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Jizi Liu
Nano and Heterogeneous Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China

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Journal article
Published: 31 August 2020 in Journal of Alloys and Compounds
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The post-deformation aging response and underlying precipitation kinetics in ultrafine-grained, age-hardened alloys processed by severe plastic deformation are critical and heretofore poorly understood phenomena that ultimately influence mechanical behavior. In this study, a supersaturated solid solution 7075 Al alloy was processed by equal-channel-angular pressing (ECAP) route Bc at 250 °C for 6 passes to attain ultrafine grained (UFG) structures. Thermal and mechanical analyses revealed that there are three sequential phase transitions that govern post-deformation aging: first, dissolution reactions of Guinier-Preston (GP) zones, metastable ηp and η′ precipitates which correspond to slight decreases in strength and ductility; second, afresh precipitating of GP zones, metastable ηp and η′/stable η phases corresponding to an increase in strength with significant decrease in ductility; and third, subsequent η transformation of the metastable η′ and ηp as well as coarsening of stable η phases corresponding to a dramatic decreases in strength. Microstructural analysis suggests that the significant decrease in ductility may be attributed to grain boundary precipitation of the metastable ηp and η′/stable η phases.

ACS Style

Yonghao Zhao; Jizi Liu; Troy D. Topping; Enrique J. Lavernia. Precipitation and aging phenomena in an ultrafine grained Al-Zn alloy by severe plastic deformation. Journal of Alloys and Compounds 2020, 851, 156931 .

AMA Style

Yonghao Zhao, Jizi Liu, Troy D. Topping, Enrique J. Lavernia. Precipitation and aging phenomena in an ultrafine grained Al-Zn alloy by severe plastic deformation. Journal of Alloys and Compounds. 2020; 851 ():156931.

Chicago/Turabian Style

Yonghao Zhao; Jizi Liu; Troy D. Topping; Enrique J. Lavernia. 2020. "Precipitation and aging phenomena in an ultrafine grained Al-Zn alloy by severe plastic deformation." Journal of Alloys and Compounds 851, no. : 156931.

Paper
Published: 14 February 2020 in Nanoscale
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The enhanced thermoelectric performance is achieved in nanostructured SnTe with band convergence and resonant level prepared by a green and facile hydrothermal method.

ACS Style

Wenqi Lu; Tiantian He; Shuang Li; Xinru Zuo; Yao Zheng; Xunuo Lou; Jian Zhang; Di Li; Jizi Liu; Guodong Tang. Thermoelectric performance of nanostructured In/Pb codoped SnTe with band convergence and resonant level prepared via a green and facile hydrothermal method. Nanoscale 2020, 12, 5857 -5865.

AMA Style

Wenqi Lu, Tiantian He, Shuang Li, Xinru Zuo, Yao Zheng, Xunuo Lou, Jian Zhang, Di Li, Jizi Liu, Guodong Tang. Thermoelectric performance of nanostructured In/Pb codoped SnTe with band convergence and resonant level prepared via a green and facile hydrothermal method. Nanoscale. 2020; 12 (10):5857-5865.

Chicago/Turabian Style

Wenqi Lu; Tiantian He; Shuang Li; Xinru Zuo; Yao Zheng; Xunuo Lou; Jian Zhang; Di Li; Jizi Liu; Guodong Tang. 2020. "Thermoelectric performance of nanostructured In/Pb codoped SnTe with band convergence and resonant level prepared via a green and facile hydrothermal method." Nanoscale 12, no. 10: 5857-5865.

Journal article
Published: 27 December 2019 in Journal of Alloys and Compounds
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Nature aging (NA) is believed to produce solute nanostructures, including solute clusters and GPI zones in Al–Zn–Mg alloys. Here we report the first observation that GPII (GPη’) zones with an average Zn/Mg ratio near 1.3–1.4 formed in the Al–Zn–Mg alloys during long-term natural aging. High-angle-annular-dark-field scanning transmission electron microscopy and atom probe tomography were used to study the evolution of solute nanostructures during natural aging. Early clusters were found to have a wide spread of Zn/Mg ratios and their number density increased sharply with a dramatic hardening effect during the first month ageing. Further ageing up to 3 months made the Zn/Mg ratios of the solute clusters gradually converge to near 1.2 (GPI zones), but produced no change in the morphology, size distribution and volume fraction of the solute nanostructures, as well as hardness. At room temperature, GPII (GPη’ type) zones formed very slowly and provided stronger hardening effects than early clusters. Importantly, unlike solute-rich clusters, GPI and GPη’ zones are easy to transform into η′ during subsequent artificial ageing, avoiding hardness drop at the early stage of subsequent artificial aging at 120 °C.

ACS Style

Jizi Liu; Rong Hu; Jialing Zheng; Yidong Zhang; Zhigang Ding; Wei Liu; Yuntian Zhu; Gang Sha. Formation of solute nanostructures in an Al–Zn–Mg alloy during long-term natural aging. Journal of Alloys and Compounds 2019, 821, 153572 .

AMA Style

Jizi Liu, Rong Hu, Jialing Zheng, Yidong Zhang, Zhigang Ding, Wei Liu, Yuntian Zhu, Gang Sha. Formation of solute nanostructures in an Al–Zn–Mg alloy during long-term natural aging. Journal of Alloys and Compounds. 2019; 821 ():153572.

Chicago/Turabian Style

Jizi Liu; Rong Hu; Jialing Zheng; Yidong Zhang; Zhigang Ding; Wei Liu; Yuntian Zhu; Gang Sha. 2019. "Formation of solute nanostructures in an Al–Zn–Mg alloy during long-term natural aging." Journal of Alloys and Compounds 821, no. : 153572.

Journal article
Published: 28 October 2019 in Metals
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An Al-Mg-Si alloy 6061 and an Al-Zn-Mg alloy 7A52 were joined by friction stir welding successfully. Pre- and post- heat treatment were employed to improve the strength of the weld. The results show a best weld joint with the lowest hardness of 100 HV in 6061 matrix, being achieved by post-solid-solution and subsequent two-stage artificial aging for the whole weld joint of the 7A52 and 6061 solid solution. Under this condition, the weld nugget zone (WNZ) is stronger than 6061 matrix but it has lower hardness than 7A52 matrix. The hardness of WNZ is contributed by the combination of η′ and L precipitates, dynamically changes along with the ratios between the number of η′ and L precipitates. The higher the number density of η′ precipitates, the hardness of WNZ is closer to that of the 7A52 matrix. Otherwise, the higher number density of L precipitates, the hardness of WNZ is closer to that of 6061 matrix. The coexistence of η′ and L precipitates is a direct result from the mixture of 7A52 and 6061 alloys achieved by stirring. Precipitates identification and composition analysis reveal a dynamic WNZ with constituent transition in hardness and composition.

ACS Style

Yang Jia; Sicong Lin; Jizi Liu; Yonggui Qin; Kehong Wang. The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys. Metals 2019, 9, 1162 .

AMA Style

Yang Jia, Sicong Lin, Jizi Liu, Yonggui Qin, Kehong Wang. The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys. Metals. 2019; 9 (11):1162.

Chicago/Turabian Style

Yang Jia; Sicong Lin; Jizi Liu; Yonggui Qin; Kehong Wang. 2019. "The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys." Metals 9, no. 11: 1162.

Journal article
Published: 25 September 2019 in Materialia
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High-entropy alloys (HEAs), containing at least five major metal elements in equal or near equal atomic ratios, have drawn increasing attention because they open entirely new materials avenues for designing alloys with exceptional properties. In the literature, a well-studied equiatomic, face-centered cubic CrMnFeCoNi HEA reportedly exhibits a yield strength of 410 MPa and a ductility of 57% as well as a deformation mechanism of dislocation slip at room temperature [B. Gludovatz, et al., Science, 345 (2014) 1153–1158]. Some recent works also observed that twinning actually happens more or less in the equiatomic CrMnFeCoNi alloy at room temperature [Z.J. Zhang, et al., Nature Comm. 6 (2015) 10143]. In this study, we prepared a non-equiatomic, face-centered cubic Cr26Mn20Fe20Co20Ni14 HEA with a comparatively low stacking fault energy (SFE) by making an appropriate adjustment of the composition ratio. Our HEA has a yield strength of 180 MPa and a high strain hardening exponent, n, of 0.46 as well as a higher ductility (73%) than those of the CrMnFeCoNi alloy. Investigation of the deformation mechanisms at specific strain levels revealed a clear transition from planar slip dislocations in the initial deformation stage to twinning at high tensile strain. Cooperative planar slipping and twinning resulted from the comparatively low SFE and were responsible to the extraordinary ductility and strain hardening capability. Besides deformation twins, other hardening mechanisms including forest dislocations, sessile Lomer–Cottrell locks, dislocation-stacking fault interactions, sub-grain boundary and phase boundary were revealed.

ACS Style

Xuzhou Gao; Yiping Lu; Jizi Liu; Jun Wang; Tongming Wang; Yonghao Zhao. Extraordinary ductility and strain hardening of Cr26Mn20Fe20Co20Ni14 TWIP high-entropy alloy by cooperative planar slipping and twinning. Materialia 2019, 8, 100485 .

AMA Style

Xuzhou Gao, Yiping Lu, Jizi Liu, Jun Wang, Tongming Wang, Yonghao Zhao. Extraordinary ductility and strain hardening of Cr26Mn20Fe20Co20Ni14 TWIP high-entropy alloy by cooperative planar slipping and twinning. Materialia. 2019; 8 ():100485.

Chicago/Turabian Style

Xuzhou Gao; Yiping Lu; Jizi Liu; Jun Wang; Tongming Wang; Yonghao Zhao. 2019. "Extraordinary ductility and strain hardening of Cr26Mn20Fe20Co20Ni14 TWIP high-entropy alloy by cooperative planar slipping and twinning." Materialia 8, no. : 100485.

Journal article
Published: 28 January 2019 in Metals
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A new method of thermo-mechanical processing has been designed by introducing pre-aging before general cold rolling for an Al-Zn-Mg alloy. This process results in an increase of 200 MPa in yield strength compared to that of the peak-aged samples. The microstructures were examined by transmission electron microscope and X-ray diffraction. It has been found that the enhanced strength is mainly contributed to by ultra-fine lamella structures containing a high density of dislocations pinned by nanoprecipitates. Extra strength is provided by the “interlocking” of precipitates and dislocations. Fractographic features analysis shows that crack propagation along the interface of the lamella structures is the direct reason for resulting in fracture, due to intra-granular strength exceeding grain boundary cohesion.

ACS Style

Yonggui Qin; Sicong Lin; Shenbao Jin; Jizi Liu. Strengthening Al-Zn-Mg Alloys via Ultra-Fine Lamella Structures Containing a High Density of Dislocations and Clusters. Metals 2019, 9, 140 .

AMA Style

Yonggui Qin, Sicong Lin, Shenbao Jin, Jizi Liu. Strengthening Al-Zn-Mg Alloys via Ultra-Fine Lamella Structures Containing a High Density of Dislocations and Clusters. Metals. 2019; 9 (2):140.

Chicago/Turabian Style

Yonggui Qin; Sicong Lin; Shenbao Jin; Jizi Liu. 2019. "Strengthening Al-Zn-Mg Alloys via Ultra-Fine Lamella Structures Containing a High Density of Dislocations and Clusters." Metals 9, no. 2: 140.

Journal article
Published: 06 July 2018 in Metals
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A high strength Al-Zn-Mg alloy 7A52 with T6 treatment was successfully friction stir welded. The grain structure, dislocations and precipitates in typical regions of the weld joint, including the weld nugget zone (WNZ), thermos-mechanically affected zones (TMAZ) and heat affected zones (HAZ) were investigated to understand the mechanical properties of each zone and the weld joint. In WNZ, a relatively higher density of dislocations is observed on the advancing side, caused by vacancy collapse induced by severe plastic deformation during stirring. However, in the center and on the retreating side, the dislocation density is very low. The strength of the WNZ is influenced by grain refinement, solution strengthening, or natural ageing hardening. In TMAZs, different mechanical properties on each side are due to different grain structures and precipitates introduced by the asymmetrical thermo-mechanical cycle. In HAZs, the mechanical properties are a strong function of the ratio of η′ to η phase. Compared to the micro-tensile results, premature failure of the weld joint occurs in HAZs on the advancing side, resulting from stress concentration near the area with the lowest hardness.

ACS Style

Yang Jia; Yonggui Qin; Yiwen Ou; Kehong Wang; Jizi Liu. The Influence of Microstructural Heterogeneity on Mechanical Properties of Friction Stir Welded Joints of T6-Treated Al-Zn-Mg Alloy 7A52. Metals 2018, 8, 527 .

AMA Style

Yang Jia, Yonggui Qin, Yiwen Ou, Kehong Wang, Jizi Liu. The Influence of Microstructural Heterogeneity on Mechanical Properties of Friction Stir Welded Joints of T6-Treated Al-Zn-Mg Alloy 7A52. Metals. 2018; 8 (7):527.

Chicago/Turabian Style

Yang Jia; Yonggui Qin; Yiwen Ou; Kehong Wang; Jizi Liu. 2018. "The Influence of Microstructural Heterogeneity on Mechanical Properties of Friction Stir Welded Joints of T6-Treated Al-Zn-Mg Alloy 7A52." Metals 8, no. 7: 527.

Journal article
Published: 29 May 2018 in Journal of Alloys and Compounds
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A simplified hydrogenation-dehydrogenation approach is demonstrated to achieve high strength powder metallurgy Ti-6Al-4V alloy by introducing 0.90 wt.% hydrogen in the green compact, without the help of hydrogen flow. The refined cross-linked network microstructure, where ultra-fine β phase dispersed in between refined α phase, produces a high tensile strength of ∼1062 MPa. A fixed orientation relationship was determined between these refined α phase and ultrafine β phase, which predicts a coherent interface makes the alloy stronger and showing transgranular and ductile fracture, avoiding intergranular fracture along the β grain boundary as in vacuum sintered sample. The influence of hydrogen content on mechanical properties and microstructures is also investigated in detail. The critical hydrogen content of 0.36 wt.% was revealed for presenting the beneficial effect of hydrogen.

ACS Style

Jizi Liu; Yonggui Qin; Jialing Zheng; Chao Chen; Ping'an Xiao. New approach to achieve high strength powder metallurgy Ti-6Al-4V alloy through a simplified hydrogenation-dehydrogenation treatment. Journal of Alloys and Compounds 2018, 763, 111 -119.

AMA Style

Jizi Liu, Yonggui Qin, Jialing Zheng, Chao Chen, Ping'an Xiao. New approach to achieve high strength powder metallurgy Ti-6Al-4V alloy through a simplified hydrogenation-dehydrogenation treatment. Journal of Alloys and Compounds. 2018; 763 ():111-119.

Chicago/Turabian Style

Jizi Liu; Yonggui Qin; Jialing Zheng; Chao Chen; Ping'an Xiao. 2018. "New approach to achieve high strength powder metallurgy Ti-6Al-4V alloy through a simplified hydrogenation-dehydrogenation treatment." Journal of Alloys and Compounds 763, no. : 111-119.