新型铝锂合金大应变热力耦合条件下显微组织遗传演变调控机理研究

The Al-Li alloys are known to offer an attractive combination of properties for structural applications: these alloys generally have a low density, a high elastic modulus and high specific strength, largely attributed to highly efficient precipitation strengthening. This combination of properties has led to their use primarily in aerospace applications. Until recently, however, their application has been limited by integrated forming technology. In the context of high fuel prices and fierce competition between composite materials and aluminium alloys, a new Al-Li alloys, X2A66, have been developed that overcome most of the technical issues of integrated forming which can achieve 15~18% weight reduction. As such, there is currently a renewal of interest in this alloy system as demonstrated by their inclusion in several new airplane solutions. In present study, the impact of the Cu/LiMg ratio on the sequence and kinetics of solid-state precipitation will be studied for recently developed Al-Cu-Li-Mg-Zn alloys: X2A66. A quantitative evaluation of the alloy microstructure is carried out using In-suit SAXA, In-suit TEM and In-suit EBSD. Because of the evolvement and distribution of the microstructure in the forming process have a direct influence on the mechanical properties, dimensional accuracy and residual stress of the parts. So, among the various parameters of the forming process, the simulation and optimization of the microstructure are pivotal and integrant. The optimal methods based on the sensitivity analysis and genetic algorithm are researched and constructed. Based on the above analysis, the multiple objective perform optimal design of the X2A66 alloy during plastic deformation will be studied.

有效的微观组织调控，是"精、近、净"制造技术实现性能控制、尺寸精度控制和残余应力控制的关键。本项目针对铝锂合金中Li、Mg、Cu三原子在"热-力"耦合条件下与缺陷结构的交互作用机制，及其对材料的应变过程、晶界类型、晶粒大小、缺陷结构、微观织构和析出相的影响规律这个核心科学问题，从不同"热-力"耦合条件下δ'相和θ'相析出和演变规律；微观组织遗传因子对X2A66铝锂合金塑性变形行为的影响规律；微观组织遗传因子在热塑性加工过程中的演变规律三个方面的研究出发，采用In-suit EBSD、In-siut SAXS和In-suit TEM相结合的现代化微观组织观察手段，运用"微观模拟"技术与"微观遗传数值模拟算法"，剖析X2A66铝锂合金在大应变条件下的微观组织遗传机制，阐明析出相、晶粒、晶界、织构、残余相和缺陷结构六种遗传基因的调控机理，获得新型国产铝锂合金无余量整体挤压壁板结构制造技术的原型。

X2A66铝锂合金为新一代高强韧耐损伤铝锂合金，其合金成分接近500℃高温饱和临界线，是新一代铝（锂）合金发展的代表。伴随高组分出现的组织遗传演化规律是发展新一代铝（锂）合金亟需解决的科学问题。.本项目基于以前的研究认识，针对具有临界饱和成分的X2A66新一代铝锂合金，研究了均匀化退火的高温温度场及时间效应下的X2A66铝锂合金铸锭组织及性能演化规律；研究了包括锻造、挤压及轧制等成形工艺的“高低温交替变形热-力耦合场”对X2A66铝锂合金组织及性能的演化规律；研究了X2A66铝锂合金固溶高温温度场下组织演化及第二相析出演化行为；研究了时效温度场及时间效应下第二相析出演化行为。.从金相照片和SEM背散射照片可以看出，合金铸锭的基体存在较为严重的枝晶偏析，且合金的晶界处分布着大量的非平衡共晶相。能谱分析可知，这些晶界处分布的非平衡共晶相主要为融入了Mg的Al2Cu相。采用双阶均匀化处理可以提高均匀化温度，从而改善均匀化效果。500°C/8h+520°C/48h处理后铸锭显微组织中的非平衡相减少，晶界逐渐清晰，各元素分布趋于均匀。.X2A66铝锂合金“热-力耦合场”作用下的组织结构演化规律表现为：在变形量为10%时，位错趋于低能状态，软化机制为动态回复，但动态回复进行的不充分，形成的亚晶组织不完整，还没有细化；当变形量达到50%时，随着变形的进行，变形产生更多的空位，使位错的运动速度加快，同时部分异号位错相互抵消也降低了位错的密度；变形量为75%时，基体内形成了典型了亚晶粒，亚晶的晶粒形状规整，晶界平直清晰，说明基体内已经发生了充分的动态回复。.X2A66-T3合金的主要强化相是δ'相，不存在晶间无析出带；X2A66-T6合金数量最多的强化相是δ'相和θ'相，同时存在部分T1，存在晶间无析出带；X2A66-T8合金数量最多的强化相是T1相和θ'相，同时存在少量δ'相，不存在晶间无析出带。.本项目解决了高组分Li、Mg、Cu三种原子在不同“热-力”耦合条件下的应力-应变过程、晶界类型、晶粒大小、缺陷结构、微观织构、宏观织构和析出相形貌/分布影响机理这个核心科学问题，最终建立了新型铝锂合金在大应力“热-力”耦合条件下以变形微观组织和形状为优化目标的多相场优化遗传设计技术原型，完成了新高组分一代铝锂合金制备技术关键科学问题探索，为展新一代高性能铝（锂）合金发展奠定了基础。