Predict the evolution of mechanical property of Al-Li alloys in a marine environment

The ocean is one of the essential fields of national defense in the future,and more and more attention is paid to the lightweight research of Marine equipment and materials.This study it is to develop a Machine learning(ML)-based prediction method to study the evolution of the mechanical properties of Al-Li alloys in the marine environment.We obtained the mechanical properties of Al-Li alloy samples under uniaxial tensile deformation at different exposure times through Marine exposure experiments.We obtained the strain evolution by digital image correlation(DIC).The strain field images are voxelized using 2D-Convolutional Neural Networks(CNN)autoencoders as input data for Long Short-Term Memory(LSTM)neural networks.Then,the output data of LSTM neural networks combined with corrosion features were input into the Back Propagation(BP)neural network to predict the mechanical properties of Al-Li alloys.The main conclusions are as follows:1.The variation law of mechanical properties of2297-T8 in the Marine atmosphere is revealed.With the increase in outdoor exposure test time,the tensile elastic model of 2297-T8 changes slowly,within 10%,and the tensile yield stress changes significantly,with a maximum attenuation of 23.6%.2.The prediction model can predict the strain evolution and mechanical response simultaneously with an error of less than 5%.3.This study shows that a CNN/LSTM system based on machine learning can be built to capture the corrosion characteristics of Marine exposure experiments.The results show that the relationship between corrosion characteristics and mechanical response can be predicted without considering the microstructure evolution of metal materials.

焊丝成分对2050铝锂合金焊接性能影响研究

采用十字搭接试验方法测定2050铝锂合金焊接裂纹敏感性,研究了焊丝成分变化对2050铝锂合金焊接结晶裂纹率、液化裂纹率的影响,并对焊接接头的组织形貌、断裂特征和力学性能等进行了测试和分析。研究结果表明:采用钨极氩弧焊匹配Al-Cu-Si-Ti-Sc-Ce-B系焊丝对2050铝锂合金进行焊接,获得的焊接接头结晶裂纹率K1和液化裂纹率K2均为0,其强度系数可达母材的70%。

Characterization of localized corrosion pathways in 2195-T8 Al-Li alloys exposed to acidic solution

The corrosion properties of aluminum-lithium(Al-Li) alloys, which are potential materials used to construct for tanks of liquid rockets or missiles, are essential for safe propellant storage and transport. In order to manifest the corrosion resistance of the 2195 Al-Li alloy in practical propellant tanks filled with N2O4, the alloy was soaked in 30% nitric acid solution, an accelerating corrosion environment, to test its corrosion behavior. Scanning electron microscopy(SEM) and transmission electron microscopy(TEM)were used to characterize microstructure and corrosion morphology of the alloy. Focused ion beam(FIB),combined with SEM, was used to demonstrate localized corrosion features and the propagation of corrosion pathways beneath the alloy surface. It was found that the corrosion network was formed with most intergranular corrosion and sparse intragranular corrosion. Additionally, the distribution and number of intermetallic particles influenced the localized corrosion degree and the direction of corrosion pathways. Aggregated particles made corrosion pathways continuously and caused more severe corrosion. The results from this work were valid and useful to corrosion prevention and protection for storage safety on propellant tanks in N_(2)O_(4).

预变形量对2050 Al−Li合金显微组织和力学性能的影响

研究经不同轧制预变形处理(0~20%)后2050 Al−Li合金T8时效状态的显微组织演变和力学性能。通过透射电子显微镜(TEM)和扫描电子显微镜(SEM)对其显微组织进行表征。结果表明:随着预变形量的增加,晶粒尺寸沿ND方向显著变小,晶内畸变增大。位错等的缠结为T1相的析出提供了大量的形核位点。这导致析出相数量增多,析出相之间的距离缩小,从而提高了对位错运动的阻碍作用和合金强度。当预变形量为16%时,T1相数量密度和合金强度最高(屈服强度和抗拉强度分别达到568和584 MPa,伸长率为8.6%);当预变形量进一步增加到20%时,由于位错缠结,原子扩散通道减少,T1相数量的减少最终导致合金强度降低。

2050 Al-Li合金的流变曲线修正及加工图（英文）

采用热压缩实验研究2050 Al-Li合金在变形温度为340~500°C、应变速率为0.001~10 s^(-1)范围内的热变形行为。分析摩擦及温度变化对流变应力的影响,并对流变曲线进行修正处理;基于动态材料模型及修正后的真应力数据,获得真应变为0.5条件下合金的加工图;利用金相显微镜对压缩试样显微组织变化进行观察。结果表明,在热变形过程中材料的摩擦及温度变化对流变应力有显著影响;合金合适加工区域位于变形温度为370~430°C、应变速率为0.01~0.001 s^(-1)区域,以及变形温度为440~500°C、应变速率为0.3~0.01 s^(-1)区域内;失稳区位于高应变速率下(3~10 s^(-1))所有温度范围内;动态回复和动态再结晶是2050 Al-Li合金在稳定加工区域内主要变形机理,而在失稳区合金变形机理主要表现为流变集中。

固溶温度对2050铝锂合金挤压棒材组织和性能的影响

在一定固溶时间下,固溶温度决定淬火后基体的过饱和度和再结晶程度,是影响材料时效后性能的重要因素。通过对2050铝锂合金挤压棒材进行不同温度(450~570℃)下保温2 h的固溶热处理和170℃/40 h的人工时效处理,结合多种性能检测和微观组织观察进行表征分析,研究固溶温度对2050铝锂合金挤压棒材组织和性能的影响。结果表明:随固溶温度逐渐升高,残余相不断回溶,固溶温度为525℃时残余相主要为含Fe相,升至550℃时棒材发生轻微过烧,达到570℃时棒材严重过烧;固溶温度为500℃时棒材发生局部再结晶,570℃时棒材完全再结晶。450~550℃固溶的2050铝锂合金挤压棒材经170℃/40 h的人工时效后,随固溶温度的升高θ′相和T1相数量增加,且强度呈先快速增加后缓慢线性增加的趋势,550℃固溶的棒材屈服强度和抗拉强度最高,分别为505 MPa和567 MPa;伸长率随着固溶温度的升高先快速下降后保持稳定,由固溶温度为450℃时的13.4%降低至500~550℃时的10.7%~10.4%。

Effect of Rare Earth Cerium on Yield Strength Anisotropy of Al-Li Alloy Sheet and Its Theoretical Prediction

The variation of yield strength along rolling direction, transverse direction and 45° to transverse direction of 2090 Al-Li alloy and 2090+Ce alloy sheet containing rare earth cerium was comparatively investigated. The difference of deformation texture in these two alloy sheets was analyzed by means of X-ray orientation distribution function (ODF). The results show that cerium has the effects of enhancing the Brass and S rolling texture components and reducing the recrystallized texture components of Cube and Goss. This is the reason that the anisotropic degree of yield strength in 2090+Ce sheet is higher than that of 2090 alloy sheet. The prediction of yield strength along various orientations in two alloy sheets was done based on Taylor/Bishop-Hill model, and the strengthening effect of grain boundary was evaluated using Hall-Petch relationship. A modified plastic inclusion model was proposed using the concept of grain-orientation factor and T1 phase orientation factor by fitting with tensile test results.

Preparation and Corrosion Resistance of Anodic Oxidation Coatings on 2198 and 5A90 Al-Li Alloys

2198 and 5A90 Al-Li alloys were anodized with a constant DC potential in 18%H_2SO_4solution(Solu.A) and the mixture solution of 18%H_2SO_4+5%C_2H_2O_4(Solu.B) at room temperature. 12 and 11 V was optimized as the applied oxidation potential for 2198 and 5A90 alloys, respectively. Cross-sectional morphology, surface morphology and elements distribution of anodic oxidation coatings were observed by scanning electron microscope equipped with energy dispersive X-ray analysis(SEM/EDX). Corrosion resistance was tested by potentiodynamic polarization plot in 3.5%NaCl solution. The results showed that the thicknesses of coatings obtained at the selected potential in Solu.A and Solu.B were about 50 μm/110 μm for 2198 alloy and 80 μm/110 μm for 5A90 alloy. In both solutions, anodic oxidation coatings of 2198 alloy were primarily composed of Al oxides; those of 5A90 alloy were mainly consisted of Al oxides and a small amount of Mg oxides. The results of potentiodynamic polarization showed that anodic oxidation coatings of 2198 and 5A90 Al-Li alloys had better corrosion resistances than that of untreated alloys.

Effects of cooling rates on microporosity in DC casting Al-Li alloy

During the direct chill(DC)casting process,primary cooling from the mold and bottom block,and secondary cooling from the waterjets produce a concave solid shell.The depth of this liquid pocket and mushy zone not only depends on the solidification range of the alloy but also the boundary conditions such as cooling rates.Al-Li alloys solidify in a long solidification range increasing the susceptibility of porosity nucleation in the semi-solid region.In this study,the effects of cooling rate on the porosity formation were quantified for the large ingot casting using X-ray computed tomography(XCT).By characterizing pore size distributions at four different cooling conditions,the correlation between the mechanical properties at both room and high temperatures and the microstructure features was identified.The constitutive equations were constructed.It is found that increasing the cooling rate reduces the grain size,increases the number density of micropores,and minimizes the number of large pores,thereby improving the mechanical performance.Therefore,long mushy zones and deep liquid pockets in Al-Li alloys can be effectively controlled by controlling the boundary conditions of the DC casting solidification process,thereby obtaining castings with excellent mechanical properties.

DYNAMIC RECRYSTALLIZATION AND SUPERPLASTICITY IN Al-Li ALLOY

The behavior of dynamic recrystallization in the superplastic deformation of 8090 and 2091 aluminum-lithium alloys have been investigated.TEM observations indicated that dynamic recrystallization occurs at thetriple junction of grain boundaries.The measurement of grain boundary angle showed that recrystallization indynamic equilibrium exists in the process of superplastic deformation of 8090 Al-Li alloy.It is also indicatedthat,besides the role of refining grains and the grain boundary sliding,dynamic recrystallization playsconcurrently a role of stablizing microstructure.Thus dynamic rccrystallization can be used to induce metalssuperplasticity,which leads to a simplification of pretreatment for superplastic deformation.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 8090 Al-Li ALLOY

The change of mechanical properties of the 8090 Al-Li alloy influenced by aging is attributed to the change of δ′-phase particle size and the precipitation of S′-phase.The δ′-phase may easily precipitate and rapidly grow,but the S′-phase can only precipitate with a longer stage of incubation.The precipitation of S′-phase would be promoted by cold working prior to ag- ing.The co-precipitation of δ′- and S′-phase could improve the strength and plastieity of the alloy,for which aging at 190℃.for 20—30 h seems to be optimal.In addition,the precipitate free zone( PFZ)can form at high angle grain boundary and its width is over 200 nm in peak aging condition.But at sub-grain boundary,the formation of PFZ is difficult.

Influence of Ce on the Extrinsic Strengthening Effect of Al-Li Alloy

The influence regular and mechanisms of rare earth element cerium and aged condition on the propertiesand fracture feature of monotonic tension for aluminum-lithium alloy 2090 were researched. The evident plasti-cation effect can be achieved by adding cerium into alloy 2090, and the aged condition has a significant influ-ence on this effect. The plastication effect of cerium at peckaging is strongest, and at underaging and overagingis weader. The mechanisms of strengthening and plastication of cerium for aluminum-lithium alloys were dis-cussed in the theory of the extrinac strengthening and the intrinsic toughening. According to the research results about fracture feature, first the theory of extrinsic strengthening was presented, and then the role of ceri-um on aluminum-lithium alloy 2090 was explored from the unite energy, the anti-phase baundary energy andthe electron bonds.

Milling Parameters Optimization of Al-Li Alloy Thin-Wall Workpieces Using Response Surface Methodology and Particle Swarm Optimization

To improve the milling surface quality of the Al-Li alloy thin-wall workpieces and reduce the cutting energy consumption.Experimental research on the milling processing of AA2195 Al-Li alloy thin-wall workpieces based on Response Surface Methodology was carried out.The single factor and interaction of milling parameters on surface roughness and specific cutting energy were analyzed,and the multi-objective optimization model was constructed.The Multiobjective Particle Swarm Optimization algorithm introducing the Chaos Local Search algorithm and the adaptive inertial weight was applied to determine the optimal combination of milling parameters.It was observed that surface roughness was mainly influenced by feed per tooth,and specific cutting energy was negatively correlated with feed per tooth,radial cutting depth and axial cutting depth,while cutting speed has a non-significant influence on specific cutting energy.The optimal combination of milling parameters with different priorities was obtained.The experimental results showed that the maximum relative error of measured and predicted values was 8.05%,and the model had high reliability,which ensured the low surface roughness and cutting energy consumption.It was of great guiding significance for the success of Al-Li alloy thin-wall milling with a high precision and energy efficiency.

ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY DURING CORROSION PROCESS OF 8090 Al-Li ALLOY IN EXCO SOLUTION

The corrosion behavior and electrochemical impedance spectroscopy (EIS) features of 8090 Al-Li alloys in EXCO solution were investigated, and the EIS was simulated using an equivalent circuit. At the beginning of immersion in EXCO solution, the EIS is comprised by a depressed capacitive arc at high-mediate frequency and an inductive arc at low frequency, and the inductive component decreases and disappears with im- mersion time. Once exfoliation or severe pitting corrosion is produced, two capacitive arcs appear in the EIS. These two capacitive arcs are originated from the two parts of the corroded alloy surface, the original flat alloy surface and the new inter-face exposed to the aggressive EXCO solution due to the exfoliation or pitting corrosion. Some corrosion development features of 8090 Al-Li alloys in EXCO solution can be obtained through simulated EIS information.

ELECTRO-SUPERPLASTICITY IN 2091 Al-Li ALLOY

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2050铝合金热压缩过程表面开裂与应力-应变曲线关联性分析

对喷射态2050铝合金进行了温度为350~530℃,应变速率为0.01~10 s~(-1)的热压缩实验,分析了试样表面开裂情况及其与应力-应变曲线间的关联性。结果表明,应变速率低于1 s~(-1)时,变形温度越高、应变速率越低,试样表面越容易开裂。试样在应变速率为0.01 s~(-1)、温度为470℃压缩时表面出现了肉眼可见的微裂纹;随着温度增加至530℃,试样开裂程度加剧。在温度为530℃时,随着应变速率由0.01 s~(-1)增加至10 s~(-1),试样开裂程度先减小后增大,应变速率为1 s~(-1)的试样开裂程度最小。应变速率一定时,不同温度下应力-应变曲线变化趋势基本一致,变形温度越低、应变速率越大,变形抗力越高,温度为350℃、应变速率为10 s~(-1)时峰值应力最高,为119.8 MPa,温度为530℃、应变速率为0.01 s~(-1)时峰值应力最低,为15.3 MPa。对比开裂与未开裂试样的应力-应变曲线,未发现试样表面开裂对应力-应变曲线造成明显影响,可见应力-应变曲线不能反映热压缩过程中试样表面的开裂情况。

INTERFACE MORPHOLOGIES AND SOLUTE SEGREGATION OF Al-Li ALLOY 8090 DURING UNIDIRECTIONAL SOLIDIFICATION

The solid-liquid interface morphology and solute segregation behaviour of AI-Li alloy 8090 during unidirectional solidification were studied by the liquid metal quenehing method under varied processing conditions.When solidification rate,R<O.13 or>O.75 mm/min (temper- ature gradient,G_L=130℃/cm),the structure revealed of planar or dendritic interface respectively.With the increase of R,the interface morphology becomes cellular from planar gradually,within a narrow range.And the greater the R,the,finer the dendrite.Segregation of element Cu and impurity elements Fe and Si are quite severe,the interface morphology markedly influences on solute segregation.During solidification at coarse dendrite interface, their segregation ratios are rather great and solidified structure is coarse.

Thermal Stress Analysis of Welded Joint in 1420 Al-Li Alloy Induced by Thermal Cycling

A model of double grains under plane stress state has been established. According to the double grain model, thermal stress induced by thermal cycling in welding fusion zone is numerically simulated by finite element method, and the microstructures before and after thermal cycling are observed. The effect of thermal stress on weld microstructure is discussed. Experimental and analysis results show that the difference between the coefficients of thermal expansion and elastic modulus for grains along different crystal directio n can produce alternate thermal misfit stress and strain near boundaries under thermal cycling. At the temperature of upper and lower limit, thermal stress nearby grain boundary reaches maxima. Thermal stress induced changes in microstructure, which expressed by the sending dislocations from boundaries to matrix, piling up against the boundaries and the increasing of dislocation density.

THE CORROSION RESISTANCE OF AN Al-Li ALLOY IN 3.5 wt.-%NaCl

The influences of heal treatment and pH value on corrosion potential and cyclic polarization curve or an Al-Li alloy in 3.5 wt.-%NaCl were investigated.Microstructures of the alloy were combined to analyze and explain the development of cyclic polarization curves and the variation of corrosion potential within 24 h.The results revealed that the preferential dissolution of the precipitates in the alloy increased the susceptibility of the alloy to localized corrosion.Prolonging artificial ageing treatment caused heavy precipitation of T1 phase in matrix and both precipitation of phases containing copper and widening of PFZ along the grain boundary,and thus worsened the corrosion resistance.

PRECIPITATION IN BINARY Al-Li ALLOYS

Studies were carried out on the precipitation in two sets of binary Al-Li alloys by means of hardness tests,DSC analyses and TEM observations.When the alloys were aged for constant time,a peak appeared on the plot of temperature dependence upon their hardness in the range of low temperatures,and the endothermic dissolution peak was quite distinct on the DSC curve also at low temperatures.These are believed that an Li-rich GP zone formed in the al- loys aged at low temperatures,but no more GP zone if aging at elevated temperatures.The hardness of the alloys raises rapidly with coarsening of δ′-phase grains.The two endothermic peaks of δ′ dissolution on the DSC curve relate to the structural adjustment at twice of the δ′ precipitation.The equilibrium δ-phase,being of higher thermal stability,nucleates and grows directly from the supersaturated solid solution with the aid of the gram boundary.