【作者】 田畅；

【导师】 李荣德；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2014， 博士

【摘要】 本文基于密度泛函理论的第一性原理研究了Cu、Mg、Si原子对Al基体所产生的固溶强化机理；根据质点（溶质、空位）间的相互作用分析了Al-Si-Cu、Al-Si-Mg、Al-Si-Cu-Mg合金时效初期的团簇形成过程；结合动力学蒙特卡罗（Kinetic Monte Carlo,简称KMC）法模拟获得了合金时效初期动态、直观的团簇形成图像；分析了Al-Si系合金中θ、β序列沉淀相的析出行为及性能。利用第一性原理计算了含溶质Cu、Mg、Si原子的铝合金超胞结构的电子参数。根据态密度分析结果表明：Cu、Mg与Al基体存在较强的结合，而Si与Al原子间的结合相对较弱。利用电子局域化函数（ELF）对Al107X1超胞结构中化学键进行定量分析，从超胞结构中化学键络的增强程度及范围发现Mg原子的固溶强化效果比Cu原子显著，Si原子的固溶强化效果最弱，与根据错配度分析的元素的强化效果相吻合。利用第一性原理计算了面心立方结构Si相的内聚能，进而获得Si原子相关的模拟参数，为含Si原子的铝合金时效初期微观组织演变的模拟提供了可能。Al-Si二元合金时效初期的微观组织演变模拟结果表明：在十几秒内含几百个Si原子的Si团簇便能够形成，这与Al-Si二元合金中Si相能够快速析出的结论相一致。Al-Si-Cu合金时效初期团簇形成行为的第一性原理计算结果表明，富Si团簇及富Cu团簇均能形成，而Si原子占据空位的能力更强，富Si团簇形成较快，相对而言，富Cu团簇形成较慢。含Si、Cu原子的团簇结构也能够形成，由于扩散能力的差异，Si-Cu团簇富Si贫Cu，因此可能向Si相转变。这可能是合金中Si和Cu原子组成的沉淀相未出现的原因。对Al-Si-Cu合金时效初期微结构演变的模拟结果表明：富含Si原子的团簇形成较快，与Al-Si合金相比，Cu元素的加入未对Si团簇的形成长大有明显的影响。部分Si团簇中含有极少量的Cu原子，而小尺寸的富Cu团簇出现较晚，这与电子理论计算结果相符。富Cu团簇的形成为θ序列沉淀相的析出提供了成分基础。沉淀序列中θ相、θ相的形成焓及态密度分析表明θ相具有更强的稳定性。在535K左右，θ相与θ相的稳定性发生转变，即在高温下θ相稳定性更强，这与已有计算及实验结论相符。对两相的键布局分析结果表明：θ相中的共价键结合能力较强，抵抗变形的能力越强，宏观上表现为更高的硬度，当该相存在时对合金的硬化效果要好于θ相。当θ相演变为θ相后合金硬度值发生下降可能与二者硬化效果的差异有关。Al-Si-Mg合金时效初期团簇形成行为的研究表明：Si、Mg原子均能够通过空位快速扩散，富含Si原子的团簇以及富含Mg原子的团簇均形成较快。Mg原子间相互排斥，Mg原子更倾向与Si原子结合，而主要存在于Si-Mg团簇结构中。对Al-Si-Mg合金时效初期团簇形成行为的模拟表明：合金基体中出现了大量富含Si和Mg原子的团簇。与Cu原子对Si团簇的形成影响不同，Mg原子的加入促进了基体中富含Si、Mg原子团簇的析出，为β序列沉淀相的形成提供了成分基础。β序列沉淀相中具有多个结构成分的β相，成分为Mg9Si5的相为最稳定的β相结构。β沉淀序列中GP区、β相、β相、β相的热力学稳定性依次增强，随着时效时间的延长或温度的升高，沉淀相将依次析出，这与沉淀相析出序列SSS-GP区-β-β-β完全符合。采用3DAP技术对富Si、高Cu/Mg比的Al-Si-Cu-Mg（wt%）合金时效初期的微观组织的研究表明：合金时效0.25h时，基体中主要存在小尺寸的富含Si、Mg原子的点状Si-Mg-Cu团簇和Si-Mg团簇。这一实验结果很好地证实了KMC模拟结果的正确性。同时与三元合金相比，四元合金中团簇数量更多，尺寸更小。3DAP实验表明合金时效0.25~4h的过程中，团簇结构逐渐向板条状的Q相转变。并且时效4h时出现了小尺寸的富Cu原子结构。更多还原

【Abstract】 The solid solution hardening efficiency of different alloying elements such as Cu, Mg,and Si on Al solid solutions were investigated according to the chemical bonding of Al solidsolutions in this thesis by using the first-principles. The cluster formation behaviors wereanalyzed according to the interactions between particles (solutes, vacancy) in Al-Si-Cu,Al-Si-Mg and Al-Si-Cu-Mg alloys. The Kinetic Monte Carlo (KMC) method was applied tosimulate the distribution of time-dependent solute in Al-Si base alloys. The precipitationbehavior and property of precipitates in β and θ sequences were studied by means offirst-principles calculations.The interactions between particles (solutes， vacancy) were studied by means offirst-principle calculations to obtain the binding energies and stable structures of complexes.Density of State (DOS) shows strong interaction between Cu and Al atom, Mg and Al atomand weak interaction between Si and Al atom. A quantitative understanding on the chemicalbonding of Al107X1solid solutions can be gained by analyzing the electron LocalizationFunction (ELF). The order of solid solution hardening efficiency of Cu, Mg and Si in Al maybe understood according to the increased bonding strength and range of Al107X1solidsolutions.The coherent energy of Si phase with face centered cubic lattice structure and thesimulation parameter were calculated by first-principles. The simulation results of clusterformation behavior in Al-Si alloy show that Si clusters with hundreds of Si atoms may form intens seconds. This is consistent with the conclusions that Si phase precipitates quickly.The analysis of clusters formation behavior according to the interactions betweenparticles (solute, vacancy) in Al-Si-Cu alloy shows that Si-rich clusters and Cu-rich clusterscould form. The formation of Si clusters is rapid due to the powerful occupying to vacancy bySi atoms. Clusters contains Si and Cu atoms may appear and with higher Si and less Cucontent. Si-Cu clusters may transform to Si phase. The KMC simulation results show that Siclusters form and Cu atoms have no impact on the formation of Si clusters in Al-Si-Cu alloyscompared to Al-Si alloy. Si-Cu clusters appear with less Cu atoms and Cu-rich clusters appearlater. It is consistent with the calculation. The precipitation behavior and property of precipitates in θ and θ phase were studied by means of first-principle calculations. θ phasehas stronger heat stability according to the analysis of formation enthalpy and DOS. The bondpopulation analysis results show that the covalent bonding ability of θ ’ phase is stronger, thegreater the ability of resistance to deformation, the higher the hardness of the alloy, hardeningefficiency may be better when θ ’ phase exists rather than θ phase. Alloy hardness valuesdecline when θ ’ phase transforms to θ phase may be relation to the differences of propertybetween them.The analysis of cluster formation behavior on the basis of the interactions betweenparticles (solute, vacancy) in Al-Si-Mg alloy shows that similar to Al-Si-Cu alloy Si clusterscould form quickly.(Si, Mg)-rich clusters also form quickly because Mg atom could diffuserapidly and has a stronger tendency to bind with Si atom than with Mg atom. The KMCsimulation results show that Si-Mg clusters form and Mg atom promotes the formation of (Si,Mg)-rich clusters compared to Al-Si alloy.(Si, Mg)-rich clusters provide the componentfoundation for the β precipitation sequence. Formation enthalpy calculations of β’ phase showthat Mg9Si5phase is the most stable β’ phase structure. The thermodynamic stability issuccessively increased from GP zone, β’’ phase, β ’ phase and to β phase. With theimprovement of aging temperature, the precipitates will sequentially appear. It is consistentwith the aging precipitation sequence supersaturated from solid solution (SSS)-GP zone-β’’-β’-β.Evolution behavior of clusters and subsequent precipitation in Al-Si-Cu-Mg alloy withexcess-Si and high Cu/Mg ration during aging were studied by means of three DimensionalAtom Probe (3DAP).3DAP experiment results show that dot-like (Si, Mg)-rich clustersincluding Si-Mg and Si-Mg-Cu clusters appear in alloy aged at175℃for0.25h, which isconsistent with the first-principles calculation that the strong binding between Si atoms, Si andMg atoms, Si, Mg and Cu atoms and clusters with corresponding component can exist stably.The KMC simulation results show that Si-Mg clusters and Si-Mg-Cu clusters form. Thenumber of clusters is more and the size of clusters is smaller.3DAP results show that at0.25to4h clusters continue transition to Q’ phase (Al4Cu2Mg8Si7) and small Cu-rich clusters appear at4h.更多还原