摘要
7xxx系铝合金具有高的比强度和刚度、易加工、较好的抗应力腐蚀能力等特性,在飞机关键部件上得以应用。本文的研究内容作为863高技术研究项目研究内容的一部分,主要以7075-T651铝合金为基础来探究热处理后7xxx系高强铝合金的疲劳断裂性能,附带进行拉伸断裂性能的测试,并使用扫描电子显微镜观察其断口形貌,分析疲劳断裂机理;同时为了改善7xxx系铝合金的断裂性能,又以7055铝合金为研究对象,通过添加稀土Y,采用坩埚炉熔炼,借助金相分析、X—射线衍射分析、扫描电子显微镜分析以及力学性能测试等分析手段,来研究稀土Y对于7055合金微观组织和力学性能的影响机理。为日后本课题后序7xxx系铝合金的断裂研究打好基础。
7075-T651合金断裂性能的研究表明:合金非轧向拉伸断裂有着准解理和韧窝断裂的混合特征。疲劳试验的S-N曲线没有水平部分,只是随着应力的降低,循环周次不断增大,估算的疲劳极限为223MPa。疲劳裂纹都萌生于合金表面或内部夹杂缺陷处,裂纹扩展中产生大量疲劳辉纹,同时观察到轮胎花样,疲劳台阶,二次裂纹等其它一些疲劳特征。疲劳瞬断区都具有静拉伸断口的微观特征,表现为脆性和延性的混合断裂。合金当中的析出相粒子对合金的疲劳性能都产生一定影响。具体而言,粗大的析出相粒子可能会导致裂纹萌生,而细小弥散分布的微小析出相和对合金的疲劳性能的有着积极的影响。
7055合金微合金化结果表明:将稀土元素Y加入7055合金当中可以形成YAl_3与Al_6Cu_6Y等化合物相。Y加入到7055合金后虽然牺牲较少的拉伸强度和硬度,却大幅提高了合金的韧性。同时Y的添加显著地细化合金在铸态下的显微组织,抑制了粗大共晶组织形成,使二次枝晶间距减小,原来骨骼状的第二相变得细化并在一定Y含量下出现球化。因此使部分难以消除的共晶组织在后续热处理过程中得以完全消除,减少了裂纹的扩展源,对7055合金的综合性能提升具有一定现实意义。
7xxx series aluminum alloys used in key components of airplane are characterized by high specific strength and stiffness,excellent machining and SCC property.This paper reports on the tensile and fatigue fracture performances of 7075 alloy in the T651 temper were studied.The rapture mechanisms of 7075 alloy were concluded on the observation of fractography using scanning microscope.Aiming at promoting fatigue performance of 7xxx series alloy,the effects of addition of yttrium on as-cast microstructure and mechanical property of 7055 aluminum alloy were investigated using optical microscope,scanning electron microscope,X-ray diffraction,etc.
The tensile fracture face of 7075-T651 alloy in its short-transverse direction displayed a mix of quasi-cleavage crack and dimple crack.There is no horizontal part on the S-N curve of 7075-T651 and the cycle numbers just increased with the reduction of stress amplitude.The fatigue crack initiations derived from the surface or inner contaminant,and lots of fatigue fringe were generated in the age of crack propagation, meanwhile other fatigue characters such as tyre patterns,fatigue sidestep and secondary crack also can be found on the fracture face.The fatigue failure region showing mixed failure mode of brittle and ductile rapture was similar with the character of tensile fracture.The precipitated phase particles of 7075 alloy have some effects on its fatigue performance.Specifically,the crack initiation resulted from the massive precipitated phase particles,while dispersion of small precipitated phase particles have positive effects on fatigue performance.
The micro-alloying research showed that the Al_6Cu_6Y and YAl_3 resulting from addition of yttrium to the 7055 alloy is distributed at the grain boundary.And the 7055 alloy obtains wide-range rate of growth in its toughness with little loss in its tensile strength and hardness with the addition of yttrium,while the as-cast microstructure of 7055 aluminum alloy was fined remarkably and the formation of massive eutectic was restrained.The addition of yttrium narrowed the spacing of second arborescent crystals and skeleton-shape second phase of the 7055 alloy were sphericized and fined,so the elimination of the hard-to-remove eutectic texture reduce the crack initiation field in the subsequent heat treatment.It makes practical sense in promoting the mechanical performance of 7055 alloy.
引文
[1]Warren A S.Developments and challenges for aluminum-a Boeing perspective[C].Proceedings of the 9th International Conference on Aluminum Alloys,2004.24
[2]Lukasak D A,Hart R M.Strong aluminum alloy shave airframe weight[J].Advanced Materials &Processes,1991,10:46-49
[3]Srivatsan T S.Microstructure,tensile deformation and fracture behavior of aluminum alloy 7150[J].Journal of Materials Sci.1992,27(17):4772.
[4]陈昌麒,超高强度铝合金的发展[J].中国有色金属学报,2002(3):22-27
[5]李红英,董显娟.高强高韧铝合金研究现状及展望[J].湖南有色金属,2002,18(5):33-34
[6]弗得良捷尔,吴学译.高强度变形铝合金[M].上海科技出版社,1963
[7]李海.Ag、Sc合金化及热处理工艺对7055铝合金的微观组织与性能影响的研究[D].中南大学博士论文,2005,5
[8]Soeidel M O.In:Proc of the 6th Inter Cpnfon on Light Metals.London,1981,67
[9]KUKASAK D A,HART R M.Aluminum alloy development efforts for compression dominated structure of aircraft[J].Light Metal Age.1991,49(5):11-15
[10]刘昌斌,夏长清,戴晓元.高强高韧铝合金的研究现状及发展趋势[J].矿冶工程,2003,10
[11]林学丰.高强高韧铝合金国内外发展趋势[J].铝加工,1999,52-55
[12]黄继武,尹志民等.均匀化处理对7055合金硬度和电导率的影响[J].稀有金属,2004,2.
[13]徐正.7005/7075中高强度铝合金的应用研究[D].南京理工大学工程硕士论文,2007,5
[14]Ringer S P,Hono K.Microstructural evolution and age hardening in aluminum alloy:atom probe filed- ion microscopy and transmission electron microscope studies[J].Materials Characterization,2000,44:101-104
[15]Lenevai J.Precipitation and strengthening in aluminum alloy[J].Mater Sci Forum,1996,217-222:45-56
[16]Auld J H,Cousland Smck.The structure of the metastable η' phases in aluminum-zinc-magnesium alloy[J].Journal of the Australian Institute of Metals,1974,19:194-201
[17]D Thevenet,The effect of precipitation on portevin-Le Chatelier effect in an Al-Zn-Mg-Cu alloys[J].Mater.Sci.Eng,1999,A266:175.
[18]Loffler H,Kovacs I,Lendvai J.Decomposition processes in Al-Zn-Mg Alloys[J].J Mat Sci,1983,18:2215-2240
[19]李春梅.Al-Zn-Mg-Cu系超高强铝合金热处理工艺的研究[D].西南师范大学硕士论文,2005,4
[20]Adler P N,Delasi R.Influence of microstructure on the mechanical properties and stress corrosion susceptibility of 7075 aluminum alloy[J].Metallurgical Transactions,1972,3(9):3191-3200.
[21]曾渝,超高强.AI-Zn-Mg-Cu-Zr合金组织与性能研究[D].中南大学博士论文,2004,11
[22]Seamans G M,Alani R,Swann P R.Pre-exposure embritlement and stress carrosion failure in Al-Zn-Mg alloys[J].Corrosion Science,1976,16,443-456
[23]T.Ogura,S.Hirosawa,T.Sato.Quantitative Characterization of Precipatate Free Zones in Al-Zn-Mg(-Ag) Alloys by Microchemical Analysis and Nanoindentation Measurement[J].Sci.Tech.Adv.Mater.2004,5:491-496
[24]T.S.Srivatsan.Microstructure,tensile properties and fracture behavior of aluminum alloy 7150[J].Mater.Sci,1992,27(7):4772-4778
[25]王仁智,周培远.疲劳失效分析[M].北京:机械工业出版社,1987
[26]李雪.2124铝合金板材断裂韧性和高周疲劳特性研究[D].中南大学硕士论文,2007,11
[27]陈传尧.疲劳与断裂[M].武汉:华中科技大学出版社,2002
[28]高镇同,熊峻江.疲劳/断裂可靠性研究现状与展望[J].机械强度,1995,17(3):62-73
[29]郑治沙,王中光.疲劳研究的历史回顾[J].材料科学与工程,1993,11(1):56-63
[30]Suresh R A.材料的疲劳.王中光.北京:国防工业出版社,1993.
[31]Mughrabi H.Microscope mechanisms of metal fatigue.In:Haasen P,Gerold V,Kostorz G[J].The strength of metals and alloys,Vol.3.Oxford:PergamonPress,1980:1615-1639.
[32]王弘.材料疲劳裂纹扩展和断裂定量规律的研究[D].西北工业大学博士论文,2002,3
[33]Suresh S.Fatigue of Materials[M].第2版.王中光等译.北京:国防工业出版社,1999
[34]束德林.工程材料力学性能[M].北京:机械工业出版社,2003
[35]曹大力,石忠宁,杨少华等.稀土在铝及铝合金中的作用[J].稀土,2006,27(5):88-92
[36]胡鹏飞,张伟.稀土在铝合金中的应用[J].河南科技,2006,1:35-36
[37]周晓霞,张仁元,刘银岇.稀土元素在铝合金中的作用和应用[J].材料与表面处理,2003,6:18-20
[38]李隆盛.铸造合金及熔炼[M].北京:机械工业出版社,1989
[39]马永庆,关德林,杨道正,等.稀土铝合金综合变质处理的研究[J].材料工程,1991,(6):27-29
[40]王经涛,王海波.微量稀土对铝合金枝晶间距的影响[J].稀土,1996,17(2):1-5
[41]Bian X F.A master alloy for spheriodisation of needle-form iron compounds in aluminum alloy [J].Cast Metals,1993,6(3):257.
[42]胡晓菊,高洪吾,李长茂.微量元素对Mg-Al-Zn系合金铸态组织及性能的影响[J].上海有色金属,2004,9.
[43]黄崇祺,陈秀琴,丁关森.用稀土优化综合处理技术生产的电工铝导体[J].电线电缆,1992,(5):60-65.
[44]Ling E P,Taubenblat W.High conductivity copper and aluminum alloys[M].New York:Edward Arnold Limited Press,1984.31-50.
[45]Katsuhisa N,Sadao I.Heat resistant and highly electronconductive aluminum alloys[P].Japan Patent:7001540,1970-01-15.
[46]唐定骧,王成辉.我国独具特色的稀土电工铝和铝稀土合金[J].四川有色金属,2003,(2):19-24
[47]侯显智,刘显东,冯正海等.7055铝合金的热处理与微观组织研究[J].轻合金加工技术,2007,35(7):47-49
[48]李红英,董显娟.高强高韧铝合金研究现状及展望[J].湖南有色金属,2002,10:33-36.
[49]刘晓涛,崔建忠.Al-Zn-Mg-Cu系超高强铝合金的研究进展[J].材料导报,2005,3:47-51.
[50]张新梅,郝丽华,蒋大鸣等.Al-Mg-Si合金拉伸断口研究[J].材料工程,1996,5:35.
[51]桂立丰.机械工程材料测试手册(力学篇)[M].辽宁:辽宁科学技术出版社,2001
[52]BEACHEM.C.D,Microscope fatigue fracture surface features in 2024-T3 aluminum and the influence of crack propagation angle upon their formation[J].Tran.ASM,1967,60:324-343
[53]崔约贤,王长利.金属断口分析[M].哈尔滨:哈尔滨工业出版社,1998
[54]布鲁克斯著,谢斐娟等译.工程材料的失效分析[M].北京:机械工业出版社,2003.
[55]钟群鹏,赵子华.断口学[M].北京:高等教育出版社,2006
[56]Neumann P.Coarse slip model of fatigue[J].Aeta.Metallurgica,1969,17:1219-1225.
[57]杨友.AZ91系列镁合金的高周疲劳行为[D].吉林大学博士学位论文,2007,4
[58]刘文辉.基于位错滑移的铝合金断裂行为的研究[D].中南大学博士论文,2008,4
[59]李雪.2124铝合金板材断裂韧性和高周疲劳特性研究[D].中南大学硕士论文,2007,11
[60]段玉波,唐剑,曾苏民.阶段均匀化处理对7A04合金均匀化程度和过烧温度的影响[J].合金与热处理,2003,3:22
[61]Hahn G.T,Rosen field A R.Metallurgical factors affecting fracture toughness of Aluminum alloys[J].Metal.Trans.A,1975,6A:653.
[62]王武,舒光翼,何德坪.稀土元素在Al-Mg合金中的分布及对结晶组织的影响[J].中国稀土学报.1990,8(3):252-256.
[63]阮海琼.稀土元素铒(Er)在Al-Zn-Mg合金中的作用[D].北京工业大学硕士学位论文,2004,5
[64]王经涛,崔建忠;马龙翔.元素之间的交互作用强度及其在铸态稀土铝合金中的应用[J].西安冶金建筑学院学报.1993,25(4):445-449
[65]王经涛,王海波,许育中等.铸态稀土铝合金中元素分布与枝晶偏析[J].轻合金加工技术,1995,23(5):35
[66]B.H.邦达列夫,B.H.那帕尔科夫,B.H.塔拉雷什金著.王永海,张新明,高革译.变形铝合金的细化处理[M].冶金工业出版社,1988.8
[67]Kishi.Y,Hirose.Y,Tsukuda.I et al.,Relationship between fracture toughness and second phase particles in extruded high strength Al-Zn-Mg-Cu-La system alloys with high stress corrosion cracking resistance[J].Journal of the Society of Materials Science,1994,43(495):1571-1577
[68]王庆良,王大庆.稀土钇对AlZnMgCu合金组织及性能的影响[J].中国矿业大学学报,1999.7
