铸造Al-Si合金中稀土与硼的组织调控作用及对性能的影响

发布时间：2018-01-16 20:13

本文关键词：铸造Al-Si合金中稀土与硼的组织调控作用及对性能的影响　出处：《东南大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文以铸造Al-Si系合金为研究对象,通过添加微量稀土元素La和元素B,综合采用OM、SEM、TEM等组织观察、凝固过程热分析和拉伸测试等分析手段,探究La和B对合金微观组织及拉伸性能的影响。在Al-11Si合金中添加Ti、La、B及Sr四种元素,并改变元素的添加顺序,考察了Ti、La、B、Sr之间的交互作用对合金铸态组织及拉伸性能的影响。结果表明,在0.02wt.%Sr变质的Al-11Si合金中,进一步添加0.05wt.%B,会使共晶Si由细小的纤维状转变为粗大的板片状,Sr所引起的IIT机制被抑制,共晶Si以TPRE机制生长,即引起了 Sr、B毒化。Ti可以解除Sr、B毒化,使得共晶Si生长由TPRE机制再次转变为IIT机制,共晶Si形貌相应地由粗大的板片状转变为细小、均匀的纤维状,从而显著提高合金的延伸率。La同样可以解除Sr、B毒化,只是这种解除毒化的作用还取决于元素的添加顺序,与此同时,La的添加还可以使合金的α-Al枝晶得到显著的细化。以近共晶及过共晶Al-Si合金为研究对象,考察了 B单独添加及La、B联合添加对合金中Si相的影响。结果表明,在未经变质的Al-Si合金中添加B可以促进Si相的形核,并使得共晶Si中孪晶发生单方向的增殖,促进共晶Si的不断分枝,从而导致共晶区扩大,且使得共晶Si由粗大的片状转变为更为密集、细小的片状。LaB6相的密排面{110}与Si相的密排面{111}之间具有良好的晶体学位相关系,LaB6可能作为Si相的形核基底促进Si相的形核。LaB6相与富Fe相之间在多对原子面上均存在着良好的晶体学匹配关系,因而LaB6可能作为富Fe相的形核基底促进富Fe相的形核,进而富Fe相作为Si相的异质形核核心促进Si相的形核。利用熔体反应原位合成法,使用工业纯铝,A1-3B和Al-10La中间合金制备了Al-2La-1B中间合金。在金属型浇注的条件下,Al-2La-1B中间合金可以对Al-7Si、Al-11Si合金以及ZL101合金进行有效细化,但不能细化ZL101A合金;在砂型浇注的条件下,Al-2La-1B中间合金不能有效细化ZL101A合金,而能有效细化ZL104合金,并提升ZL104合金的铸态拉伸性能。在Al-11 Si-1.2La-0.6B合金中添加足量的Ti,可以置换LaB6中的La而生成TiB2,La在随后的凝固过程中以富La化合物的形式析出。
[Abstract]:In this paper, the cast Al-Si alloy was studied. The microstructure of the cast Al-Si alloy was observed by adding trace rare earth element La and element B, etc. The effect of La and B on the microstructure and tensile properties of Al-11Si alloy was investigated by means of thermal analysis and tensile test. The effect of the interaction between Ti-Li La-B-Sr on the as-cast microstructure and tensile properties of the alloy was investigated by changing the addition order of the elements. The addition of 0.05wt.B to the Al-11Si alloy modified by 0.02wt.and Sr can change the eutectic Si from fine fibrous to coarse lamellar. Sr-induced IIT mechanism was inhibited, and eutectic Si was grown by TPRE mechanism, which caused SrB poisoning. The growth of eutectic Si was changed from TPRE mechanism to IIT mechanism, and the morphology of eutectic Si changed from coarse sheet to fine and uniform fiber. Thus, the elongation of the alloy. La can also be detoxified, but the effect of this detoxification also depends on the addition order of elements, at the same time. The addition of La can also refine the dendrite of 伪 -Al. Taking the near eutectic and hypereutectic Al-Si alloys as research objects, the addition of B and La were investigated. The results show that the addition of B to the unmodified Al-Si alloy can promote the nucleation of Si phase and make the twin in eutectic Si propagate in one direction. It promotes the continuous branching of eutectic Si, which results in the enlargement of eutectic region and the transition of eutectic Si from coarse flake to more dense. There is a good crystal degree phase relationship between the compact plane {110} and the dense plane {111} of the small lamellar 路LaB6 phase. LaB6 may act as the nucleation substrate of Si phase to promote the nucleation of Si phase. There is a good crystallographic matching relationship between Fe rich phase and Fe rich phase. Therefore, LaB6 may be used as the nucleation substrate of Fe-rich phase to promote the nucleation of Fe-rich phase, and then Fe-rich phase as the heterogeneous nucleation core of Si phase to promote the nucleation of Si phase. The melt reaction in-situ synthesis method is used. The Al-2La-1B master alloy was prepared by using industrial pure aluminum alloy A1-3B and Al-10La master alloy. Al-2La-1B master alloy can refine Al-7Si-Al-11Si alloy and ZL101 alloy effectively, but it can not refine ZL101A alloy. The Al-2La-1B master alloy can not refine ZL101A alloy effectively, but can refine ZL104 alloy effectively under the condition of sand mold pouring. The as-cast tensile properties of ZL104 alloy were improved. Adding sufficient amount of Ti to Al-11 Si-1.2La-0.6B alloy, La in LaB6 could be replaced to form TiB2. La precipitates in the form of La-rich compounds during subsequent solidification.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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