Coupling of dislocations and precipitates: Impact on the mechanical behavior of ultrafine grained Al-Zn-Mg alloys
Coupling of dislocations and precipitates: Impact on the mechanical behavior of ultrafine grained Al-Zn-Mg alloys
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DOI：
10.1016/j.actamat.2015.09.017
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发表时间：
2016-01-15
期刊：
影响因子：
9.4
通讯作者：
Schoenung, Julie M.
中科院分区：
文献类型：
--
作者：
Ma, Kaka;Hu, Tao;Schoenung, Julie M.
位错和沉淀物的晶内耦合在超细晶铝7000系列合金中通过独特的热机械加工路线来完成，该路线包括在环境温度下的高应变率挤压作为最后步骤。挤压材料还表现出独特的双峰微观结构，包括：（1）细长的片状晶粒，尺寸接近1 μ m，由通过小角度晶界的亚晶粒组成，和（2）超细晶粒，尺寸约为100 nm，具有大角度晶界。我们的研究表明，在超细晶粒内位错和沉淀物的耦合对机械行为具有有益的影响，并导致极高的强度，即，极限拉伸强度类似于878 MPa，断裂时的均匀延伸率为4.1%应变。有趣的是，T6回火导致具有晶内位错的超细晶粒材料的强度降低，同时其增强延展性，这与在不含高密度晶内位错的超细晶粒材料中观察到的行为相反。这种现象是由于位错强化和晶界强化的损失，而不能通过析出引起的强度增加来补偿。在原位加热的基础上讨论了相关机制。透射电子显微镜，扩散控制沉淀和微观结构表征的理论分析，包括透射菊池衍射。(c)2015 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Intragranular coupling of dislocations and precipitates is accomplished in an ultrafine grained aluminum 7000 series alloy through a unique thermo-mechanical processing route that involves high strain rate extrusion at ambient temperature as the last step. The as-extruded materials also exhibited a unique bimodal microstructure consisting of: (1) elongated lamellar grains with dimensions of similar to 1 mu m consisting of sub-grains via low angle grain boundaries, and (2) ultrafine grains approximately similar to 100 nm in size with high angle grain boundaries. Our investigation shows that coupling of dislocations and precipitates within the ultrafine grains has a beneficial impact on the mechanical behavior, and results in an extremely high strength, i.e., ultimate tensile strength similar to 878 MPa, with uniform elongation of 4.1% strain at fracture. Interestingly, the T6 temper leads to a decrease in strength for the ultrafine grained material with intragranular dislocations while it enhances ductility, which is opposite the behavior observed in the ultrafine grained material that does not contain a high density of intragranular dislocations. This phenomenon is attributed to the loss in dislocation strengthening and grain boundary strengthening, which could not be compensated for by the strength increase due to precipitation. The underlying mechanisms are discussed on the basis of in-situ heating in.a transmission electron microscope, theoretical analysis of diffusion controlled precipitation and microstructure characterization, including transmission Kikuchi diffraction. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.