Al-Si-X-P熔体中Al-P团簇演变行为与化学稳定性的研究

发布时间：2018-06-15 18:07

本文选题：Al-Si熔体 + Al-P原子团簇　；参考：《山东大学》2016年博士论文

【摘要】：A1P与Si相晶格结构相同,品格参数相近,是Si相的良好异质形核衬底,在工业上被广泛用于变质、细化近共晶及过共晶Al-Si合金。近年来,A1P也被用于细化过共晶Al-Mg2Si合金。在A1P析出前,P在铝熔体中以A1-P原子团簇(简称A1-P团簇)形式存在,作为A1P相的前驱体团簇,其在多元铝合金熔体中的演变行为及其化学稳定性,对A1P相的析出及最终磷变质效果具有重要影响。本文采用实验、第一性原理模拟、热力学分析与电负性理论分析相结合的方法,研究了Al-Si-X-P熔体中A1-P团簇的演变行为；分析了该团簇在γ-Al2O3薄膜处的富集及A1P析出行为,以及诱发形成Al-Si合金表面富Si层的机理；系统研究了合金元素对A1-P团簇化学稳定性的影响；研究了Al-Si-Mg合金中Al-P团簇与初晶Mg2Si相异质形核衬底的演变规律与形核机制。(1)Al-P团簇在凝固过程中的演变及在γ-Al2O3表面的富集析出通过第一性原理模拟二元A1-P熔体结构发现, P原子之间相互排斥,而易与A1形成A1nP型(3≤n≤10)A1-P团簇。其中,A1配位数并不恒定,但以六配位为主,其平均配位数为6.32。即使在3×1014。C/s的冷速下,A1-P团簇仍对温度变化敏感,可克服粘度障碍,向晶态结构方向演变。一方面,A1-P团簇单体不断调整配位A1原子数目；另一方面,不同A1-P团簇单体相互聚集,通过A1原子桥接形成大团簇,进而形成A1P晶胚或A1P微晶。发现γ-Al2O3薄膜可吸附熔体内A1-P团簇,加快该团簇演变与A1P微晶化,并弥散分布于其薄膜上。在磷变质A1-Si合金熔体冷却凝固(冷凝)过程中,通过‘'γ-Al2O3/AlP/Si"三相传递异质形核机理,合金表面γ-Al2O3薄膜处先后析出大量以(111)为择优取向的A1P与初晶Si,形成Al-Si合金表面富Si层。其中,近共晶Al-Si合金表面富Si层中初晶Si为被(111)晶面覆盖的六角板片状；而过共晶Al-Si合金表面富Si层中靠近合金表面的初晶Si(111)面可在较大温度梯度的影响下,沿[111]晶向继续生长,使{311}晶面外露,形成六棱台／锥状。(2) Al-Si-X-P熔体中Al-P团簇化学稳定性研究通过实验、第一性原理模拟、热力学分析及电负性理论分析相结合的方法,系统研究了Al-Si-X-P熔体中X元素对A1-P团簇化学稳定性的影响。绘制出元素对A1-P团簇化学稳定性影响程度分区图,将合金元素X分为三类：①毒化元素((p2.9),即能显著破坏Al-P团簇化学稳定性的元素；②两性元素(2.9(p3.6),该类元素含量较低时,基本不影响Al-P团簇的化学稳定性,但含量超过某一临界浓度便可表现出破坏Al-P团簇化学稳定性的能力；③非毒化元素(φ3.6),对Al-P团簇化学稳定性无影响。研究还发现, Si原子及Al原子可通过与合金元素(主要是两性元素)结合而在一定程度上促进Al-P团簇形成或者抑制两性元素对Al-P团簇的破坏作用。(3)Al-Si-Mg合金中Al-P团簇及初晶Mg2Si相形核衬底的演变与控制发现Mg与A1-P中间合金的添加顺序可影响近共晶Al-Si熔体中A1-P团簇的化学稳定性及磷变质效果。先加Al-P中间合金后加入Mg时,Mg可破坏熔体中已经存在的A1-P团簇,阻碍A1P微晶的析出,使磷变质效果失效。当先加入Mg后加入Al-P中间合金时,Mg可与熔体内大量存在的Si原子优先结合为Mg-Si团簇,降低自身活性,而与后溶解于熔体的A1-P团簇在相当时间内共存,不影响最终磷变质效果。因此,建议工业生产中先加合金化元素Mg再磷变质处理。研究了磷细化Al-Mg2Si合金中初晶Mg2Si异质形核衬底的演变规律与多重异质形核机制。在Al-Mg-Si熔体中,AlP可与熔体反应,发生"AlP→Mg3P2/AlP复合粒子→Mg3P2"的演变,且演变速率随熔体内Mg含量升高而加快。晶体错配度计算表明,磷化物衬底的演变可提高其对初晶Mg2Si相的形核能力。研究还发现,在Al-Mg-Si熔体内新生成的Mg3P2为Al掺杂型Mg3P2；在Al-Mg-Si-Ca熔体中,磷化物衬底可进一步演变为Al、Ca共同掺杂型Mg3P2。掺杂型Mg3P2具有更高的化学稳定性,表现出抗Ca“中毒”能力。同时,随熔体中Mg含量升高,磷化物衬底的抗Ca“中毒”能力也随之增强。
[Abstract]:A1P and Si have the same lattice structure and similar character parameters. It is a good heterogeneous nucleation substrate for Si phase. It is widely used in industry for metamorphism and refinement of eutectic and hypereutectic Al-Si alloys. In recent years, A1P has been used to refine hypereutectic Al-Mg2Si alloys. Before A1P precipitation, P exists in the form of A1-P atomic cluster (A1-P cluster) in aluminum melt. For the precursor cluster of A1P phase, its evolution behavior and chemical stability in multiple aluminum alloy melts have an important influence on the precipitation of A1P phase and the final effect of phosphorus modification. In this paper, the experiments, first principle simulation, thermodynamic analysis and electronegativity theory analysis were used to study the A1-P clusters in Al-Si-X-P melts. The concentration and A1P precipitation behavior of the cluster at the -Al2O3 film and the mechanism of inducing the formation of Si layer on the surface of Al-Si alloy were analyzed. The effect of the alloy elements on the chemical stability of the A1-P cluster was studied. The evolution law of the heterogeneous nucleation substrate of the Al-P cluster and the primary Mg2Si phase in the Al-Si-Mg alloy and the nucleation machine were studied. (1) the evolution of the Al-P cluster in the solidification process and the enrichment and precipitation on the surface of the gamma -Al2O3 show that the two element A1-P melt structure is simulated by the first principle, and the P atoms are mutually exclusive, and the A1nP type (3 < 10 N < 10) A1-P clusters is formed easily with A1. Among them, the A1 coordination number is not constant, but it is mainly six coordination, and the average coordination number is 6.32. even in 3. At the cold speed of X 1014.C/s, the A1-P cluster is still sensitive to the temperature change, which can overcome the viscosity obstacle and change direction to the crystal structure. On the one hand, the A1-P cluster monomer constantly adjusts the number of the coordination A1 atoms; on the other hand, the different A1-P cluster monomers gather together to form large clusters by A1 atom bridging, and then form the A1P or A1P microcrystals. And the discovery of gamma -Al2 is found. The O3 thin film can adsorb the A1-P cluster in the melt to accelerate the cluster evolution and A1P microcrystallization and disperse on its thin film. In the process of cooling solidification (condensation) of the A1-Si alloy melt in the phosphorous metamorphic alloy, through the "gamma -Al2O3/AlP/Si" three phase transfer heterogeneous nucleation mechanism, the alloy surface gamma -Al2O3 film has precipitated a large number of (111) as the preferred orientation A1P successively. With the initial crystal Si, a rich Si layer on the surface of the Al-Si alloy is formed. Among them, the initial crystal Si in the surface of the eutectic Al-Si alloy is covered with (111) crystal surface, and the initial crystal Si (111) surface near the alloy surface in the eutectic Al-Si alloy surface can continue to grow along the [111] crystal and make the {311} crystal surface under the influence of the larger temperature gradient. Six prism / conical form is formed. (2) the chemical stability of Al-P clusters in Al-Si-X-P melts is studied by experiments, first principle simulation, thermodynamic analysis and electronegativity theoretical analysis. The effects of X elements on the chemical stability of A1-P clusters in Al-Si-X-P melts are systematically studied. The chemical stability of elements to A1-P clusters is drawn. The alloying element X is divided into three categories: 1. ((p2.9) elements (2.9 (P3.6), which can destroy the chemical stability of Al-P clusters. The chemical stability of Al-P clusters is not affected when the content of these elements is low, but the chemical stability of Al-P clusters can be shown to be more than a certain critical concentration. The qualitative ability; the non toxic element (phi 3.6) has no effect on the chemical stability of the Al-P clusters. It is also found that the Si and Al atoms can promote the formation of Al-P clusters or inhibit the destruction of the amphoteric elements to the Al-P clusters to a certain extent by combining with the alloying elements (mainly amphoteric elements). (3) Al-P clusters in Al-Si-Mg alloys. The evolution and control of the primary Mg2Si phase nucleation substrate found that the addition order of the Mg and A1-P intermediate alloys could affect the chemical stability of the A1-P cluster in the eutectic Al-Si melt and the effect of phosphorus modification. When adding Al-P intermediate alloy after adding Mg, Mg could destroy the existing A1-P clusters in the melt and hindered the precipitation of A1P microcrystals, so that the effect of phosphorus metamorphism was lost. When Mg is added to the Al-P intermediate alloy first, Mg can combine with a large number of Si atoms in the melt into a Mg-Si cluster, which reduces the self activity, and coexists with the A1-P cluster dissolved in the melt for a considerable time, and does not affect the final phosphorus modification effect. Therefore, it is suggested that the alloying element Mg is first added to the phosphorous modification treatment in industrial production. The evolution of the heterogeneous nucleation mechanism of the initial Mg2Si heterostructure in the Al-Mg2Si alloy is investigated. In Al-Mg-Si melts, AlP can react with the melt, and the evolution of "AlP to Mg3P2/AlP composite particles to Mg3P2" occurs, and the rate of transmission is accelerated with the increase of Mg content in the melt. The calculation of crystal mismatch shows that the phosphide substrate is on the substrate. The evolution can improve the nucleation ability of the Mg2Si phase in the primary crystal. It is also found that the newly generated Mg3P2 in the Al-Mg-Si melt is Al doped Mg3P2; in the Al-Mg-Si-Ca melts, the phosphide substrate can be further evolved into Al, and the Ca Co doped Mg3P2. doped Mg3P2 has higher chemical stability, showing the ability to resist Ca "poisoning". With the Mg content in the melt increases, phosphide substrate Ca anti poisoning ability is enhanced.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.21;TG292

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