时效强化Al-Mg-Si-Cu合金GP区和亚稳相的热力学和弹性研究

因时效过程析出纳米尺度的GP(Guinier-Preston)区和系列亚稳强化相，Al-Mg-Si-Cu合金具有优异的成形性和较高的比强度。定量描述GP区和亚稳相的生成与相互转变过程是Al-Mg-Si-Cu合金性能优化和提高的关键。当前仅凭实验很难准确阐明GP区和亚稳相之间的转变。本项目拟集成第一原理计算、相图计算和关键实验开展如下工作：1)基于文献报道的GP区和亚稳相的结构，通过第一原理计算寻找稳定构型，并计算各相高温热力学及弹性性质，从而预测不同温度下各析出相的结构稳定性与相变；2)制备含亚稳相的样品，综合多尺度实验技术验证第一原理预测的结构和弹性性质；3)采用相图计算方法建立含GP区和亚稳相的Al-Mg-Si-Cu体系热力学和弹性数据库，从而构筑亚稳相图并预测时效强化过程的相变序列。项目的完成将扩展相图计算的应用范围，为设计和改善铝合金的热处理工艺与性能提供理论基础。

Al-Mg-Si-Cu alloys are widely used due to their great compatibility, low density and good strength. Nano-sized Guinier-Preston (GP) zones and needle-like metastable precipitates are strengthening phases for Al-Mg-Si-Cu alloys during aging, the formation and transformation of these metastable phases are crucial information for the design and control of the performance of Al alloys, but it is difficult to identify these metastable phases and their effects to the properties of alloys only by experiments. The present project plans to incorporate first-principles calculations, CALPHAD (CALculation of PHase Diagram) method and key experiments to work on the following aspects: 1) Using first-principles calculations to find the stable compositions, crystal structures, energies and elastic properties of the GP zones and metastable phases by searching all the possible configurations, using first-principles lattice dynamics and quasi-harmonic approximation to study the finite temperature thermodynamic and elastic properties, and determine the phase stability and transformation of the metastable phases at different temperatures. 2) Prepare key samples with metastable phases by following the industrial Aluminum production processes, and using comprehensive experimental characterization techniques to verify the predicted results predicted from fist-principles. 3) Using CALPHAD method to establish a thermodynamic and elastic databases containing GP zones and metastable phases based on the crystal structure, thermodynamic and elastic date, and predict the phase transition sequences during ageing and metastable phase diagrams. The completion of this project will implement the thermodynamic properties of the GP zones and metastable phases in the thermodynamic and elastic database, extend the application area of CALPHAD method. It is highly expected that the present work will provide the theoretical basis to the design and control of the performance and heat treatment parameters of Al alloys.