Machine Learning Design of Aluminum-Lithium Alloys with High Strength

Due to the large unexplored compositional space,long development cycle,and high cost of traditional trial-anderror experiments,designing high strength aluminum-lithium alloys is a great challenge.This work establishes a performance-oriented machine learning design strategy for aluminum-lithium alloys to simplify and shorten the development cycle.The calculation results indicate that radial basis function(RBF)neural networks exhibit better predictive ability than back propagation(BP)neural networks.The RBF neural network predicted tensile and yield strengths with determination coefficients of 0.90 and 0.96,root mean square errors of 30.68 and 25.30,and mean absolute errors of 28.15 and 19.08,respectively.In the validation experiment,the comparison between experimental data and predicted data demonstrated the robustness of the two neural network models.The tensile and yield strengths of Al-2Li-1Cu-3Mg-0.2Zr(wt.%)alloy are 17.8 and 3.5 MPa higher than those of the Al-1Li4.5Cu-0.2Zr(wt.%)alloy,which has the best overall performance,respectively.It demonstrates the reliability of the neural network model in designing high strength aluminum-lithium alloys,which provides a way to improve research and development efficiency.

自然时效态2198铝锂合金板材各向异性晶体塑性有限元模拟

基于电子背散射衍射(EBSD)数据建立了自然时效态2198铝锂合金板材的晶体塑性有限元模型,并利用控制变量法研究了5个塑性基本参数(初始硬化模量、应变率敏感系数、参考应变率、初始临界分剪切应力和饱和流动应力)对塑性变形行为的影响,通过引入代价函数,并对各个塑性参数进行优化,最终得到了能够描述自然时效态2198铝锂合金板材各向异性的塑性参数,所预测的沿RD和TD方向的应力-应变曲线与试验结果符合较好。通过晶体塑性有限元法,预测了自然时效态2198铝锂合金板材单向拉伸过程中晶体取向演变与12个滑移系对塑性变形的贡献。发现(111)[10-1]滑移系对自然时效态2198铝锂合金板材单向拉伸的塑性变形贡献最大。沿RD方向拉伸时,自然时效态2198铝锂合金板材出现强烈的[011]//TD织构。

2198铝锂合金稀土铈化学转化膜的制备及耐蚀性研究

2198铝锂合金具有较高的比强度及比刚度,在航空航天领域有广泛应用,但其局部腐蚀敏感性较高,需进行适当的表面处理以提高其耐蚀性能。通过化学浸泡法将2198铝锂合金放入0.02 mol/L CeCl_(3)+0.029 mol/L H_(2)O_(2)水溶液中分别处理20、60 min,在其表面获得了稀土化学转化膜。使用扫描电镜(SEM)和能谱仪(EDS)观察和分析了稀土化学转化膜的形貌和成分;用X射线光电子能谱(XPS)分析了转化膜的元素价态;通过测试动电位极化曲线、电化学阻抗能谱(EIS)和Mott-Schottky(M-S)曲线研究了稀土化学转化膜在0.1 mol/L NaCl溶液中的腐蚀行为及耐蚀机制。结果表明:2198铝锂合金稀土化学转化膜由Ce^(4+)和Ce^(3+)的氢氧化物和氧化物、Al^(3+)的氧化物和少量的单质Cu组成,各元素在表面均匀分布;稀土化学转化膜由表面到内部氢氧化物含量减少,氧化物含量增加。处理20 min和60 min获得的稀土化学转化膜的厚度约为0.81μm和1.50μm。在0.1 mol/L NaCl溶液中,稀土化学转化处理能够抑制2198铝锂合金的阴极吸氧过程,降低合金的自腐蚀电流密度,提高合金的耐蚀性;在2198铝锂合金表面制备稀土化学转化膜能使合金的耐蚀性能提高;且与处理20 min的试样相比,处理60 min获得的稀土化学转化膜的耐蚀性较高。同时,稀土化学转化处理改变了合金的腐蚀机制,使与Cl~-吸附相关的感抗弧消失,这是由于具有n型半导体特征的稀土化学转化膜中的载流子密度降低,载流子密度呈现正电荷,不利于Cl~-的吸附。

2198-T8铝锂合金多轴疲劳性能及裂纹扩展行为

对2198-T8铝锂合金薄壁管状试样在不同加载条件下进行了拉扭复合疲劳裂纹扩展试验。结果明,随着裂纹扩展阶段的等效应力幅降低,试样的多轴疲劳寿命升高。当应力幅比升高时,多轴疲劳寿命降低,轴向应变变大,扭向应变变小,扭向应变集中滞后于轴向应变集中。结合数字图像相关技术,拟合疲劳裂纹扩展速率模型,并采用两种临界平面模型对裂纹扩展方向进行预测,其中最大正应力平面对裂纹扩展方向的预测效果最好。随着应力幅比的升高,裂纹扩展区微观形貌由磨损形貌变为磨损与疲劳条带共存的形貌,裂纹扩展模式由II型变为I+II型,最终变为以I型为主。

Stress-corrosion behavior and characteristics of the friction stir welding of an AA2198-T34 alloy

To better understand the stress-corrosion behavior of friction stir welding(FSW),the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated.The experimental results show that the low-angle grain boundary(LABs)of the stir zone(SZ)of FSW is significantly less than that of heated affected zone(HAZ),thermo-mechanically affected zone(TMAZ),and parent materials(PM),but the grain boundary precipitates(GBPs)T1(Al2CuLi)were less,which has a slight effect on the stress corrosion.The dislocation density in SZ was greater than that in other regions.The residual stress in SZ was+67 MPa,which is greater than that in the TMAZ.The residual stress in the HAZ and PM is-8 MPa and-32 MPa,respectively,and both compressive stresses.The corrosion potential in SZ is obviously less than that in other regions.However,micro-cracks were formed in the SZ at low strain rate,which indicates that the grain boundary characters and GBPs have no significant effect on the crack initiation in the stress-corrosion process of the AA2198-T34.Nevertheless,the residual tensile stress has significant effect on the crack initiation during the stress-corrosion process.

Influence Mechanism of Cerium on the Threshold of Short Fatigue Crack for Aluminum-lithium Alloy 2090

The thresholds of short fatigue cracks for aluminum-lithium alloys 2090 and 2090+Ce are quantitatively evaluated. The essential reason resulting in stronger short crack effect has been ascertained. Influence of cerium on the threshold of short fatigue cracks for aluminum-lithium alloy 2090 was investigated. The results show that, by adding Ce into this alloy, DeltaK(i) and DeltaK(Cl.th) are increased. The influence mechanism of Ce on the threshold of short fatigue crack for alloy 2090 was explored fi om the bound energy, T, phase, the energy of anti-phase boundary, the energy of super-lattice intrinsic stacking fault and the electron bonds. By adding Ce into alloy 2090, the bound energy of Cu atom in this alloy is increased; the effect of thinning and dispersing T, phase is obtained; the effect of increasing the energy of anti-phase boundary and decreasing the energy of super-lattice intrinsic stacking fault for delta ' phase can be achieved.

2198铝锂合金板材温热成形极限实验研究

采用化学腐蚀网格法,通过刚模胀形实验和网格应变测量分析系统,研究了2198铝锂合金板在温热状态下的成形性能,获得了不同温度下的成形极限图。结果表明,温度显著影响2198铝锂合金板的成形极限曲线,随着温度的升高,合金成形极限曲线逐渐上升,合金塑性成形性能增强。同时,建立了不同温度下2198铝锂合金板成形极限的计算模型。

搅拌摩擦焊工艺参数对2198铝锂合金焊缝成形及接头力学性能的影响

对2198铝锂合金薄板进行了搅拌摩擦焊试验,分析了搅拌头旋转速度和焊接速度对焊缝成形及接头力学性能的影响。结果表明:旋转速度(n)与焊接速度(v)的比值大于15.7时,能形成表面成形良好,且内部致密无缺陷的焊缝;接头焊核区形成了细小的等轴晶,前进侧热力影响区大部分为等轴状晶粒,后退侧热力影响区的板条状组织发生了变形,其周围出现了细晶粒;焊接速度为30mm·min-1时,接头的抗拉强度随旋转速度的增大而变小,其最大值为432.17MPa,焊缝的硬度低于母材的,热力影响区的硬度最低,焊核区的硬度略高于热力影响区的。随着n/v的增大,热影响区的软化区间变宽。

2198铝锂合金充液拉深成形的本构模型及数值模拟

为建立能准确描述2198-T3态铝锂合金充液拉深成形的本构模型并合理制定成形工艺参数,采用单向拉伸实验测定2198-T3态铝锂合金0°、45°、90°方向的真实应力-应变曲线,并通过不同本构方程拟合材料变形抗力曲线。结果表明,具有初始屈服应力的幂函数本构方程对板材不同方向的试验数据拟合较好;2198-T3态铝锂合金板材塑性应变比r为0.931,具有良好的拉深性能;采用DYNAFOM有限元分析软件对充液拉深成形过程进行数值模拟,并对获得的成形性能参数进行验证。

时效成形工艺参数对搅拌摩擦焊对接2198铝锂合金回弹的影响

针对2198铝锂合金搅拌摩擦焊对接蒙皮开展时效成形工艺试验,研究时效时间、时效温度、弹性预弯量等工艺参数对回弹规律的影响。结果表明,回弹率随时效时间增加而降低,随时效温度升高而下降,随预弯半径增大而增加。并通过正交多项式回归分析,建立了时效成形工艺参数与回弹的函数关系。

2198铝合金硫酸-己二酸阳极氧化膜耐蚀性

以2198铝-锂合金为研究对象,在硫酸-己二酸电解质溶液中进行阳极氧化,并对氧化后的试样进行沸水封闭处理。采用场发射扫描电子显微镜(FE-SEM)和原子力显微镜(AFM)对氧化膜的表面和截面的形貌进行观察。通过电化学阻抗谱(EIS)、塔菲尔(Tafel)曲线和浸泡实验来分析阳极氧化膜的耐蚀性能。结果表明铝-锂合金在阳极氧化过程中由于含铜合金相的影响,形成的氧化膜孔洞不完整出现连通现象;电化学测试结果表明封闭之后的氧化膜的耐蚀性明显提高,并且随着浸泡时间的延长拟合等效电路发生改变,同时多孔层和阻挡层的阻抗值在降低,说明在浸泡的过程中氧化膜的结构发生改变,耐蚀性降低。

2198铝锂合金新淬火状态旋压成形研究

为了开发2198铝锂合金板材塑性成形技术,分别测试了其在新淬火、自然时效和人工时效状态的力学性能,结果表明,在新淬火状态下合金具有最低的屈服强度和最高的伸长率,数值分别为99 MPa和20.8%;经过自然时效和人工时效后,材料虽然得到了强化,但伸长率明显下降。因此选择在新淬火状态下旋压成形2198铝锂合金的零件,并进一步测试了零件的硬度分布,利用光镜和透射电镜观察了不同位置的微观组织。新淬火状态的低变形抗力和高塑性可实现大变形量的塑性成形且不产生裂纹缺陷,塑性变形阶段引入的位错促进了接下来人工时效阶段T1时效相的析出,提高了强度,硬度达到了180 HV。可见,新淬火状态成形方法是一种高效的2198铝锂合金板材成形成性一体化的制造技术。

2198-T3S铝锂合金组合工艺搅拌摩擦焊接头组织性能分析

为探究搅拌摩擦焊(FSW)焊接铝锂合金板材的最佳工艺参数,采用圆柱形螺纹搅拌头,焊前对板材背面开槽,在保持焊接速度不变的情况下对2198-T3S铝锂合金板材进行不同转速下的焊接组合工艺实验,焊后对接头进行了微观组织分析与力学性能测试。研究结果表明:采用组合工艺后焊缝的根部未出现弱连接缺陷;随着转速的提高,焊缝内部的缺陷消失,焊核区的晶粒呈粗大化趋势,第二相回溶,使焊缝的力学性能呈现“先升后降”的趋势。在最优组合参数下接头的抗拉强度和屈服强度分别为359 MPa(母材的81.5%)和248 MPa(母材的77.5%)。同时,转速的提高使焊缝的断裂方式发生了改变,由脆性-韧性混合断裂向韧性断裂转变。

划痕损伤对含铆钉孔2198-T8铝锂合金疲劳性能的影响

针对飞机蒙皮搭接处的划痕损伤问题,研究了含划痕缺陷的含铆钉孔2198-T8铝锂合金板材的疲劳性能。首先,利用Abaqus有限元仿真软件,通过正交试验法确定了划痕关键影响参数,优化了疲劳试验方案。其次,预制了9类划痕损伤试样,分析了划痕参数对其疲劳性能的影响,并结合数字图像相关技术对裂纹扩展路径进行了讨论。最后,利用体视显微镜及扫描电子显微镜对断口进行了表征并分析了疲劳断裂机理。结果表明,划痕尖端角度θ对力学性能影响最小;划痕深度D是影响疲劳性能的主要因素。在D=0.8 mm、c=72 mm、θ=45°的损伤条件下,疲劳寿命下降至1795次,较无损试样下降97.66%。当D>D_(s)=0.15 mm时,断裂位置由铆钉孔截面转移至划痕截面,且断裂模式由单一疲劳源扩展的韧性断裂转变为多疲劳源放射状扩展的准解理断裂。

Effect of Rare Earth Elements on Anisotropy and Microstructure of Al-Li Alloy 2195 Sheets

For the purpose of decreasing the applied limitation resulting from the anisotropic mechanical property of Al-Li alloy 2195, this study employed a complex heat treatment process, involving the pre-tension, thermo-infiltration of the rare earth element Ce, solution treatment, and artificial aging technology. The results indicate that the infiltration of rare earth element Ce benefits the abatement of anisotropy of Al-Li alloy 2195 sheet, in contrast with that of the normal heat treatment process. The gradient of the Vickers-hardness decreases at least 50% through the thickness, and the tensile strength in the rolling direction also increases significantly. If Ce was infiltrated into the alloy under the optimum pre-deformation, the yield strength （σ0.2） increased by 30 MPa while the tensile strength （σb） enhanced by 25 MPa compared to the rare earth free samples. Meanwhile, the fractography illustrated that the fracture surface of the sample became more desirable.

Co-strengthening contribution of δ′and T_1 precipitates in Al-Li alloys 2090 and 2090+Ce

The microstructure of dislocation in two kinds of ahiminum-lithium alloys 2090 and 2090 ＋ Ce was observed by means of TEM technology. The contributions of δ＇ and T1 precipitates to strength were separately calculated by using the results of quantitative metallography and analysis of micro-deformation behavior; the co-strengthening effect of δ＇ and T1 precipitates was studied. The results show that the adding relationship of co-strengthening of δ＇ and T1 is in accordance with q = 1.4 form at the near peak-aged condition, i.e., △τ^1.4δ = △τ^1.4δ＋ △τ^1.4T1, but the adding relationship is approximately a linear relation （q = 1） at the under-aged condition and becomes the parabola form when over-aged （q = 2）. The adding relationship of co-strengthening contribution of δ＇ and T1 is obviously dependent on aging time.

EFFECTS AND MECHANISMS OF EXTRINSIC STRENGTHENING DURING AGING FOR AL ALLOY 2090+Ce

The influence of aging temperature and time on fracture feature of monotonic tensile samples of alumi-num-Iithium alloy 2090+Ce was investigated.The effects and mechanisms of extrinsic strengthening during aging for this alloy with a flat unrecrystallized structure were discussed.The mechanisms were analysed from four aspects.The theory of extrinsic strengthening from the delamination strengthening was presented.The results in this research show that the strength and ductility of aluminum-lithium alloy with a flat unrecrystallized structure are superior to those with recrystallized structure.Several reasons have been advanced for the ductility improvement effect of flat uncrystallized structure,including wedging action between flat grain,action of short-transverse delamination on impeding the growth of main crack,action on the reduction in the detrimental influence of weak grain boundaries and action on impeding the intergranular fracture on main fracture surface.The strengthening effect of flat uncrystallized structure is attributed to the extrinsic strengthening derived from delamination strengthening.From underage to peakage,the fracture mode of this alloy is transgranular fracture plus short-transverse delamination.The tendency of short-transverse delamination in creases with aging,thereby enhancing the delamination strengtheniag effect.Under overaging condition,the fracture mode is predominately intersubgranular,which results in the loss of delamination strengthening.

Influence of Rare Earth Element on Short Fatigue Crack Threshold for Al－Li Alloy 2090

Curves of △Kth vs.△ath and △Kcl·th vs.△ath for aluminum-lithium alloy 2090 have been determined and compared with those for traditional aluminum alloy 2024.The growth resistance of short fatigue cracks for aluminum-lithium alloy 2090 is quantitatively evaluated.The essential reason resulting in stronger short cracks effect has been ascertained.Influence of cerium on the growth behavior of short fatigue cracks for aluminum-lithium alloy 2090 was investigated.The results show that by adding cerium into this alloy a significant improvement in △Ki can be achieved and at the same time △Kcl·th is increased.Consequently,the essential factor resulting in lower growth resistance of short fatigue cracks for this alloy is removed and the growth resistance of long and short fatigue cracks is increased.

Strain localization and damage development in 2060 alloy during bending

The microstructure evolution and damage development of the third-generation Al-Li alloy 2060 （T8） were studied using in situ bending tests. Specimens were loaded with a series of punches of different radii, and the microstructure evolution was studied by scanning electron microscopy, electron backscatter diffraction, and digital image correlation （DIC） methods. The evolution of the microscopic fracture strain distribution and microstructure in 2060 alloy during bending was characterized, where the dispersion distribution of precipitates was recorded by backscattered electron imaging and later inputted into a DIC system for strain calculations. The experimental results showed that strain localization in the free surface of bent specimens induced damage to the microstructure. The region of crack initiation lies on the free surface with maximum strain, and the shear crack propagates along the macro-shear band in the early stages of bending. Crack propagation in the later stages was interpreted on the basis of the conventional mechanism of ductile fracture.

Evolution of the texture and mechanical properties of 2060 alloy during bending

In this study, we examined the evolution of the texture and mechanical properties of 2060 （T8） alloy during bending. A pixel rotation method （PRM） was proposed and used to characterize the textural evolution during bending determined by electron backscatter diffraction. The results showed that the textural components changed insignificantly, with the exception of a decrease in the cube texture. The tensile and yielding properties of the alloy were evaluated at three different orientations with respect to the rolling direction. The mechanical strength was found to increase in three directions with decreasing bending radius; thus, it was concluded that the 2060 （T8） alloy sheet satisfies the usage requirement after bending deformation.