發(fā)布時(shí)間：2018-03-27 18:31

  本文選題：Al-Mg合金　切入點(diǎn)：鈧　出處：《合肥工業(yè)大學(xué)》2016年博士論文

【摘要】：高性能鋁合金由于低密度、強(qiáng)度適中、高塑性、耐腐蝕等優(yōu)異的綜合性能廣泛地應(yīng)用在食品包裝、化學(xué)加工等行業(yè)。然而,為了進(jìn)一步擴(kuò)大合金在航天航空、交通運(yùn)輸?shù)阮I(lǐng)域的應(yīng)用,合金需要具備更高的強(qiáng)度。而提高鋁合金強(qiáng)度的一個(gè)有效途徑是向合金中添加微量的Sc作為合金元素。本文采用鑄錠冶金方法制備了不同Sc、Zr含量的Al-Mg-Sc-(Zr)合金。采用金相顯微鏡(OM)、電子背散射衍射(EBSD)、透射電子顯微鏡(TEM)和拉伸實(shí)驗(yàn)研究了Sc和Sc、Zr復(fù)合合金化對(duì)Al-Mg合金組織與性能的影響；調(diào)查了Al-Mg-Sc和Al-Mg-Sc-Zr鑄態(tài)合金中初生粒子的外部形貌、內(nèi)部結(jié)構(gòu)與空間分布規(guī)律;探討了Sc和Sc、Zr在Al-Mg合金中的存在形式與作用機(jī)理。結(jié)果表明：(1)在Al-5Mg合金添加微量的Sc可顯著改善合金的微觀組織。Sc添加量為0.2wt.%時(shí),合金細(xì)化效果不明顯；而當(dāng)Sc添加量增加至0.4wt.%時(shí),合金微觀組織由粗大樹枝晶轉(zhuǎn)變?yōu)榧?xì)小等軸晶,顯著細(xì)化晶粒,其晶粒尺寸由259.1μm減至77.2μm；當(dāng)Sc含量繼續(xù)增至0.6wt.%,合金得到進(jìn)一步細(xì)化,平均晶粒尺寸為50.3 μm。Al-5Mg合金中Sc添加量分別為0.2 wt.%、0.4 wt.%、0.6 wt.%時(shí),合金的抗拉強(qiáng)度增幅為4%、30%和40%,屈服強(qiáng)度增幅為18%、78%和111%,而塑性減幅為12%、33%和44%。當(dāng)Sc添加量為0.4wt.%時(shí),合金的綜合性能達(dá)到最佳,此時(shí)合金的抗拉強(qiáng)度、屈服強(qiáng)度和塑性分別為280.2 MPa、153.6 MPa和14.8%。(2)Sc在Al-5Mg合金中主要以兩種形式存在：一是Sc添加量超過共晶點(diǎn)成分時(shí)(0.4wt.%),合金在凝固過程中析出初生的Al3Sc顆粒；由于與基體α-Al相具有相同的晶體結(jié)構(gòu)(αAl=0.4050nm,αAl3Sc=0.4106nm)和一致的取向,位于晶粒內(nèi)和晶界處的初生粒子能夠有效地?cái)M制有害擴(kuò)散和作為α-Al基體的異質(zhì)形核核心,起到細(xì)化晶粒的作用。但是,并不是所有的初生粒子都可以作為異質(zhì)核心。二是Sc含量未達(dá)到共晶點(diǎn)成分時(shí),Sc主要固溶在基體中形成過飽和固溶體,在后續(xù)的熱加工處理中分解并析出大量的、彌散的次生Al3Sc沉淀相,這些與基體共格的Al3Sc粒子有效的釘扎位錯(cuò),阻礙亞晶界的遷移與合并,對(duì)合金產(chǎn)生強(qiáng)烈的亞結(jié)構(gòu)強(qiáng)化和彌散強(qiáng)化效果。(3)Al-Mg-Sc合金中析出的初生粒子在熔體中的氧化物上形核并且呈現(xiàn)"cellular-dendritic"模式生長(zhǎng),即優(yōu)先在111)方向生長(zhǎng)形成樹枝晶的主干,然后在110)和(100)方向生長(zhǎng)出二次枝晶和三次枝晶,最后由于元素的擴(kuò)散與偏聚而形成"Al3Sc+α-Al+Al3Sc+…"多層結(jié)構(gòu)特征。(4)基于EBSD分析結(jié)果引入了一種特殊的計(jì)算方法。通過這種方法計(jì)算出交截面分別為(100)、(110)、(111)的三個(gè)不同形貌顆粒在觀察面上的三個(gè)慣習(xí)面分別為(3,2,1),(2,3,0),(1,1,4)、(0,1,0),(6,0,1),(1,1,6)和(4,0,1),(0,4,1),(1,1,4)。通過變換得出相對(duì)應(yīng)的坐標(biāo)軸分別為(3,2,1),(2,3,0),(1,1,4)、(2,0,3),(0,1,0),(3,0,2)和(3,1,4),(3,1,2),(0,3,1)。結(jié)果表明初生粒子呈現(xiàn)隨機(jī)分布,而不是簡(jiǎn)單的{100}、{110}或{111面。(5) 0.2wt.% Sc和0.1 wt.% Zr復(fù)合修飾Al-5Mg合金時(shí)產(chǎn)生顯著的晶粒細(xì)化效果。合金中析出的初生粒子由于與基體α-Al相同的晶體結(jié)構(gòu)和一致的晶體取向,有效地作為基體的異質(zhì)核心,起到細(xì)化晶粒的作用。并且,Al-Mg-Sc-Zr合金中析出的初生顆粒為Al3(Sc,Zr)相和α-Al相組成的共晶體,內(nèi)部組織呈現(xiàn)"Al3(Sc,Zr)+α-Al+Al3(Sc,Zr)"多層結(jié)構(gòu)和"cellular-dendritic"樹枝晶亞結(jié)構(gòu)特征。Sc、Zr復(fù)合修飾Al-5Mg的時(shí)效強(qiáng)化比Sc單獨(dú)修飾時(shí)的效果強(qiáng)。
[Abstract]:High performance Aluminum Alloy due to low density, moderate strength, high plasticity, corrosion resistance and other excellent is widely used in food packaging, chemical processing and other industries. However, in order to further expand the application of alloys in aerospace, transportation and other fields, with higher alloy needs an effective strength. Ways to improve the strength of Aluminum Alloy is adding trace Sc to the alloy as an alloying element. In this paper, different Sc were prepared by ingot metallurgy method, the content of Zr Al-Mg-Sc- (Zr) alloy. By using optical microscope (OM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile experiments Sc and Sc effect of Zr alloying on Microstructure and properties of Al-Mg alloy; investigated the external morphology of Al-Mg-Sc and Al-Mg-Sc-Zr as primary particle state in the alloy, the internal structure and the spatial distribution of Sc; and Sc, Zr in Al-Mg alloy The existing form and mechanism. The results showed that: (1) the addition of trace Sc in Al-5Mg alloy can significantly improve the microstructure of the alloy.Sc was added to 0.2wt.%, the refinement effect is not obvious; and when the amount of Sc increases to 0.4wt.%, the microstructure changes from coarse dendrites to fine equiaxed grains obviously, grain refinement, the grain size from 259.1 m to 77.2 m; when the Sc content continued to 0.6wt.%, alloy can be further refined, the average grain size of 50.3 mu m.Al-5Mg alloy in the amount of Sc was 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, an increase of tensile strength of the alloy was 4% and 30%. 40%, the yield strength increased by 18%, 78% and 111%, and the plasticity reduction of 12%, 33% and 44%. when the Sc content is 0.4wt.%, the best comprehensive properties of the alloy, the tensile strength, yield strength and plasticity were 280.2 MPa, 153.6 MPa and 14.8%. (2) S C in Al-5Mg alloy mainly has two kinds: one is more than the amount of Sc eutectic component (0.4wt.%), Al3Sc alloy primary particles precipitated in the solidification process; the matrix and a -Al phase has the same crystal structure (alpha Al=0.4050nm, alpha Al3Sc=0.4106nm) and a primary particle orientation. Located inside the grains and grain boundaries can effectively be harmful as diffusion and heterogeneous nucleation core base of a -Al, play a role in grain refinement. However, not all of the primary particles can be used as a heterogeneous core. Two is the content of Sc did not reach the eutectic composition, Sc is mainly dissolved in matrix in the formation of supersaturated solid solution, the decomposition in thermal processing and subsequent release of Al3Sc, the secondary dispersion of precipitates, the coherent matrix and Al3Sc particle effective pinning of dislocations, hinder the migration and merging sub grain boundaries, to produce alloy Strong substructure strengthening and dispersion strengthening effect. (3) the primary nucleation of oxide particles precipitated in Al-Mg-Sc alloy in the melt on and show "cellular-dendritic" mode of growth, which is priority in 111) growth direction of dendrite trunk form, and then in 110) and (100) out of two times the growth direction of dendrite and the three dendrite, finally because the element diffusion and segregation and the formation of "Al3Sc+ alpha -Al+Al3Sc+... "澶氬眰緇撴瀯鐗瑰緛.(4)鍩轟簬EBSD鍒嗘瀽緇撴灉寮曞叆浜?jiǎn)涓�縐嶇壒孌婄殑璁＄畻鏂規(guī)硶.閫氳繃榪欑鏂規(guī)硶璁＄畻鍑轟氦鎴潰鍒嗗埆涓，

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