本文選題：Al-Si熔體 + Al-P原子團(tuán)簇�。� 參考：《山東大學(xué)》2016年博士論文

【摘要】：A1P與Si相晶格結(jié)構(gòu)相同,品格參數(shù)相近,是Si相的良好異質(zhì)形核襯底,在工業(yè)上被廣泛用于變質(zhì)、細(xì)化近共晶及過共晶Al-Si合金。近年來,A1P也被用于細(xì)化過共晶Al-Mg2Si合金。在A1P析出前,P在鋁熔體中以A1-P原子團(tuán)簇(簡(jiǎn)稱A1-P團(tuán)簇)形式存在,作為A1P相的前驅(qū)體團(tuán)簇,其在多元鋁合金熔體中的演變行為及其化學(xué)穩(wěn)定性,對(duì)A1P相的析出及最終磷變質(zhì)效果具有重要影響。本文采用實(shí)驗(yàn)、第一性原理模擬、熱力學(xué)分析與電負(fù)性理論分析相結(jié)合的方法,研究了Al-Si-X-P熔體中A1-P團(tuán)簇的演變行為；分析了該團(tuán)簇在γ-Al2O3薄膜處的富集及A1P析出行為,以及誘發(fā)形成Al-Si合金表面富Si層的機(jī)理；系統(tǒng)研究了合金元素對(duì)A1-P團(tuán)簇化學(xué)穩(wěn)定性的影響；研究了Al-Si-Mg合金中Al-P團(tuán)簇與初晶Mg2Si相異質(zhì)形核襯底的演變規(guī)律與形核機(jī)制。(1)Al-P團(tuán)簇在凝固過程中的演變及在γ-Al2O3表面的富集析出通過第一性原理模擬二元A1-P熔體結(jié)構(gòu)發(fā)現(xiàn), P原子之間相互排斥,而易與A1形成A1nP型(3≤n≤10)A1-P團(tuán)簇。其中,A1配位數(shù)并不恒定,但以六配位為主,其平均配位數(shù)為6.32。即使在3×1014。C/s的冷速下,A1-P團(tuán)簇仍對(duì)溫度變化敏感,可克服粘度障礙,向晶態(tài)結(jié)構(gòu)方向演變。一方面,A1-P團(tuán)簇單體不斷調(diào)整配位A1原子數(shù)目；另一方面,不同A1-P團(tuán)簇單體相互聚集,通過A1原子橋接形成大團(tuán)簇,進(jìn)而形成A1P晶胚或A1P微晶。發(fā)現(xiàn)γ-Al2O3薄膜可吸附熔體內(nèi)A1-P團(tuán)簇,加快該團(tuán)簇演變與A1P微晶化,并彌散分布于其薄膜上。在磷變質(zhì)A1-Si合金熔體冷卻凝固(冷凝)過程中,通過‘'γ-Al2O3/AlP/Si"三相傳遞異質(zhì)形核機(jī)理,合金表面γ-Al2O3薄膜處先后析出大量以(111)為擇優(yōu)取向的A1P與初晶Si,形成Al-Si合金表面富Si層。其中,近共晶Al-Si合金表面富Si層中初晶Si為被(111)晶面覆蓋的六角板片狀；而過共晶Al-Si合金表面富Si層中靠近合金表面的初晶Si(111)面可在較大溫度梯度的影響下,沿[111]晶向繼續(xù)生長(zhǎng),使{311}晶面外露,形成六棱臺(tái)／錐狀。(2) Al-Si-X-P熔體中Al-P團(tuán)簇化學(xué)穩(wěn)定性研究通過實(shí)驗(yàn)、第一性原理模擬、熱力學(xué)分析及電負(fù)性理論分析相結(jié)合的方法,系統(tǒng)研究了Al-Si-X-P熔體中X元素對(duì)A1-P團(tuán)簇化學(xué)穩(wěn)定性的影響。繪制出元素對(duì)A1-P團(tuán)簇化學(xué)穩(wěn)定性影響程度分區(qū)圖,將合金元素X分為三類：①毒化元素((p2.9),即能顯著破壞Al-P團(tuán)簇化學(xué)穩(wěn)定性的元素；②兩性元素(2.9(p3.6),該類元素含量較低時(shí),基本不影響Al-P團(tuán)簇的化學(xué)穩(wěn)定性,但含量超過某一臨界濃度便可表現(xiàn)出破壞Al-P團(tuán)簇化學(xué)穩(wěn)定性的能力；③非毒化元素(φ3.6),對(duì)Al-P團(tuán)簇化學(xué)穩(wěn)定性無影響。研究還發(fā)現(xiàn), Si原子及Al原子可通過與合金元素(主要是兩性元素)結(jié)合而在一定程度上促進(jìn)Al-P團(tuán)簇形成或者抑制兩性元素對(duì)Al-P團(tuán)簇的破壞作用。(3)Al-Si-Mg合金中Al-P團(tuán)簇及初晶Mg2Si相形核襯底的演變與控制發(fā)現(xiàn)Mg與A1-P中間合金的添加順序可影響近共晶Al-Si熔體中A1-P團(tuán)簇的化學(xué)穩(wěn)定性及磷變質(zhì)效果。先加Al-P中間合金后加入Mg時(shí),Mg可破壞熔體中已經(jīng)存在的A1-P團(tuán)簇,阻礙A1P微晶的析出,使磷變質(zhì)效果失效。當(dāng)先加入Mg后加入Al-P中間合金時(shí),Mg可與熔體內(nèi)大量存在的Si原子優(yōu)先結(jié)合為Mg-Si團(tuán)簇,降低自身活性,而與后溶解于熔體的A1-P團(tuán)簇在相當(dāng)時(shí)間內(nèi)共存,不影響最終磷變質(zhì)效果。因此,建議工業(yè)生產(chǎn)中先加合金化元素Mg再磷變質(zhì)處理。研究了磷細(xì)化Al-Mg2Si合金中初晶Mg2Si異質(zhì)形核襯底的演變規(guī)律與多重異質(zhì)形核機(jī)制。在Al-Mg-Si熔體中,AlP可與熔體反應(yīng),發(fā)生"AlP→Mg3P2/AlP復(fù)合粒子→Mg3P2"的演變,且演變速率隨熔體內(nèi)Mg含量升高而加快。晶體錯(cuò)配度計(jì)算表明,磷化物襯底的演變可提高其對(duì)初晶Mg2Si相的形核能力。研究還發(fā)現(xiàn),在Al-Mg-Si熔體內(nèi)新生成的Mg3P2為Al摻雜型Mg3P2；在Al-Mg-Si-Ca熔體中,磷化物襯底可進(jìn)一步演變?yōu)锳l、Ca共同摻雜型Mg3P2。摻雜型Mg3P2具有更高的化學(xué)穩(wěn)定性,表現(xiàn)出抗Ca“中毒”能力。同時(shí),隨熔體中Mg含量升高,磷化物襯底的抗Ca“中毒”能力也隨之增強(qiáng)。
[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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG146.21;TG292

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1 朱向鎮(zhèn);Al-Si-X-P熔體中Al-P團(tuán)簇演變行為與化學(xué)穩(wěn)定性的研究[D];山東大學(xué);2016年

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本文編號(hào)：2023005