Hydrogen storage properties of cold rolled magnesium hydrides with oxides catalysts

In this work, we compared ball milling and cold rolling as a mean to add transition metal oxides to magnesium hydride. We found that irrespective to the mixing technique the oxides NiO and Nb₂O₅ gave the fastest desorption kinetics. In general, sorption kinetics were slightly slower for cold rolled samples compared to their ball milled counterparts. Ball milling 30 min is more effective to get a nanocrystalline structure than rolling 5 times. However, as rolling was performed in air for a limited number of times, it could be expected that rolling under inert atmosphere for a larger number of times will be as effective as ball milling to produce nanocrystalline structure and enhance hydrogen storage properties.     

Effect of air contamination on ball milling and cold rolling of magnesium hydride

In this letter we address the problem of air contamination in high energy milling and cold rolling of magnesium hydride. We found that for short milling time (30 min) milling under argon or air leads to the same crystal structure and same hydrogen sorption behaviour. In the case of the cold rolled sample, the hydrogen sorption behaviour is similar but the crystal structure shows some differences with ball milled samples. As expected, prolonged milling time in air leads to formation of magnesium oxide and degradation of hydrogen sorption capacities. However, kinetics do not seems to show degradation. This investigation shows that, for short milling time, air contamination is not as detrimental as was expected.     

花键冷敲精密成形过程数值模拟与分析

本文基于ABAQUS软件,采用动态显式有限元法建立了花键冷敲精密成形过程的有限元模型,通过三维数值模拟,研究并揭示了花键冷敲成形过程中滚打力随时间的变化规律和应变分布与演变规律。结果表明:花键冷敲初始阶段滚打力较大,之后平稳上升,并呈现断续周期性变化。分析了冷敲过程结束后,由于齿形部分等效应变分布不均匀,导致花键齿顶出现弓形和齿槽表面出现皱纹等缺陷,提出了改进措施。     

Prediction of rolling force in cold rolling by using physical models and neural computing

In this study physical models and a neural network theory have been integrated to a program package in order to predict rolling force in cold rolling. The parameters required by the model such as the friction parameter and the deformation resistance of the materials have been determined from measured rolling parameters and materials alloying elements by applying the Bland-Ford-Ellis (BFE) rolling force model and an artificial neural network model (ANN). Measured data of over 6000 coils have been used in the training of the ANN. The calculated results were in good agreement with measurements.     

Preparation and characterization of magnesium coating deposited by cold spraying

Magnesium (Mg) and its alloys have a great potential as structural materials due to their beneficial combination of high strength to weight ratio, high thermal conductivity and good machinability. However, few works about Mg coatings fabricated by cold spraying can be found in the literature. Thus, Mg coatings prepared at different main gas temperatures by cold spraying were investigated as well as their microstructure, phase structure, oxygen content and microhardness. The critical velocity of the particle was evaluated through numerical simulations. The particle deformation behavior and bonding mechanism were discussed. The result of the oxygen content measurement shows that the oxygen contents of coatings did not increase compared with that of the feedstock powder. The simulation results show that the critical velocity of Mg particles was in the range from 653 m/s to 677 m/s. The observation of the coating fracture morphology shows that the formation of the coating was due to the intensive plastic deformation and mechanical interlocking. The microhardness of the coating increased with the increase of the main gas temperature from 350 °C to 450 °C due to the decrease of the coating porosity.     

Microstructure and mechanical properties of AM31 magnesium alloys processed by differential speed rolling

Ingot casted AM31 alloys were rolled at a warm temperature of 350 °C and subsequently rolled at 300 °C using equal speed rolling (ESR) and differential speed rolling (DSR) with speed ratios of top roll to bottom roll, 1.2 and 1.5, respectively. Microstructures, textures and mechanical properties of the as-rolled AM31 sheets were examined. Ductility was improved by DSR due to inclination of basal poles and weakened texture. The sheets produced by DSR with a speed ratio of 1.2 showed highest strength and ductility at room temperature, which can be attributed to homogeneous fine grain distribution and tilted basal texture.     

ZK60镁合金异步降温轧制显微组织与力学性能的演变（英文）

将异步降温轧制应用于制造沿轧制方向具有弱基面织构的细晶ZK60镁合金板。结果表明,多道次降温轧制可以显著改善显微结构的均匀性,细化晶粒尺寸。同时,在轧制过程中逐渐形成沿横向的纤维织构。重要的是,沿轧向的剪切变形使基面的c轴向轧向旋转,削弱沿此方向的基面织构。受这种显微结构变化的影响,由于连续的晶粒细化和柱面滑移的增加,沿横向的屈服强度持续增加,而由于应变硬化能力的下降,均匀伸长率下降。相反,沿轧向的基面织构的持续减弱大大抵消晶粒细化所带来的强化效果,从而导致屈服强度的轻微下降。     

Review of chatter studies in cold rolling

In the past, many different modes of vibration and causes of rolling chatter have been presented, yet no complete and clear picture of the basic mechanics emerged. In order to control chatter in cold rolling operations, a much better understanding of the basic mechanics of the problem is required. To provide, therefore, a ground work for developing such a basic understanding, in this paper, existing models of a mill stand as well as of the rolling process in the open literature are presented. In addition, existing chatter models, which are formulated to investigate chatter as the consequence of the interaction between the structural dynamics of the mills and the dynamics of the rolling process, are also reviewed.     

轧制速度对AZ31镁合金管材冷轧成形的影响

轧制速度是三辊式冷轧成形过程中关键的工艺参数,决定其力学特征及温升情况。基于此,本文以冷轧AZ31镁合金管材为研究对象,通过全流程数值仿真计算,对比分析不同轧制速度在各特征变形段对等效应力、等效塑性应变及节点温度的影响规律。结果表明,等效应力、等效塑性应变及节点温度均随轧制速度的增大而增大。通过元胞自动机模型及实验等手段,探明了晶粒在轧制过程中产生连续再结晶并细化的初步组织演变规律;对比分析实验与模拟结果并结合多方面因素,得到800mm/s的轧制速度可以更好的满足工艺要求的结果,为冷轧镁合金管材轧制速度的选择提供依据。     

Deformation behaviors and conditions in L-section profile cold ring rolling

Three-dimensional FE model of plastic penetration in L-section profile cold ring rolling is established under ABAQUS software. Based on this model, the expanding rules of plastic zone in roll gap are revealed by FE simulation, and three deformation behaviors of L-section ring that exist in the rolling process are exposited. Conditions for three deformation behaviors are studied and verified by rolling simulation and experiment. The deformation behavior, which is needed for normal rolling of L-section ring, and its conditions are determined at last.     

Planning feed speed in cold ring rolling

Feed speed needs to be controlled during cold ring rolling but first it must be planned. However, up to now, it has been set mainly by trials and experience, as the existing method is inefficient. This paper aims to find a convenient method to plan feed speed. In this study, the ring outer diameter growth rate was regarded as the basic quantity to determine the feed speed. A mathematical model is built on analysis of the reason for the ring enlargement during rolling. The model defines the relationship between the ring outer diameter growth rate and feed speed. Using the model, the feed speed was planned versus the thickness of the rolling ring. The extrema of the feed speed and the ring outer diameter growth rate were also determined. The method of planning the feed speed based on the ring outer diameter growth rate is efficient and economical, and it facilitates process control for cold ring rolling.     

Predictive modeling of grain refinement during multi-pass cold rolling

Recently, grain refinement and grain misorientation have been experimentally studied for various materials with ultra-fine grained microstructures, which are achieved by the multi-pass cold rolling process. In this paper, a numerical framework is developed to model the evolution of grain size and grain misorientation based on a dislocation density-based material model. Novel finite element models embedded with the dislocation density-based material subroutine are developed to model the plastic deformation and microstructural evolution during the multi-pass cold rolling process. The multi-pass cold rolling processes of commercially pure titanium (CP Ti) and aluminum (AA 1200) are simulated in order to assess the validity of the numerical solution through comparison with experiments. The dislocation density-based material models are developed for CP Ti and AA 1200, which reproduce the observed material constitutive mechanical behavior under various strains, strain rates and temperatures occurring in the cold rolling process. It is shown that the developed model captures the essential features of the material mechanical behaviors and predicts a minimum grain size of below 100 nm after five-pass cold rolling of CP Ti with equivalent strains up to 2.07 and the average incidental dislocation boundary (IDB) misorientation angle increased to 4.6° after six-pass cold rolling of AA 1200 with equivalent strains accumulated to 5.77.     

A neural network-based shape control system for cold rolling operations

In cold steel rolling, strip shape is crucial to product quality. For modern rolling mills, there are a number of different ways to control the strip shape, including adjusting the side depression, bending the work rolls and axial shifting the middle roll. However, these controls are not independent and hence, must be used with great care. This paper introduces a new method for strip shape control. It takes two steps: the first step is to use an Artificial Neural Network (ANN) to recognize the strip shape pattern. The second step is to apply one or a combination of several controls accordingly. This process may take several iterative steps. The new method is validated on an 8000 KN HC mill. The results demonstrated the new method could reduce the strip shape error step by step.     

不同润滑条件下带钢冷轧后表面形貌演变规律研究

在3种润滑条件下对酸洗后的热轧带钢试样进行了冷轧实验,采用扫描电镜跟踪观察冷轧前后试样的表面形貌,采用TR200型粗糙度测量仪测试轧制前后试样的表面粗糙度轮廓,研究了润滑条件对冷轧带钢表面形貌演变规律的影响。结果表明：轧件表面形貌主要取决于表面凹坑和辊痕的尺寸,随着轧制道次的增加,轧件与轧辊表面的实际接触面积增加,轧件表面凹坑和辊痕的尺寸均减小,轧件表面光洁度提高;轧制5道次后,干摩擦条件下轧制的试样表面显微凹坑最少,但表面存在明显的辊痕;油润滑条件下轧制的试样表面辊痕较少,但存在少量未被轧合的显微凹坑;乳化液润滑条件下轧制的试样表面残留的显微凹坑和辊痕都很少,表面质量最好。     

外螺纹冷滚压精密成形工艺研究进展

螺纹冷滚压成形技术是一种少无切削加工工艺,具有生产效率高、成形零件机械性能增加、零件表面质量好等优点,在航空、航天、车辆等工业中高性能、高强度螺纹类零件生产中广泛应用。分别从有限元建模仿真、表面硬化、工艺参数等方面评述了目前螺纹冷滚压成形工艺研究的国内外研究现状、存在的问题和发展趋势,指出了该工艺应用发展方向及需要解决的关键技术问题:局部加载多道次耦合下螺纹冷滚压成形高效建模仿真与优化技术;系统的螺纹冷滚压成形工艺理论;螺纹冷滚压成形过程运动特征研究及成形过程精确控制;大直径重载丝杠的精确滚压成形核心技术及新工艺。     

Effect of grain shape on the texture evolution during cold rolling of Al-Mg alloys

The hot bands of continuous cast AA 5754 and high-Fe AA 5754 aluminum alloys exhibited elongated grains in the rolling direction after recrystallization annealing. The annealed hot bands were cold rolled to different reductions along the original rolling direction and transverse direction, respectively. The effect of grain shape on texture evolution was investigated by X-ray diffraction. It was found that straight-rolling resulted in a higher rate of disappearance of the r-cube + cube component and a slightly higher rate of formation of the β fiber component than cross-rolling. The elongated grains in the rolling direction were easier to rotate from initial orientations to the β fiber in straight-rolling than in cross-rolling.     

Effect of rolling parameters on cold rolling of thin strip during work roll edge contact

In some cold rolling mills, a problem has been found that the sides of work rolls touch and deform when thin strip is rolled. The problem of work roll contact at the edges, which forms a new deformation feature in rolling, is analysed. In this paper, the authors focus on the research of the effects of rolling parameters on specific force such as rolling force, intermediate force, edge contact force and the profile of thin strip in cold rolling when the work roll edges contact. An influence function method is developed to simulate this special rolling process. Based on numerical simulation, the effects of the rolling parameters on the mechanics and deformation of the cold rolled thin strip are obtained. Numerical simulation tests have verified the validity of this developed method.     

Effect of sizes of forming rolls on cold ring rolling by 3D-FE numerical simulation

During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed △h and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree ofinhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.     

Modeling and optimization of threading process for shape control in tandem cold rolling

A theoretical model is presented to dynamically simulate the threading process and predict the shape of thin strip in tandem cold rolling. Fluctuations in the process are theoretically analyzed and taken into account of the simulation. The model can be used to deal with the setup of both rolling force and roll-bending force. To obtain the best shape and therefore alleviate threading delay, the bending forces and/or reduction schedule are optimized. The simulation has been conducted based on a set of plant data and the results correspond well with the measurements from the plant.