發(fā)布時間：2018-04-14 19:37

  本文選題：鋁合金 + 連續(xù)大塑性變形��； 參考：《湖南大學》2015年碩士論文

【摘要】：大塑性變形可以使金屬或合金獲得極細甚至納米晶組織,從而大幅度提高金屬材料的綜合性能。本文利用硬度、拉伸試驗以及電導率測量等性能檢測手段,以及光學顯微鏡(OM)、電子背散射衍射分析技術(EBSD)、X射線衍射儀(XRD)、掃描電鏡(SEM)、透射電子顯微(TEM)等微觀組織分析手段,對Al-0.74Fe-0.23Cu合金分別在低速(5rpm)和高速(21rpm)重復連續(xù)擠壓過程中組織與性能的演變規(guī)律進行研究,探討鋁合金重復連續(xù)擠壓實現(xiàn)連續(xù)大塑性變形工藝方法的可能性及其效果。主要研究結果如下:1.水平連鑄(HCC)Al-0.74Fe-0.23Cu合金橫截面、縱截面的組織在晶粒大小、晶粒形貌、晶體取向分布方面不同。在水平連續(xù)鑄造凝固過程中產(chǎn)生Al Fe,Al Fe Si以及Al Si析出相。2.在低速重復連續(xù)擠壓過程中,連續(xù)擠壓可以提高水平連鑄合金強度和塑性,但隨著擠壓道次的增加,合金的強度和硬度逐漸降低而延伸增加,表現(xiàn)出一種明顯的加工軟化現(xiàn)象。3.在低速重復連續(xù)擠壓過程中,第一道次連續(xù)擠壓后,Al-0.74Fe-0.23Cu合金形成明顯的擠壓纖維組織,表明合金軟化機制以回復為主,但在后續(xù)的重復連續(xù)擠壓過程中,發(fā)現(xiàn)了應變累積誘發(fā)連續(xù)動態(tài)再結晶的發(fā)生。此外,在低速重復連續(xù)擠壓過程中,第一道次連續(xù)擠壓可以誘導一些相溶解和誘導Al7Cu2Fe新相的動態(tài)析出,并且明顯改變原始組織的晶粒取向和共晶相的分布狀態(tài)。進一步的連續(xù)擠壓對合金組織的晶粒取向分布影響不大,但隨著擠壓道次的增加,析出相進一步破碎細化、分布變得越來越均勻。4.與低速重復連續(xù)擠壓相比,高速重復連續(xù)擠壓時合金的力學性能演化規(guī)律與低速重復連續(xù)擠壓相似,但高速重復連續(xù)擠壓明顯加速了合金組織和力學性能演化的進程。5.高速重復連續(xù)擠壓加速了合金中沉淀相的均勻分布行為,但沒有加速沉淀相的破碎行為。第一道次連續(xù)擠壓過程后合金中出現(xiàn)了部分晶粒細化,表明再結晶發(fā)生。隨著擠壓道次的增加,再結晶過程不斷加速,因此合金的強度低于低速重復連續(xù)擠壓的強度。此外,發(fā)現(xiàn)在高速重復連續(xù)擠壓的開始階段,合金中出現(xiàn)了剪切帶,因此可以認為新的細晶粒的產(chǎn)生可能與高速連續(xù)擠壓時形成的剪切帶有關。
[Abstract]:Large plastic deformation can make metal or alloy obtain very fine or even nanocrystalline structure, thus greatly improve the comprehensive properties of metal materials.In this paper, hardness, tensile test and electrical conductivity measurement were used, as well as optical microscope, electron backscatter diffraction analysis technique, X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and so on.The evolution law of microstructure and properties of Al-0.74Fe-0.23Cu alloy during repeated continuous extrusion at low speed (5rpm) and high speed (21rpm) were studied, and the possibility and effect of repeated continuous extrusion of aluminum alloy to realize continuous large plastic deformation were discussed.The main results are as follows: 1.In horizontal continuous casting, the microstructure of HCCU Al-0.74Fe-0.23Cu alloy is different in grain size, grain morphology and crystal orientation distribution.During the solidification process of horizontal continuous casting, Al Fe Fe Si and Al Si precipitated phases. 2.In the process of low speed repeated continuous extrusion, continuous extrusion can improve the strength and plasticity of the horizontal continuous casting alloy, but with the increase of extrusion pass, the strength and hardness of the alloy gradually decrease and increase, showing an obvious softening phenomenon of machining.In the low speed repeated continuous extrusion process, the Al-0.74Fe-0.23Cu alloy formed obvious extrusion fiber structure after the first continuous extrusion, which indicated that the softening mechanism of the alloy was mainly the recovery mechanism, but in the subsequent repeated continuous extrusion process,Continuous dynamic recrystallization induced by strain accumulation was found.In addition, during the low speed repeated continuous extrusion, the first continuous extrusion can induce the dissolution of some phases and induce the dynamic precipitation of the new phase of Al7Cu2Fe, and obviously change the grain orientation of the original microstructure and the distribution of the eutectic phase.The further continuous extrusion had little effect on the grain orientation distribution of the alloy, but with the increase of extrusion pass, the precipitation phase was further broken and refined, and the distribution became more and more uniform.Compared with low speed repeated continuous extrusion, the evolution law of mechanical properties of alloy under high speed repeated continuous extrusion is similar to that of low speed repeated continuous extrusion, but high speed repeated continuous extrusion obviously accelerates the evolution of microstructure and mechanical properties of alloy.High speed repeated continuous extrusion accelerates the uniform distribution of precipitate phase in the alloy, but does not accelerate the fracture behavior of the precipitated phase.After the first continuous extrusion process, some grain refinement occurred in the alloy, indicating that recrystallization occurred.The recrystallization process accelerates with the increase of extrusion pass, so the strength of alloy is lower than that of low speed repeated continuous extrusion.In addition, it is found that in the initial stage of high speed repeated continuous extrusion, shear bands appear in the alloy, so it can be concluded that the production of new fine grains may be related to the shear bands formed during high speed continuous extrusion.
【學位授予單位】：湖南大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG379;TG146.21

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本文編號：1750725