructure.The factors influencing the semisolid alloy3) Under current experimental conditions, propermicrostructure mainly include casting temperature,casting temperature of 660 - 690 C for AlMg3 alloy andsloping angle and cooling strength. Casting temperature660- 680 C for AISi6Mg2 alloy are suggested foand cooling strength can affect alloy temperaturepreparing semisolid billets. Preparing AISi6Mg2 slurrydistribution on the sloping plate. Low castingconditions are also proposed: the sloping plate preheatingtemperature will cause a large semisolid region on thetemperature is 300 C, and the casting temperature is 680sloping plate. If the casting temperature is too low, thesemisolid region even occupies the whole plate surface,at the same time, alloy with high solid fraction has soReferenceslarge an apparent viscosity that can not flow down thesloping plate. In some cases, there remain solidification[1] FLEMMING M C. Behavior of metal and aloys in the semi-solidstate []. Metal Trans, 1991, A22: 957-969.shells on the plate. But on the contrary, if the casting[2] CHINO y, KOBATA M, IWASAKI H, MABUCHI M. Antemperature is too high, liquid region on the sloping plateinvestigation of compressive deformation behavior for AZ91 Mgis too long, the semisolid zone is very short. The shearalloy containing a small volume of liquid [J]. Acta Materialia, 2003,51.3309-1318 .strength and apparent viscosity depend on the alloyFAN Z. Semisolid metal processing []. Intermational Materialstemperature, high temperature alloy has a good flowability and flows over the sloping plate rapidly, which[4] YANG Xiang-jie. The rheological behavior for thixocasting ofcauses the effective shear time to be very short. In thissemisolid aluminum alay (A356) []. J Materi Proc Tech, 2002,130-131:569- 573.case, dendrite coarsens severely. Under the current[5] LUO Shou-jing, TIAN Wen tong, XIE Shui- sheng, MAO Wei min.experimental conditions, proper casting temperatureTechnology and applications of semi-solid forming []. The Chineseranges of 660-690 C for preparing semisolid billet ofJourmal of Nonferrous Metals, 2000, 10(6): 765 -769.AlMg3 alloy and 660- -680 C for AISi6Mg2 alloy are[6] HAGA T. Semisolid strip casting using a twin roll caster with acooling slope [0]. J of Mater Proc Tech, 2002, 130: 558-561.suggested. Both the sloping plate preheating temperature[7] HAGA T, KENTA T, MASAHIKO I. Twin roll casting aluminumis 300 C and the casting temperature is 680 C arealloy strips []. J Mater Proc Tech, 2004, 153: 42- -47.GUAN Ren-guo, LI Jun-peng, SHI Lu, WEN Jing-in.proposed for preparing AlSi6Mg2 slurry. Sloping angleManufacturing semisolid Al-Mg based alloy by sloping cooling anddetermines the component of gravity accelerationshearing [D]. Joumal of Northeastem University (Natural Science),parallel to the sloping plate and influences alloy flow2005, 26(5): 448-451. (in Chinese)velocity. Large velocity gradient between melt layers will[9] GUAN Ren-guo, WANG Shun-cheng, WEN Jing-in, LIU Xiang-hua.A continuous semisolid extending extrusion process for producingresult in strong shear action between them and causeAA2017 aluminum alloy flat bar[]. Materials Science & Technology,grain refining and spheroidization. However, if th2006, 22(6): 706- -712.sloping angle is too big, alloy will flow over the sloping(CHEN Ai-bua)中国煤化工MHCNMHG
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