超细晶Al-Mg合金中溶质Mg原子调控韧性和强度的机制

In an effort to improve ductility of ultra-fine grained (UFG) Al-Mg alloys, this project suggests to pin dislocations using solute Mg atoms, enabling the dislocation accumulation at grain interiors and thus improving the work-hardening ability during tensile testing, and to utilize the structural uniformity of Al-Mg solid solutions to minimize stress concentration during tensile straining, delaying the occurrence of strain localization (necking) and thus achieving high uniform elongation (ductility). To accomplish the above goals, this project will study the mechanisms underlying the influence of solute concentration, grain size and the existing dislocations inside the ultra-fine grains on dislocation accumulation and work hardening, and on strain localization, generated by pinning of solute Mg atoms, during tensile straining. Moreover, in order to tailor the strength of UFG Al-Mg alloys, this project will also explore the possibility for a high density of existing intragranular dislocations, which are induced by the presence of solute Mg atoms, to activate the operation of the intragranular dislocation sources during tensile yielding, and study the corresponding mechanisms. Based on the above strengthening and toughening mechanisms revealed, this project will tailor the solute Mg concentration, grain size and existing dislocation density inside the ultra-fine grains to achieve excellent ductility and ultra-high strength in the UFG Al-Mg alloys.

为了提高超细晶Al-Mg合金的韧性，本项目提出用溶质Mg原子钉扎位错，实现拉伸过程中位错的累积和加工硬化能力的提高；利用固溶体结构的均匀性最大限度降低应力集中，推迟加工硬化过程中应变局部化（颈缩）的发生，即获得高的均匀延伸率（韧性）。为实现上述目标，本项目将研究拉伸变形过程中超细晶Al-Mg合金的溶质Mg浓度、晶粒尺寸、超细晶中已存位错影响溶质Mg原子钉扎位错引起位错累积和加工硬化的机制、影响上述加工硬化过程中应变局部化的机制。同时，为调控超细晶Al-Mg合金的强度，本项目也将研究拉伸屈服过程中超细晶内由于溶质Mg原子存在引起的高密度已存位错诱发晶内位错源开动的可能性及相应的机制。基于这些强韧化机制，本项目将调控溶质Mg浓度、晶粒尺寸、超细晶中已存位错密度，获得同时具有良好韧性和超高强度的超细晶Al-Mg合金。

像其它超细晶金属材料一样，超细晶Al-Mg合金的韧性较差，特别是拉伸韧性，严重限制了它们在航空航天工业、轨道交通装备制造业、新型节能环保汽车制造业等高端制造产业中的广泛应用。为了提高超细晶Al-Mg合金的韧性，本项目提出用溶质Mg原子钉扎位错，实现拉伸过程中位错在晶内的累积和加工硬化能力的提高。本项目确认了超细晶Al-Mg中溶质Mg原子提高加工硬化能力和韧性的效果，研究了溶质Mg原子调控超细晶Al-Mg合金韧性和强度的机制，包括：溶质Mg原子提高位错存储能力和加工硬化能力的具体机制、高密度位错诱发位错源强化机制的可能性，研究同时具有良好韧性和超高强度的Al-Mg超细晶合金中Mg 溶质浓度、晶粒尺寸和已存位错密度的特点。研究表明，在本项目研究的超细晶Al-(1-10)wt%Mg合金中，溶质Mg原子提高位错存储能力和加工硬化能力的机制有两种：溶质原子偏聚于位错线形成的Cottrell气团对运动位错钉扎、溶质原子迟滞位错运动从而使位错之间交互作用形成的位错缠结对位错运动的阻碍；在本项目研究的Al-(1-10wt%)Mg超细晶合金中，高达7.12E14 m-2的位错密度并没有诱发位错源强化机制；具有高溶质浓度、小晶粒尺寸、高密度位错的超细晶Al-Mg合金能同时获得超高强度和良好韧性，本项目研究中通过液氮温度下轧制到厚度压下量95%获得的超细层片状Al-10wt%Mg合金能够同时获得超高强度和良好韧性，轧制态拉伸屈服强度高达625 MPa、均匀延伸率5.1%，100 C退火1小时后拉伸屈服强度仍高达530 MPa、均匀延伸率提高到11.2%。用溶质原子钉扎位错来提高位错在晶内累积和加工硬化能力提供了一条提高超细晶材料韧性的新途径，为发展具有高强度和良好韧性匹配的超细晶合金开辟了一条新道路。

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