Gas Quenching during Age Hardening of the Aluminium Casting Alloy AI-7Si-0.3Mg Gas Quenching during Age Hardening of the Aluminium Casting Alloy AI-7Si-0.3Mg

Gas Quenching during Age Hardening of the Aluminium Casting Alloy AI-7Si-0.3Mg

  • 期刊名字:材料热处理学报
  • 文件大小:604kb
  • 论文作者:A.Rose,O.Kessler,F.Hoffmann,H.
  • 作者单位:Stiftung Institut fur Werkstofftechnik
  • 更新时间:2020-09-15
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论文简介

TRANSACTIONS OF MATERIALS AND HEAT TREATMENTVol.25 No.PROCEEDINGS OF THE 14TH IFHTSE CONGRESSOctober 2004Gas Quenching during Age Hardening of the Aluminium Casting AlloyAl-7Si-0.3MgA. Rose, O. Kessler, F Hoffmann, H.W. ZochStifung Institut fir Werkstofftechnik, Bremen, GermanyAbstract: For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used,which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to thermal stresses.Particularly at thin-walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. Inrelation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological,ecological and economical advantages. In comparison to liquid quenching media, gas does not change its phase duringquenching. Moreover, the cleaning problem of the parts can be avoided. The quenching intensity can be adjusted by thevariable parameters gas pressure and gas speed as well as the kind of gas and thus can be adapted to the requirements of thealloy. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. Thegoal of these investigations is to clarify, if the cooling rate during gas quenching is sufficient to obtain the specific requiredstrength after age hardening of the alloy Al-7Si-0.3Mg. For this purpose different tests in high-pressure gas quenchingfacilities, gas nozzle fields and water quenching baths were performed.Key words: aluminium, precitation hardening, gas quenching, mechanical propertiesGAS QUENCHING can take place by high-pressurehand cooling should be as slow as possible to reducegas quenching in single- or multi-chamber facilities anddistortion and residual stresses of the part. In order toby gas quenching in nozzle fields.achieve both requirements, high-pressure gasAt high-pressure gas quenching in double-chamberquenching and nozzle field gas quenching offer afacilties compared to a single- .chamber system, higherpotential to reduce distortion of the parts.quenching rates are possible, because only the batchand not the chamber has to be cooled down. For this1. Experimentalreason higher temperature gradients between batch andThe used aluminium cast material of the alloyquenching gas exist, which can lead to heat- transferAl-7Si-0.3Mg (diameter: 22 mm, length: 240 mm) wascoefficients of higher than 1000 W/m2K [1-3]. Themanufactured in permanent mold casting. Threequenching intensity during high-pressure gasdifferent shapes of quenching specimen withquenching is strongly dependent on the kind of gas anddimensions of 0 19x 115 mm; 0 13x 80 mm andthe used gas pressure and velocity. From previousresearch work it is known that helium achieves07 x 45 mm have been manufactured from the castsatisfying results for numerous aluminium alloys at amaterial. The diameters were selected exemplary asgas pressure of 16bar [4]. Due to the physicalpossible wall thicknesses of aluminium cast parts.The samples were solution annealed and quenchedproperties, helium is a particularly suitable quenchingby the use of different quenching methods. Thegas, however it is more cost-intensive than nitrogen,parameters of solution annealing were equal to thewhich was used as the second quenching gas.During individual part quenching in a gas nozzlevalues of the conventional precipitation hardening forfield at ambient pressure, a gas flow welll directed onthis alloy and not varied during the investigations. Thethe part can be achieved. High gas flow rates can beapplied quenching methods were the high-pressure gasrealized by the variation of primary pressure, number,quenching, the gas quenching in a nozzle field and theshape and arrangement of the nozzles [2, 3]. With air orconventional water quenching.Solution annealing and high-pressure gas quenchingnitrogen at ambient pressure heat-transfer coefficientswere realized in a double-chamber vacuum fumaceof higher than 1000 W/m2K can be realized, which aretype IPSEN: RVTC-600x400x400 (Fig. 1). In the sidesituated in the range of the cooling efficiency of oil andview the left chamber is the heating chamber, in whichsalt baths.Quench sensitive aluminium alloys require a highthe cylindrical samples were solution annealed atcooling rate after solution annealing to avoid prematureThe solution annealing as well as the transport of the540°C for 8h.precipitation. The supersaturated solution of thebatch into the cooling chamber has taken place inalloying elements is the necessary requirement for thevacuum. After solution annealing the batch wasformation of fine intermetallic precipitates during aging,which improve the mechanical properties. On the other中国煤化工the sepate “o”"TYHCNMHGVol.25 No.5TRANSACTIONS OF MATERIALS AND HEAT TREATMENT499due to the better thermo-physical properties and thehigher pressure.600_500士War20rHeluin10Dai400. Mortle ieles Bnm?min3002001050100 150 200 250 300 350Quenching rate (K/s]Fig. 1: Scheme of a double-chamber vacuum furmaceIPSEN: RVTC-600x400x400 [Ipsen, Kleve, Germany]Fig. 3: Quenching rates of Al-7Si-0.3Mg with a sampleThe high-pressure gas quenching has taken placediameter of 7 mm for different quenching mediawith nitrogen at 10 bar and helium at 16 bar. TheQuenching in the gas nozzle field with nitrogen by acooling gas is continuously circulating in the chambervolume rate of 8000 nm3/min leads to comparableby a fan and has been re-cooled by a heat exchanger.quenching rates as the high-pressure gas quenchingwith helium at 16 bar. The maximum quenching rate inwater (20°C with agitation) achieves clearly highervalues than gas quenching. The characterstics with twomaximum quenching rates of up to 300 K/s is becauseof the Leidenfrost phenomenon.2.2 Aging BehaviourAccording to the results of previous work [4], theaging behaviour was determined and adapted by theinvestigation of hardness in dependence of the agingtime after gas quenching. Aging of the samples hastaken place without natural aging after quenching.Fig. 2: Gas nozzle field with four nozzle rows and a13specimen in the centre (0 19 mm)The individual quenching of single parts in a gas120nozzle field represents a further altermative to the; 115conventional quenching in liquid media. Solutionannealing was realized in a conventional fumace with? 10air-circulation at 540°C for 8 h. After solutionannealing, the specimens were dropped into the nozzle号90一field (Fig. 2) and were quenched with nitrogen100(8000 nm2/min) at ambient pressure.Aging time间Fig. 4: Aging behaviour of AI-7Si-0.3Mg at 160°C2. Results and DiscussionAs demonstrated in Fig. 4, the aging behaviour of2.1 Quenching Ratehe alloy Al-7Si-0.3Mg was determined forThe cooling rate was determined with thermocoupleshigh-pressure gas quenching with nitrogen at 10 bar(D 1.5 mm) in the sample centre during quenching. Inand for water quenching with agitation. The VickersFig.3 the cooling rates are pictured for the samplehardness HV10 was measured in dependence of thediameter of 7 mm. Starting from the solution annealingaging time from 6 to 48h at 1609C. Because Itemperature of 540°C, samples quenched with nitrogeninfluence on the hardness of the sample diameter wasat 10 bar achieve a maximum cooling rate of approx.determined, the hardness is averaged over the three40 K/s. Helium quenched samples at 16 bar achieve adiameters. The hardness of the nitrogen quenchedmaximum cooling rate of approx. 80 K/s. The higherquenching intensity of helium compared to nitrogen is中国煤化工lime af IDbctiquenched samples isTHCNMHG500PROCEEDINGS OF THE 14TH IFHTSB CONGRESSOctober 2004nearly constant over the aging time between 6 and 48 h.12It could be demonstrated that for the aluminium castalloy Al-7Si-0.3Mg an aging time of 16h at 160°C1心Nitrogen 10 bar。Water 20°C女Hellum 16 bar。Nozle fleldafter gas quenching leads to similar hardness values,like an aging time of 6h at 160°C after theconventional water quenching.2.3 Mechanical PropertiesAfter aging of the quenching specimens, five tensilespecimens have been manufactured from eachquenching method and each diameter corresponding toDlemetermm41620DIN 50125-Form B. From the diameters of 7, 13 andFig. 7: Total elongation to fracture of Al-7Si-0.3Mg as19 mm the tensile specimens B4 x 20 mm, B8 x 40 mma function of the diameterand B12 x 60 mm were manufactured. Aging of 160°C6h or 16h was chosen for water resp. gas quenching.The elongation of the specimens after water and gasThe mechanical properties of the alloy Al -Si7-0.3Mgquenching is compared in Fig. 7. Minimum values ofT6 are pictured in Fig 5-7.4% elongation, which are required by DIN EN 1706can be attained of the specimen diameters up to 13 mm.280The lower elongation for the 19 mm samples is not due270to the gas quenching, because the elongation afterwater quenching also does not reach 4%.? 2602502.4 Quench Factor Analysis臣240.Quench Factor Analysis (QFA) is a procedure to心-Nitrogen10ber。 Water 20°Ccorrelate the quenching rate in a part with th230 :a Nozzle fieldisothermal precipitation behaviour (“C-curve") during220the quenching process [5]. .0121416182(High quenching rates are associated with low quenchDlameter [mm]factors (< 1), minimum precipitation during quenchingFig. 5: Yield strength of Al-7Si-0.3Mg as a function ofand therefore high strength after aging. Conversely,the diameterhigher quench factors (> 1) indicate slower quenchingAfter conventional heat treatment with waterrates and lower strength values.The quench factors of the slowest quenching methodquenching as well as after gas quenching, the yield(high-pressure gas quenching with nitrogen at 10 bar,strengths exceed the minimum value of 210 MPa019 mm) and the fastest method (water quenchingaccording to DIN EN 1706, whereby the yield strengths20°C with agitation, 0 7 mm) are specified in table 1.after water and gas quenching are nearly similar.The determination of the quench factors has taken place350 Tin the temperature range between 450°C and 150°C.The yield strength of all investigated variants o330 IAl-7Si-0.3Mg T6 is situated between 90% and 99,5%of the yield strength maximally attainable.310 t是29Table. 1: Calculated quench factors270-心Nitrogen 10 bar 心Water 20°C女Hellum 16 bera Nozle fieldWaterNitrogen 10 barquenching)121416182(07mm.019mmDiemoter [mm]Fig. 6: Utimate tensile strength of Al-7Si-0.3Mg as aC-curve90%99,5%99,5% .function of the diameterfor Rp0.2of max.The tensile strengths after age hardening with water中国煤化工and gas quenching also reached the minimum value of1,0855290 MPa according to DIN EN 1706.:YHCNMHGVo1.25 No.5TRANSACTIONS OF MATERIALS AND HEAT TREATMENT5013. Summaryyield strength of all invetigated variants of the alloyThe mechanical properties of the aluminium castAl-7Si-0.3Mg T6 is situated between 90% and 99,5%of the yield strength maximally atainable.alloy Al-7Si-0.3Mg T6 after gas quenching wereSummarizing,the conditions for successful gasinvestigated. At cylindrical samples with differentquenching of the cast alloy Al-7Si-0.3Mg are given.diameters of 7 mm, 13 mm and 19 mm the coolingThe advantages of gas quenching regarding distortionrates in the core were measured after solution annealinghave to be shown in future work.for different quenching media. In comparison to theconventionally water quenching with maximumAcknowledgmentcooling rates of approx. 300 K/s, the high-pressure gasquenching with nitrogen at 10 bar and helium at 16 barThe authors wish to thank the Artbeitsgemeinschaftreached maximum cooling rates of approx. 40 K/s andindusriller Forschungsvereinigungen AiF and the80 K/s respectively. The quenching rates measured in aBundesministerum fur Wirtschaft und Arbeit BMWA forgas nozzle field with nitrogen by a volume rate offinancial support of this work (AiF-project 13959) and the8000 nm2/min are similar to the quenching ratesFachausschuss 24 der Arbeitsgemeinschaft W armebehandlungreached by using helium during the high-pressure gasund Werkstofftechnik AWT for advising the work.quenching.To determine the influence of gas quenching on theReferencesaging behaviour, the hardness of gas-_ and the1. Edenhofer B An Overview of Advances in Atmosphere andwater- quenched samples was investigated. The resultsVacuum Heat Treatment. Heat Treatment of Metals, 199,show a hardness increase after gas quenching up to an26: 1-5.aging time of 16 h at 160°C, which was chosen for the2. Hoffmann FT, Libben T and Mayr P. Innovations intensile specimens. The hardness after 16 h aging for gasQuenching Systems and Equipment: Current Status andquenching is similar to the hardness level of waterFuture Developments. Heat Treating of Metals, 999, 26(3):quenched samples aged for 6 h at 160°C.63-67For the characterisation of mechanical properties3. Winning J. Single _part quenching of serial parts with gasafter age hardening of Al-7Si-0.3Mg T6 tensile testsjets located in a mold. Harterei-Technische Mtteilungen,were performed. After gas quenching_ and adapted1993, 48(3): 199-204aging time of 16 h at 160°C comparable mechanical4. Kesser 0, Iretier A, Hoffmann F and Mayr P.properties could be achieved as after the conventionalZukunfspotential der Hochdruck -Gasabschreckung beimwater quenching and aging for 6h at 160°C. TheAusscheidungshiarten von Aluminiumlegierungen. Harterei-mechanical properties of the. samples afterTechnische Miteilungen, 2002, 57: 116-122high-pressure gas quenching with nitrogen at 10 bar,,Evancho JW and Staley JT. Kinetics of Precipitation inwith helium at 16 bar and in the nozzle field withAluminum Alloys During Continuous Cooling.nitrogen at a volume rate of 8000 nm%/min are nearlyMetallurgical Transactions, 1974, 5: 43-47similar. With exception of the elongation of the thickestsamples all quenching variants reached at least theCorresponding author. Dipl. Ing. Andrea Rose,minimum values according DIN EN 1706.In a range of the sample diameter from 7 to 19 mmEmail; rose @iwt-bremen.de,Mail addres: Stiftung Institut fuir Werkstoftechnik1o significant dependence of hardness and tensileproperties on the sample diameter could be determined.Badgasteiner Str. 3, 28359 Bremen, Germany,Moreover, quench factor analysis shows that theTel +49 (0)421 218 5427, Fax: +49 (0)421 218 5333中国煤化工MYHCNMHG

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