基于稀土元素Sc改性Al-Mg新型铝合金的组织控制与强化机理研究

发布时间：2018-03-27 18:31

  本文选题：Al-Mg合金　切入点：钪　出处：《合肥工业大学》2016年博士论文

【摘要】：高性能铝合金由于低密度、强度适中、高塑性、耐腐蚀等优异的综合性能广泛地应用在食品包装、化学加工等行业。然而,为了进一步扩大合金在航天航空、交通运输等领域的应用,合金需要具备更高的强度。而提高铝合金强度的一个有效途径是向合金中添加微量的Sc作为合金元素。本文采用铸锭冶金方法制备了不同Sc、Zr含量的Al-Mg-Sc-(Zr)合金。采用金相显微镜(OM)、电子背散射衍射(EBSD)、透射电子显微镜(TEM)和拉伸实验研究了Sc和Sc、Zr复合合金化对Al-Mg合金组织与性能的影响；调查了Al-Mg-Sc和Al-Mg-Sc-Zr铸态合金中初生粒子的外部形貌、内部结构与空间分布规律;探讨了Sc和Sc、Zr在Al-Mg合金中的存在形式与作用机理。结果表明：(1)在Al-5Mg合金添加微量的Sc可显著改善合金的微观组织。Sc添加量为0.2wt.%时,合金细化效果不明显；而当Sc添加量增加至0.4wt.%时,合金微观组织由粗大树枝晶转变为细小等轴晶,显著细化晶粒,其晶粒尺寸由259.1μm减至77.2μm；当Sc含量继续增至0.6wt.%,合金得到进一步细化,平均晶粒尺寸为50.3 μm。Al-5Mg合金中Sc添加量分别为0.2 wt.%、0.4 wt.%、0.6 wt.%时,合金的抗拉强度增幅为4%、30%和40%,屈服强度增幅为18%、78%和111%,而塑性减幅为12%、33%和44%。当Sc添加量为0.4wt.%时,合金的综合性能达到最佳,此时合金的抗拉强度、屈服强度和塑性分别为280.2 MPa、153.6 MPa和14.8%。(2)Sc在Al-5Mg合金中主要以两种形式存在：一是Sc添加量超过共晶点成分时(0.4wt.%),合金在凝固过程中析出初生的Al3Sc颗粒；由于与基体α-Al相具有相同的晶体结构(αAl=0.4050nm,αAl3Sc=0.4106nm)和一致的取向,位于晶粒内和晶界处的初生粒子能够有效地拟制有害扩散和作为α-Al基体的异质形核核心,起到细化晶粒的作用。但是,并不是所有的初生粒子都可以作为异质核心。二是Sc含量未达到共晶点成分时,Sc主要固溶在基体中形成过饱和固溶体,在后续的热加工处理中分解并析出大量的、弥散的次生Al3Sc沉淀相,这些与基体共格的Al3Sc粒子有效的钉扎位错,阻碍亚晶界的迁移与合并,对合金产生强烈的亚结构强化和弥散强化效果。(3)Al-Mg-Sc合金中析出的初生粒子在熔体中的氧化物上形核并且呈现"cellular-dendritic"模式生长,即优先在111)方向生长形成树枝晶的主干,然后在110)和(100)方向生长出二次枝晶和三次枝晶,最后由于元素的扩散与偏聚而形成"Al3Sc+α-Al+Al3Sc+…"多层结构特征。(4)基于EBSD分析结果引入了一种特殊的计算方法。通过这种方法计算出交截面分别为(100)、(110)、(111)的三个不同形貌颗粒在观察面上的三个惯习面分别为(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)。通过变换得出相对应的坐标轴分别为(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)。结果表明初生粒子呈现随机分布,而不是简单的{100}、{110}或{111面。(5) 0.2wt.% Sc和0.1 wt.% Zr复合修饰Al-5Mg合金时产生显著的晶粒细化效果。合金中析出的初生粒子由于与基体α-Al相同的晶体结构和一致的晶体取向,有效地作为基体的异质核心,起到细化晶粒的作用。并且,Al-Mg-Sc-Zr合金中析出的初生颗粒为Al3(Sc,Zr)相和α-Al相组成的共晶体,内部组织呈现"Al3(Sc,Zr)+α-Al+Al3(Sc,Zr)"多层结构和"cellular-dendritic"树枝晶亚结构特征。Sc、Zr复合修饰Al-5Mg的时效强化比Sc单独修饰时的效果强。
[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+... "澶氬眰缁撴瀯鐗瑰緛.(4)鍩轰簬EBSD鍒嗘瀽缁撴灉寮曞叆浜嗕竴绉嶇壒娈婄殑璁＄畻鏂规硶.閫氳繃杩欑�嶆柟娉曡�＄畻鍑轰氦鎴�闈㈠垎鍒�涓，

本文编号：1672722