稀土元素Gd对Al-Si-Mg铸造合金微观组织和力学性能的影响
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摘要
为了系统地研究稀土Gd对铸造Al-Si-Mg(A357)合金组织和性能的影响,采用OM,SEM,EPMA,XRD,DSC,TEM及拉伸实验等方法对不同Gd含量A357合金进行研究。结果表明:Gd的添加可以细化A357合金的晶粒并减小二次枝晶间距。此外,Gd可以有效地细化合金中的共晶硅,但是对片状共晶硅的形貌影响不大。晶粒和共晶硅的细化及二次枝晶间距的减小使添加Gd后的A357合金的力学性能有了显著的提高。其中,A357-0.5Gd(质量分数/%)合金热处理态抗拉强度为355MPa,相对于未添加Gd元素的A357合金提高了37MPa。当Gd质量分数为1.0%时,尽管组织得到进一步细化,但是大量粗大Al_2Si_2Gd第二相的形成导致了合金力学性能的下降。同时对Gd的细化机制进行探究,结合TEM分析结果可以推断,Gd变质处理后共晶硅上的孪晶密度并不足以引起共晶硅形貌的转变,使得Gd变质效果较弱。而Gd对共晶硅的细化作用可能与Gd增加成分过冷以及形成纳米相阻碍共晶硅生长有关。
To systematically investigate the effect of rare earth element Gd on microstructure and mechanical properties of Al-Si-Mg(A357) cast alloy, A357 alloys with different Gd additions were investigated by OM, SEM, EPMA, XRD, DSC, TEM and tensile test. The results show that the addition of Gd can refine the grain and secondary dendrite arm spacing of the alloy. Besides, Gd refines eutectic Si, instead of transforming its morphology. The mechanical properties are improved by Gd addition due to obvious refinement of the grain and eutectic Si, the reduction of secondary dendrite arm spacing. For the A357-0.5 Gd(mass fraction/%) alloy, the ultimate tensile strength(UTS) is 355 MPa, which is 37 MPa higher than that of the alloy without Gd. However, when increasing the Gd mass fraction to 1.0%, the formation of a high number of coarse Al_2Si_2 Gd results in the decrease of the mechanical properties of the alloy.The refinement mechanism of Gd was investigated.Combined with the TEM observation, it can be inferred that the Gd addition produces fewer twins but some nanosized particles within eutectic Si. The density of twins is not high enough to cause the morphology transition of eutectic Si. The refinement effect of Gd on eutectic Si may be attributed to the increase of constitutional overcooling and the formation of nanosized particles, inhibiting the growth of eutectic Si during solidification.
To systematically investigate the effect of rare earth element Gd on microstructure and mechanical properties of Al-Si-Mg(A357) cast alloy, A357 alloys with different Gd additions were investigated by OM, SEM, EPMA, XRD, DSC, TEM and tensile test. The results show that the addition of Gd can refine the grain and secondary dendrite arm spacing of the alloy. Besides, Gd refines eutectic Si, instead of transforming its morphology. The mechanical properties are improved by Gd addition due to obvious refinement of the grain and eutectic Si, the reduction of secondary dendrite arm spacing. For the A357-0.5 Gd(mass fraction/%) alloy, the ultimate tensile strength(UTS) is 355 MPa, which is 37 MPa higher than that of the alloy without Gd. However, when increasing the Gd mass fraction to 1.0%, the formation of a high number of coarse Al_2Si_2 Gd results in the decrease of the mechanical properties of the alloy.The refinement mechanism of Gd was investigated.Combined with the TEM observation, it can be inferred that the Gd addition produces fewer twins but some nanosized particles within eutectic Si. The density of twins is not high enough to cause the morphology transition of eutectic Si. The refinement effect of Gd on eutectic Si may be attributed to the increase of constitutional overcooling and the formation of nanosized particles, inhibiting the growth of eutectic Si during solidification.
引文
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[2] TSAI Y C,CHOU C Y,LEE S L,et al.Effect of trace Ce addition on the microstructures and mechanical properties of A356 (Al-7Si-0.35Mg) aluminum alloys[J].Journal of Alloys and Compounds,2009,487(1/2):157-162.
[3] EL-SEBAIE O,SAMUEL A M,SAMUEL F H,et al.The effects of mischmetal,cooling rate and heat treatment on the hardness of A319.1,A356.2 and A413.1 Al-Si casting alloys[J].Materials Science and Engineering:A,2008,486(1/2):241-252.
[4] KUMAR G S V,MURTY B S,CHAKRABORTY M.Develop-ment of Al-Ti-C grain refiners and study of their grain refining efficiency on Al and Al-7Si alloy[J].Journal of Alloys and Compounds,2005,396(1/2):143-150.
[5] 徐建辉,龙文元,方立高.钠盐变质铝硅合金中的共晶硅相[J].航空材料学报,2000,20(1):18-21.XU J H,LONG W Y,FANG L G.Eutectic Si-phase in Al-Si alloy modified by Na-salt[J].Journal of Aeronautical Materials,2000,20(1):18-21.
[6] SRIRANGAM P,CHATTOPADHYAY S,BHATTACHARYA A,et al.Probing the local atomic structure of Sr-modified Al-Si alloys [J].Acta Materialia,2014,65:185-193.
[7] HEGDE S,PRABHU K N.Modification of eutectic silicon in Al-Si alloys[J].Journal of Materials Science,2008,43(9):3009-3027.
[8] 曾松岩,张虎,李庆春.Sr变质对Al-Si合金共晶硅中孪晶产生的影响 [J].材料工程,1993(5):13-15.ZENG S Y,ZHANG H,LI Q C.The effect of modification of Sr on the formation of twins in eutectic Si of Al-Si alloy[J].Journal of Materials Engineering,1993(5):13-15.
[9] EMADI D,GRUZLESKI J E,TOGURI J M.The effect of Na and Sr modification on surface tension and volumetric shrinkage of A356 alloy and their influence on porosity formation[J].Metallurgical and Materials Transactions B,1993,24(6):1055-1063.
[10] 胡心平,谢玲,张娟.混合 RE 不同冷速下对 Al12Si 硅相的变质效果研究[J].稀有金属材料与工程,2012,41(增刊2):431-434.HU X P,XIE L,ZHANG J.Modification effects on silicon phase in Al12Si alloys with misch metal under different cooling rates[J].Rare Metal Materials and Engineering,2012,41(Suppl 2):431-434.
[11] WAN D Q.Si phase morphology and mechanical properties of ZL107 Al alloy improved by La modification and heat treatment[J].Transactions of Nonferrous Metals Society of China,2012,22(5):1051-1054.
[12] 刘福才,崔春翔,董天顺,等.熔体快淬Al-Ce合金变质对ZL108组织和性能的影响[J].稀有金属材料与工程,2009,38(1):312-315.LIU F C,CUI C X,DONG T S,et al.Influence of melt rapid solidification Al-Ce alloy modification on microstructure and mechanical property of ZL108[J].Rare Metal Materials and Engineering,2009,38(1):312-315.
[13] LI J H,WANG X D,LUDWIG T H,et al.Modification of eutectic Si in Al-Si alloys with Eu addition[J].Acta Materialia,2015,84:153-163.
[14] WAN D Q.In-situ fibrous Si phase formation in as-cast Al-7Si hypoeutectic alloy under the combined effects of rapid solidification and modification[J].Rare Metal Materials and Engineering,2010,39(6):216-218.
[15] SHI Z M,WANG Q,ZHAO G,et al.Effects of erbium modification on the microstructure and mechanical properties of A356 aluminum alloys[J].Materials Science and Engineering:A,2015,626:102-107.
[16] LI B,WANG H W,JIE J C,et al.Microstructure evolution and modification mechanism of the ytterbium modified Al-7.5%Si-0.45%Mg alloys[J].Journal of Alloys and Compounds,2011,509(7):3387-3392.
[17] 唐定骧,刘余九.稀土金属材料[M].北京:冶金工业出版社,2011.TANG D X,LIU Y J.Rare metal materials[M].Beijing:Metallurgical Industry Press,2011.
[18] LU S Z,HELLAWELL A.The mechanism of silicon modifi-cation in aluminum-silicon alloys:impurity induced twinning [J].Metallurgical and Materials Transactions A,1987,18(10):1721-1733.
[19] KANG H S,YOON W Y,KIM K H,et al.Effective parameter for the selection of modifying agent for Al-Si alloy[J].Materials Science and Engineering:A,2007,449(12):334-337.
[20] 张启运,郑朝贵,韩万书.稀土元素对Al-Si共晶合金的变质作用[J].金属学报,1981,17(2):130-136.ZHANG Q Y,ZHENG C G,HAN W S.The modification of Al-Si eutectic alloys with rare-earth elements[J].Acta Metallurgica Sinica,1981,17(2):130-136.
[21] 刘政,谌庆春.Gd对半固态A356合金初生α相的细化机制[J].特种铸造及有色合金,2013,33(9):793-796.LIU Z,CHEN Q C.Refining mechanism of rare earth Gd on primary α phase in semisolid A356 alloy[J].Special Casting & Nonferrous Alloys,2013,33(9):793-796.
[22] 刘政,谌庆春,郭颂,等.A356-RE合金中稀土铝化合物/初生α相界面二维错配度的计算及验证[J].稀有金属材料与工程,2015,44(4):859-865.LIU Z,CHEN Q C,GUO S,et al.Calculation of planar disregistries between compounds of rare earth-Al and primary α phase in A356-RE alloy and its verification[J].Rare Metal Materials and Engineering,2015,44(4):859-865.
[23] 史玉亭,王强,赵鸽.钆和钬变质对铝-硅-镁合金铸态组织的影响[J].稀土,2013,34(2):47-51.SHI Y T,WANG Q,ZHAO G.Effects of Gd and Ho modification on microstructure of Al-Si-Mg cast aluminum alloy[J].Chinese Rare Earths,2013,34(2):47-51.
[24] SHI Z M,WANG Q,SHI Y T,et al.Microstructure and mechanical properties of Gd-modified A356 aluminum alloys[J].Journal of Rare Earths,2015,33(9):1004-1009.
[25] 刘剑军.Al-Si-Gd(0-33.33at%)三元系合金相图的室温等温截面及相结构之研究[J].上海第二工业大学学报,1991(2):53-58.LIU J J.Isothermal section of Al-Si-Gd(0-33.33at%) at room temperature and the structure of ternary compounds[J].Journal of Shanghai Second Polytechnic University,1991(2):53-58.
[26] BRAMFITT B L.The effect of carbide and nitride additions on the heterogeneous nucleation behavior of liquid iron[J].Metallurgical Transactions,1970,1(7):1987-1995.
[27] 李豹.AlSi7Mg合金共晶硅变质规律及其微观机制[D].哈尔滨:哈尔滨工业大学,2011.LI B.Modification evolution of eutectic silicon in Al7SiMg alloy and micro-mechanism[D].Harbin:Harbin Institute of Techno-logy,2011.
[28] HO C R,CANTOR B.Heterogeneous nucleation of solidification of Si in Al-Si and Al-Si-P alloys[J].Materials Science and Engineering:A,1995,173(1/2):37-40.
[29] FLOOD S C,HUNT J D.Modification of Al-Si eutectic alloys with Na[J].Metal Science,1981,15(7):287-294.
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