温度场和应变场耦合作用下Al-Zn-Mg-Cu合金时效析出机制研究

In the thermal-strain process, the coupling effect from the temperature and strain obviously influence the precipitation behavior of Al-Zn-Mg-Cu alloy, which determine the precipitates feature and properties of Al-Zn-Mg-Cu alloy. In order to regulate the microstructure and improve properties of Al-Zn-Mg-Cu alloy after thermal deformation, the research on the precipitation mechanism and regulation of Al-Zn-Mg-Cu alloy under the coupling condition of the thermal field and strain field is necessary. The main investigation on the precipitation mechanism and regulation of Al-Zn-Mg-Cu alloy during the thermal-strain process includes: (1) investigating the precipitation thermodynamics of Al-Zn-Mg-Cu alloy during the thermal-strain process, through calculating the dissolved curve of solid solution atom and precipitates formation-enthalpy, (2) investigating the precipitation kinetics of Al-Zn-Mg-Cu alloy during the thermal-strain process, through calculating the diffusion activation energy and diffusion parameters of solid solution atom, (3) characterizing the precipitates feature and evolution of Al-Zn-Mg-Cu alloy on atom scale by 3DAP and HRTEM during the thermal-strain process. Based on the above researches, the precipitation mechanism and precipitation regulation can be revealed. The investigation can also enrich the precipitation theory and improve properties of Al-Zn-Mg-Cu alloy under the coupling condition of the thermal field and strain field.

热-应变耦合作用下Al-Zn-Mg-Cu合金中固溶元素的析出行为显著制约着该合金的析出组织特征和合金性能。为了调控该铝合金热变形后的析出组织，提高合金性能，本课题针对温度场和应变场耦合作用下Al-Zn-Mg-Cu合金中固溶元素的析出行为展开系统研究。拟通过(1)第一性原理计算Al-Zn-Mg-Cu合金热应变条件下固溶元素的溶解曲线和析出能垒，研究热-应变耦合过程该合金析出的热力学机制，(2)计算Al-Zn-Mg-Cu合金热应变条件下固溶元素的扩散热/动力学参数,研究热-应变耦合过程该合金析出的动力学机制；(3)利用HAADF和3DAP技术从原子尺度上表征热-应变耦合作用下Al-Zn-Mg-Cu合金内固溶元素的团簇和析出行为。以此揭示热-应变耦合作用下该合金内固溶元素的析出机制与析出规律，丰富铝合金时效析出理论，也为将来利用温度和应变变化精细调控该合金析出组织提供理论支持。

本项目针对温度场和应变场耦合作用下Al-Zn-Mg-Cu合金中固溶元素的时效析出动力学行为和析出机制展开系统研究。本项目选择商用的7050合金轧板作为研究对象，分别进行应力时效和应变时效，然后通过(1)定量表征应力时效和应变时效后合金内析出相的尺寸和分布，通过计算揭示了外加应力场促进Al-Zn-Mg-Cu合金时效析出的热力学机制。(2)金相显微镜、透射电镜(HRTEM)和DSC技术详细表征应变时效过程中Al-Zn-Mg-Cu合金内固溶元素的析出行为，并研究了应变量对Al-Zn-Mg-Cu合金时效析出行为的影响规律，推导得到该合金的析出动力学方程。(3)利用分子动力学软件(LAMMPS)计算Al-Zn-Mg-Cu合金热应变条件下固溶元素的扩散热/动力学参数，研究热-应变耦合过程该合金析出的动力学机制。(4)分析了外加应变场对Al-Zn-Mg-Cu合金时效后力学性能和腐蚀性能的影响规律，优化了Al-Zn-Mg-Cu合金热-应变耦合时效工艺，提升了该合金的综合性能。本项目研究较好地揭示了热-应变耦合作用下该合金内固溶元素的析出机制与析出规律，丰富铝合金时效析出理论，也为利用温度和应变变化精细调控该合金析出组织提供理论支持。