利用EBSD, TEM和压缩测试研究了平均晶粒尺寸为0.8—5 μm的烧结细晶Al的微观组织与力学性能.研究表明, 随着晶粒尺寸的减小, 烧结细晶Al的力学行为发生转变: 平均晶粒尺寸小于1.3μm时,由于可动位错源的缺失, 细晶Al的应力--应变曲线表现出明显屈服降落现象; 平均晶粒尺寸减小至0.8μm时,细晶Al在变形过程中晶粒内部很少形成或不形成位错界面, 其应力-应变曲线表现为屈服后缺乏加工硬化.平均晶粒尺寸为5.2μm的细晶Al相比于常规粗晶Al来说, 由于晶界作用增加以及氧化物颗粒的影响,其位错界面取向差角的演变速率要更快. 总体来说, 由于氧化物颗粒的贡献,烧结细晶Al的强度要高于常规形变退火方法制备的具有相同平均晶粒尺寸的细晶Al,对于平均晶粒尺寸小于1.3μm的细晶Al, 位错源缺失也起着一定的强化作用.

Fine-grained metals have attracted much interest due to the possibility to obtain both high strength and high ductility. Studies of the deformation mechanisms in fine-grained metals are therefore important, and can also help fill a gap in knowledge between nano-grained metals and conventional coarse-grained metals, which is an area of both scientific and industrial interest. For such an investigation it is very important to use a starting material with a simple microstructure. For this purpose spark plasma sintering (SPS) has been used to prepare samples of fully dense, fine-grained Al with average grain sizes ranging from 0.8 μm to 5.2 μm, in a fully recrystallized condition, with equiaxed grains and a random texture. The microstructures and mechanical properties of these sintered fine-grained Al samples have been studied using EBSD, TEM and compression testing. Based on these studies, relationships between the microstructure and mechanical properties have been established. The results show that the formation of deformation microstructure depends on grain size. During deformation, all grains in samples with an average grain size of 5.2 μm show grain subdivision by dislocation boundary formation, though few grains in a sample with an average grain size of 0.8 μm show dislocation boundary formation. The mechanical properties of fine-grained Al show a transition in behavior with decreasing average grain size. For samples with an average grain size of 1.3 μm, stress-strain curves show yield drop phenomenon, attributed to source-limited hardening. For a sample with an average grain size of 0.8 μm, the stress-strain curveshows only limited work-hardening after yielding, in agreement with the observation of the limited formation of dislocation boundaries inside grains during deformation. For a sample with average grain size of 5.2 μm the average dislocation boundary misorientation angle increases more quickly than in deformed conventional coarse-grained Al deformed to the same strain, due to the effect of increased volume fraction of grain boundaries and oxide particles. The strength of the SPS-prepared Al samples is higher than found for samples with identical grain sizes prepared by thermo-mechanical deformation, due to the presence of oxide particles, and to source-limited hardening for samples with average grain sizes smaller than 1.3 μm.