AA 7055铝合金时效析出强化模型

利用小角度X射线散射技术获得的系列定量信息,综合运用时效析出动力学理论和析出相切过、绕过强化机制,研究了AA 7055铝合金在120和160℃时效过程中的屈服强度演变模型。结果表明,在时效早期盘状析出相的盘面半径和半厚度均与t^1/2(t为时效时间)成线性关系;在时效后期,析出相尺寸则与t^1/3成线性关系。时效过程中析出相体积分数与t的变化关系遵循JMA (Johnson-Mehl-Avrami)型表达式。综合考虑了GPI区和η’相2类析出相对合金强度的贡献,并且分别考察了这2类析出相的模量强化机制和共格应变强化机制,最终建立了AA 7055铝合金在120和160℃时效过程中的屈服强度变化模型,确定了该合金时效过程中析出相与屈服强度之间的定量关系。

Precipitation Strengthening Model of AA 7055 Aluminium Alloy

AA 7055 aluminium alloy has been widely applied in aviation and aerospace applications,especially after T7751 heat treatment, owing to its excellent properties, such as high strength and good stress corrosion and fatigue resistances. For 7XXX aluminium alloys, aging hardening is the main strengthening mechanism, and the hardening effect is determined by the microstructural features of precipitates including morphology, composition, volume fraction, nucleation density, and size distribution. To further improve the property of alloy and expand the breadth of applications, establishing a precise predictive model regarding strength performance associated with the precipitates is necessary. In this work,based on the quantitative results of the precipitates obtained using small angle X-ray scattering techniques, the strengthening models of AA 7055 Al alloys aged at 120 and 160 ℃ were investigated. Precipitation kinetics show that at the early stages of aging, the evolution of radius and the half thickness of plate-like precipitates are both linear with t^1/2(t means the aging time). Conversely, at the later stages of aging, they are linear with t^1/3. The evolution of the volume fraction of the precipitates follows a JMA(Johnson-Mehl-Avrami)-type equation. Strength contributions from both GPI zones and η’ precipitates are considered. Moreover, strengthening modeling considered both the modulus and coherency strain strengthening mechanisms of these two kinds of precipitates that had been built for the AA 7055 Al alloy aged at 120 and 160 ℃. Therefore, yield strength during aging can be predicted.