Zr-4合金管电子束焊接瞬态温度场和应力场的数值模拟

Zr-4合金广泛用作大多数压水堆和反应堆的燃料包壳材料,因此针对其焊接的研究有非常重要的现实意义。论文采用数值模拟方式研究Zr-4合金电子束焊接的瞬态过程,采用双椭球热源模型,结合接触及辐射等边界条件,采用变密度六面体网格,耦合温度场和应力场,建立了Zr-4合金管电子束焊接的有限元瞬态数学模型,采用自适应时间步,计算了Zr-4合金管真空电子束焊接的三维瞬态温度场和应力场。数值模拟结果表明:在电子束功率相对较小的条件下,焊缝深宽比较小,采用双椭球热源模型进行数值模拟,所获熔池形状与实验所得焊缝成形吻合良好,证明了该数学模型的合理性,从而可为制定实际焊接工艺提供理论指导。在所设定的计算条件下,筒盖和筒体均变形均匀,主要表现形式为沿径向突出,且筒盖变形大于筒体,和实际焊接现象基本一致;焊后最大整体变形约0.02 mm。     

M42高速钢/X32弹簧钢电子束焊接温度场的数值模拟与实验研究

选择双椭球热源模型对M42高速钢/X32弹簧钢双金属带锯的电子束焊接的温度场进行Ansys数值模拟,确定焊接的最佳工艺参数,并进行焊接试验,利用扫描电镜观察M42/X32接头的微观组织。结果表明,最佳焊接工艺为焊接电压U=140 k V,焊接电子束电流Ib=20 m A,焊接速度v=2 m/min。在此工艺条件下进行电子束焊接实验,焊缝宽度实验值和计算值的相对误差为-3%~1.5%,二者吻合较好,验证了双椭球热源模型在电子束焊接温度场模拟中的适用性。M42/X32接头的焊缝中心为等轴晶和柱状晶的典型铸态组织;M42熔合区(FZ)组织为马氏体和M2C型碳化物,M42热影响区(HAZ)组织为马氏体、残余奥氏体及碳化物。X32熔合区(FZ)由类马氏体层和马氏体组织组成,X32热影响区(HAZ)组织为马氏体、残余奥氏体以及M23C6。     

WE43镁合金电子束焊接温度场的数值模拟研究

通过分析焊接温度场数据,相关工作人员可以及时了解焊接温度分布状态。研究人员基于WE43镁合金电子束焊接模型,对焊接温度场进行网格划分并建立热源模型,在使用SYSWELD元件对WE43镁合金电子束焊接时,还需要对温度场数据变化情况进行模拟。此外,研究人员基于温度场云图,总结WE43镁合金焊接过程中金属板材温度分布变化的特点,并对焊接工艺参数进行优化,以期提高电子束焊接水平。     

激光焊接1Cr17铁素体不锈钢温度场数值模拟

采用SYSWELD有限元软件,建立了激光焊接铁素体不锈钢的3D有限元模型.考虑材料的热物性参数与温度的非线性关系以及表面对流和辐射热交换的影响,分析了激光焊接过程中温度场的分布及焊缝表面不同点的热循环变化,并进行了实验验证.结果 表明:焊接一段时间后,焊接温度场呈现准稳定状态,随焊接热源的继续移动,焊缝区各点的温度基本...     

锆基块体非晶合金力学性能的研究进展

锆基块体非晶合金具有优良的非晶形成能力,可在很小的冷却速率条件下获得.锆基非晶合金具有高强度、超塑性、高弹性、高硬度、高耐磨性和高耐腐蚀性能等,有着广阔的应用前景.总结了锆基非晶合金的形成机制,着重对锆基非晶合金的力学性能、耐腐性能等进行了综述.     

电弧焊接数值模拟中热源模型的研究与发展

焊接过程的数值模拟作为一种有效的计算手段,在焊接温度场及残余应力分布的评价中获得了广泛应用,而焊接热源模型的选择及模型参数的确定直接影响到计算和评价结果的准确性.本文通过对近年来常用的电弧焊接热源模型进行梳理,介绍了其研究进展,分析了不同热源模型的特点及适用性.高斯面热源模型和双椭球体热源模型作为基础热源模型,广泛应用于较小尺寸工件和规则轨迹的焊接过程数值模拟,且具有较高的计算精度;简化热源模型和温度替代型热源模型多用于大厚工件的多层多道焊接及复杂轨迹焊接过程的数值模拟,能够实现效率和精度的统一;多丝电弧焊接热源较为复杂,采用修正后的双椭球体叠加热源模型,计算结果能保证一定的精度;结合型热源模型对熔池形状的描述更灵活,在深熔电弧焊的数值模拟中具有优势.本文可为电弧焊接过程数值模拟的热源模型选择和模型参数确定提供有益参考.      

铁基非晶合金的辐照性能

铁基非晶合金由于成本低较、易制备、较好的温度稳定性等优点,并具优异的机械性能、磁性能和耐腐蚀性能而被广泛研究.并且其固有的无序结构有助于抵抗辐照导致的损伤,使得铁基非晶合金可作为抗辐照材料使用.辐照既可以试验铁基非晶合金的性能也是优化铁基非晶合金结构和性能的有效方法.本文综述了铁基非晶合金中子辐照、离子辐照和电子辐照性能的研究进展,探讨了铁基非晶合金的结构和性能与非晶合金的成分以及辐照粒子的类型、能量、注量之间的关系,以及辐照晶化的机制,为进一步促进高性能铁基非晶合金的研究提供了有价值的参考.      

TiAl合金建筑材料焊后热处理组织及性能研究

对建筑用TiAl合金电子束焊接接头进行了两种热处理试验研究,借助金相显微镜(OM)分析了接头不同区域的显微组织,并对焊接接头进行显微硬度测试,分析了两种热处理方式对建筑TiAl合金焊接接头组织及硬度带来的变化.研究表明,TiAl合金电子束焊接后焊缝组织主要为α2相,B相与O相.焊接接头局部热处理后接头硬度较高的区域有所增加,但整体呈下降趋势;热处理后,TiAl合金电子束焊接后合金焊缝区的B2相尺寸减小,但B2相分解的O相板条尺寸变大.整体热处理后焊接接头的显微硬度整体有所降低.两种热处理均能降低焊缝区显微硬度,并分布较为平稳.     

热喷涂Fe基非晶合金涂层的研究现状

综述了超音速火焰喷涂(HVOF),等离子喷涂(PS)技术的性能特征,以及运用热喷涂技术制备Fe基非晶涂层的发展历史与现状。从非晶合金涂层的高硬度、耐磨性及腐蚀性能等方面阐述了非晶合金涂层的优越性,对新型Fe基非晶涂层的形成机理进行研究,探讨采用超音速火焰喷涂技术制备高质量非晶合金涂层的关键因素。并展望了采用热喷涂技术制备非晶合金涂层的未来发展趋势。     

镁基非晶合金的研究进展

近年来,Mg基非晶合金以低密度、高非晶形成能力等优点受到人们越来越多的关注。介绍了Mg基非晶合金的发展现状和现有的合金体系,综述了其力学性能的优势,指出了其应用过程中存在的问题。对其作为生物医用材料应用进行了探讨,并对今后发展进行了展望。     

Numerical Investigation of Residual Stress in Thick Titanium Alloy Plate Joined with Electron Beam Welding

A finite-element (FE) simulation process integrating three dimensional (3D) with two-dimensional (2D) models is introduced to investigate the residual stress of a thick plate with 50-mm thickness welded by an electron beam. A combined heat source is developed by superimposing a conical volume heat source and a uniform surface heat source to simulate the temperature field of the 2D model with a fine mesh, and then the optimal heat source parameters are employed by the elongated heat source for the 3D simulation without trial simulations. The welding residual stress also is investigated with emphasis on the through-thickness stress for the thick plate. Results show that the agreement between simulation and experiment is good with a reasonable degree of accuracy in respect to the residual stress on the top surface and the weld profile. The through-thickness residual stress of the thick plate induced by electron beam welding is distinctly different from that of the arc welding presented in the references.     

预热对铍环激光束钎焊过程的影响研究

研究预热对铍环激光束钎焊过程温度场和应力场分布的影响。采用轴对称模型和热力解耦的有限元方法，并假定沉积到钎缝表面的激光束能量为Gauss分布，预热通过在焊接加热前添加一个能量密度低、有效加热半径大的单独工况实现。结果表明，预热使镀环钎缝外表面焊接最高温度增加，温度梯度减小，但焊深明显增加；采用预热工况焊接后，钎缝附近塑性变形区焊接残余应力明显减小，而热影响区残余应力增大。从整体分布来看，预热使铍环外表面焊接残余应力分布均匀化。对铍环外表面钎缝附近焊接残余应力进行X射线应力测试，并与有限元分析结果对比，二者应力变化趋势基本一致。     

A new finite element model for welding heat sources

A mathematical model for weld heat sources based on a Gaussian distribution of power density in space is presented. In particular a double ellipsoidal geometry is proposed so that the size and shape of the heat source can be easily changed to model both the shallow penetration arc welding processes and the deeper penetration laser and electron beam processes. In addition, it has the versatility and flexibility to handle non-axisymmetric cases such as strip electrodes or dissimilar metal joining. Previous models assumed circular or spherical symmetry. The computations are performed with ASGARD, a nonlinear transient finite element (FEM) heat flow program developed for the thermal stress analysis of welds.* Computed temperature distributions for submerged arc welds in thick workpieces are compared to the measured values reported by Christensen¹ and the FEM calculated values (surface heat source model) of Krutz and Segerlind.² In addition the computed thermal history of deep penetration electron beam welds are compared to measured values reported by Chong.³ The agreement between the computed and measured values is shown to be excellent.     

A study on heat source equations for the prediction of weld shape and thermal deformation in laser microwelding

In the area of laser welding, numerous studies have been performed in the past decades using either analytical or numerical approaches, or both combined. However, most of the previous studies were process oriented and modeled conduction and keyhold welding differently. In this research, various heat source equations that have been proposed in previous studies were calculated and compared with a new model. This is to address the problem of predicting, by numerical means, the thermomechanical behavior of laser spot welding for thin stainless steel plates. A finite-element model (FEM) code, ABAQUS, is used for the heat transfer and mechanical analysis with a three-dimensional plane assumption. Experimental studies of laser spot welding and measurement of thermal deformation have also been conducted to validate the numerical models presented. The results suggest that temperature profiels and weld deformation vary according to the heat source equation of the laser beam. For this reason, it is essential to incorporate an accurate model of the heat source.     

CO2 laser beam welding of 6061-T6 aluminum alloy thin plate

Laser beam welding is an attractive welding process for age-hardened aluminum alloys, because its low heat input minimizes the width of weld fusion and heat-affected zones (HAZs). In the present work, 1-mm-thick age-hardened Al-Mg-Si alloy, 6061-T6, plates were welded with full penetration using a 2.5-kW CO₂ laser. Fractions of porosity in the fusion zones were less than 0.05 pct in bead-on-plate welding and less than 0.2 pct in butt welding with polishing the groove surface before welding. The width of a softened region in the-laser beam welds was less than 1/4 times that of a tungsten inert gas (TIG) weld. The softened region is caused by reversion of strengthening β″ (Mg₂Si) precipitates due to weld heat input. The hardness values of the softened region in the laser beam welds were almost fully recovered to that of the base metal after an artificial aging treatment at 448 K for 28.8 ks without solution annealing, whereas those in the TIG weld were not recovered in a partly reverted region. Both the bead-on-plate weld and the butt weld after the postweld artificial aging treatment had almost equivalent tensile strengths to that of the base plate.     

Relationship Between Microstructure,Strength, and Fracture in an Al-Zn-Mg Electron Beam Weld: Part II: Mechanical Characterization and Modeling

This paper presents an experimental and modeling study of the mechanical behavior of an electron beam welded EN-AW 7020 aluminum alloy. The heterogeneous distribution of mechanical properties is characterized by micro-tensile tests and by strain field measurements using digital image correlation technic. These results are related to the microstructural observation presented in the companion paper. The mechanical behavior of the weld is simulated by a finite element model including a Gurson-type damage evolution model for void evolution. The model is shown to be capable of describing accurately experimental situations where the sample geometry is varied, resulting in stress triaxiality ratios ranging from 0.45 to 1.3.     

数值模拟在镁合金焊接接头深冷处理中的应用

利用所建立的有限元模型,对焊接接头进行深冷处理前后的温度场分析,再把模型转化成结构单元进行应力应变场分析。计算结果表明:深冷处理后,受焊接热源影响的焊缝及附近区域横向残余应力和纵向残余应力均增大,距焊缝较远的母材区产生了预压应力;深冷处理后,横向和纵向残余变形均减小。     

Weld metal composition change during conduction mode laser welding of aluminum alloy 5182

Selective vaporization of volatile elements during laser welding of automotive aluminum alloys affects weld metal composition and properties. An experimental and theoretical study was carried out to seek a quantitative understanding of the influences of various welding variables on vaporization and composition change during conduction mode laser welding of aluminum alloy 5182. A comprehensive model for the calculation of vaporization rate and weld metal composition change was developed based on the principles of transport phenomena, kinetics, and thermodynamics. The calculations showed that the vaporization was concentrated in a small high-temperature region under the laser beam where the local vapor pressure exceeded the ambient pressure. The convective vapor flux driven by the pressure gradient was much higher than the diffusive vapor flux driven by the concentration gradient. The computed weld pool geometry, vaporization rates, and composition changes for different welding conditions agreed well with the corresponding experimental data. The good agreement demonstrates that the comprehensive model can serve as a basis for the quantitative understanding of the influences of various welding variables on the heat transfer, fluid flow, and vaporization occurring during conduction mode laser welding of automotive aluminum alloys.     

Ti基大块金属玻璃的研究与应用

阐述了Ti基大块金属玻璃(BMG)的成分设计原则及制备方法，并对Ti基非晶合金及其部分晶化复合材料的力学性能及断裂机理进行了评述。结果表明：Ti基大块金属玻璃具有较高的断裂强度、弹性延伸率及一定的塑性延伸率，而经过部分晶化获得的非晶合金基纳米颗粒复合材料，其室温塑性获得很大的改善。在此基础上探讨了该合金目前所存在的问题、研究热点以及其应用前景。     

Simulation of Heat Flow During the Welding of Thin Plates

Based on the finite difference method and the enthalpy model of Shamsundar, a computer model was developed to describe the steady state, two-dimensional heat flow during the welding of thin plates. In order to allow accurate computations of the weld pool configuration, the size of the mushy zone and the temperature distribution near the heat source, a grid mesh of variable spacings was used. The heat of fusion, the size and distribution of the heat source, the temperature dependence of thermal properties, the heat conduction in the welding direction and the surface heat loss during welding were considered. The model was first checked with Rosenthal’s analytical solution of welding heat flow using pure aluminum for examples. Experimental results of 6061 aluminum, including the width of the fusion zone and the thermal cycles at positions in both the fusion and the heat affected zones, were then compared with the calculated results of the heat flow model. The agreement was very good. Finally, in order to demonstrate systematically the quantitative effect of welding parameters such as the heat input, the welding speed and the preheating of the workpiece, a series of computations were made based upon 6061 aluminum.