金属半固态铸造成形技术

金属的半固态铸造是近年来出现的一种新的铸造加工成形方法。该方法与传统的全液态铸造相比，具有节约能源、生产率高、产品质量好等优点。本文介绍了半固态金属浆料的制备方法，半固态压铸、半固态连铸等金属半固态铸造成形技术，并指出了存在的问题及进一步研究工作。     

Investigation of spherisation in microstructures of aluminium casting alloys for thixoforging process

Thixoforging combined with low superheat casting (LSC) is a promising shaping process for aluminium casting alloys. LSC process is based on rapid solidification of an alloy which cast with low pouring temperature. With this method, a feedstock material is produced with non-dendritic microstructure that ready for spherisation in reheating sequence of further semi-solid process. Al-Si alloys are still castable even at low temperatures due to their excellent fluidities. This study subjects to present spherisation of A356 and A380 alloy billets cast with LSC process that provides appropriate beginning material with relatively high sphericity. Obtained billet parts were reheated for different times at a semi-solid state temperature. Some of these billets were directly quenched for observing the effects of reheating and the others were thixoforged. With sufficient reheating time, deformation of thixoforging process did not significantly affect on the spherical microstructure. Unnecessarily long reheating period caused excessive grain growth. A356 alloy had higher spherisation tendency than A380 alloy under similar process conditions.     

稀土铝合金结晶过程的研究

半固态成型正在成为有色金属成型的一种新技术.目前大部分铝合金是为了满足液态成型或塑性成型的特性而设计的,难以较好地满足半固态成型的特性要求,因此,设计出新的铝合金以满足半固态成型要求就十分必要.为此,本文讨论了稀土元素对铝结晶过程的影响.实验结果表明:在纯铝中加入稀土元素后,不但使合金的结晶温度区间加宽,而且使合金的结晶时间延长,这样将有利于半固态成型技术的实现.     

Simulation of Cooling of Liquid Metal in an Inclined Slope to Predict the Condition for Semi Solid Forming and Its Experimental Validation

In semi solid processing, the preparation of slurry with globular microstructure is very important. A recent technique named the inclined slope casting, to produce the semi-solid metal slurry, has been evolved. The microstructure of casting depends on several process parameters like initial temperature of liquid metal, length of the slope, cooling rate and the rate of flow of liquid metal. In the present work numerical modelling of cooling of liquid was carried out. Modelling was done for different mass influx velocities, temperature of pouring and different inclinations of the slope set-up. In this work, a CFD model based on finite volume method for simulating flow along the inclined slope was carried out. Heat transfer, fluid flow and solidification were studied by varying the process parameters like slope angle and inlet pouring rate. The numerical results were verified with experiments for same conditions.     

Grain Boundary Characteristics of As-cast Semi-solid Processed Ultra-high Carbon Steel

The microstructure of 1.4?% carbon steel produced either by ordinary casting or semi-solid casting with different primary fraction of solids using cooling plate technique was investigated. The microstructure of ordinary ultrahigh-carbon steel (O-UHCS), was improved by the semi-solid processing. Grain boundary cementite thickness of UHCS and its morphology is affected by semi-solid process. Grain boundary cementite thickness of about 2???m can be achieved by pouring the semi-solid slurry with 0.31 fraction of solid. The pearlitic interlamellar spacing of semi-solid processed UHCS is shorter compared to O-UHCS.     

半固态铸造技术研究现状与展望

半固态铸造是一种新的材料成形技术，综述了半固态铸造合金的组织变化，坯料制备，充型过程数值模拟和应用等方面的研究成果，同时对我国发展半固态铸造技术得出了若干值得重视的问题。     

Differential Scanning Calorimetry (DSC) and Thermodynamic Prediction of Liquid Fraction vs Temperature for Two High-Performance Alloys for Semi-Solid Processing (Al-Si-Cu-Mg (319s) and Al-Cu-Ag (201))

Metallurgical and Materials Transactions A - There is a need to extend the application of semi-solid processing (SSP) to higher performance alloys such as 319s (Al-Si-Cu-Mg) and 201 (Al-Cu-Ag). The...     

Computational fluid dynamics applied to twin-roll casting

Near-net-shape casting technology is one of the most important research areas in the iron and steel industry today. Driving forces for the development of this technology include a reduction in the number of operations needed for conventionally produced strip. This is especially true of hot rolling operations. The consequent reduction in investment costs, when considering new industrial facilities, makes near-net-shape casting operations extremely attractive from a commercial standpoint.Various processes for near-net-shape casting of steel are currently being developed around the world. Of these processes, the twin-roll casting machines represent a major area of concentration. We believe that one of the main issues concerning the design of twin-roll casters is the metal delivery system and its effects on the homogeneity of solid shell formation, segregation and surface quality.In the present work, computational fluid dynamics has been used to study different metal delivery systems for twin-roll casting. The METFLO code has been adapted to simulate three dimensional turbulent fluid flow, heat transfer and solidification in this type of machine. The enthalpy-porosity technique was used to couple fluid flow and solidification phenomena. Two configurations for metal delivery system have been studied to date, one is a conventional tubular nozzle with horizontal outlets in the directions of the side dams. The other is a slot nozzle with a vertical inlet stream.These simulations have been applied to a pilot caster being studied in Canada, with a roll radius of 0.30 m, producing steel strips with thicknesses ranging from 4 to 7 mm, at relatively low roll speeds ranging between 4 and 12 m⧹min. Different positions and penetrations of the nozzles in the liquid pool have also been analysed. It has been shown that the tubular nozzle leads to the formation of a solid shell that is thicker at the centre of the caster. The slot nozzle gives a more uniform thickness of the solid shell along the roll width. In both configurations, a thicker solid shell is formed close to the roll edges, due to the presence of the side dams.It has also been demonstrated that the slot nozzle gives lower levels of turbulence at the free surface, which can have positive effects on the product quality.     

铜镍合金化及半固态处理工艺对ZrCoAl系非晶合金组织的影响

向以Zr80Co15Al5为基体的非晶合金中添加微量铜和镍,利用铜模吸铸法和半固态处理工艺制备棒状(Zr0.88Cu0.12)95-2x Al5(NiCu)x(x=1.5、2.5、3.5)非晶合金。利用SEM、XRD和光学显微镜(OM)分析研究了半固态处理工艺对非晶合金的微观组织结构、玻璃形成能力及断口形貌的影响。结果表明,在半固态处理工艺基础上对Zr80Co15Al5添加微量铜和镍后有较好的晶体形成能力。     

Effects of Solid–Liquid Mixing on Microstructure of Semi-Solid A356 Aluminum Alloy

The desired starting material for semi-solid processing is the semi-solid slurry in which the solid phase is present as fine and globular particles. A modified solid–liquid mixing (SLM) is reported wherein semi-solid slurry can be produced by mixing a solid alloy block into a liquid alloy, and mechanical vibration is utilized to enhance the mixing. Effects such as liquid alloy temperature, mass ratio, and mixing intensity on the microstructure and the cooling curves during SLM were evaluated. 2D and 3D microstructure analysis of treated A356 aluminum alloy shows that microstructure can be refined significantly with a considerable morphology change in primary Al phase. It is critical that the temperature of mixture after mixing is lower than its liquidus temperature to obtain a valid SLM process. Specially, mixing intensity is identified as a primary factor for a favorable microstructure of semi-solid slurry.     

奥氏体不锈钢板坯连铸结晶器锥度的优化

针对奥氏体不锈钢连铸中的质量问题 ,对太钢三炼钢 1260mm× 160mm板坯结晶器的锥度进行了分析。通过不锈钢铸坯在结晶器内收缩的计算和拉坯速度、过热度等工艺参数对铸坯收缩影响的分析 ,得出采用双锥度结晶器比单锥度结晶器更符合铸坯在结晶器内的收缩规律 :液面附近 80～200mm区域采用较大锥度 ,液面下 200～800mm的结晶器下部 ,采用较小锥度 ,并在此基础上设计了曲线锥度结晶器。生产试验表明 ,双锥度设计显著改善了铸坯质量 ,消除了窄面鼓肚和中间凹陷等缺陷     

EBSD and DTA Characterization of A356 Alloy Deformed by ECAP During Reheating and Partial Re-melting

Recrystallization and partial re-melting processes have been developed for producing semi-solid feedstock in a solid state in which a globular microstructure is obtained by plastic deformation followed by reheating. In this research, to induce strain, a cast- and solution-treated Aluminum A356 (7 wt pct Si) alloy was subjected to a repetitive equal channel angular pressing process using a 90 deg die, up to a total accumulated strain of approximately 8 in route A (increasing strain through a sequence of passes with no rotation of the sample after each pass) at ambient temperature. The microstructural evolutions of deformed and reheated materials were studied by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction analysis. In addition, the influences of pre-deformation on the recrystallization mechanism and liquid formation of A356 alloy were presented and discussed. The results are also supported by differential thermal analysis experiments. Evaluation of the observations indicated that the average cell boundary misorientation increased with increasing strain, so this increased misorientation accelerated the mobility of boundaries and recrystallization kinetics. Therefore, the recrystallization mechanism and kinetics affected by deformation, reheating condition, and intrinsic material properties determined the particle size in the semi-solid state.     

Direct Strip Casting (DSC) ‐ an Option for the Production of New Steel Grades

With two pilot plants in operation, the Direct Strip Casting (DSC) technology has reached a state from which it can be concluded that a DSC production process is feasible. The core of the process consists of a caster in which liquid steel is fed on an intensively cooled revolving belt. After solidification in a protective atmosphere, the yielded strip of about 10 mm in thickness is directly hot rolled without intermediate reheating. Thus, due to the reduced expenditures for hot rolling and reheating, substantial energy savings compared to conventional slab casting can be achieved. Moreover, the production of new high‐strength, light‐weight steels with an increased content of manganese, aluminium and/or silicon is enabled by the special features of the DSC process. The use of these steels in automotive applications would lead to further energy savings induced by significant weight reductions and an enhanced life cycle of the car body. Furthermore, also a higher share of scrap based strip steel production, requiring less than half of the energy needed for the blast furnace route, becomes conceivable for quality steel grades, as a higher content of tramp elements, e.g. copper and tin, is tolerable without quality losses (surface cracks). Finally, the compact design and the high productivity of the DSC process save capital and processing costs. In the paper, process development steps, material properties and energy saving potentials are outlined.     

我国压铸模具钢研究新进展

介绍了我国压铸模具钢材料研究新进展。通过研究合金元素对压铸模具材料性能影响,开发出低Si、V及含Ni、Co、W等新型压铸模具钢;通过降低钢中S含量、采用Re改变夹杂形态和优化锻造工艺,材料等向性能达到90%以上;比较常规电渣重熔、气保电渣重熔和真空自耗三种工艺生产压铸材料,钢中N含量由150×10^-6、90×10^-6和40×10^-6,O含量由24×10^-6、15×10^-6和6×10^-6;利用ASPEX Explorer型金属质量分析仪对三种工艺夹杂物指数统计分析,采用真空自耗冶炼的非金属夹杂物数量呈指数减少,并且没有＞5 um的非金属夹杂物,材料冲击性能大幅提升,7mm × 10mm无缺口冲击功可达到450 J;制定高端压铸模具材料显微组织、无缺口冲击评价指标和规范;随着新能源汽车一体化压铸技术发展,未来压铸模具材料应用范围和需求量会越来越大,模具材料向着大型化、超纯净、高精度和长寿命方向发展。     

Development of new grade of steel shots for casting cleaning

A technology has been developed for producing a new grade of steel shots used in casting cleaning. The developed technology is based on obtaining molten steel with the specified chemical composition microalloyed with titanium and using a highly efficient method of dispersing molten steel stream by water jet under high pressure followed by spheroidisation of produced particles and their solidification in water bath. The chemical composition and tapping temperature have been adjusted and different parameters of atomization process such as molten stream nozzle internal diameter, impact angle, water nozzle system and water pressure have been optimized to attain steel shots with the desired mechanical properties, microstructure, density and grain size. After drying, the steel shots are screened to different sizes. The desired grain size is then subjected to only one‐step tempering process. This technique reduces the processing steps (by omission of the reheating‐quenching treatment) and consequently gives significant savings in processing cost.     

Development of continuous casting at OAO MMK

The introduction of continuous casting at OAO MMK was a historic event, marking the end of uneconomical chill casting. Thanks to the introduction of continuous casting in the oxygen-converter shop, improvement in casting-machine design, and expansion of the range of steel that can be cast, unique casting characteristics have been attained: high productivity (more than 10 million t/yr), long casting runs (up to 208 melts), infrequent accidents, low rejection rates of the steel, and high quality of the continuous-cast slabs. The introduction of continuous casting in the converter shop provided a stimulus to the reconstruction of the open-hearth shop as an electrosmelting shop and the installation there of two bar-casting machines and one slab-casting machine.     

Steel strips in the context of near net shape casting production

Following the replacement of ingots by continuously cast slabs the next logical step towards near net shape casting has been the development of thin slab casting machines. These are now beginning to match the quality and productivity levels possible with conventional machines. The next step in this evolution towards lower cost operation is high speed thin strip casting machines. The merits of twin roll casters versus belt casting machines for friction free casting of low carbon steels, suggest that a belt caster will be needed for achieving high productivities and associated cooling lengths required for the production of hot strip in the 5–20 mm thickness range.     

An induction heating process with coil design and solutions avoiding coarsening phenomena of Al-6 Pct Si-3 Pct Cu-0.3 Pct Mg alloy for thixoforming

During the thixoforming process, it is very important to obtain a uniform temperature, which affects the uniformity of the solid fraction, throughout the billet. Consequently, a heating method that can provide a suitable temperature profile throughout the billet must be chosen. Other parameters that must be considered include heating time (in order to minimize the total processing time), the level of control, and temperature consistency. An optimal design of the induction coil has been identified that best meets these criteria. In a previous study, the theoretical optimal coil design was verified through the FEM simulation of the induction heating process by using a general purpose finite element analysis code, ANSYS. So, in this study, the suitability of the coil design was also demonstrated by conducting induction-heating experiments. The optimal reheating conditions to apply the thixoforming (thixoforging and semisolid die casting) process were investigated by varying the reheating time, the holding time, the reheating temperatures, the capacity of the induction heating system, and the size of the adiabatic material. The final holding time was observed to be the most important factor in obtaining a fine globular microstructure and to prevent coarsening in the three-step reheating process.     

Influence of Casting Technique on the Mechanical Properties of Bimetal Composites

According to the characteristic of two liquid and bimetal composite interface,the influence of the casting techniques on the interface microstructure,wear and comprehensive properties were researched by using scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX).The results show that the casting technique has an effect on the surface quality and the stress state of the composites,but also has great effect on the interface microstructure,morphology and constitute phase.In this paper,a special casting technology was used to prepare the bimetal composites.No two-metal mixture layer was observed at the interface.On the contrary,a metallurgy interface was found,which provides high working security.A product rate of 95% was achieved by this special casting process.The service life is 50% higher than that of the commercial products.