Numerical Simulation and Experimental Validation of MIG Welding of T-Joints of Thin Aluminum Plates for Top Class Vehicles

Metallurgical and Materials Transactions A - The integration of experiments with numerical simulations can efficiently support a quick evaluation of the welded joint. In this work, the MIG welding...     

Heat Flow during the Autogenous GTA Welding of Pipes

A theoretical and experimental study of heat flow during the welding of pipes was carried out. The theoretical part of the study involves the development of two finite difference computer models: one for describing steady state, 3-dimensional heat flow during seam welding, the other for describing unsteady state, 3-dimensional heat flow during girth welding. The experimental part of the study, on the other hand, includes: measurement of the thermal response of the pipe with a high speed data acquisition system, determination of the arc efficiency with a calorimeter, and examination of the fusion boundary of the resultant weld. The experimental results were compared with the calculated ones, and the agreement was excellent in the case of seam welding and reasonably good in the case of girth welding. Both the computer models and experiments confirmed that, under a constant heat input and welding speed, the size of the fusion zone remains unchanged in seam welding but continues to increase in girth welding of pipes of small diameters. It is expected that the unsteady state model developed can be used to provide optimum conditions for girth welding, so that uniform weld beads can be obtained and weld defects such as lack of fusion and sagging can be avoided.     

CSP连铸中间包不同控流装置对钢水流动行为影响模拟研究

基于有限元方法,研究了酒钢CSP薄板连铸中间包采用不同的控制流装置布置对中间包流场的影响,结果表明,仅有挡渣墙无挡坝的控流装置钢水在中间包内停留时间最短,流场分布最不合理,第一道挡坝与挡渣墙的距离200 mm,高度200 mm的工况下,中间包流场分布较为合理,研究结果为中间包流场进一步优化改善提供了理论上的指导。     

薄板坯连铸结晶器内流动传热行为的研究

基于珠钢CSP薄板坯连铸机设备工艺条件和所采用扁平浸入式水口结构,结合铜板测温导出的热流密度分布进行了漏斗形结晶器内钢水流动、自由液面以及传热凝固等冶金现象的综合描述和数值分析.结晶器熔池中以两个上旋涡为主的钢水循环流动局限在漏斗形结晶器内,上旋涡流股冲击和离开熔池液面分别对液面起伏波动有所贡献,弯月面下距窄边100 mm范围内有二次涡形成.除水口下方两侧存在两个具有明显过热的高温区外,熔池中绝大部分钢水的温度在液相线附近保持恒定,铸坯表面温度分布和坯壳发育过程均反映出水口高温射流的影响,铸坯表面最高温区位于熔池液面下方靠近结晶器窄边的地方.     

Numerical Simulation of Fluid Flow and Heat Transfer in Funnel Shaped Mold of Thin Slab Continuous Caster

SymbolList Ab,An———Surfaceareaofbroadfaceandnarrowfaceof moldrespectively,m2;Cp———Effectiveheatcapacity,J·kg-1·K-1;Cp,s———Heatcapacityofsolidphase,J·kg-1·K-1;Cp,l———Heatcapacityofliquidphase,J·kg-1·K-1;Cw———Waterheatcapacity,J·kg-1·     

中间包连浇过程非稳态流场与温度场的数值模拟研究

通过计算得出在浇注过程中连铸中间包包壁瞬态热量损失作为边界条件的基础上,建立了连铸中间包内钢液流动与传热耦合数学模型,对连浇过程中中间包内非稳态的温度场和流场进行了数值模拟,考察了中间包连浇5个包次过程中钢液热量损失、温度分布以及流场情况,为现场操作和工艺优化提供依据和指导。     

内置隔板流化床气固两相流动数值模拟

基于EMMS模型、耦合双流体模型对内置隔板流化床内气固两相流动规律进行研究,包含流化床内气固两相的速度分布规律、固相颗粒体积分数分布规律、粒径对固相颗粒体积分数分布的影响规律等内容。结果表明:流化床内存在固体颗粒的返混现象,多个隔板的存在增强流化床内的返混现象;局部固相颗粒体积分数较高,表明固体颗粒发生了团聚现象;固相颗粒体积分数呈现出上稀下浓和,核稀边密的分布规律,且在高度方向的变化规律呈现出S曲线;随着颗粒粒径的减小,被气体携带进入高度h=0.1~0.4 m区域的固体颗粒增多。研究结果可为深入理解内置隔板流化床内磁化焙烧过程中气固两相流动规律提供理论指导。     

大热输入焊接Q460D结构钢的研制及焊接热模拟试验

利用50 kg真空电炉、小型试验轧机等设备进行了大热输入焊接Q460D结构钢板的试制.试制钢板以Cu作为主要强化元素,未添加Mo、Cr元素,有效控制了钢板成本.钢板采用全Ti脱氧工艺冶炼,然后经过控轧控冷及回火热处理获得最终成品.对钢板进行了不同回火温度后的力学性能检验和焊接热模拟试验.结果表明,610℃回火热处理时,钢板本身的强韧性匹配最佳.该回火工艺处理的钢板在100～120 kJ/cm大热输入焊接条件下,焊接热影响区粗晶区(CGHAZ)-20℃低温冲击功大于100 J,CGHAZ强度不低于基材.     

Influence of the Tool Shoulder Contact Conditions on the Material Flow During Friction Stir Welding

Friction stir welding (FSWing) is a solid-state joining process of special interest in joining alloys that are traditionally difficult to fusion weld. In order to optimize the process, various numeric modeling approaches have been pursued. Of importance to furthering modeling efforts is a better understanding of the contact conditions between the workpiece and the weld tool. Both theoretical and experimental studies indicate the contact conditions between the workpiece and weld tool are unknown, possibly varying during the FSW process. To provide insight into the contact conditions, this study characterizes the material flow in the FSW nugget by embedding a lead (Pb) wire that melted at the FSWing temperature of aluminum alloy 2195. The Pb trace provided evidence of changes in material flow characteristics which were attributed to changes in the contact conditions between the weld tool and workpiece, as driven by temperature, as the tool travels the length of a weld seam.     

Texture Development and Material Flow Behavior During Refill Friction Stir Spot Welding of AlMgSc

The microstructural evolution during refill friction stir spot welding of an AlMgSc alloy was studied. The primary texture that developed in all regions, with the exception of the weld center, was determined to be 〈110〉 fibers and interpreted as a simple shear texture with the 〈110〉 direction aligned with the shear direction. The material flow is mainly driven by two components: the simple shear acting on the horizontal plane causing an inward-directed spiral flow and the extrusion acting on the vertical plane causing an upward-directed or downward-directed flow. Under such a complex material flow, the weld center, which is subjected to minimal local strain, is the least recrystallized. In addition to the geometric effects of strain and grain subdivision, thermally activated high-angle grain boundary migration, particularly continuous dynamic recrystallization, drives the formation of refined grains in the stirred zone.

     

Thixoforging of Wrought Aluminum Thin Plates with Microchannels

A direct die-filling thixoforging method is designed to fabricate aluminum thin plates with a pattern of microchannels in a single forming operation. Extruded AA2024 and AA7075 wrought aluminum billets are used. A recrystallization and partial remelting process is used to prepare the semisolid slurries required for the forming process. Under a thixoforging pressure of 70 MPa, AA7075 thin plates are successfully thixoforged in a temperature range of 883 K to 893 K (610 °C to 620 °C), corresponding to liquid fractions of ~30 to 50 pct in the semisolid slurry. AA2024 thin plate requires a thixoforging temperature range of 888 K to 898 K (615 °C to 625 °C), corresponding to the liquid fractions of ~45 to 60 pct. Final microstructures of the thin plates comprise primary α-Al equiaxed globular grains in a matrix of a solidified liquid phase. With increasing thixoforging temperature, the yield strength values continuously decrease. The ultimate tensile strength (UTS) values of the thin plates initially decrease with increasing thixoforging temperature from 883 K to 888 K (610 °C to 615 °C) and from 888 K to 893 K (615 °C to 620 °C) for the AA7075 and AA2024 thin plates, respectively. The UTS values stabilize and slightly enhance when the thixoforging temperatures are further increased to 893 K and 898 K (620 °C and 625 °C) for the AA7075 and AA2024 thin plates, respectively. Very brittle behavior (elongation value of ~1 pct) is observed for the AA7075 thin plates thixoforged at 883 K and 888 K (610 °C and 615 °C). The elongation value increases to 3 pct with increasing the thixoforging temperature to 893 K (620 °C). In contrast, larger elongation values (between 4 and 6 pct) are achieved for the AA2024 thin plates. Increasing the thixoforging pressures from 70 to 100 MPa and then to 150 MPa improves the tensile properties of the thin plates. The tensile properties of the thixoforged thin plates are linked to their microstructural characteristics and processing conditions and are discussed here in detail.     

异钢种连浇过程中钢液流动与混合的数值模拟

研究了换钢种操作时，中间包及结晶器内钢液非稳态湍流流动及混合的计算过程。使用CFX5．6商业软件建立三维模型模拟了中间包及结晶器内钢液的流动和混合过程；绘制了中间包及结晶器出口处浓度分布曲线和中间包内钢液停留时间分布曲线（RTD）；确定了包内各区域的体积分数；并分析了不同中间包构形对钢液在包内的混合与流动的影响。它对研究异钢种连浇的混合过程具有一定的指导意义。     

Finite Element Simulation of Flow Localization During Equal Channel Angular Pressing

The hardening or softening behavior of materials is one of the major factors affecting the deformation homogeneity in work-pieces during processing by equal channel angular pressing. In the present study, the difference between plastic flow behavior and deformation homogeneity of strain hardening and strain softening materials were investigated with the aid of finite element simulation. Results showed that localization of plastic strain occurred in the strain softening materials and fluctuations were observed in the strain distribution along work-piece. In strain hardening materials, a more uniform distribution of plastic strain was obtained compared to strain softening material.     

薄板坯连铸连轧流程物流仿真系统的开发

开发了唐钢薄板坯连铸连轧流程物流仿真系统.该系统分为调度、炼钢、精炼、连铸、加热炉、连轧六个子系统,其中调度子系统负责仿真参数的初始化、计划的编制、实时调整等:其他子系统负责工序仿真、参数产生以及故障模拟生成等.所编软件能够较好地模拟实际生产流程,实现了整个生产线的合理衔接匹配;可以根据实际生产情况,进行计划的制定和实时调整,并实现了对常见故障及时、灵活的处理.     

反向凝固结晶器中流动与传热的数值模拟

文中根据连续统一模型建立了描述反向凝固结晶器中的流动与传热的数学模型。研究结果表明了反向凝固工艺母带增长的三阶段规律。即快速增长。平衡相持和快速回熔^[1,3,5]。通过母带厚度的实验值和模拟值的比较。验证了模型的正确性。     

两种不同强塑性薄钢板抗弹性能的试验和数值模拟

 利用51B式7.62mm手枪弹对不同强度和塑性的薄钢板进行枪击试验,采用ANSYS/LS-DYNA软件对试验过程进行数值模拟,对试验和数值模拟过程的钢板破坏形貌、背凸高度、残余弹丸长度等宏观形貌进行比较。结合抗弹过程中弹丸和钢板消耗的能量,分析了强度和塑性对钢板抗弹性能的影响。结果表明：尽管两种钢板的抗拉强度和断后伸长率差异较大,但其抗51B式7.62mm手枪弹性能相当。试验和数值模拟结果吻合较好,模拟方法能够正确地反映弹丸冲击靶板过程。因较高强度钢板使弹丸变形消耗的能量大于较低强度钢板,塑性较好钢板本身变形消耗的能量大于较低塑性钢板,从而解释了两种钢板抗弹性能相当的试验结果。     

薄板坯连铸结晶器流场模拟和验证

针对薄板坯连铸结晶器内钢液的流动特征,利用有限差分方法对薄板坯结晶器内钢液的流动进行了模拟,建立了结晶器内三维流动的数学模型,模拟了复杂水口结构对结晶器中钢液流动的影响。通过水力学模拟对流场模拟进行了验证。结果表明：流场模拟能够准确反映具有复杂水口结构特点的结晶器中的流动现象。     

单孔射流冲击流动与换热过程的数值模拟

应用三种RNG k-ε湍流模型对单孔气体射流冲击流动与换热过程进行了数值仿真计算,与实验结果的比较分析表明;RNG k-e系列模型能够对射流冲击流动和换热过程进行较为准确的预测.在此基础上,进一步对局部Nu数、平均Nu数分布的分析表明:喷孔直径D对冲击点处Nu的数值大小无明显影响;射流冲击高度HI/D对Nu数的分布规律...