铸轧镁合金薄带组织演变实验研究与模拟

以镁合金薄带双辊铸轧新技术为背景,开展了铸轧成形过程中组织性能的模拟研究。镁合金薄带双辊铸轧是以液态镁合金为原料,用两个反向转动的水冷铸辊为结晶器,直接制备1.5~3.0 mm镁合金薄带的短流程新工艺。对双辊铸轧轻合金薄带的凝固组织演化过程进行数值模拟,用以优化和指导制备技术,具有重要的理论意义和应用前景。项目研究组通过对双辊铸轧过程动态凝固成形的有限元数值模拟研究、镁合金薄带铸轧实验研究以及后续加工过程中的组织演变规律研究,得到了主要工艺参数对铸轧工艺稳定性及组织性能的影响规律。     

薄带连铸镁合金的研究与思考

综述了单辊铸造和双辊铸造镁合金薄带的研究进展与产业化现状,提出了存在的问题,分析了影响镁合金薄带浇铸速度的因素,指出,改善浇铸系统的传热能力是提高镁合金薄带浇铸速度的关键;立式双辊连铸系统具有更高的传热能力,镁合金薄带连铸应借鉴立式双辊连铸钢带技术.     

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.     

Fundamental investigation of interfaces in particle reinforced steel sheets processed by thin strip casting

Along the steel industry history, the production of flat‐steel products has technologically evolved towards reducing slab thickness at the output of the continuous casting machine. This development has been related to the incessant requirement of providing a certain steel quality at lower costs. As a result of this procedure, the thin strip casting technology emerged in a commercial scale at the end of the nineties, with all the advantages of a near‐net‐shape manufacturing process. In particularly, the higher energy efficiency and reduced environmental impact turned it as a very promising and attractive technology for the steel industry. With the purpose of obtaining new types of steel sheets, characterized by improved mechanical and tribological properties, reinforced steel strips have been produced by introducing slight modifications to a twin‐roll caster. In this regard, a considerable enhancement of the mechanical properties has been achieved.     

Microstructure and texture assessment of Al–Mn–Fe–Si (3003) aluminum alloy produced by continuous and semicontinuous casting processes

Aluminum sheets are currently produced by the direct-chill process (DC). The need for low-cost aluminum sheets is a challenge for the development of new materials produced by the twin roll caster (TRC) process. It is expected that sheets produced from these different casting procedures will differ in their microstructure. These differences in microstructure and in the crystallographic texture have great impact on sheet mechanical properties and formability. The present study investigated microstructure and evaluated texture of two strips of Al–Mn-Fe–Si (3003) aluminum alloy produced by TRC and by hot-rolling processes. It was possible to notice that the microstructure, morphology, and grain size of the TRC sample were more homogenous than those found in hot-rolled samples. Both strips, obtained by the two processes, showed strong texture gradient across the thickness.     

Microstructural evaluation of melt conditioned twin roll cast Al–Mg alloy

Abstract

Aluminium alloy strip has been successfully cast using the melt conditioned twin roll casting (MC-TRC) process. The liquid metal to be strip cast was fed into a melt conditioner, where it was intensively sheared under conditions of high shear rate and high turbulence induced by corotating twin screws. Melt conditioning provides a melt which has a uniform temperature and chemical composition and well dispersed nuclei. The conditioned melt was then fed into a twin roll caster. The MC-TRC process produced high quality Al–Mg alloy strip with fine and uniformly distributed intermetallics throughout the cross-section with minimal centreline segregation compared to conventional TRC strip. The Erichsen height value of MC-TRC sheet was superior to that of TRC sheet. The lower formability of the TRC sheet is attributed to the severe centreline segregation.     

High shear dispersion technology prior to twin roll casting for high performance magnesium/SiCp metal matrix composite strip fabrication

SiC particulate (SiC_p) reinforced AZ31 magnesium alloy composite strips were produced by a novel process. In the process, a high shear technique was utilised to disperse the reinforcing particles uniformly into the matrix alloy, and AZ31/5 vol%SiC_p slurry was solidified into thin strip by a horizontal twin roll caster. The experimental results showed that the AZ31/5 vol%SiC_p strip obtained with high shear treatment exhibited a significantly refined microstructure and uniform distribution of reinforcing SiC particles. High cooling rate in the TRC process was also considered to contribute to the grain refinement of the matrix alloy, together with the possible heterogeneous nucleation effect of the reinforcing particles. The mechanical properties of the high shear treated composites strips showed enhanced modulus, yield strength and ductility by hardness and tensile tests. The experimental results were discussed in terms of the microstructural features and the macroscopic reliability, where necessary, analytical and statistical analyses were conducted.     

铝薄板热顶—电磁铸造成型工艺研究

依据铝薄板的特点，提出了热顶－电磁铸造的基本思想，设计了一套完整的制取铝薄板的热顶－电磁成型系统，测量了电磁场分布，研究了铝薄板热顶－电磁铸造成型条件，经过大量工艺试验确定了液固界面位置，浇注温度，液柱高度和冷却水量等参数，获得了较佳的铸速０－时间曲线，成功地制取了厚２０ｍｍ，高８５０ｍｍ，宽４８０ｍｍ的铝薄板。     

Inverse and centreline segregation formation in twin roll cast AZ31 magnesium alloy

Two microstructure defects formed in the twin roll cast AZ31 strips were investigated: inverse and centreline segregations. A two-dimensional finite element thermal–fluid–stress model was employed to study the thermomechanical response of the AZ31 strip during twin roll casting process. The results showed that the key parameter for centreline segregation is the mushy zone thickness at centreline. For inverse segregation, the interaction between the yy peak stress at the centreline in the mushy zone and the solidified shell on the roll surface is the determinant parameter. The modelling results suggested increasing the setback distance decreases the risk of both defects. Moreover, scaling up the caster reduces the propensity to inverse segregation but appears to have a minor effect for centreline segregation formation.     

基于CAFE模拟双辊连铸纯铝凝固微观组织

鉴于双辊薄带连铸等轴晶区半固态铸轧组织对产品性能的重要性,基于热传输、流动传输、溶质传输等基本传输过程以及晶粒生长物理过程,建立了双辊连续铸轧纯铝凝固过程的宏观温度场、浓度场、微观组织及枝晶形貌演化的三维数学模型.采用CA-FE法对双辊连续铸轧纯铝在水冷钢辊连续铸轧中的凝固过程进行了模拟,采用光学显微镜研究了铸轧工艺参数对凝固组织的影响.数值模拟结果表明,所建立的数学模型能够合理描述晶粒沿任意角度生长的过程,温度场、溶质场和微观组织形貌的模拟计算结果合理.模拟结果与实验结果基本吻合,检验了模型的正确性.     

Technique of Aluminum Alloy Composite by Inversion Casting

The influence of the temperature of liquid aluminum alloy,the dipping time in liquid alloy and the thickness of base strips on the solidified layer was studied during the process of producing aluminum alloy composite strips used in automobile radizator with inversion casting.It is concluded that there is welding as well as diffusion of alloying elements between the base strip and the coating.Experiments proved that the interface has a good bonding.     

Microscopic analysis of Fe–Cr alloy produced by single roll strip casting

Abstract

In the present investigation, the microstructures and mechanical properties of Fe–Cr alloy prepared by single roll strip casting were studied. Optical microstructure showed subgrain boundaries inside large grains. Cracks were observed along the grain boundary. Scanning electron microscopy, X-ray diffraction study confirms the formation of chromium carbide at the grain boundary in the case of as cast alloy. Electron backscatter diffraction showed preferred orientation of grains in the as cast alloy. Carbides and undesired phases were not observed in heat treated alloy. Pores present in as cast samples expand after heat treatment process. Mechanical properties, like tensile strength, yield strength, elongation and hardness, of Fe–Cr single roll strip casting alloys were improved after heat treatment.     

铝基复合材料薄带中SiC分布均匀性的研究

本文研究了用双辊铸机生产的SiCp/A356复合材料薄带中SiC的分布规律,着重分析了SiC颗粒的体积分数(3%～16%)和薄带的铸造速度(0.5～10m/min)对SiC颗粒分布均匀性的影响,结果表明,较高的SiC含量或较高的铸造速度均可抑制薄带表面贫SiC层的形成。     

Solidification Structure of Low Carbon Steel Strips with Different Phosphorus Contents Produced by Strip Casting

In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.     

铝(镁)合金消失模铸造近净成形技术研究进展

阐述了铝(镁)合金消失模铸造技术的研究现状,着重介绍了铝(镁)合金消失模铸造在金属液充型、振动凝固、压力凝固以及消失模壳型铸造等技术方面的最新研究进展。研究表明,铝(镁)合金在消失模铸造过程中,需重点解决针孔、缩松等缺陷,提高液态合金的充型能力和铸件的力学性能;通过采用振动凝固和压力凝固的手段,可以提高金属液充型能力、细化组织、提高组织致密性,明显提高铸件力学性能。真空低压消失模壳型铸造技术,可以解决普通消失模铸造易于出现的孔洞和夹杂等缺陷以及浇不足和浇注温度高等问题,是一种生产复杂薄壁高质量铝、镁合金精密铸件的新方法。     

反重力铸造对高强度铝合金凝固组织影响的研究

采用反重力铸造方法生产高强度铝合金铸件已成为航空、航天领域内获得优质构件的重要途径。研究了反重力铸造对高强度铝合金ZL114A和ZL205A铸件凝固组织的影响。结果表明,合金的凝固组织存在着不同的位置效应,对于ZL114A合金铸件,冷端晶粒尺寸最小,靠近浇口处晶粒尺寸粗大。对于ZL205A合金铸件,随距浇口处距离的减少,枝晶间分布的网格状θ(A l2Cu)相逐渐由粗变细,α(Al)枝晶内分布的黑色点状T(Al12CuMn2)相逐渐减少。分析表明,在反重力铸造补缩压力相同的情况下,合金的凝固温度范围不同是造成凝固组织不同位置效应的主要原因。     

Numerical analysis of the twin-roll casting of thin aluminium-steel clad strips

The production of thin aluminium-steel clad strips by means of twin-roll casting is one of the prospective trends in the development of sheet production. The main advantages of twin-roll casting are low specific energy and resource consumption. Besides this, the resulting compound has a high bonding strength owing to the presence of a continuous thin layer of intermetallic phases having an approximate thickness of 3 µm at the interface of the two metals. At the same time, the quality of the clad strip depends on the microstructure and properties of the aluminium layer formed directly from a melt. A deformation immediately following the solidification of the metal between the two rotated, internally water-cooled rolls has a substantial influence on this aluminium layer. Due to the complexity of observing the processes occurring in the melt pool, a numerical simulation became one of the main methods for their investigation. Simulation is widely used to describe the process of twin-roll casting of monomaterial strips, but so far it has not been used for to comprehensively analyse the process of twin-roll casting of clad strips. In the present paper, a two-dimentional finite-element simulation of the system “clad strip—water-cooled rolls” using the ANSYS software is proposed. A joint analysis is carried out of the heat transfer, viscous flow of aluminium melt, its solidification and deformation resulting in the temperature distribution in the cast metal as well as in the tool. The dependences of the deformation strain and outlet temperature of the clad strip on the main technological process parameters; obtained by numerical simulation, are shown.     

轧制变形量对铸轧铅合金板带性能的影响

从阳极极化稳定电位、腐蚀速率、阳极极化前后表面形态与物相组成、导电性能、力学性能等方面研究了轧制变形量对铸轧铅合金板带性能的影响。结果表明:轧制前后铅合金板带的阳极极化电位变化不大,但能明显提高铅合金的抗腐蚀性能和力学性能。同时随着轧制变形量的增大,铅合金板带的导电性能有所下降。特别是经过两道次变形量为30%的轧制后,抗腐蚀性能是轧制前的1.48倍;同时铅合金板带的抗拉强度σb和屈服强度σp0.2分别提高了28.5%和79.4%,硬度HBS提高了2.8。     

一种高性能铸轧辊套材料的研制

分析了目前铝常规铸轧与极限铸轧(快速铸轧)工艺要求之间的差距,提出大幅度提高铸轧辊套材料的综合性能是实现极限铸轧的先决条件.通过选择铍铜合金材料为研制对象,优化合金成分设计与精细调控热处理工艺,初步实现了强度、硬度、导热性、热强性和抗疲劳性良好匹配的目的.通过对材料的检测分析与工艺实验,证明研制出来的材料的综合性能优良,为极限铸轧技术的应用提供了有力支持.     

Effect of Injection Velocity on Structure Part Characteristic in AZ50 Die Casting Process with High Vacuum System

When diecasting large and thin Mg alloy parts,material defects occur,which include porosity,nonuniform mechanical properties,irregular surfaces,and incomplete filling.To resolve these problems,it is necessary to have uniform injection velocities and temperatures as well as control the melt.This study investigated the feasibility of producing large and thin components using a die caster by attaching a high vacuum system.In particular,the effects of injection velocity on surface quality and the mechanical properties of the products were investigated.Hence,an injection velocity scheme and a die structure capable of casting in a vacuum were proposed.As a result,it was found that the critical low injection velocity was 0.2 m/s to produce large thin Mg alloy structures having good mechanical properties.