高压扭转变形制备梯度微纳晶Al-Cu-Mg合金及其强化机制研究

Ultrafine-gained (UFG)/nano-grained (NG) aluminum alloys fabricated by severe plastic deformation (SPD) have garnered an intense scientific interest because strengths and the hardness of these alloys are significantly increased. However, after SPD processing, plasticity and toughness of these alloys become worse. UFG/NG Al alloys lose their potential to deform further. In order to achieve the excellent overall mechanical properties, it is of great meaning to fabricate the UFG/NG gradient microstructures. On the other hand, the alloying atoms and solute clusters show a trend to segregate to dislocations, UFG and NG boundaries, along which nano-precipitates nucleate and grow into coarse particles. As a result, the behaviors of alloying atoms and solute clusters contribute to the improvement of overall mechanical properties, and play a role in enhancing the thermal stability of Al alloys. Referred to the concept of nanostructured grain gradient, this project aims at designing and fabricating the UFG/NG gradient Al-Cu-Mg alloys. Furthermore, it aims at establishing a fundamental theory that reveals the intrinsic relationship between UFG/NG gradient, the behaviors of alloying elements/solute clusters and their mechanical properties. The studies in this project involve four parts: (1) the dislocation migration and accumulation; (2) the grain fragment and refinement, (3) solute clusters segregation, and (4) nano precipitation and precipitate coarsening in each specific grain size range. It will be the first time to export grained gradient effects in UFG/NG Al-Cu-Mg alloys. A multiply strengthening model can be established to explain the difference in mechanisms between homogeneous and non-homogeneous microstructures. This project reveals its great importance in scientific researches: it will provide a novel way to fabricate the UFG/NG gradient Al alloys, of which possess excellent properties; furthermore, it will enrich the fundamental theories on non-uniform severe plastic deformation and the UFG/NG grain gradient strengthening theories.

大塑性变形技术制备微纳晶铝合金具有极高的强度和硬度而备受关注，但伴随着塑韧性和变形潜力的显著下降，通过构建晶粒尺寸梯度结构，对实现铝合金综合性能的优化具有重要意义。而合金元素在微纳晶结构中团簇偏聚及形成纳米相，将使铝合金的机械性能和热稳定性显著提高。本项目借鉴纳米梯度结构的概念，采用高压扭转变形工艺设计制备梯度微纳晶Al-Cu-Mg合金；解决梯度微纳晶结构、合金元素行为与力学性能内在关系这一关键科学问题。本项目拟系统考察各个特征尺度微纳晶结构Al-Cu-Mg合金位错迁移、塞结，晶粒破碎、细化，溶质原子、原子团簇偏聚，纳米沉淀相析出、粗化等过程；率先探索Al-Cu-Mg超细合金晶粒尺寸梯度效应，构建非均匀变形多重强化机制模型，阐明其与均匀结构变形机制之间的差异。本项目将为高性能铝合金材料制备提供了新思路，并丰富大塑性非均匀变形的基础理论和晶粒尺度梯度强化理论，具有重要的科学研究意义。

本项目采用高压扭转变形工艺设计制备非均匀超细晶Al-Cu-Mg合金，解决非均匀超细晶结构、合金元素行为与力学性能内在关系这一关键科学问题。高压扭转变形技术具有变形量大、变形效率高、变形过程中不引入杂质等优点。本项目探讨了Al-Cu-Mg单向回转变形、反复大塑形变形（如设定如下周期：(1/4r-1/4r)n、(1/2r-1/2r)n等变形模式）时，相析出行为、位错演变方式、晶界运动行为。发现高压扭转变形中，合金的晶粒尺寸明显细化，位错密度增加，其变形方式与位错密度增量紧密相关。溶质原子及团簇偏聚在超细晶结构，促进了S纳米相析出；提高了合金机械性能及其热稳定性。构建了非均匀变形多重强化机制模型，阐明了其与均匀结构变形机制之间的差异。.本项目将Al-Cu-Mg合金高压扭转变形力学强化模型应用在Al-Mg-Si合金体系中，为高性能铝合金材料制备提供了新思路，丰富了大塑性非均匀变形的基础理论，具有重要的科学研究意义。Al-Mg-Si合金先析共格针状β″相在高压扭转变形溶解，随着变形量的增加，位错密度显著增加，晶粒尺寸显著降低。通过在其他合金（如3D打印316L不锈钢）高压扭转变形非均匀变形力学及物理化学性能（如耐腐蚀性等方面）探索，获得普适金属及合金强化模型理论，可用于指导工业生产上热处理与机械加工相互协调，以综合提高金属及合金的机械性能及物理化学性能，具有潜在应用前景。