Al-Zn-Mg合金中的双峰时效析出硬化建模(英文)

Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

Al-Zn-Mg合金在长时间的时效中存在双峰硬化现象,为了模拟析出硬化动力学,基于改进的Langer–Schwartz方法发展了不同析出物形成的双峰硬化模型。该物理模型考虑了Al-Zn-Mg合金在时效过程中新析出物的形核、生长、粗化,同时考虑了颗粒相互作用的2种机制(剪切和绕过)。将模型预测结果和实验结果进行了对比,结果表明两者吻合很好。系统和定量模拟研究结果表明:通过在生长方程中添加形函数,硬度曲线与测量值吻合;模型根据析出物的尺寸和体积分数定量评价该合金的力学性能;强化机制包括剪切和绕过2种机制,剪切机制向绕过机制的转变发生在颗粒生长的早期,而绕过机制是主要强化机制。

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.