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Al-3.5Cu-(0.4Mg,1.0Li)合金组织性能及In的微合金化作用研究

【作者】 潘峥嵘

【导师】 郑子樵;

【作者基本信息】 中南大学 , 材料学, 2010, 硕士

【摘要】 上世纪五十年代,Silcock等人就发现在Al-Cu合金中添加微量(~0.05wt.%)铟(In),镉(Cd),锡(Sn)等能显著促进合金时效动力学并提高峰值强度。关于In元素对Al-Cu-Mg,Al-Cu-Li等体系的微合金作用也已有一些研究,但In元素的作用机理至今没有统一的解释。因此,系统地进行三体系加铟元素的研究,并从中总结得出统一可信的作用机理,对铝合金的微合金化设计非常有指导意义。本研究设计并熔铸了Al-Cu,Al-Cu-Mg,Al-Cu-Li三组有In无In对比合金,另加Al-Cu-Li-Mg-In合金。利用硬度测试,拉伸性能测试等方法研究了In对合金力学性能的影响;示差量热扫描法(DSC),透射电镜(TEM,HREM),三维原子探针(3DAP)等微观组织观察手段系统直观地研究In对各合金组织结构的影响,对合金中出现的异常相进行初步确认,最后统一分析In在2xxx铝合金中的作用机理。主要结论如下:(1)在Al-Cu合金中加入微合金化元素In后,加快了合金的时效响应速率,175℃峰值时效所需时间不到基础合金的1/3,时效峰值强度提高了20HV,时效后期三元合金θ’相的粗化速率远远小于基础Al-Cu合金。实验不仅发现了位于刃面θ’相端头的In’粒子,还观察到了位于宽面θ’相顶角处的In’粒子,证实了In’粒子几乎全部作为0’相的非均匀形核位置。(2)Al-Cu-In时效析出序列研究表明基础合金析出序列:SSSS→GP区→θ"+θ’→θ’→θ,在加入微合金化元素In后变为:SSSS→In’→In’+θ’;这是由于In元素与空位之间的强相互作用力使得淬火态空位大部分被In原子捕获,不利于GP区的形成;而与空位结合的In’粒子活动能力增加,运动中的In’-V团簇一旦碰到铜原子团簇就会作为θ’相的形核位置。In对Al-Cu合金的微合金化作用主要通过空位实现。(3)Al-Cu-Li合金T6态主要析出T1和θ’相,加入0.5wt.%In后合金组织发生了根本性的改变:T1相数量稀少,取而代之的是一种弥散分布的方块相,同时0’相析出数量也较基础合金有增多。时效前加入6%预变形后方块相消失,而T1相数量大幅度增加,证明方块相形成与T1相呈竞争关系。(4)通过各种测试分析手段研究方块相,证实其为简单立方相,晶格常数约为0.84nm,与基体位向关系为{001)p//{001)α,<010>p//<010>α。分析结果显示该相可能为富锂的γ1或Al5Cu6Li2。(5)方块相在基体内均匀形核,而片状T1相应变能大导致其更容易在位错或其它非均匀形核位置形核长大。微合金化元素铟与空位间的强相互作用力使其在淬火态或时效早期捕捉了大量空位,从而减少了T1相形核非常关键的位错环,T1相析出动力减少,析出困难。此时T1相无力争夺方块相形核所需的Cu原子,Li原子,方块相大量析出。(6)175°CT6人工时效,Al-Cu-Mg合金的抗拉强度为345 MPa,屈服强度为258 MPa,合金主要析出相为θ’与S’,另外存在少量Ω相。时效前加入预变形Al-3.4Cu-0.34Mg合金抗拉强度提高40MPa,屈服强度提高74MPa,合金析出大量Ω相,θ’相较T6状态细小,数目稍有增加,S’相数目减少。在Al-Cu-Mg合金与Al-Cu-Mg-Ag合金中位错均可作为Ω相的非均匀形核位置,后者预变形对Ω相的抑制作用主要因为位错破坏了该相更优越的非均匀形核位置:Mg-Ag co-clusters,而前者的促进作用是从没有适合的非均匀形核位置到位错作为非均匀形核处。(7)在Al-Cu-Mg合金中添加0.5wt.%In,合金抗拉强度增加25MPa,屈服强度增加50MPa;在时效早期,与二元Al-Cu合金中一样,In抑制GPB区形成,促进S’与θ’相析出。与Al-Cu-Li-In合金不同的是,再添加0.4%Mg元素,四元合金中的方块相不再出现,T1相此时为五元合金的最主要的析出强化相,合金强度比四元合金高80MPa。这是因为Mg元素的添加如预变形位错一样会为T1相提供众多的非均匀形核位置,降低该相的形核驱动力,争夺方块相形成所需的Cu,Li原子。同样In元素在五元合金中会促进S’与θ’相析出。(8)In元素在2xxx系铝合金中的作用可概括为:一方面由于In与溶质原子的强相互作用,In粒子作为富Cu相(θ’)与富Mg相(S’)的非均匀形核质点,促进其析出;另一方面通过减少T1相非均匀形核位置间接促进方块相的析出。

【Abstract】 Silcock had found that trace addition (~0.05 wt.%) of In, Cd or Sn in Al-Cu alloys could dramatically accelerate the precipitation kinetics, and increase the peak strength.There were also some researches about Indium effecting on Al-Cu-Mg, Al-Cu-Li, yet no unified mechanism was established up to date.Thus, systematically and comprehensively works on the microalloying effects of In to 2xxx series Aluminums are aspired to a reliable mechanism, and instructional significance for alloy design.Three groups of Al-Cu, Al-Cu-Mg and Al-Cu-Li alloys with-or-without In, and another Al-Cu-Li-Mg-In alloy were prepared. Micro Vickers Hardness, ambient tensile properties measurements were used to study the effects on mechanical properties.Microstructure evolution, precipitate identification were carried out by Differential Scanning Calorimetry (DSC), Transmission Electron Microscope (TEM and high resolution TEM) and three dimensional atom probe (3DAP). Finally this paper comes to the following conclusions:(1)Indium additions speed aging response rate comparing to In-free Al-Cu alloy, the time needed to peak hardness is even less than 1/3 of base alloy aging at 175℃;peak hardness is 20HV higher; theθ’ precipitates coarse much slower at the late stage of aging. In’were also observed at one corner of platelets having their broad faces in the plane of view other than the traditional heads of edge-on platelets positions, proving that almost all In’could act as the heterogeneous nucleation sites forθ’.(2)The base alloy precipitates process:SSSS→GP. zones→θ"+θ’→θ’→θ, has transformed to:SSSS→In’→In’+θ’with 0.5 wt.% Indium additions. Most quenched-in vacancies were seized by Indium atoms due to the strong interaction between Indium atoms and vacancies, thus depressed the formation of GP. zones; the vacancies-seized In’ could move freely, the moving In’-V clusters would act as the heterogeneous nucleation sites for ;θ’once meeting to Cu atoms. In general, Indium affects Al-Cu alloy mainly through vacancies. (3) T1 and 0’phase dominate the Al-Cu-Li microstructure in T6 temper, an earth-shaking change take place after adding 0.5% Indium:In place of the{111}αplate T1 phase, the significant occurrence of a novel disperse cubic phase was detected, meantimeθ’was also found a little increasing. Inversely, the cubic phase was then substituted by T1 in T8 temper (6% predeformation+155℃).(4)Further study of the cubic phase shows that it belongs to the cubic system, lattice constant a≈8.4A, following the orientation with the aluminum matrix:{001}p//{001}α,<100>p//<100>α.3DAP and Simulation for HREM analysis indicate it to be Li-richγ1(Al4Cu9) orχ(Al5Cu6Li2).(5)The cubic phase tend to nucleated in the matrix homogenously, while plate-like T1 nucleated easier in dislocations heterogeneously because of it’s big volumetric energy. Just like in Al-Cu-In alloy, most quenched-in vacancies, which would collapsed into loops, were seized by Indium atoms. T1 phase precipitation become hard without these loops acting as heterogeneous nucleation sites.The cubic phases then precipitate fluently without T1 competitive for Cu and Li atoms.(6) The tensile strength and yield strength of Al-Cu-Mg alloy is 345 MPa and 258 MPa, respectively, withθ’and S’dominating the microstructure, and a little amount ofΩ.6% prior aging deformation give 40MPa and 74MPa rise to US and YS, respectively, there are large amount ofΩphase,θ’become finer and a little more, while S’decrease. There comes to a conclusion:dislocations could act as the heterogeneous nucleation sites in both Al-Cu-Mg and Al-Cu-Mg-Ag alloy. The depressing phenomenon ofΩin the latter one is just because deformation disturbed the superior sites:Mg-Ag co-clusters and the acceleration can’t compensate it’s lose.While in the former one, the heterogeneous sites rise from none to some dislocations, thus it shows a promotion ofΩ.(7) 0.5% Indium addition increase the US 25MPa and YS 50MPa, suppress GPB zones formation, like GP zones depressed in Al-Cu alloy, and make S’andθ’in a greater amount. In quinary Al-Cu-Li-Mg-In alloy, T1 phase again substitute cubic phase, the strength is 80MPa higher. Mg atoms will nucleate T1 just like dislocations do, consuming Cu, Li atoms which are required by cubic phase.S’andθ’are still increased.(8) The microalloying effects of Indium in 2xxx series could be summarised as:accelerateθ’and S’for the strong interaction between Indium and Cu and Mg; on the other hand, reduce heteregeneous nucleation sites of T1 phase, making cubic phase precipitate swimmingly.

【关键词】 2xxx系铝合金In微合金化T1相θ’相S’相方块相
【Key words】 2xxx aluminummicroalloyingIndiumT1cubic phase
  • 【网络出版投稿人】 中南大学
  • 【网络出版年期】2011年 03期
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