ZK60镁合金表面滚压强化试验研究

试验研究了ZK60镁合金表面滚压加工中工艺参数对试件表面粗糙度、表面形貌、表面残余应力和表层显微硬度的影响,结果表明滚压力和重复滚压次数对试件的表面粗糙度、表面形貌以及表面残余应力和表层硬度影响程度较大,滚压速度影响较小。对精车ZK60镁合金试件进行滚压加工,试件表面粗糙度R a、R z最大减小了50.3%和48.1%;残余压应力最大可达-54.55 MPa;显微硬度从试件表层到内部基体材料逐渐降低,表层硬度值最大为92.83 HV 0.25,比基体材料硬度提高了15.32%。     

Heat removal analysis on steel billets and slabs produced by continuous casting using numerical simulation

Simulation of a continuous casting process (CCP) is very important for improving industrial practices, reducing working times, and assuring safety operating conditions. The present work is focused on the development of a computational simulator to calculate and analyze heat removal during continuous casting of steel; routines for reading the geometrical configuration and operating conditions were developed for an easy management. Here, a finite difference method is used to solve the steel thermal behavior using a 2D computational array. Conduction, radiation, and forced convection equations are solved to simulate heat removal according to a steel position along the continuous casting machine. A graphical user interface (GUI) was also developed to display virtual sketches of the casting machines; moreover, computational facilities were programmed to show results such as temperature and solidification profiles. The results are analyzed and validated by comparison with industrial trials; finally, the influence of some industrial parameters such as casting speed and quenching conditions is analyzed to provide some recommendations in order to warrant safety operating conditions.     

A new shell casting process based on expendable pattern with vacuum and low-pressure casting for aluminum and magnesium alloys

A new shell casting process, with the adoption of the foam pattern of lost foam casting (LFC) as prototype and the combination of the thin shell fabrication technology of investment casting and vacuum and low-pressure casting process, was proposed for manufacturing complicated and thin-walled aluminum and magnesium alloy precision castings. Loose-sand uniting vacuum was used in the new process to further reinforce the thin shell, and the new process proves to be a process with simple process, low cost, and high thin shell strength. Because the molten metal filling and solidification are completed under air pressure and vacuum level, the filling capability and feeding capacity of the molten metal are greatly improved, and the castings become denser. This paper mainly investigated the fabrication technology of thin shell based on foam pattern prototype, the removing foam and roasting shell process and vacuum and low-pressure casting process. The few-layer compound thin shell of silica sol–sodium silicate was adopted for the new process. Removing foam pattern was carried out at 250°C for 30 min, and the shell was roasted at 800°C for 1 h. Combined with the vacuum and low-pressure casting process, this new shell casting process has successfully produced thin wall and complex aluminum and magnesium alloy parts with high quality. In addition, comparisons in terms of filling ability, microstructure, mechanical properties, porosity, and surface roughness among this new shell casting, gravity casting, and LFC were also made to show the characterization of this new shell casting process.     

Design and implementation of an automated secondary cooling system for the continuous casting of billets

This paper describes a heat transfer model based automatic secondary cooling system for a billet caster. The model aims to minimize the variation in surface temperature and excessive reheating of the billet strands. It is also used to avoid the low ductility trough of the solidifying steel, which aggravates the tendency of steel to crack. The system has been designed and implemented in an integrated steel plant. A Programmable Logic Controller (PLC) based automation system has been developed to control the water flow in the secondary cooling zones of the strand. The results obtained through field trials have shown complete elimination of internal and off-corner cracks for the fifty billet samples that were monitored.     

ZK60镁合金锻造拔长工艺及组织性能研究

研究了铸态ZK60镁合金拔长工艺,对锻造拔长过程的现象进行了分析,结果表明,通过光学显微镜对不同拔长工艺条件下的组织进行分析。随着锻造比的增大,晶粒组织逐渐细化,锻件力学性能提高。     

高温铸锻件内部温度场电磁超声重构方法研究

针对高温严苛条件下铸锻件内部温度场非接触测量困难这一问题,提出了基于弯曲效应和三角形前向展开法的高温铸锻件温度场非接触电磁超声斜入射横波重构方法。结合数值仿真和730℃电磁超声检测实验,对直入射横波的三角形追踪数学模型进行了验证,并研究了声束入射角、温度梯度对斜入射横波的传播路径和渡越时间的影响,比较了不同入射角的斜入射横波的温度灵敏度系数。结果表明:基于三角形前向展开法的高温锻件温度场直入射横波重建误差在3%以内。当采用斜入射横波时,声线传播路径受温度梯度、入射角度的影响较大,且对温度梯度的变化更加敏感,无论使用横波渡越时间还是横波出射点位置偏移量均可重构高温铸锻件的内部温度场。     

等径角轧制ZK60镁合金板材的组织与性能

对采用等径角轧制工艺（ECAR）制备的ZK60镁合金板材研究发现,与直接轧制的板材相比,等径角轧制板材的晶粒取向由（0002）基面取向演化为非基面取向,经等径角轧制后,板材晶粒没有得到细化,同时形成了大量的平行排列的细密孪晶,强度明显提高。与1个道次直接轧制的板材相比,1个道次等径角轧制的板材其抗拉强度由271．7Mea增大到328．3MPa,但伸长率由25．5％降低至8．5％。     

深冷处理对铸态ZK60镁合金显微组织和力学性能的影响

选用工业化生产的半连铸ZK60镁合金为研究对象,采用力学性能检测设备、光学显微镜、X射线衍射仪和透射电镜等研究了深冷处理(77 K)对其显微组织和力学性能的影响.结果表明:深冷处理可以细化ZK60合金的显微组织,引起一定程度的晶粒转动并促进微细第二相析出,产生了细晶强化及第二相析出强化,使ZK60合金的屈服强度由150...     

The effects of casting and forging processes on joint properties in friction-welded AISI 1050 and AISI 304 steels

The aim of the present study was to investigate the effects of investment casting and forging process on the microstructure and mechanical properties of friction weldments, AISI 1050–AISI 304. A continuous-drive friction welding device with the automatic control ability of friction time and forging pressure was designed and constructed. Factorial design of experiments was performed to join investment cast AISI 1050 steels and forged AISI 1050 steels with AISI 304 austenitic stainless steel with respect to the optimized process parameters. The joint performance was evaluated by tensile and hardness tests performed parallel and perpendicular to the weld interface. Microstructure of forged parts under friction welding was examined using optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Results of microstructural studies were compared with those of friction welding of investment cast parts. The results reveal that a recrystallized region or a mechanically mixed layer was formed on the AISI 304 side near the weld interface, depending on friction time and friction pressure. Friction welding of forged parts always exhibited higher tensile strength, lower hardness, and more upset than the cast parts.     

Impedance analysis of forging process and strategy study on compliance for forging manipulator

In the field of heavy forging, there are numerous researches on deformation rule in forging process by FEM simulation, however, not many scholars take the equipment constraint and the mutual reaction load between the forging manipulator clamp and the forging blank into account, which will impact on safety of manipulator body and quality of forging blank. This paper presents an impedance model to describe the load and formulates compliance strategies correspondingly to reduce the mutual reaction load for forging manipulator. Firstly, an FEM model of forging process is built. Meanwhile, the clamp of forging manipulator is added to the model as movement constraint and interaction part between the manipulator and the forming process. Secondly, a typical forging process is simulated by changing the movement constraint, and then an impedance model is established to describe the relationship between the load and movement constraint. Finally, two kinds of compliance strategies are formulated according to the impedance model, one is called free compliance, and the other is initiative/passive compliance. The simulation results show that compliance strategies reduce the load amounting to 5 000 kN in z direction between the manipulator clamp and the forging blank obviously, which may lead to serious accidents, such as the capsizing of forging manipulator, the fracture of manipulator clamp, and so on. The proposed research simulates the more real forging process, gets the initiative/passive compliance strategy which is more simple and suitable to the real producing and better for forming a forging process planning and control system in the modern production, and improves the quality and efficiency of heavy forging.     

大型镁合金压铸机哥林柱断裂原因分析及其结构改进

哥林柱是压铸机的关键部件,其强度条件直接影响到压铸机的正常使用和铸件的质量。针对大型镁合金压铸机哥林柱在实际使用中存在的断裂现象,基于ANSYS对哥林柱螺纹副的受力特征进行了深入研究,讨论了哥林柱失效的原因,并结合其失效原因提出了二种简单、可靠的哥林柱螺纹副结构改进方案。     

Evaluation of cellulose electro-active paper made by tape casting and zone stretching methods

Cellulose has been discovered as a smart material that can be used as sensor and actuator material. In this paper, cellulose smart material termed as electro-active paper (EAPap) is prepared by an automated process that includes tape casting and zone stretching. To evaluate characteristics of the EAPap, its Young’s modulus and piezoelectric charge constant are measured depending on the orientation angle, in comparison with the manually fabricated EAPap results. The zone stretching method can effectively align the cellulose fibers in the EAPap so as to improve its Young’s modulus as well as piezoelectric charge constant. The 0 degree oriented sample shows its maximum Young’s modulus and the 45 degree oriented sample exhibits the maximum piezoelectric charge constant. This 45 degree is associated with its shear piezoelectricity. The actuator performance of EAPap is evaluated by measuring its bending displacement depending on the orientation angle and the excitation voltage. The 45 degree oriented sample exhibits the maximum bending displacement. Details of the material preparation, the automation process, characterization and the actuator performance are addressed. This automated process that includes tape casting and zone stretching is suitable for mass production of the EAPap.     

Preform design in forging process of complex parts by using quasi-equipotential field and response surface methods

The International Journal of Advanced Manufacturing Technology - The preform design is the key to bulk metal forming. An approach to optimize 3D preform shape in multi-step die forging based on...     

Comparative analysis of dental enamel polyvinylsiloxane impression and polyurethane casting methods for SEM research

Dental casting is a very common procedure for making high-quality replicas of paleo-anthropological remains. Replicas are frequently used, instead of original remains, to study both fossil and extant Primate teeth in morphological and metrical analyses. Several commercial products can be used in molds. This study analyzed SEM image resolution and enamel surface feature definition of tooth molds at various magnification levels and obtained, with both Coltène and 3M low-viscosity body polyvinylsiloxane impression, materials and polyurethane casts. Results, through comparison with the original teeth, show that both the negative molds and the positive casts are highly reliable in replicating enamel surfaces. However, positive cast quality is optimal for SEM observation only till the fourth consecutive replica from the original mold, especially at high SEM magnification levels.     

A study on precision forging of spur gear forms and spline by the upper bound method

Precision forging is an important manufacturing procedure of spline and spur gear forms. It has advantages of improved strength, good tolerance, saving billet material, dispensing with the cutting, etc. In this paper, a mathematical model using an upper bound method is proposed for forging of spur gear forms and spline to investigate the plastic deformation behavior of billet within the die cavity. The material of solid billet was assumed as rigid–plastic and the shape of the tooth profile was accounted for the mathematical modeling of the kinematically admissible velocity field assumed for the plastic zone. The non-uniform velocity was employed for simulating the inhomogeneous deformation and the effect of barreling during the forging. Using the present model, various effects of forming parameter such as the friction factor, reduction, number of teeth, etc. upon the non-dimensional forging pressure, forging force and barreling of the spur gear forms and spline were analyzed systematically and the results compared with those of other researcher's analytical and experimental work. It is shown that the present modeling of the process improves knowledge of the process design performance for the precision forging of spur gear form and spline.     

Sliding friction and wear of magnesium alloy AZ91D produced by two different methods

Alloy AZ91D is a leading magnesium alloy used for structural applications. It contains aluminum and zinc as principal alloying elements. This alloy is normally die-cast, but recent developments in semi-solid injection molding (Thixomolding^®), which offers certain processing advantages, produces a slightly different microstructure than die-casting, and it was of interest to determine whether the two processing routes would measurably affect the friction and wear of AZ91D. The present work involved ambient air, room temperature testing of die-cast (DC) and Thixomolded^® (ThM) AZ91D, in both unidirectional and reciprocating sliding motion, using stainless steel type 440C as the counterface. After running-in, the average sliding friction coefficients in both types of test fell into the range of 0.29–0.35, irrespective of processing method. The formation of a built-up edge raised the friction slightly in unidirectional tests compared with reciprocating tests. The average wear rate of the ThM alloys in reciprocating sliding was approximately 25% lower than that for DC alloys. However, the wear rates of the magnesium specimens in unidirectional sliding were comparable for DC and ThM materials. Owing to the transfer of magnesium, there was no measurable wear on the stainless steel 440C balls. The wear mechanism during sliding involves the formation of thin, narrow shards along the edges of wear grooves which break off to produce loose particles.     

基于图像处理的连铸板坯测控系统

本文介绍了基于计算机图像处理连铸板坯长度测量和切割控制系统的硬件构成和软件功能。讨论了摄像机参数标定方法和系统测量误差。     

Metrological challenges for reconstruction of 3‐D microstructures by focused ion beam tomography methods

The development of combined focused ion beam and scanning electron microscopes has enabled significant advances in the characterization of the 3‐D structure of materials. The repeated removal of thin layers or slices with an ion beam and imaging or mapping the chemical or crystallographic structure of each slice enables a 3‐D reconstruction from the images or maps. The accuracy of the reconstruction thus depends on the accuracy with which the slice thickness is measured and maintained throughout the process, and the alignment accuracy of the slices achieved during acquisition or by postacquisition corrections. A survey of papers published in this field suggests that the reconstruction accuracy is not often considered or reported. Using examples from examination of the 3‐D structure of hardmetals, issues affecting the accuracy of slice thicknesses and image realignments are examined and illustrated and potential errors quantified by the use of fiducial markers and the expected isotropy of the hardmetal structure itself.     

A study on deburring of magnesium alloy plate by magnetic abrasive polishing

Drilling is one of the most important machining operations in manufacture process. When drilling process is applied, unexpected burrs will be formed on the surface of workpiece. Even a small burr can cause unwanted problems, resulting in low quality products. In order to get better drilled parts, it is very important to know characteristics of burr formation and to remove the burr from the drilled surface with machining process. In this study, magnetic abrasive polishing (MAP) was used to research the deburring factors of magnesium alloy. Moreover, design of experiments was performed to evaluate parameters’ effect on the MAP process. As a result, it was seen that the MAP was useful to remove the burrs on the workpiece without damage from its original surface.