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
Effect of Pre-Deformation on Microstructure and Mechanical Properties of Ultra-High Strength Al-Zn-Mg-Cu Alloy After Ageing Treatment
通讯作者: 徐严谨,xuyj020@avic.com,主要从事航空铝合金研制与应用研究
责任编辑: 毕淑娟
收稿日期: 2019-11-25 修回日期: 2020-03-26 网络出版日期: 2020-07-11
基金资助: |
|
Corresponding authors: XU Yanjin, senior engineer, Tel: (010)85701427, E-mail:xuyj020@avic.com
Received: 2019-11-25 Revised: 2020-03-26 Online: 2020-07-11
Fund supported: |
|
作者简介 About authors
韩宝帅,男,1985年生,工程师,博士
利用TEM、XRD、SEM、DSC以及室温拉伸等方法,研究了预变形对超高强Al-Zn-Mg-Cu合金组织与性能的影响。通过对比未经预变形和预变形量为3%及4%的Al-Zn-Mg-Cu合金时效态微观组织与拉伸力学性能,发现:预变形可以提高铝合金时效析出速率和密度,变形量为3%时可促进析出相在晶内弥散分布,但增加到4%会导致析出相粗化;经预变形处理后晶间析出相尺寸减小,晶界无析出带宽度降低;抗拉强度和屈服强度提高,伸长率略微提高,经3%预变形以及80 ℃、12 h和120 ℃、8 h时效后的抗拉强度可达到(813±4) MPa,伸长率为10.10%±0.77%。分析认为,预变形产生的位错为析出相形核提供了异质形核的质点,改善了其在晶内与晶间的分布状态。
关键词:
Ultra-high strength Al-Zn-Mg-Cu alloy is a promising lightweight structural material, and there is still room to improve its mechanical property. As a typical precipitation strengthening material, controlling the size and distribution of precipitate is an effective way to enhance the mechanical properties of the ultra-high strength Al-Zn-Mg-Cu alloy. The influence of pre-deformation on the microstructures and properties of the ultra-high strength Al-Zn-Mg-Cu alloy after ageing treatment was studied by TEM, XRD, SEM, DSC and tensile tests. The microstructures and the tensile mechanical properties of Al-Zn-Mg-Cu alloy without pre-deformation and with 3% and 4% pre-deformation were compared. It is found that the pre-deformation can promote the ageing precipitation rate and enhance the precipitate density in the Al-Zn-Mg-Cu alloy, and the pre-deformation ratio of 3% can promote the dispersion of the precipitate phase in the grain interiors, but the pre-deformation ratio of 4% may result in coarsening of precipitate. The size of precipitate along the grain boundaries and the width of precipitation free zones decreased in the pre-deformation treated ultra-high strength Al-Zn-Mg-Cu alloys. The tensile strength and yield strength of the pre-deformation treated ultra-high strength Al-Zn-Mg-Cu alloys increased, and the elongation also increased slightly, in which the tensile strength and elongation of 3% pre-deformation alloy combined with 80 ℃ for 12 h and 120 ℃ for 8 h ageing were (813±4) MPa and 10.10%±0.77%, respectively. The results show that the dislocations produced by pre-deformation may provide more heterogeneous nucleation sites for the precipitate formation, and improve the precipitate's distribution.
Keywords:
本文引用格式
韩宝帅, 魏立军, 徐严谨, 马晓光, 刘雅菲, 侯红亮.
HAN Baoshuai, WEI Lijun, XU Yanjin, MA Xiaoguang, LIU Yafei, HOU Hongliang.
超高强铝合金是指抗拉强度在800 MPa左右的Al-Zn-Mg-Cu合金[1,2],其合金元素含量较高,Zn含量通常大于10% (质量分数,下同)。相较于500 MPa级的7075[3,4]、7050[5]和600 MPa级的7150[6]、7055[7]等合金,超高强Al-Zn-Mg-Cu合金强度可提升30%~60%。将超高强铝合金应用于航空航天结构件,可显著减轻结构重量,对实现轻量化具有重要意义[8]。尽管具有明显的强度优势,但超高强Al-Zn-Mg-Cu合金的塑性与7055、7075等有较大差距,现阶段强度在750 MPa以上的Al-Zn-Mg-Cu合金伸长率普遍低于9%[9,10,11,12,13],部分甚至低于5%,影响了可加工性与使用可靠性。
作为典型的析出强化材料,析出相形态对铝合金的力学性能有直接的影响。超高强Al-Zn-Mg-Cu合金的元素含量接近Al固溶体极限,具有比7075、7055等合金更高的脱溶驱动力和原子扩散速率[14],析出相容易粗化,导致其塑性较低。为提高力学性能,需要采用合理的方式控制析出过程。
本工作研究了较小预变形量对超高强Al-Zn-Mg-Cu合金的峰时效析出相形态与分布的影响规律,优化材料性能,并分析其强韧化机理。
1 实验方法
实验材料为喷射成形制备的超高强Al-Zn-Mg-Cu合金,使用ICP-AES Agilent 5100电感耦合等离子体-原子发射光谱仪测定的实际成分为Al-11.88Zn-2.85Mg-1.10Cu-0.13Zr (质量分数,%)。铸锭直径为600 mm,经挤压制成直径70 mm的棒材。实验试样取自棒材R/2 (R为半径)位置的同心圆环区域,经450 ℃保温2 h、480 ℃保温2 h固溶处理后立即淬火,转移时间不得超过5 s,淬火介质为(50±5) ℃的水。
式中,
为排除自然时效的影响,预变形后的试样应立即进行人工时效处理,固溶完毕与开始时效间隔不超过2 h。时效工艺为80 ℃保温12 h后再在120 ℃保温8 h (简称12+8),随后空冷至室温。此外,本工作将未经预变形的试样经80 ℃保温12 h后再经120 ℃保温10 h (简称12+10)作为对照。时效工艺参数如表1所示。
表1 时效工艺参数
Table 1
Sample No. | Heat treatment process | Abbreviation |
---|---|---|
1 | No deformation alloy+80 ℃, 12 h+120 ℃, 8 h | 12+8 |
2 | 3% deformation alloy+80 ℃, 12 h+120 ℃, 8 h | 3%+12+8 |
3 | 4% deformation alloy+80 ℃, 12 h+120 ℃, 8 h | 4%+12+8 |
4 | No deformation alloy+80 ℃, 12 h+120 ℃, 10 h | 12+10 |
采用JEM-2100透射电镜(TEM)观察析出相形貌,并利用Image J 软件统计析出相的尺寸、面积分数以及晶界无析出带宽度。使用STA 449热分析仪采用差示扫描量热法(DSC)分析样品加热过程的吸热与放热行为,最高测试温度为500 ℃,升温速率为10 ℃/min。
室温拉伸实验在Instron 5569电子万能试验机上进行,拉伸速率为2 mm/min,实验选用板状拉伸试样,厚度为2 mm,其余尺寸按照GB/T 228.1-2010计算。采用S-4300扫描电镜(SEM)观察拉伸测试后的断口形貌。
2 实验结果
图1
图1
不同变形量下固溶态Al-Zn-Mg-Cu合金的XRD谱
Fig.1
XRD spectra (a) and local amplifications (b, c) of the solid solution Al-Zn-Mg-Cu alloy with different deformations
不同时效工艺下晶内析出相微观形貌如图2所示。12+8处理后,析出相弥散分布在合金基体中,占据的面积分数为39% (图2a);这些析出相按形状可分为近圆形和杆状2类。经3%+12+8处理后,晶内析出相体积分数略有提高,面积分数为44% (图2c);同时尺寸变得细小,以杆状析出相为例(下同),12+8处理后长度分布范围为3.5~6.9 nm,而3%+12+8处理后长度为2.7~5.4 nm。经4%+12+8处理后,析出相长度增加为4.5~10.4 nm,面积分数提高到51% (图2e)。相比之下,12+10处理后,析出相尺寸与4%+12+8态接近、长度为4.8~9.2 nm,但面积分数略低,约为45% (图2g和h)。
图2
图2
不同时效条件下超高强Al-Zn-Mg-Cu合金的微观组织
Fig.2
TEM images and SAED patterns (insets) (a, c, e, g), and HRTEM and high magnified images (insets) (b, d, f, h) of the ultra-high strength Al-Zn-Mg-Cu alloys with ageing process parameters of 12+8 (a, b), 3%+12+8 (c, d), 4%+12+8 (e, f) and 12+10 (g, h)
图3
图3
不同时效状态下超高强Al-Zn-Mg-Cu合金晶间析出相形貌
Fig.3
Intergranular precipitates morphologies of ultra-high strength Al-Zn-Mg-Cu alloy under different ageing process parameters (PFZ—precipitation free zone)
(a) 12+8 (b) 3%+12+8 (c) 4%+12+8 (d) 12+10
表2 不同时效状态下超高强Al-Zn-Mg-Cu合金的力学性能
Table 2
Ageing process parameter | Ultimate strength / MPa | Yield strength / MPa | Elongation / % |
---|---|---|---|
12+8 | 796±5 | 772±7 | 9.77±0.51 |
3%+12+8 | 813±4 | 786±4 | 10.10±0.77 |
4%+12+8 | 807±3 | 781±5 | 10.63±0.74 |
12+10 | 803±2 | 770±8 | 9.57±0.66 |
图4为不同时效状态下超高强Al-Zn-Mg-Cu合金的断口形貌,断裂方式包括沿晶断裂和穿晶断裂。不同于12+8、3%+12+8处理工艺,4%+12+8处理后的合金断口上的韧窝数量较多,主要分布在穿晶断裂的晶粒内部。12+10处理后的合金断口上也有一定量的韧窝,但明显少于4%+12+8处理后的合金。这表明,4%+12+8处理后的合金在断裂前经历了明显的位错运动与塞积过程,与其较好的伸长率相吻合。
图4
图4
不同热处理状态下超高强Al-Zn-Mg-Cu合金的断口形貌
Fig.4
Fracture morphologies of ultra-high strength Al-Zn-Mg-Cu alloy under different ageing process parameters
(a) 12+8 (b) 3%+12+8 (c) 4%+12+8 (d) 12+10
3 分析讨论
Al-Zn-Mg-Cu合金时效过程中析出序列为[30]:α (过饱和固溶体)-GP区 (Guinier-Preston zone,脱溶原子偏聚区)-η′相(亚稳态MgZn2)-η相(稳定态MgZn2)。关于预变形对析出序列的影响,韩念梅等[16]认为,预变形引入的位错降低了空位密度,不利于η′相形核析出,但有利于形成粗大的η相;而同时也有学者[29,30]认为,变形加工后析出序列与未进行预变形的合金相同。在本工作的实验结果中,既未在SAED图中观察到η相的衍射斑点,也未在高分辨图像中观察到不共格的析出相,故η相并未在晶内形成。本工作中,随变形量增加,η′相与基体的关系由共格转变成半共格。DSC实验结果(图5)显示,在4%+12+8与12+10处理合金的热分析曲线中,对应η'向η相转变的峰(235 ℃附近)强度[31]显著高于12+8和3%+12+8处理后的合金。这表明,增加变形量与延长时效时间均可以促进η′相的长大进程[32],二者的作用是一致的。继续增加预变形量或延长时间,会进一步促进η′相长大,当尺寸增加到一定程度,析出相与基体不再保持共格关系,形成不共格的η相[33],这与文献[16,17,18]中较大预变形量或过时效态析出相形态相对应。所以,预变形量虽增加了析出相含量,加快了时效析出进程,但并未改变时效析出序列,支持了文献[29,30]中的说法。
图5
图5
不同时效状态下超高强Al-Zn-Mg-Cu合金的DSC曲线
Fig.5
DSC curves of ultra-high strength Al-Zn-Mg-Cu alloys under different ageing process parameters
上述析出相形态的改变,对超高强Al-Zn-Mg-Cu合金力学性能的变化具有重要影响。当析出相尺寸较小时,位错以切过方式作用于析出相。根据析出强化模型,铝合金屈服强度强化效果可以表示为[35]:
式中,
式中,
4 结论
(1) 预变形产生的异质形核作用有利于促进超高强Al-Zn-Mg-Cu合金晶内析出相的形核与析出,经80 ℃保温12 h、120 ℃保温8 h后,3%预变形超高强Al-Zn-Mg-Cu合金晶内形成了细小弥散、与合金基体呈共格关系的析出相,4%预变形合金晶内析出相粗化,与基体的关系开始由共格向半共格转变。
(2) 预变形处理后合金晶内与晶间的析出速率差异减弱,晶间偏聚的现象减弱,析出相尺寸变小,晶间无析出带变窄。
(3) 由于晶内和晶间析出相尺寸与分布的改变,经预变形处理后超高强Al-Zn-Mg-Cu合金的强度与伸长率提高;相比于延长时效时间,预变形处理具有更好的强化效果。
参考文献
Development of high strength aluminum alloys and processing techniques for the materials
[J].The fundamental theories for the development of high strength aluminum alloys and processing techniques for the materials are briefly reviewed in this paper. It specifically focuses on alloying design, casting, homogenization, solution treatment, quenching, pre-stretching and ageing that have been extensively studied recently. Based on these discussions, some perspectives and suggestions have been proposed, which will benefit the development and applications of high strength aluminum alloys.
高强铝合金的发展及其材料的制备加工技术
[J].本文简述了国内外高强铝合金发展的理论基础及其材料的制备加工技术. 针对大规格高性能铝合金材料的成分设计、熔炼、均匀化、固溶、淬火、预拉伸以及时效各工序的相关技术的研究热点和发展进行了介绍和讨论. 并对我国该类铝合金及其发展和应用提出了建议.
Al-Zn-Mg-Cu alloys with strength of 800MPa
[J].
800MPa级Al-Zn-Mg-Cu系合金
[J].
Effects of multi-direction forging on improving properties of 7075 aluminum alloy
[J].
多向锻造对改善7075铝合金性能的作用
[J].
Effect of promotively-solutionizing heat treatment on the mechanical properties and fracture behavior of Al-Zn-Mg-Cu alloys
[J].
强化固溶对Al-Zn-Mg-Cu合金力学性能和断裂行为的影响
[J].
Cryogenic processing high-strength 7050 aluminum alloy and controlling of the microstructures and mechanical properties
[J].
高强7050铝合金超低温大变形加工与组织、性能调控
[J].
Effect of solution treatment on microstructures and mechanical properties of 7150 aluminum alloy
[J].
固溶处理对7150铝合金组织和力学性能的影响
[J].
Precipitates and the evolution of grain structures during double-step rolling of high-strength aluminum alloy and related properties
[J].
两阶段轧制变形过程中高强铝合金析出相与晶粒结构演变及其对性能的影响
[J].
Recent developments in advanced aircraft aluminium alloys
[J].
Influence of second phases on mechanical properties of spray-deposited Al-Zn-Mg-Cu alloy
[J].
Isothermal deformation of spray formed Al-Zn-Mg-Cu alloy
[J].
Microstructure and mechanical properties of spray-deposited Al-Zn-Mg-Cu alloy processed through hot rolling and heat treatment
[J].
Mechanical behavior and strengthening mechanisms in ultrafine grain precipitation-strengthened aluminum alloy
[J].
Microstructural and mechanical characterization of various modified 7XXX series spray formed alloys
[J].
Characterization and modeling of precipitation kinetics in an Al-Zn-Mg alloy
[J].
A conventional thermo-mechanical process of Al-Cu-Mg alloy for increasing ductility while maintaining high strength
[J].
Effect of prestretching on fracture toughness of 7050 aluminum alloy
[J].
预拉伸对7050铝合金断裂韧性的影响
[J].
Effects of pre-stretching on mechanical properties and localized corrosion of 7085 aluminum alloy
[J].
预拉伸对7085铝合金力学及局部腐蚀性能的影响
[J].
Effect of pre-strain on microstructure and stress corrosion cracking of over-aged 7050 aluminum alloy
[J].
Microstructures and properties of ultra-high-strength Al-Zn-Mg-Cu-Zr-Sr alloy with pre-deformation
[J].
预变形对超高强铝合金Al-Zn-Mg-Cu-Zr-Sr组织与性能的影响
[J].
Nanocrystalline Al-Mg alloy with ultrahigh strength and good ductility
[J].
Microstructures and mechanical properties of ultrafine grained 7075 Al alloy processed by ECAP and their evolutions during annealing
[J].
Precipitation behaviors and properties of solution-aging Al-Zn-Mg-Cu alloy refined with TiN nanoparticles
[J].
Characterisation of the composition and volume fraction of η′ and η precipitates in an Al-Zn-Mg alloy by a combination of atom probe, small-angle X-ray scattering and transmission electron microscopy
[J].
Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy
[J].
Effects of Mg and Cu on microstructures and properties of spray-deposited Al-Zn-Mg-Cu alloys
[J].
Effect of two-step aging treatment on microstructure and mechanical properties of spray-deposited Al-10.8Zn-2.8Mg-1.9Cu alloy
[J].
双级时效处理对喷射沉积Al-Zn-Mg-Cu合金微观组织和力学性能的影响
[J].
Microstructures and properties evolution of spray-deposited Al-Zn-Mg-Cu-Zr alloys with scandium addition
[J].
Effect of pre-strain and two-step aging on microstructure and stress corrosion cracking of 7050 alloy
[J].
Precipitation kinetics in a severely plastically deformed 7075 aluminium alloy
[J].
Accelerated precipitation and growth of phases in an Al-Zn-Mg-Cu alloy processed by surface abrasion
[J].
Improved bake-hardening response of Al-Zn-Mg-Cu alloy through pre-aging treatment
[J].
Quantitative characterization on the precipitation of AA 7055 aluminum alloy by SAXS
[J].
AA7055铝合金时效析出过程的小角度X射线散射定量表征
[J].
Effect of non-isothermal retrogression and re-ageing on microstructure and properties of Al-8Zn-2Mg-2Cu alloy thick plate
[J].2 phase wider. Therefore,the logical matching between the dislocation cutting off mechanism and the dislocation by-passing mechanism effectively reduces the loss of hardness. Meanwhile, the electrical conductivity is significantly improved. After the treatment of 105 ℃, 24 h (pre-ageing) and non-isothermal regression (120 min) with slow heating rate and 120 ℃, 24 h re-ageing, the Al-8Zn-2Mg-2Cu alloy thick plate possesses an excellent comprehensive performance than those of T6 and T73 states. The tensile strength, yield strength and electrical conductivity are 620 MPa, 593 MPa and 21.1 MS/m, respectively. The NRRA treatment with slow heating rate is more suitable for the ageing treatment of thick plate.]]>
非等温回归再时效对Al-8Zn-2Mg-2Cu合金厚板组织及性能的影响
[J].2相的尺寸分布范围宽化。因此,位错切过和位错绕过强化机制的合理匹配有效地降低了硬度的损失,同时合金的电导率得到显著提升。以105 ℃、24 h为预时效制度,经过慢速升温非等温回归处理120 min后再经120 ℃、24 h峰时效,Al-8Zn-2Mg-2Cu铝合金厚板的抗拉强度、屈服强度及电导率分别为620 MPa、593 MPa和21.1 MS/m,其综合性能优于单级峰时效(T6)及双级过时效(T73),且包含慢速升温的非等温回归再时效技术更适用于厚板的时效热处理。]]>
Effects of pre-stretching and ageing on the strength and fracture toughness of aluminum alloy 7050
[J].
A process model for age hardening of aluminium alloys—I. The model
[J].
/
〈 |
|
〉 |
