本文選題：Al-Si合金 + 第一性原理��； 參考：《沈陽(yáng)工業(yè)大學(xué)》2015年碩士論文

【摘要】：鑄造Al-Si-Cu-Mg合金作為一種可熱處理強(qiáng)化的鋁合金具有較高的強(qiáng)度，較低的密度以及優(yōu)異的耐蝕性能。不同的材料具有不同的性能，材料的組織決定材料的性能，要想獲得優(yōu)良的宏觀性能就必須了解材料的內(nèi)部的微觀組織結(jié)構(gòu)。對(duì)于鑄造Al-Si-Cu-Mg合金而言，其微觀組織結(jié)構(gòu)與其時(shí)效過(guò)程中的納米級(jí)析出相密切相關(guān)，因此對(duì)Al-Si-Cu-Mg合金時(shí)效析出行為進(jìn)行研究是解釋其時(shí)效強(qiáng)化機(jī)理的有效途徑。 本文選取鑄造Al-10Si-1.5Cu-0.5Mg合金作為研究對(duì)象，運(yùn)用透射電子顯微鏡（TEM）以及三維原子探針（3DAP）等實(shí)驗(yàn)手段，對(duì)合金的時(shí)效過(guò)程中時(shí)效析出相形態(tài)與析出序列以及時(shí)效初期鋁基體內(nèi)各溶質(zhì)原子的分布情況進(jìn)行了研究。同時(shí)結(jié)合第一性原理計(jì)算，對(duì)合金時(shí)效析出相的結(jié)構(gòu)穩(wěn)定性、熱穩(wěn)定性以及彈性性質(zhì)進(jìn)行了定量計(jì)算，從實(shí)驗(yàn)和理論兩個(gè)方向相互佐證，對(duì)合金時(shí)效“雙峰”現(xiàn)象、時(shí)效初期沉淀相的析出序列以及時(shí)效機(jī)理給出合理的解釋。 合金經(jīng)175℃人工時(shí)效1h后即可觀察到細(xì)小彌散的點(diǎn)狀Q'相均勻地分布在合金基體中。時(shí)效4h后可觀察到數(shù)量極少的針狀θ"相，時(shí)效至6h時(shí)θ"相的尺寸和密度仍較小，但Q相的尺寸、數(shù)量達(dá)到了峰值，體現(xiàn)為合計(jì)硬度曲線上的第一個(gè)峰值；隨著時(shí)效時(shí)間繼續(xù)增加（6h-12h），Q相以及θ亞穩(wěn)相繼續(xù)長(zhǎng)大，但Q相密度逐漸降低，同時(shí)θ亞穩(wěn)相的尺寸及數(shù)量?jī)?yōu)勢(shì)得到體現(xiàn)，當(dāng)時(shí)效至12h時(shí)，θ亞穩(wěn)相的數(shù)量及尺寸達(dá)到峰值，體現(xiàn)為合金硬度曲線上的第二個(gè)硬度峰；時(shí)效后期（12h以后）析出相會(huì)發(fā)生明顯的粗化現(xiàn)象。 根據(jù)3DAP的實(shí)驗(yàn)結(jié)果表明175℃時(shí)效15minMg、Si原子存在不同程度的偏聚，同時(shí)大量的Cu原子卻仍處在一種均勻分布的狀態(tài)，，合金基體中尚未形成Mg/Si/Cu復(fù)合團(tuán)簇；時(shí)效2h后合金基體中Si、Mg原子聚集程度加劇，且Cu原子也發(fā)生一定的聚集，合金基體中出現(xiàn)Mg/Si/Cu復(fù)合團(tuán)簇；時(shí)效4h后合金基體中Si、Mg、Cu原子聚集程度加劇，Mg/Si/Cu復(fù)合團(tuán)簇?cái)?shù)量增多，尺寸變大與合金的TEM實(shí)驗(yàn)結(jié)論一致。 θ'，θ''以及Q'相這三個(gè)亞穩(wěn)相中，Q'相要先于θ'相和θ''相析出。Al2Cu相的塑性好于Mg2Si相。Al2Cu相和Mg2Si相的各向異性程度相差不多，Al2Cu相為韌性相，Mg2Si相為脆性相。
[Abstract]:The cast Al-Si-Cu-Mg alloy has higher strength, lower density and excellent corrosion resistance as a kind of heat-treated reinforced aluminum alloy. Different materials have different properties. The microstructure of the material determines the properties of the material. In order to obtain excellent macroscopic properties, the internal microstructure of the material must be solved. The microstructure of Al-Si-Cu-Mg alloy is closely related to the nanoscale precipitates in the aging process. Therefore, it is an effective way to study the aging precipitation behavior of Al-Si-Cu-Mg alloy.
In this paper, the cast Al-10Si-1.5Cu-0.5Mg alloy is selected as the research object. By means of transmission electron microscope (TEM) and three dimensional atomic probe (3DAP), the distribution of the phase morphology and precipitation sequence of the aging precipitation and the distribution of each solute atom in the aluminum base of the aging period in the aging process of the alloy are studied. The structural stability, thermal stability and elastic properties of the alloy aging precipitates are calculated quantitatively by the calculation of the principle of sex principle. From the two directions of experiment and theory, it is proved that the aging "Shuangfeng" phenomenon of alloy aging, the precipitation sequence of the precipitate phase and the aging mechanism at the early stage of aging are explained reasonably.
After aging for 1H at 175 C, the small dispersed dot Q'phase can be observed uniformly in the alloy matrix. After aging 4h, a small number of needle like theta phases can be observed. The size and density of the phase is still small, but the size and quantity of Q phase is the first peak value on the aggregate hardness curve. The aging time continues to increase (6h-12h), the Q phase and the theta metastable phase continue to grow, but the Q phase density decreases gradually, while the size and quantity advantage of the theta metastable phase is reflected. At that time to 12h, the number and size of the theta metastable phase reached the peak, which was the second hardness peak on the hardness curve of the alloy; the precipitate phase in the later period of aging (after 12h) There will be obvious coarsening.
According to the experimental results of 3DAP, it is shown that the Si atom has different degrees of segregation at 175 C, while a large number of Cu atoms are still in a uniform distribution state, and the Mg/Si/Cu composite clusters have not been formed in the alloy matrix. The aggregation range of Si, Mg atoms in the alloy matrix after aging 2H is aggravated, and the Cu atom also has a certain aggregation. Mg/Si/Cu composite clusters appear in the matrix, and the aggregation degree of Si, Mg, Cu atoms in the alloy matrix increases after aging 4h, and the number of Mg/Si/Cu clusters increases, and the size becomes larger in accordance with the TEM experimental conclusion of the alloy.
In the three metastable phases of theta, theta and Q'phase, the plasticity of Q' phase precipitated by the phase of theta and theta is better than the anisotropy of the Mg2Si phase.Al2Cu phase and the Mg2Si phase, the Al2Cu phase is ductile and the Mg2Si phase is brittle phase.

【學(xué)位授予單位】：沈陽(yáng)工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG156.92

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