Al-Zn-Mg-Cu铝合金变温双级蠕变时效模型（英文）

针对Al-Zn-Mg-Cu铝合金变温双级蠕变时效过程,建立了一种考虑蠕变应变与屈服强度的本构框架,通过实验数据的简单拟合方法获得了模型参数。模型不仅以简单的形式具备了处理蠕变时效过程中的应力松弛、强化响应和温度变化的能力,而且能够应用到有限元软件中模拟构件的蠕变量、屈服强度和回弹。模型结果不仅能够适应不同外加应力下实测的蠕变应变曲线,且有限元模拟结果与实测结果能够很好地吻合。     

椭球曲面薄壁构件蠕变时效成形仿真与试验

基于2219铝合金宏微观统一蠕变时效本构模型,应用大型商业有限元分析软件MSC.MARC对其进行二次开发,实现以运载火箭燃料贮箱瓜瓣为代表的椭球曲面薄壁构件的蠕变时效成形过程模拟仿真,分析了仿真过程中构件内部应力、应变、屈服强度分布以及变化规律,并开展了贮箱瓜瓣的蠕变时效成形试验。对比仿真与试验结果可知,构件各位置仿真与试验成形偏差在1.95 mm以内,构件力学性能最优位置位于底边中点区域,典型位置处屈服强度分布规律与仿真结果一致,其测试值与仿真值偏差在6.62%以内,构件各个位置沿轧制不同角度的屈服强度值呈现出0°45°90°的趋势。仿真模拟与试验结果存在较好的一致性,验证了蠕变时效本构模型和有限元仿真模型的正确性。     

7B04铝合金时效成形本构模型研究与有限元应用

通过ABAQUS软件的二次开发,将蠕变-时效本构模型应用于铝合金时效成形的有限元分析,得出铝合金等厚板在时效成形过程中的等效蠕变应变、屈服强度,以及析出相尺寸和分布的变化规律,并通过铝合金等厚板弯曲-时效成形的实验,验证了模型的准确性。     

铝合金7075马鞍外形蠕变时效成形数值模拟及试验

蠕变时效成形技术是利用金属的蠕变特性,将成形与时效同步进行的一种成形方法。文章针对铝合金7075T651进行温度在160℃下的蠕变拉伸试验,基于蠕变试验数据,采用非线性最小二乘法确定了7075T651铝合金蠕变本构方程中的材料常数,并应用有限元软件通过编写蠕变子程序,建立了该材料的蠕变时效成形过程有限元模型。针对马鞍典型外形零件进行蠕变时效成形-回弹分析,就成形过程中的应力应变分布进行分析。在相应条件下进行了蠕变时效成形试验,并对模拟结果进行验证。结果表明,采用该本构方程,可以较好的对蠕变时效成形过程及回弹进行模拟预测。     

Al-7Si-Mg铸造铝合金拉伸过程应力-应变曲线和力学性能的模拟

屈服强度、抗拉强度和伸长率是Al-7Si-Mg铝合金铸件常用的力学性能评判指标,因此建立相应的定量化模型进行拉伸力学性能的预测具有重要工程应用价值。本文建立了时效析出动力学、屈服强度、应变硬化模型,模拟Al-7Si-Mg合金在拉伸过程的应力-应变曲线和相应的拉伸力学性能。针对Al-7Si-0.4Mg合金,开展相应的实验研究,获得不同时效工艺下的拉伸应力-应变曲线以及力学性能数据,归纳出σUTS-σY与σY之间的关系式。模拟了该合金在180℃时效条件下屈服强度、抗拉强度和伸长率随时效时间的变化规律并进行实验结果对比,同时分析了时效工艺对合金应变硬化的影响规律。     

应力应变状态对蠕变时效7050合金硬化行为及拉伸性能的影响

通过三点弯曲加载方式对7050铝合金板材进行蠕变时效处理,研究了蠕变时效过程中的应力和应变状态对合金的时效硬化行为、拉伸性能及其各向异性的影响。结果表明,蠕变时效降低了合金的峰值时效硬度,应力状态对蠕变时效合金的时效硬化行为有一定的影响,压应力延长了合金达到峰值时效的时间,且压应力状态时效合金的峰值硬度比拉应力状态时效合金的峰值硬度稍低;在弹塑性应变状态下进行蠕变时效的合金具有较高的起始硬度,但在蠕变时效过程中,合金的硬化速率明显低于在弹性状态下进行蠕变时效的合金,当达到峰值时效时,弹塑性应变状态和弹性应变状态蠕变时效合金的硬度没有明显差别;与无应力时效合金相比,蠕变时效合金的强度和塑性都有所下降,弹塑性状态蠕变时效合金的强度和塑性比弹性状态蠕变时效合金的强度和塑性下降幅度稍大,但总体上,应变状态对蠕变时效合金拉伸性能的影响较小;蠕变时效7050合金的拉伸性能仍具有明显的各向异性,但在弹塑性状态下进行蠕变时效可以减小合金垂直于变形方向上的拉伸强度的下降。     

晶粒大小对AA2050铝合金蠕变时效的影响

采用恒应力蠕变拉伸、TEM、SEM、室温拉伸等手段,研究了晶粒大小对AA2050铝合金蠕变时效的影响。结果表明:AA2050铝合金试样经不同恒应力和不同温度蠕变拉伸后,蠕变应变随温度和应力升高而增大;原始晶粒小的比原始晶粒大的蠕变应变更大,抗拉强度和屈服强度更小,而伸长率则更大。     

铜合金单向静拉伸颈缩失稳的有限元模拟

在实验基础上,基于ANSYS软件的APDL语言和NLISO模型,建立铜合金单向静拉伸颈缩快速失稳的有限元模型.运用ANSYS的General Post Processor工具和Time Hist Post Processor工具获得了拉伸数值模拟过程中的直观物理图像、不同部位应力随时间变化曲线、应变随时间变化曲线以及真应力-真应变曲线.结果表明:模拟得到Mises等效最大真应力为580 MPa,与理论误差不超过10％;模拟所得屈服强度与实测误差不超过2.5％;模拟所得铜合金的硬化系数为558 MPa.     

7075铝合金蠕变时效成形过程数值模拟

蠕变时效成形技术是利用金属的蠕变特性,将成形与时效热处理同步进行的一种成形方法。文章运用有限元对成形过程进行数值模拟,就成形过程中的应力应变分布、主要成形参数对回弹的影响进行分析,为实际工艺参数的确定及优化提供参考。     

热处理强化铝合金焊接热-力过程数值模拟的改进

采用热加工历史不相关的屈服强度-温度单自变量材料模型进行热处理强化铝合金的焊接残余应力有限元分析，通常得到与材料屈服极限Rp0.2相当的纵向残余拉应力，这与实际测量结果明显不符。针对这一问题，通过分析热处理强化铝合金在焊接过程中经历的热循环、组织及性能变化特点，提出了包含固溶-软化和时效-硬化现象的热处理强化铝合金的热加工历史相关材料模型，建立了屈服强度与时间-空间-温度均相关的三自变量函数关系式。将该模型用于淬火-自然时效态2A12-T4铝合金TIG焊过程的有限元分析，得到53％Rp0.2的纵向残余应力，数值模拟的准确性具有实质性的改进。     

Microstructure Evolution of Extruded Mg-6Gd Alloy Under 175 °C and 150 MPa

The tensile creep behavior of extruded Mg-6Gd alloy, having the tensile yield strength of~110 MPa at 175 °C, has been investigated under 175 °C and 150 MPa. In this study, the extruded Mg-6Gd sample exhibits the total tensile strain of~10.5% after the creep time of 1100 h, and the fast plastic strain of~4.6% at the beginning of the creep test. The microstructure result suggests that the dislocation deformation is the main deformation mode during creep, and the grains with orientation close to〈0001〉|| ED disappear after creep. The creep process containing a low creep strain has no effective promotion for the precipitation compared with the aging process without strain. The origination of creep crack is related to the formation of precipitate-free zone during creep. The work offers an important implication to research the microstructure evolution under an applied stress in a weak aging response Mg alloy.     

A physically based methodology for predicting anisotropic creep properties of Ni-based superalloys

This paper is focused on developing suitable methodology for predicting creep characteristics(i.e., the minimum creep strain rate, stress rupture life and time to a specified creep strain) of typical Ni-based directionally solidified(DS) and single-crystal(SC) superalloys. A modern method with high accuracy on simulating wide ranging creep properties was fully validated by a sufficient amount of experimental data, which was then developed to model anisotropic creep characteristics by introducing a simple orientation factor defined by the ultimate tensile strength(UTS). Physical confidence on this methodology is provided by the well-predicted transitions of creep deformation mechanisms. Meanwhile, this method was further adopted to innovatively evaluate the creep properties of different materials from a relative perspective.     

新型铸造镁合金Mg-3.0Nd-1.5Gd-0.25Zn-0.5Zr的组织和力学性能

研究了新型铸造镁合金Mg-3.0Nd-1.5Gd-0.25Zn-0.45Zr的组织和力学性能。研究表明,试验合金的铸态组织为近等轴晶,主要由α-Mg基体和晶界处的(α-Mg+Mg12Nd)共晶组成。试验确定了固溶试验合金的较优时效处理工艺。试验合金经T6热处理后,室温屈服强度较ZM6合金显著提高。同时,试验合金的高温瞬时抗拉强度、屈服强度以及抗蠕变性能均显著优于ZM6合金。     

Creep aging behavior of retrogression and re-aged 7150 aluminum alloy

Creep aging behavior of retrogression and re-aged (RRAed) 7150 aluminum alloy (AA7150) was systematically investigated using the creep aging experiments, mechanical properties tests, electrical conductivity tests and transmission electron microscope (TEM) observations. Creep aging results show that the steady-state creep mechanism of RRAed alloys is mainly dislocation climb (stress exponent≈5.8), which is insensitive to the grain interior and boundary precipitates. However, the total creep deformation increases over the re-aging time. In addition, the yield strength and tensile strength of the four RRAed samples are essentially the same after creep aging at 140 °C for 16 h, but the elongation decreases slightly with the re-aging time. What's more, the retrogression and re-aging treatment are beneficial to increase the hardness and electrical conductivity of the creep-aged 7150 aluminum alloy. It can be concluded that the retrogression and re-aging treatment before creep aging forming process can improve the microstructure within grain and at grain boundary, forming efficiency and comprehensive performance of mechanical properties and electrical conductivity of 7150 aluminum alloy.     

准静态加载下时效态Inconel 718薄板的各向异性屈服准则及硬化模型构建

当金属件的特征尺寸缩小到微尺度时,会产生尺寸效应,从而使对微成形的理解变得复杂。本文以0.1mm厚的时效态Inconel 718薄板为研究对象,对其进行了力学性能测试。基于力学测试数据,探究了时效态Inconel 718薄板在相同应变速率、不同拉伸方向上各向异性、延伸率、屈服强度及最大抗拉强度的变化规律,并建立了介微观尺度下各向异性及屈服强度的预测模型和考虑应变量及应变速率的准静态硬化模型。结果表明：时效态Inconel 718薄板具有明显的各向异性,其延伸率以45°为极值点呈现先增大后减小的变化规律,屈服强度和最大抗拉强度的变化规律与之相反。由于尺寸效应的存在需要两组不同的材料参数对各向异性及屈服强度进行预测。当应变速率大于0.1 s_^-1时,材料屈服强度表现出明显的应变速率敏感性,该硬化模型不再适用。     

Effects of pre-deformation mode and strain on creep aging bend-forming process of Al−Cu−Li alloy

The bending deformation method was adopted to characterize the creep deformation behavior of Al−Cu−Li alloy in the creep aging forming (CAF) process based on a series of CAF tests, and the evolution laws of its mechanical properties and microstructures under different pre-deformation conditions were studied. The results show that the bending creep strain characterization method can intuitively describe the creep variation. With the increase of the pre-deformation strain, the creep strain of the specimen firstly increases and then decreases. The increase of the pre-deformation strain can promote the course of aging precipitation, and improve the formed alloy’s tensile properties at room temperature, the Kahn tearing properties, and the fatigue propagation properties. Pre-rolled specimens produce a slightly weaker work hardening than pre-stretched specimens, but they also create a stronger aging-strengthening effect; thus the strength, toughness and damage performance can be improved to some extent. Among all the types of specimens, the specimen with 3% rolling after CAF treatment has the best comprehensive mechanical properties.     

A unified constitutive model for multiphase precipitation and multi-stage creep ageing behavior of Al-Li-S4 alloy

A unified constitutive model is presented to predict the recently observed “multi-stage” creep behavior of Al-Li-S4 alloy. The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process, including dislocations and multiple precipitates, have been characterized in detail by X-ray diffraction (XRD) and transmission electron microscopy (TEM). For the yield strength, the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms, which includes shearable T₁ precipitate strengthening, non-shearable T₁ precipitate strengthening and θ′ precipitate strengthening. Based on creep deformation mechanism, the “multi-stage” creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables, including the radius of multiple precipitates, dislocation density and solute concentration, into the creep stress-strain model. It is concluded that the results calculated by the model are in a good agreement with the experimental data, which validates the proposed model.     

工艺参数对蠕变时效2124铝合金力学性能和微观组织的影响

研究2124铝合金在蠕变时效过程中工艺参数对力学性能和微观组织的影响。结果表明，蠕变量和蠕变速率随着时效时间、温度、应力的增大而增大。硬度随着时间和应力的增加呈类似于先增加后减小的趋势。在实验温度185～195℃范围内，温度对硬度的影响不大。当蠕变条件为200MPa、185℃、8h时，试样得到最佳的力学性能，此时试样基体内同时存在强化相S＂相和S＇相。透射电镜观察表明外加应力能促进析出相的析出和长大，基体中没有发现明显的应力位向效应。     

Modeling of precipitation hardening in pre-aged AlMgSi(Cu) alloys

A new analytical method to estimate the evolution of the relative volume fraction of precipitates during artificial aging of pre-aged AlMgSi(Cu) alloys in the underaged regime is introduced. The analytical results demonstrate that the precipitation processes in AlMgSi(Cu) alloys are isokinetic in commercially relevant temperature ranges. The theory of transformations is used to model isothermal and non-isothermal aging kinetics in isokinetic systems where the precipitate nuclei pre-exist at the start of aging and definite precipitate contents are reached at the end of transformation. A simple physically based model is also developed for the prediction of the average size of precipitates during artificial aging of pre-aged alloys, when “growth” is the controlling mechanism of precipitation. The microstructural models are combined with a previously developed yield strength model and the evolution of yield strengths during isothermal and non-isothermal aging of AlMgSi(Cu) alloys, with various pre-aging histories, are modeled. The analytical method and the microstructural and yield strength models are validated using experimental results.