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金属学报  2016, Vol. 52 Issue (1): 51-59    DOI: 10.11900/0412.1961.2015.00163
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晶粒尺寸及Taylor因子对过时效态7050铝合金挤压型材横向力学性能的影响*
顾伟,李静媛(),王一德
北京科技大学材料科学与工程学院, 北京 100083
EFFECT OF GRAIN SIZE AND TAYLOR FACTOR ON THE TRANSVERSE MECHANICAL PROPERTIES OF 7050 ALUMINIUM ALLOY EXTRUSION PROFILE AFTER OVER-AGING
Wei GU,Jingyuan LI(),Yide WANG
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
引用本文:

顾伟,李静媛,王一德. 晶粒尺寸及Taylor因子对过时效态7050铝合金挤压型材横向力学性能的影响*[J]. 金属学报, 2016, 52(1): 51-59.
Wei GU, Jingyuan LI, Yide WANG. EFFECT OF GRAIN SIZE AND TAYLOR FACTOR ON THE TRANSVERSE MECHANICAL PROPERTIES OF 7050 ALUMINIUM ALLOY EXTRUSION PROFILE AFTER OVER-AGING[J]. Acta Metall Sin, 2016, 52(1): 51-59.

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摘要: 

采用常温冲击实验和拉伸实验研究了大断面7050铝合金型材横向3个典型位置的力学性能的差异, 并通过OM, EBSD和TEM分析了其显微组织. 结果表明: 晶粒尺寸约为12 μm的型材芯部比晶粒尺寸约为6 μm的边部的屈服强度高, 其原因是芯部较硬Copper取向的形变织构组分更强. 根据固溶合金元素含量所得的固溶强化项、亚晶粒尺寸所得的晶界强化项和合金的屈服强度可计算Taylor因子, 芯部为3.925, 边部为2.257. 晶界强化模型中Hall-Petch模型比Nes模型更适用于计算固溶后的晶界强化对合金屈服强度的贡献. 此外, 还建立了3种试样过时效态冲击功与亚晶粒尺寸之间的线性关系.

关键词 7050铝合金晶界强化Taylor 因子冲击功屈服强度    
Abstract

Generally, it is believed that inside the material the smaller grain size is, the higher yield strength is. In addition to this effect, grain refinement method also ensures that the toughness of the material is not reduced. However, it is found that the relationship between the grain size distribution and mechanical properties is contradiction with this law after the properties have been studied in the transverse direction of a large cross-section 7050 aluminum alloy profile. That is, the impact energy and yield strength in the center with a large grain size is higher than those at the edge with the smaller grain size in the thickest section of the profile. Besides that, during the establishment of the yield strength model in over-aging 7050 aluminum alloy, there are two models for the grain boundary strengthening which are Nes model and Hall-Petch model, so the choice from these model is found to affect the final results of the yield strength model. In order to study and understand the reasons for this phenomenon, the difference of mechanical properties distribution in the cross-section of 7050 aluminum extrusion profile has been investigated by impact test and tensile test at normal temperature, meanwhile, the microstructures have been analyzed by OM, EBSD and TEM. The results show that lots of the harder deformation textures, i.e., copper texture in the core of the profile lead to higher yield strength in the core with grain size of 12 mm than that in the edge with grain size of 6 mm. The Taylor factor could be calculated after the solution strengthening by alloying elements, grain boundary strengthening by the sub-grain and the yield stress of the alloy, at last, it reaches to 3.925 in the core, while that is just 2.257 in the edge. Compared with Nes model, the Hall-Petch model is much preferable to the calculation of grain boundary strengthening in yield stress of 7050 aluminum alloys after solid solution treatment. It is established that there is a linear relationship between impact energy and grain size of three over-aging specimens.

Key words7050 aluminium alloy    grain boundary strengthening    Taylor factor    impact energy    yield strength
收稿日期: 2015-03-25     
基金资助:国家高技术研究发展计划项目2013AA032402和广东省教育部产学研结合项目2015B090901044资助
图1  7050铝合金大断面型材及试样取样位置示意图
图2  7050铝合金型材3个位置试样经3种时效处理后的OM像
图3  不同位置试样各时效状态晶粒尺寸
图4  不同位置不同时效状态试样的冲击功
图5  不同时效状态下冲击功与晶粒尺寸关系
图6  不同位置不同时效状态下试样的屈服强度、屈强比和延伸率
图7  7050铝合金型材边部位置和芯部位置固溶态试样取向分布函数(ODF)图
图8  7050铝合金型材边部位置和芯部位置固溶态试样取向差角分布
图9  3种方案拟合二级时效不同时间下合金各位置屈服强度
Position Scheme 1 Scheme 2 Scheme 3
A1 R2 A2 B2 R2 A3 B3 R2
E 5754 0.9741 5002 61.40 0.9968 5002 61.37 0.9968
M 6122 0.9284 5002 91.28 0.9609 5164 78.20 0.9618
C 6140 0.9736 5002 92.02 0.9427 6087 4.287 0.9737
表1  3种屈服强度拟合方案的拟合参数及确定系数
图10  7050铝合金型材边部和芯部位置亚晶粒的TEM像
Position d mm Δsgb / MPa
Nes model Hall-Petch model
E 0.5 14.300 75.34
M 1.0 6.864 57.11
C 1.5 5.047 51.25
表2  采用Nes模型和Hall-Petch模型计算的不同位置晶界强化贡献值
Model Position sy MPa Δt0 MPa Δtss MPa Δsgb MPa M
Nes Edge 269.77 16 64.13 14.300 2.966
Center 389.34 5.047 4.462
Hall-Petch Edge 269.77 16 64.13 75.340 2.257
Center 389.34 51.250 3.925
表3  采用Nes模型和Hall-Petch模型推算的Taylor因子M
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