Effect of Creep Aging on Mechanical Properties of Under-Aged 7075 Aluminum Alloy
Received date: 2021-07-29
Revised date: 2021-09-23
Online published: 2022-01-07
Supported by
Construction Project of National New Material Production and Application Demonstration Platform(TC190H3ZV)
The 7075 alloy is widely used in the manufacture of aerospace components, such as aircraft wings and fuselage plates, owing to its high strength and light weight. Moreover, it is well-suited for manufacturing these massive aviation components using creep aging forming (CAF) technology. In this present study, the effect of creep aging on the mechanical properties of under-aged 7075 alloy was systematically studied in detail by means of a uniaxial creep tensile test and a stress-free artificial aging test. EBSD, SEM, and TEM observations were used to characterize the evolution of dislocations and precipitates with creep aging time. A quantitative analysis was performed on the relationship between mechanical properties and microstructure evolution. The results show that creep aging greatly improves the plasticity of the under-aged 7075 aluminum alloy while maintaining its high strength. The mechanical properties of the alloy are sensitive to creep stress. The sample aged for 6 h under 260 MPa and 426 K has the maximum yield strength, reaching 537.9 MPa. In comparison to the artificial aging sample, the dimple distribution of the creep aging sample is denser and the grain is more inclined toward a high Schmid factor orientation, which is 15% higher than the artificial aging sample. TEM results show that the primary phase in the crystal is η′ phase. The size of the precipitated phase in the crystal grows with increasing creep aging time from 3.04 nm for 2 h to 4.27 nm for 6 h and the volume fraction increases from 0.22% to 0.46%. The size of the grain boundary precipitates increases and the transition from continuous to discontinuous occurs. The EBSD results show that no significant change in the recrystallization and subgrain ratio occurred in any of the samples, and the average grain size remains approximately 80 μm. The distribution of geometrically necessary dislocations (GND) decreases first and subsequently increases with the extension of creep aging time. The contribution of grain boundary strengthening to the yield strength contribution model is shown to be essentially constant at about 17 MPa, and the coupling effect of dislocation and precipitation strengthening is the primary reason for the increase in strength.
Chuan GAO , Yunlai DENG , Fengquan WANG , Xiaobin GUO . Effect of Creep Aging on Mechanical Properties of Under-Aged 7075 Aluminum Alloy[J]. Acta Metall Sin, 2022 , 58(6) : 746 -759 . DOI: 10.11900/0412.1961.2021.00309
| 1 | Guyot P, Cottignies L. Precipitation kinetics, mechanical strength and electrical conductivity of AlZnMgCu alloys [J]. Acta Mater., 1996, 44: 4161 |
| 2 | Wang Q, Zhan L H, Xu Y Q, et al. Creep aging behavior of retrogression and re-aged 7150 aluminum alloy [J]. Trans. Nonferrous Met. Soc. China, 2020, 30: 2599 |
| 3 | Azarniya A, Taheri A K, Taheri K K. Recent advances in ageing of 7xxx series aluminum alloys: A physical metallurgy perspective [J]. J. Alloys Compd., 2019, 781: 945 |
| 4 | Shan D, Zhen L. 10-Aging behavior and microstructure evolution in the processing of aluminum alloys [A]. Microstructure Evolution in Metal Forming Processes [M]. Cambridge: Woodhead Publishing, 2012: 267 |
| 5 | Lin Y C, Jiang Y Q, Chen X M, et al. Effect of creep-aging on precipitates of 7075 aluminum alloy [J]. Mater. Sci. Eng., 2013, A588: 347 |
| 6 | Deschamps A, Livet F, Bréchet Y. Influence of predeformation on ageing in an Al-Zn-Mg alloy—I. Microstructure evolution and mechanical properties [J]. Acta Mater., 1998, 47: 281 |
| 7 | Ma K K, Hu T, Yang H, et al. Coupling of dislocations and precipitates: Impact on the mechanical behavior of ultrafine grained Al-Zn-Mg alloys [J]. Acta Mater., 2016, 103: 153 |
| 8 | Fang H C, Luo F H, Chen K H. Effect of intermetallic phases and recrystallization on the corrosion and fracture behavior of an Al-Zn-Mg-Cu-Zr-Yb-Cr alloy [J]. Mater. Sci. Eng., 2017, A684: 480 |
| 9 | Holman M C. Autoclave age forming large aluminum aircraft panels [J]. J. Mech. Work. Technol., 1989, 20: 477 |
| 10 | Zhang J S. High Temperature Deformation and Fracture of Materials [M]. Beijing: Science Press, 2010: 84 |
| 11 | Zhu A W, Starke E A. Stress aging of Al-xCu alloys: Experiments [J]. Acta Mater., 2001, 49: 2285 |
| 12 | Seraj F, Fadaie-Vash L, Vakili-Tahami F, et al. Obtaining optimum creep lifetime of Al 7075-T6 rotating pressurized vessel based on the experimental data, using reference stress method (RSM) [J]. Int. J. Press. Vessels Pip., 2021, 192: 104390 |
| 13 | Chen K, Zhan L H, Xu Y Q, et al. Effect of pulsed current density on creep-aging behavior and microstructure of AA7150 aluminum alloy [J]. J. Mater. Res. Technol., 2020, 9: 15433 |
| 14 | Liu C H, Yang J S, Ma P P, et al. Large creep formability and strength-ductility synergy enabled by engineering dislocations in aluminum alloys [J]. Int. J. Plast., 2020, 134: 102774 |
| 15 | Jeshvaghani R A, Emami M, Shahverdi H R, et al. Effects of time and temperature on the creep forming of 7075 aluminum alloy: Springback and mechanical properties [J]. Mater. Sci. Eng., 2011, A528: 8795 |
| 16 | Jeshvaghani R A, Shahverdi H R, Hadavi S M M. Investigation of the age hardening and operative deformation mechanism of 7075 aluminum alloy under creep forming [J]. Mater. Sci. Eng., 2012, A552: 172 |
| 17 | Lin Y C, Peng X B, Jiang Y Q, et al. Effects of creep-aging parameters on aging precipitates of a two-stage creep-aged Al-Zn-Mg-Cu alloy under the extra compressive stress [J]. J. Alloys Compd., 2018, 743: 448 |
| 18 | Guo W, Guo J Y, Wang J D, et al. Evolution of precipitate microstructure during stress aging of an Al-Zn-Mg-Cu alloy[J]. Mater. Sci. Eng., 2015, A634: 167 |
| 19 | Zhan L H, Lin J G, Dean T A, et al. Experimental studies and constitutive modelling of the hardening of aluminium alloy 7055 under creep age forming conditions [J]. Int. J. Mech. Sci., 2011, 53: 595 |
| 20 | Uesugi T, Higashi K. First-principles studies on lattice constants and local lattice distortions in solid solution aluminum alloys [J]. Comput. Mater. Sci., 2013, 67: 1 |
| 21 | Ma K K, Wen H M, Hu T, et al. Mechanical behavior and strengthening mechanisms in ultrafine grain precipitation-strengthened aluminum alloy [J]. Acta Mater., 2014, 62: 141 |
| 22 | Li R X, Ren Z, Wu Y, et al. Mechanical behaviors and precipitation transformation of the lightweight high-Zn-content Al-Zn-Li-Mg-Cu alloy [J]. Mater. Sci. Eng., 2021, A802: 140637 |
| 23 | Watanabe T, Tsurekawa S. The control of brittleness and development of desirable mechanical properties in polycrystalline systems by grain boundary engineering [J]. Acta Mater., 1999, 47: 4171 |
| 24 | Hall E O. The deformation and ageing of mild steel: III Discussion of results [J]. Proc. Phys. Soc., 1951, 64B: 747 |
| 25 | Deschamps A, Brechet Y. Influence of predeformation and ageing of an Al-Zn-Mg alloy—II. Modeling of precipitation kinetics and yield stress [J]. Acta Mater., 1998, 47: 293 |
| 26 | Dixit M, Mishra R S, Sankaran K K. Structure-property correlations in Al 7050 and Al 7055 high-strength aluminum alloys [J]. Mater. Sci. Eng., 2008, A478: 163 |
| 27 | Zou Y, Wu X D, Tang S B, et al. Investigation on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys with various Zn/Mg ratios [J]. J. Mater. Sci. Technol., 2021, 85: 106 |
| 28 | Mukhopadhyay A K. Development of reproducible and increased strength properties in thick extrusions of low-alloy Al-Zn-Mg-Cu based AA 7075 [J]. Metall. Mater. Trans., 1997, 28A: 2429 |
| 29 | Liu F, Sommer F, Bos C, et al. Analysis of solid state phase transformation kinetics: Models and recipes [J]. Int. Mater. Rev., 2007, 52: 193 |
| 30 | Xia X Y, Sanaty-Zadeh A, Zhang C, et al. Experimental investigation and simulation of precipitation evolution in Mg-3Nd-0.2Zn alloy [J]. Calphad, 2018, 60: 58 |
| 31 | Hou L G, Liu M L, Wang X D, et al. Cryogenic processing high-strength 7050 aluminum alloy and controlling of the microstructures and mechanical properties [J]. Acta Metall. Sin., 2017, 53: 1075 |
| 31 | 侯陇刚, 刘明荔, 王新东 等. 高强7050铝合金超低温大变形加工与组织、性能调控 [J]. 金属学报, 2017, 53: 1075 |
| 32 | Asgharzadeh H, Mcqueen H J. Grain growth and stabilisation of nanostructured aluminium at high temperatures: Review [J]. Mater. Sci. Technol., 2015, 31: 1016 |
| 33 | Zhang X X, Knoop D, Andrä H, et al. Multiscale constitutive modeling of additively manufactured Al-Si-Mg alloys based on measured phase stresses and dislocation density [J]. Int. J. Plast., 2021, 140: 102972 |
| 34 | Jiang J, Britton T B, Wilkinson A J. Measurement of geometrically necessary dislocation density with high resolution electron backscatter diffraction: Effects of detector binning and step size [J]. Ultramicroscopy, 2013, 125: 1 |
| 35 | Cheng W J, Liu W, Fan X B, et al. Cooperative enhancements in ductility and strain hardening of a solution-treated Al-Cu-Mn alloy at cryogenic temperatures [J]. Mater. Sci. Eng., 2020, A790: 139707 |
| 36 | Zribi Z, Ktari H H, Herbst F, et al. EBSD, XRD and SRS characterization of a casting Al-7wt%Si alloy processed by equal channel angular extrusion: Dislocation density evaluation [J]. Mater. Charact., 2019, 153: 190 |
| 37 | Xiao H, Lu Z, Zhang K F, et al. Achieving outstanding combination of strength and ductility of the Al-Mg-Li alloy by cold rolling combined with electropulsing assisted treatment [J]. Mater. Des., 2020, 186: 108279 |
| 38 | Han B S, Wei L J, Xu Y J, et al. Effect of pre-deformation on microstructure and mechanical properties of ultra-high strength Al-Zn-Mg-Cu alloy after ageing treatment [J]. Acta Metall. Sin., 2020, 56: 1007 |
| 38 | 韩宝帅, 魏立军, 徐严谨 等. 预变形对超高强Al-Zn-Mg-Cu合金时效组织与力学性能的影响 [J]. 金属学报, 2020, 56: 1007 |
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