铸造Al-Si-Cu-Mg合金时效析出行为的研究

发布时间：2018-05-14 14:17

本文选题：Al-Si合金 + 第一性原理　；参考：《沈阳工业大学》2015年硕士论文

【摘要】：铸造Al-Si-Cu-Mg合金作为一种可热处理强化的铝合金具有较高的强度，较低的密度以及优异的耐蚀性能。不同的材料具有不同的性能，材料的组织决定材料的性能，要想获得优良的宏观性能就必须了解材料的内部的微观组织结构。对于铸造Al-Si-Cu-Mg合金而言，其微观组织结构与其时效过程中的纳米级析出相密切相关，因此对Al-Si-Cu-Mg合金时效析出行为进行研究是解释其时效强化机理的有效途径。本文选取铸造Al-10Si-1.5Cu-0.5Mg合金作为研究对象，运用透射电子显微镜（TEM）以及三维原子探针（3DAP）等实验手段，对合金的时效过程中时效析出相形态与析出序列以及时效初期铝基体内各溶质原子的分布情况进行了研究。同时结合第一性原理计算，对合金时效析出相的结构稳定性、热稳定性以及弹性性质进行了定量计算，从实验和理论两个方向相互佐证，对合金时效“双峰”现象、时效初期沉淀相的析出序列以及时效机理给出合理的解释。合金经175℃人工时效1h后即可观察到细小弥散的点状Q'相均匀地分布在合金基体中。时效4h后可观察到数量极少的针状θ"相，时效至6h时θ"相的尺寸和密度仍较小，但Q相的尺寸、数量达到了峰值，体现为合计硬度曲线上的第一个峰值；随着时效时间继续增加（6h-12h），Q相以及θ亚稳相继续长大，但Q相密度逐渐降低，同时θ亚稳相的尺寸及数量优势得到体现，当时效至12h时，θ亚稳相的数量及尺寸达到峰值，体现为合金硬度曲线上的第二个硬度峰；时效后期（12h以后）析出相会发生明显的粗化现象。根据3DAP的实验结果表明175℃时效15minMg、Si原子存在不同程度的偏聚，同时大量的Cu原子却仍处在一种均匀分布的状态，，合金基体中尚未形成Mg/Si/Cu复合团簇；时效2h后合金基体中Si、Mg原子聚集程度加剧，且Cu原子也发生一定的聚集，合金基体中出现Mg/Si/Cu复合团簇；时效4h后合金基体中Si、Mg、Cu原子聚集程度加剧，Mg/Si/Cu复合团簇数量增多，尺寸变大与合金的TEM实验结论一致。 θ'，θ''以及Q'相这三个亚稳相中，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相的各向异性程度相差不多，Al2Cu相为韧性相，Mg2Si相为脆性相。
[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.

【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG156.92

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