基于多相强化机制的铝锂合金蠕变时效统一本构模型研究

In the age forming of aluminum alloy parts, the synchronization of the creep forming and age hardening brings advantages at the manufacturing efficiency and the product safety, but the collaboration of the shape and property comes to be the technical difficulty. The unified constitutive modeling for the creep age forming has been recognized as a effective characterization method. However, the previous related reports so far, in which the singlephase strengthening mechanism were taken into account, can no longer keep up with the diversified developing trend of the strengthening phases in the new aerospace aluminum alloys with high comprehensive property, such as the third gerneration Al-Li alloys. In this project, the apparent activation energy and its formation mechanism for the coexisting precipitation of the Al-Li alloys during the general aging and the creep aging processes will be firstly investigated. Then, the the influencing mechanism on the creep aging behaviors from the interactions between the multi-phase-change and the deformation can be ascertained by the aluminum alloy single crystals. On the basis of the multiphase strengthening mechanism, the cross-scale constitutive model of ‘stress relaxation - multiphase - creep strain - property’ will be established. The research results would expand the application range of the unified constitutive modeling method for the creep age forming, and also can be applied to develop the age forming of the third gerneration Al-Li alloys which are urgently needed in the aerospace manufacturing fields.

铝合金时效成形技术将金属蠕变与时效强化同步进行，可降低构件性能损伤并提高制造效率，而形/性协同也成为了该技术的难点所在。在针对铝合金时效成形的形/性同步工艺设计中，蠕变时效统一本构模型是目前公认行之有效的表征方法。但迄今为止已见报道的模型都只考虑了单一强化相的作用，无法适应以第三代铝锂合金为代表的航空航天用高综合性能铝合金的强化相多元化发展趋势。本项目首先探明常规时效与蠕变时效条件下铝锂合金多元强化相共存析出的表观激活能差异及形成机理，其后基于铝锂合金单晶体探明多元相变与形变交互作用对蠕变时效行为的影响机制，形成基于铝合金多相强化机制的“应力弛豫－多元强化相析出－蠕变量－性能”跨尺度关联模型，拓展蠕变时效统一本构模型方法的适用范围，并为研发航空航天急需的第三代铝锂合金构件时效成形提供理论基础。

铝合金时效成形技术可同时实现金属蠕变与时效强化，制造的构件性能大幅度提高，但形/性协同的调控在一定程度上阻碍了该技术的发展。对于以第三代铝锂合金为代表的航空航天用多相强化铝合金，传统的只考虑单一强化相的蠕变时效统一本构模型无法完美适用。本项目为了探明铝合金蠕变时效过程中强化机制由“单相”到“多相”而引发的一系列宏微观多尺度耦合效应，建立了基于多相强化机制的“应力弛豫－多元强化相析出－蠕变量－性能”跨尺度关联蠕变时效本构模型。分别研究了时效温度为160℃，蠕变加载应力为200MPa，T6无预拉伸进行人工时效（AA）和蠕变时效(CAA)以及T8有2%预拉伸后进行人工时效(PA)和蠕变时效(CPA)。通过分析时效后析出相的TEM图片，发现析出相表观激活能T1相高于θ′相和δ′相。统计了Al-Cu-Li合金试样不同强化相体积分数、相间距、特征尺寸，发现多相混合的情况下，高表观激活能的析出相（T1 相）所占比例越大，其表观激活能越高。探明了位错组态、惯析面与加载应力位向关系对Al-Cu-Li合金蠕变时效行为的作用机制，建立了基于多相强化机制的“应力弛豫－多元强化相析出－蠕变量－性能”跨尺度关联蠕变时效本构模型，拓展了蠕变时效统一本构模型方法的适用范围，并为研发航空航天急需的第三代铝锂合金构件时效成形提供理论基础。