2A66铝锂合金板材各向异性研究

采用布氏硬度与拉伸性能测试以及OM,SEM和TEM分析,研究2A66铝锂合金板材力学性能的各向异性随时效时间变化的规律和合金时效状态下的显微组织,并探讨影响各向异性的主要因素。结果表明:165℃峰值时效前,随时效时间的延长,2A66铝锂合金力学性能的各向异性程度逐渐下降,过时效后合金的各向异性有所增强,伸长率的各向异性大于强度各向异性。峰时效(64h)时合金的σ_b,σ_(0.2),δ的IPA值均达到了最低值,分别为3.0%,3.0%,12.2%,此时合金也获得了较好的强塑性结合,轴向σ_b,σ_(0.2),δ分别为526.5,448.9MPa,10.1%。不同热处理状态下,2A66铝锂合金平面各向异性的总体表现为:纵向(0°)和横向(90°)的强度最高,45°方向最低;45°方向试样的伸长率最高,纵向和横向最低。     

2195铝锂合金的各向异性研究

通过拉伸力学性能测试和断口形貌分析,研究了2195铝锂合金冷轧薄板的各向异性随时效时间变化的规律.结果发现:在150℃时效条件下,峰值时效前,随时效时间的增加,合金的各向异性程度逐渐下降,过时效时合金的各向异性比峰值时效时有所增加;延伸率各向异性大于强度各向异性.150℃/24h时效时,与轧向成0°和45°方向试样的断裂机理不同,存在断裂方式的各向异性.最后对该合金各向异性的主要形成机理进行了初步探讨.     

铝锂合金的研究与应用

综述了Al-Li合金的研究历史和应用情况等，并着重阐述了近年来各国在改善Al-Li合金强韧性，各向异性和热稳定性等方面的新进展。     

RPC200塑性与各向异性损伤耦合本构建模研究

针对活性粉末混凝土 (RPC200：Reactive Powder Concrete 200MPa)的非线性行为,将连续损伤力学和塑性力学结合起来,建立了RPC200的弹塑性各向异性损伤耦合本构。在有效应力空间内,采用非关联流动法则和非均匀等向强化法则建立了RPC200的塑性本构。基于损伤能释放率建立了损伤准则,并由正交法则给出损伤演化法则,同时采用两个不同的损伤硬化法则来描述拉、压性能不同的损伤硬化。证明了该文所建模型与热动力学基本原理的相容性。最后,给出了RPC弹塑性各向异性损伤耦合本构模型数值计算流程,并以简单例证证明了所建模型的预测能力。     

2195铝锂合金热变形流变行为与热加工图研究

目的 研究2195铝锂合金在实验温度360~510 ℃、应变速率0.01~10 s⁻¹条件下的热压缩变形行为,建立其本构模型及热加工图,获取该合金的安全加工工艺参数。方法 采用Gleeble−3500热模拟试验机进行热变形实验,分析合金的流变行为及热加工图,结合微观组织阐述其热变形机理,并对所得最优参数进行热挤压实验验证。结果 2195铝锂合金的流变应力随变形温度增加而减小,随应变速率增加而增加;其热激活能Q为203.643 9 kJ/mol、结构因子A为1.943 9×10¹⁴、应力因子α为0.013、应变硬化指数n为5.883 9。确定合金的主要失稳区工艺参数区间为379~420 ℃、0.75~10 s^–1和480~510 ℃、1～10 s⁻¹,安全加工区间为440~510 ℃、0.01~0.25 s⁻¹。铸态2195铝锂合金的屈服和抗拉强度分别仅为(179±6)MPa和(239±11)MPa,经热挤压实验后分别达到(605±6)、(633±3)MPa,分别提高了3.5和2.6倍;铸态合金的显微硬度仅为(115±1)HV,热加工后型材达到(178±4)HV,相较于铸态合金增加了54%。结论 2195铝锂合金的流变行为符合正应变速率敏感特征,其安全加工区域集中在高温低应变速率区,主要发生了动态再结晶,实验型材在此区域表现出卓越的力学性能。     

高温合金超薄板循环塑性本构模型适用性研究

高温合金具有优良的综合性能,是航空发动机高性能构件的首选材料.由于高温合金带材屈服强度高、壁厚超薄、回弹明显、构件成形精度难以控制,因此研究现有循环本构模型对于高温合金带材变形预测的适用性具有重要意义.基于循环剪切实验,研究了不同循环塑性本构模型(Armstrong-Frederick(A-F)模型、Yoshida-Uemori(Y-U)模型和the anisotropic nonlinear kinematic(ANK)模型)对高温合金超薄带材循环塑性变形响应的表征效果.同时,通过U形弯实验和有限元仿真结果的对比,分析了不同屈服准则(Hill48,Barlat89和YLD2000-2d)结合不同循环塑性模型对于回弹预测的影响.结果表明,采用Y-U模型对高温合金超薄板循环塑性变形行为的表征能力最好,A-F和ANK模型次之.采用Y-U模型对回弹的预测精度高于各向同性模型和A-F模型,而屈服准则对回弹预测精度的影响不大,采用基于Hill48和YLD2000-2d屈服准则的Y-U模型,回弹预测误差可以控制在5％以内.     

2195铝锂合金超低温流变行为及成形特性研究

2195铝锂合金薄壁件被广泛应用于航空航天领域,提高2195铝锂合金的成形性是实现其高性能成形制造的基础和前提.本工作通过不同温度(298～77 K)和不同应变速率(0.00025～0.01 s-1)的超低温单轴拉伸试验研究了变形温度和应变速率对2195铝锂合金超低温流变规律的影响,结合埃里克森杯突实验及断口形貌观察,分析了变形温度对成形性的影响机理.结果表明:变形温度由室温(298 K)降低至超低温(77 K),2195铝锂合金试样延伸率和抗拉强度较室温分别提升78.11％和71.13％;杯突值(lE)和最大凸模力较室温提升19.2％和51.4％.同时,超低温条件下,材料加工硬化率较室温更高,并且具有更大的稳定塑形应变区间,成形性能明显提高;试样断口韧窝较室温尺寸减小、深度增加、分布更加均匀,断裂模式为典型的韧性断裂.     

GH5188合金板材高温拉伸变形流动行为与本构方程研究

目的 研究GH5188合金板材高温拉伸变形流动行为,为高温合金板材高温成形工艺的制定和优化提供指导。方法 基于GH5188合金板材高温拉伸试验,分析了变形工艺参数对GH5188合金板材高温拉伸变形时真应力、应变速率敏感性指数和应变硬化指数的影响规律,建立了本构模型对其流动行为进行描述和预测。结果 GH5188合金板材高温拉伸变形流动行为受应变硬化、流动软化和应变速率硬化的共同影响,其变形过程分为弹性变形、加工硬化、稳态流动和断裂4个阶段。随变形温度的升高和应变速率的降低,真应力减小。变形温度、应变速率和真应变对GH5188合金板材的应变速率敏感性指数和应变硬化指数具有显著影响。基于Johnson-Cook和Hensel-Spittel模型,建立了考虑应变硬化效应、流动软化效应和应变速率硬化效应耦合影响的GH5188合金板材高温拉伸变形本构模型(JC-HS模型),采用该模型预测的真应力与试验值的平均相对误差为6.02%。结论 建立的JC-HS模型能够较好地描述和预测GH5188合金板材的高温拉伸流动行为。     

新型铝锂合金的研究和发展

综述了铝锂合金的研究概况,介绍了新型铝锂合金的成分、性能、组织特征和提高强韧性的途径,并针对铝锂合金目前存在的问题,提出了今后的研究方向.     

2A97 铝锂合金超塑变形规律及其本构方程

目的研究2A97铝锂合金在390~470℃温度范围和3×10-4~3×10-2s-1应变速率范围内的超塑变形行为,揭示温度和应变速率对延伸率和峰值应力的影响规律,并建立超塑拉伸变形本构方程。方法采用单轴超塑拉伸试验方法进行研究。结果当变形应变速率低于3×10-3s-1时,2A97铝锂合金真应力-真应变曲线呈现稳态流变特征;当应变速率高于3×10-3s-1时,则呈现软化特征。在450℃,应变速率为1×10-3s-1条件下,达到最大延伸率600%。结论 2A97铝锂合金具有良好的超塑变形性能,其应变速率敏感性指数m平均值为0.35,超塑变性激活能Q值为145.87 k J/mol,远高于纯铝自扩散激活能65.6 k J/mol,表明此时铝锂合金变形机制仍以晶内滑移为主。     

Experimental and numerical investigation on ductile fracture mechanism of aluminium alloy using new modified model

In the present paper, the ductile fracture of aluminium alloy 5052P-H34 is studied by experiments and simulations. Then, the extension of the damage growth model, which captures both tension as well as shear, was employed in the present paper, and a modified Rousselier model was proposed. A stress integration algorithm based on the general backward Euler return algorithm was developed and implemented into finite element (FE) models in the ABAQUS/Explicit platform. The shear coefficient was calibrated by a FE analysis based on an inverse calibration procedure combined with the physical experiments. The predictive capability of this model was studied by comparing the experiments with the simulations, and the validity of this model was verified. The results show that the modified Rousselier model can give more accurate results for both tension and shear failure.     

Effect of Porosity and Cell Size on the Dynamic Compressive Properties of Aluminum Alloy Foams

The dynamic mechanical properties of open-cell aluminum alloy foams with different relative densities and cell sizes have been investigated by compressive tests.The strain rates varied from 700 s^-1 to 2600 s^-1.The experimental results showed that the dynamic compressive stress-strain curves exhibited a typical three-stage behavior:elastic,plateau and densification.The dynamic compressive strength of foams is affected not only by the relative density but also by the strain rate and cell size.Aluminum alloy foams with higher relative density or smaller cell size are more sensitive to the strain rate than foams with lower relative density or larger cell size.     

Study on mechanical properties and constitutive model of 5052 aluminium alloy

The stress–strain relationship of 5052 aluminium alloy was investigated via quasi-static tensile tests and split Hopkinson pressure bar tests. The specimens were exposed to various temperatures (25–500°C) and strain rates (10^?4–0.7?×?10^4?s^?1). At strain rates ranging from 0.001 to 3000?s^?1, the material underwent significant work hardening. When the strain rate exceeded 5000?s^?1, the work hardening effect decreased and the flow stress was relatively constant. The Johnson–Cook constitutive model was modified to describe the deformation behaviour of the material subjected to high temperatures and strain rates. The accuracy of the modified model was verified through ballistic impact testing.     

Defects and tensile properties of 6013 aluminum alloy T-joints by friction stir welding

In this paper, 6013-T4 T-joints were successfully fabricated with different welding parameters by friction stir welding in two different combination modes of skins and stringers. The distribution features and formation mechanisms of defects in T-joints were observed and analyzed. The effect of defects and welding parameters on tensile properties of T-joints was investigated. The result shows that the T-joint without tunnel defect only can be obtained with the traverse speed of 100 mm/min in this experiment, and the welding parameters influence the features and sizes of kissing bond defects. The fracture of T-joints along the shin is attributed to the kissing bond defect and the tunnel defect is the main factor affecting the tensile properties along the stringer.     

Effects of sleeve plunge depth on microstructures and mechanical properties of friction spot welded alclad 7B04-T74 aluminum alloy

Friction spot welding (FSpW) was applied to join the 7B04-T74 aluminum alloy successfully, and effects of sleeve plunge depth on weld appearance, microstructures and mechanical properties were investigated in detail. When the sleeve plunge depth was larger than 2 mm, a surface indentation with a depth of 0.2 mm should be applied in order to eliminate the defect of annular groove. The tensile shear properties of the joints were dependent on hook geometry, location of alclad layer, and hardness of stir zone (SZ). With increasing the sleeve plunge depth from 2 to 3.5 mm, the hook height increased, the alclad layer downward migrated further and the hardness of SZ decreased. The optimized FSpW joint was obtained when the sleeve plunge depth was 3 mm, and the corresponding tensile shear failure load was 11921 N. Two different failure modes, i.e. shear fracture mode and tensile-shear mixed fracture mode, were observed in the tensile shear tests.     

新型BTG塑料合金关于温度-频率-振幅的动态阻尼性能模型

建立了描述一种新型BTG塑料合金的温度-频率-振幅的动态阻尼性能数学模型。通过动态热分析仪DMA242, 获取了BTG塑料合金的频率扫描、温度扫描和幅值扫描的动态阻尼损耗因子实验数据。通过分析实验数据, 将温度扫描的阻尼损耗因子量分离为仅与频率相关以及与频率、温度均相关的两个分量, 并分别用Kelvin分数导数的阻尼损耗因子模型和高斯函数模型来表达这两个分量, 再以此为基准, 考虑振幅对阻尼损耗的影响, 由此建立了综合考虑温度-频率-振幅的阻尼损耗数学模型。结果表明, 所建立的综合考虑温度-频率-振幅的阻尼损耗数学模型能准确描述实验数据。      

Prediction of crack growth following a single overload in aluminum alloy with sheet and plate microstructure

The fatigue crack growth behavior under constant amplitude and under single overload of 2024 aluminum alloy in sheet and plate product form has been investigated. Constant amplitude fatigue crack growth tests showed superior crack growth resistance of the plate attributed to a pronounced roughness induced crack closure as a result of the coarse and elongated grain structure. Crack growth tests with single overload showed that the retardation effect caused by the overload is not primarily influenced by roughness crack closure at the crack path. In this case, the sheet material with lower yield strength revealed a higher retardation effect than the plate material. The observed crack growth behavior has been simulated with the LTSM-F model, which accounts for retardation of crack growth after an overload due to material strain hardening at the crack front. Dissimilar strain hardening at the crack tip due to different yield strength for the sheet and plate has been considered by means of strength gradients inside the overload plastic zone. The analytical results confirmed the observed material crack growth trends.     

汽车用铝合金板拉伸性能与成形能力的相关性

为了找到适合于评估汽车用铝合金板成形性能的参数,本文在模拟试验获得的样本数据基础上,采用回归分析方法,分析了汽车用铝合金板单向拉伸性能参数与其拉深性能、胀形性能之间的对应关系.研究表明,在单向拉伸性能参数中,硬化指数n对汽车用铝合金的拉深极限凸模行程的相关性最为显著;而总延伸率δ对胀形极限凸模行程的相关性最为显著.上述结果表明,n值和δ值分别是评估汽车用铝合金板拉深性能和胀形性能的最佳参数.     

Investigations on mechanical and tribological properties of Al-Si10-Mg alloy/sugarcane bagasse ash particulate composites

Aluminum metal matrix composites are a new generation of metal matrix composites that have the potential of sustaining the emerging demand for advanced engineering applications. These demands were satisfied due to massive mechanical and tribological properties of the aluminum hybrid composite material. In this work, abundantly available agricultural waste product (i.e., sugarcane bagasse ash) was used as a reinforcement material in AlSi10Mg alloy to enhance the alloy material properties for their better accomplishment in industrial applications. Initially, the chemical composition of the sugarcane bagasse ash particles was analyzed using Energy Dispersive X-ray Spectroscopy test, which revealed the presence of rich Silica content in the ash particles. Sugarcane bagasse ash particles of three different weight percentages (i.e., 6, 9, and 12%) are reinforced with aluminum alloy (AlSi10Mg) using stir casting process. The wear mechanisms and fractured morphology of the tensile tested specimen were analyzed with the aid of scanning electron microscopy. The result shows that the tensile, hardness, and impact strength were increased with increase in the weight percentage of sugarcane bagasse ash particles but ductility decreased when increasing the weight percentage. Further, dry sliding wear behavior of the fabricated composites was tested using Pin-on-Disc for three different loads (10 N, 20 N, 30 N). The wear rate and coefficient of friction for the hybrid matrix composites were found to be decreased while increasing the weight percentage of ash content, but they increase while increasing the applied load.