Research on the Effect of Pouring Temperature on Hot-Tear Susceptibility of A206 Alloy by Simulation

Cast alloys with wide solidification ranges are prone to hot tearing. This study deals with prediction of hot tearing location and its intensity by computer simulation. The simulation was performed at different pouring temperatures on A206 aluminum alloy. As superheat increases, the critical fraction solid time increases which means the alloy is more susceptible to hot tearing. These theoretical predictions are in complete accordance with experimental results.     

薄板坯连铸结晶器铜板温度及热流密度分布

薄板坯连铸结晶器的传热过程直接影响到铜板的寿命,有必要研究薄板坯连铸结晶器的传热特征。为了研究薄板坯结晶器的热流密度,通过开发的结晶器温度监测软件检测了珠钢结晶器铜板的温度。根据在线实测的铜板温度以及薄板坯连铸机冷却参数,建立了薄板坯结晶器铜板传热模型,计算并验证了结晶器热流密度的分布函数,同时通过二次回归得出了结晶器热流密度与结晶器高度的关系式。结果表明,在宽度方向上铜板温度和热流密度的分布具有相似的规律性,距离弯月面越近,热流密度和温度的波动越大。弯月面处热流密度值大于4．2MW／m^2,是造成结晶器铜板被侵蚀的主要原因。     

铸造温度对铝中含氢量影响规律的研究

通过测试溜槽中不同温度下铝熔体中氢含量,发现铝中氢含量随着铸造温度升高而升高,每升高1℃,铝中氢含量约升高0．013mL／100gAl;铸造开始时铝中氢含量高于铸造过程铝中氢含量。     

铸造紫铜及铜合金的湿砂型模表面涂料的研究

采用“罗90—1”表面处理涂料的结果表明:操作方便,导热性好,高温不氧化,透气性强,结合不易剥落,表面光洁,保温及润滑性好,能保证金属液应有的流动速度,不需专用工具清砂。基本上解决了原紫铜及铜合金铸件表面或表层质量差的问题,从而使铜铸件表面或表层质量在原75％的基础上再提高20％。     

薄板坯连铸结晶器锥度设计技术研究及应用

以提高结晶器使用寿命和铸坯表面质量为目标,通过建立漏斗区自有锥度、结晶器总锥度和结晶器局部锥度的计算模型,研究了漏斗区的宽度和深度、窄边铜板偏移量以及磨损对结晶器锥度沿高度方向分布的影响,提出了漏斗区自有锥度和局部锥度沿高度方向分布应与铸坯的凝固收缩相匹配的设计理念,对薄板坯连铸结晶器宽面铜板内腔形状及窄边锥度调控工艺进行了优化设计,为结晶器操作工艺及管理制度的优化提供了理论依据。基于上述研究工作,研发了适合于FTSC工艺的新型结晶器,进行了大量的工业生产试验。结果表明:在浇注宽度为1 520mm的铸坯时,窄边附加偏移量可由12mm降低到7mm,窄边铜板的使用寿命得到了大幅度的提高,过钢量为2.25万t后,窄边铜板最大磨损量由5mm降低到2mm以下;新型结晶器有效控制了铸坯窄面凹陷和表面纵裂纹的发生。     

高温合金表面激光熔铸镍基合金涂层的组织与耐磨性能

研究了高温合金ＧＨ３３表面激光熔铸镍基合金涂层的组织和耐磨性能。结果表明,基材对涂层合金的稀释作用较小;涂层与基材之间形成良好的冶金接合;涂层基体组织为γ－Ｎｉ枝晶,枝晶间为γ－Ｎｉ、Ｍ２３（ＣＢ）６、Ｎｉ３Ｂ、Ｃｒ２Ｂ、ＣｒＢ、ＷＣ等;涂层耐磨性能的平均值较基材提高４倍以上。     

Modelling Temperature Profiles and Flow Velocities During Melt Filtration in Permanent Mould Casting of AZ91E Magnesium Alloy

The objective of this research was to examine melt filtration of AZ91E magnesium alloy permanent mould castings using experimental trials and predict filtration using a commercial software package. Tensile specimens were prepared using a H13 tool steel permanent mould machined to ASTM-B108 standards. The mould and pouring temperatures were 500 and 720?°C, respectively. Without a filter, the average yield strength, tensile strength and elongation were 89.6, 153.9?MPa and 2.41?% respectively and these increased to 96.5, 167.0?MPa and 3.05?% respectively with the use of a steel mesh filter within the well of the mould. Filters enabled removal of MgO based oxides. Modelling using commercial software demonstrated that the use of filters reduced turbulence in the metal stream minimizing oxides, which are essentially sites for stress concentration. The results of the research are important for the development of processing methods to improve the melt cleanliness of magnesium alloys for automotive and aerospace industries.     

不同A1-Si原料对合金铸锭质量影响的研究

本文对不同厂家生产的Al-si中间合金在外形、实收率等方面进行了对比,分析讨论了使用两个不同厂家生产的Al-si中间合金生产工艺对4004及4032合金铸锭质量的影响,根据各项分析结果得出了初步结论。     

Prediction of Local Heat Flux and Temperature Distribution in a Mould Copper Plate for Flexible Thin Slab Casting Based on In‐plant Temperature Measurements

A three‐dimensional (3D) numerical model has been employed to predict the local temperature and heat flux distribution on the funnel‐shaped Flexible Thin Slab Casting (FTSC) H2 mould plate®. The modelling was combined with in‐plant temperature measurements from thermocouples installed in the mould. For the measurements the thermocouples are arranged to be adapted to the funnel‐curved shape of the mould such that the spatial locations of measured temperature data sets from the thermocouples can be regarded to form a plane. The method divides the geometry of the mould plate into two computational domains along the measured temperature plane in order to utilize the data as the boundary condition by interpolation. The measured data are compared with those obtained by the average heat flux and one‐dimensional (1D) heat conductivity model in the thermal analysis of the mould plate. It is found that the assumption of average heat flux only along the longitudinal direction, used in conventional billet or slab moulds, is not satisfactory to describe the heat transfer of the complex funnel‐shaped mould in the longitudinal and transverse direction. The heat flux values and hot face temperature in funnel‐shaped mould plates obtained by the 3D model are lower in comparison to the 1D model. The structure of cooling water channels has a significant influence on the uniformity of the heat flux. Some fluctuations of heat flux and temperature occur in the junction between the parallel‐curved and funnel‐curved zone along the longitudinal and transverse direction for the present case. It is expected that by utilizing the measured temperature data, the present model can be helpful to understand the thermal behaviour and define the thermal boundary condition of the funnel‐type mould plate.     

助熔剂对保护渣熔化温度的影响

通过对不同助熔剂加入量下连铸保护渣熔化温度的研究,得出助熔剂对保护渣熔化温度的影响规律,对其机理也进行了深入的讨论。     

基于数值模拟的AZ31镁合金连续流变成形浇注温度的影响

本文首先通过ANSYS数值模拟软件模拟了不同浇注温度时设备型腔内AZ31镁合金温度的变化,并确定了半固态区在型腔中的位置。然后采用连续流变成形实验设备,在不同浇注温度下进行实验,得到了部分产品。对比实验得到的产品表面质量,确定了最佳的浇注温度范围为730-750℃。同时分析了740℃浇注时型腔中合金的组织演化过程,认为合金浇注进型腔后,在工作辊的剪切搅拌作用下经历了枝晶-玫瑰晶-球状晶的演化过程。     

立弯式浇道对半固态A356铝合金浆料组织的影响

采用立弯式浇道制备A356铝合金半固态浆料,研究了浇注温度对A356铝合金半固态浆料组织的影响,并考察了浆料经过均热处理后的组织。结果表明,采用立弯式浇道可以制备出半固态浆料,在本实验条件下,获得理想的半固态A356铝合金浆料的浇注温度为630℃和640℃,而且随着浇注温度的降低,初生相的形态由树枝状→蔷薇状→颗粒状转变;经过感应均热后,初生相更圆整,且尺寸、分布都很均匀。     

板坯连铸结晶器冷却铜板的温度场分析及结构优化

采用结构分析有限元软件ABAQUS对具有不同冷却系统的两种结晶器在工作过程中的稳态温度场进行了模拟。在所采用的热材料参数和边界条件尽町能符合实际条件下。证明了采用新的设计可获得较理想的温度场分布。其结果对连铸结晶器的设计及优化、提高结晶器寿命和改善板坯质量具有指导作用。     

热处理对Gx180CrWV-20铸造合金高温磨损特性的影响

研究了Gx180CrWV-20铸造合金在不同热处理条件下组织结构和硬度的变化以及热处理温度和磨损试验温度对其高温磨损性能的影响。结果表明，1050℃淬火 480℃回火可使该合金在600℃以下的高温工况条件下具有较好的高温磨损特性。     

Fracture of Precipitation-Hardened Copper Alloy Produced by Semi-Continuous Casting at Elevated Temperature

Abstract

In semi-continuously cast slabs of precipitation-hardened copper alloy, internal cracks are often observed after homogenization, although those defects can not be found out after casting. It is considered that, before stress relief takes place during homogenization, thermal stresses generated in the slab during casting will exceed the fracture stress. It is of interest to understand how internal stresses of slabs will affect the fracture during homogenization. Fracture temperatures of the material under static tensile stresses are investigated in an attempt to demonstrate the fracture evolved during homogenization. © 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

Dans les brames d'alliage de cuivre durci par précipitation et coulées en semi-continu, on observe souvent des fissures internes après homogénéisation, bien qu'on ne trouve pas ces défauts après la coulée. On considère que les ontraintes thermiques générées dans la brame lors de la coulée vont excéder la contrainte de rupture lors de l'homogénéisation, avant que l'effet de relaxation puisse se produire. Il est intéressant de comprendre de quelle manière les contraintes internes des brames affecteront la rupture lors de l'homogeneisation. On a etudie les températures de rupture du matériel sous contraintes statiques en traction dans une tentative de démontrer que la rupture a évolué lors de l'homogénéisation. © 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

Improvement in Quality and Yield of the Low Alloy Steel Ingot Casting Through Modified Mould Design

The internal quality and yield in 4 ton steel ingot of 40cmd8 grade was studied by comparing its solidification in a square cross-section mould with a slender rectangular cross-section mould, using FEM simulation. The model predicted various solidification aspects like fluid flow, thermal and solidification profiles, mushy zone, local solidification time, porosity and piping for both the molds. The convective flow of the molten metal during solidification showed higher velocity in square ingot than rectangular ingot under similar conditions due to lower surface area to volume ratio that affected the heat transfer in the rectangular ingot. Higher amount of air gap between the ingot and the mould was formed in rectangular ingots. Lower microsegregation as measured in terms of local solidification time was observed in rectangular ingot. Based on microstructure parameters such as thermal gradient and rate of solidification, it was found that the square ingot had more equiaxed zone than rectangular ingot. The rectangular ingot solidified at a faster rate and showed more propensity for core porosity than the square ingot. The ingot yield was improved by 3.6% through mould shape modification from square to rectangular. Model was validated to limited extent by carrying out a typical experiment with square mould.     

Effect of Thin Polymer Coatings on the Mechanical Properties of Steel Plates

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.     

机械侧封对双辊薄带钢连铸稳定性及铸带质量的影响

分析了影响双辊薄带连铸稳定性和铸带质量的因素,对机械侧封技术在薄带连铸中的侧封效果进行了分析和研究,在薄带连铸试验中,对侧封的压紧方式,侧封板的材质以及侧封板的预热温度对薄带连铸稳定性和铸带质量的影响进行了试验研究。     

铌合金抗高温氧化涂层研究现状及发展趋势

铌合金表面抗高温氧化防护涂层分为耐热合金涂层、贵金属涂层、铝化物涂层以及硅化物涂层等几类。本文综述了各类涂层材料的特点、应用、研发现状以及硅化物涂层的制备技术,对硅化物涂层研究中存在的问题及今后的发展方向进行了分析和探讨。