铝电解槽电热场解析技术的发展

介绍铝电解槽电热解析模型的发展和现状 ,比较了各模型的优缺点。提出了建立铝电解槽三维电热解析模型的必要性和思路     

Development of fatigue analytical model of automotive dynamic parts made of semi-solid aluminum alloys

Automotive suspension control arm is used to join the steering knuckle to the vehicle frame. Its main function is to provide stability under fatigue stresses of loading and unloading in accelerating and braking. Conventionally, these parts were made of steel; however, fuel consumption and emission of polluting gases are strongly dependent on car weight. Recently, there is a try to develop and design much lighter and better fatigue resistant metal of semisolid A357 aluminum alloys. This work aims at a better understanding of identifying the fatigue strain-hardening parameters used for determining fatigue characteristics of aluminum suspension control arm using analytical and mathematical modeling. The most judicious method is to perform the fatigue tests on standardized test pieces and then plot two Wohler curves, mainly number of cycles as a function of the stress and as a function of the deformation. From these curves and following a certain mathematical and analytical methods, certain curves are plotted and then all of these coefficients are drawn. The new calculated parameters showed a clear improvement of the fatigue curve towards the experimental curve performed on the samples of aluminum alloy A357 compared with the same analytical curve for the same alloy.     

The increasing use of aluminum in automotive applications

The average automobile currently produced in North America contains about 90 kg of aluminum. That figure is expected to grow, driven by environmental needs, the Partnership for a New Generation of Vehicles, safety mandates, consumer preferences, and an increasingly global marketplace. This paper examines those issues, along with current automotive applications for aluminum, the technology being developed to meet future demand, and the forces driving changes in technology.     

Mechanisms of dynamic deformation and dynamic failure in aluminum nitride

Uniaxial quasi-static, uniaxial dynamic and confined dynamic compression experiments have been performed to characterize the failure and deformation mechanisms of a sintered polycrystalline aluminum nitride using a servohydraulic machine and a modified Kolsky bar. Scanning electron microscopy and transmission electron microscopy (TEM) are used to identify the fracture and deformation mechanisms under high rate and high pressure loading conditions. These results show that the fracture mechanisms are strong functions of confining stress and strain rate, with transgranular fracture becoming more common at high strain rates. Dynamic fracture mechanics and micromechanical models are used to analyze the observed fracture mechanisms. TEM characterization of fragments from the confined dynamic experiments shows that at higher pressures dislocation motion becomes a common dominant deformation mechanism in AlN. Prismatic slip is dominant, and pronounced microcrack–dislocation interactions are observed, suggesting that the dislocation plasticity affects the macroscopic fracture behavior in this material under high confining stresses.     

The use of rotating-impeller gas injection in aluminum processing

The three major characteristics of liquid aluminum quality are hydrogen content, alkaline content, and inclusion content. The past 20 years have seen considerable development in rotating gas injectors processes, at different steps of liquid metal processing in the casthouses, designed to address these three quality factors. Simultaneously, a great deal of academic work has been done to understand and model these processes, using knowledge from the fields of chemical engineering, thermodynamics, and fluid dynamics. This article shows how very simple efficiency models can be used to represent the processes, combining first-order kinetics for batch treatment and residence time distribution for in-line systems, leading to realistic efficiency laws. These laws are valid for all quality factors under the same form and involve very few parameters.     

1235铝合金动态再结晶动力学模型及氧化夹杂的影响

通过Gleeble热模拟试验建立动态再结晶动力学模型,研究氧化夹杂对1235铝合金的动态再结晶行为的影响。研究表明,经不同净化处理的1235铝合金在热变形条件下均发生一定程度的动态再结晶。动态再结晶体积分数的计算值与实测值接近(相关系数R大于0.92),相关性高。在相同热变形条件下,含杂量越低,热压缩时动态再结晶的速度越慢,细小的夹杂物阻碍了动态再结晶晶粒的长大,再结晶晶粒细小。     

The development of aluminum reduction cell process control

It was primarily the improved understanding and control of magnetic fields, assisted more recently by the use of computer modeling, that made modern aluminum reduction cells more stable and has enabled them to grow larger. However, the implementation of improved process control systems has not only underpinned the success of new cell designs, but has also enabled many older technologies to remain competitive. While there is still much room for improving reduction-cell control systems, this task is increasingly difficult due to the diminishing performance gains available. Geoffrey P. Bearne is a manager in the Reduction Division of Comalco Research and Technical Support.     

Modeling the initiation of dynamic recrystallization using a dynamic recovery model

Dynamic recrystallization flow curve was studied in AISI 410 martensitic stainless steel by performing hot compression tests in a temperature range of 900-1150 °C and at strain rates of 0.001-1 s⁻¹. The Estrin and Mecking's equation for dynamic recovery was used to model the work hardening region of the flow curves. The critical strain and stress for the initiation of dynamic recrystallization were determined using the method developed by Poliak and Jonas. The critical dislocation density for starting dynamic recrystallization was estimated using the Estrin and Mecking's dynamic recovery model. A modified Arrhenius-type equation was used to relate the critical dislocation density to strain rate and temperature. The proposed model was also verified by the model proposed by Roberts and Ahlblom and developed to describe the variation of dislocation density and fractional softening due to dynamic recrystallization up to the peak of flow curve.     

基于高斯混合模型的铝电解槽况聚类研究

铝电解是一个非常复杂的工业过程,在整个过程中产生了大量的生产数据,通过对这些数据的深入分析和挖掘,找到潜在的信息,分析其与槽况变化的联系.为了进一步发现槽况变化规律,利用具有软聚类特点的高斯混合模型分析槽况,但其存在需要人为控制聚类个数K的弊端.所以提出一种改进的自适应K值的GMM算法应用到铝电解槽况中,该方法减少了人...     

Fatigue of a laterally constrained closed cell aluminum foam

An experimental investigation into the constant stress amplitude compression–compression fatigue behavior of closed-cell aluminum foam, both with and without lateral constraint, was conducted. Results show that while the early stages of strain accumulation due to fatigue loading are independent of constraint, the rapid strain accumulation stage behaviors are sensitive to the constraint. This was ascribed to the noticeable hardening with plastic deformation observed under constraint during quasi-static loading, which in turn reduces the effective maximum stress experienced by the foam specimen during fatigue loading. This was demonstrated through a simple empirical model that connects fatigue strain accumulation without constraint to that under constraint. Complementary X-ray tomography experiments suggest that the fatigue behavior of the foams is relatively less sensitive to morphological defects such as missing walls than the quasi-static mechanical properties such as plastic strength. Evaluation of the energy absorption behavior suggests that the damage that accumulates during fatigue does not affect the energy-absorbing ability of the foam adversely.     

发泡工艺参数对闭孔泡沫铝胞结构的影响

采用压缩空气法制备闭孔泡沫铝,研究空气流量、搅拌速度和发泡温度对胞结构的影响。结果表明泡沫铝的胞直径为4-11mm,密度为0.10-0.22g/cm3,孔隙率最高达96.3%;泡沫铝的胞直径随着空气流量和发泡温度的增大而增大,随搅拌速度的增大而减小,其中空气流量对胞直径的影响最显著;壁厚和结点尺寸随空气流量和搅拌速度的变化规律与胞直径相反;在相同的搅拌速度下,泡沫铝的密度随着胞直径的增大而减小且与胞直径存在对应关系,搅拌速度为600r/min时,关系式为ρ=0.0278 0.3602.e-0.132d。     

SPF model applications for aluminum

A closed-form, plane strain model (PS2) is compared with a finite element model (SUPFORM3) in analyzing the forming of rectangular pans from 2090-OE16 aluminum sheet. The errors introduced by improperly using a plane strain model are quantified. Some preliminary verification of SUPFORM3 is shown, and the effect of friction on the distribution of thickness in the superplastic forming (SPF) of a rectangular pan is presented. SUPFORM3 is used to predict thickness distribution of male formed access doors, selecting proper starting gauges, assessing producibility, estimating forming time, and developing pressure time cycles. SUPFORM3 will be used to form complex parts and flat-bottomed pans such that post-SPF properties samples can be cut from the flat areas of the flat-bottomed pans, yet have the same strain and strain rate history as the critical areas in the complex part. It is concluded that SUPFORM3 is a useful tool for predicting thickness distributions resulting from and pressurization schedules for superplastic forming.     

Rolling process analysis of aluminum strip by a coupled thermo-elastic-plastic model

The phenomenon of longitudinal curvature on an aluminum strip caused by different heat conduction boundary conditions on the top and bottom surfaces of the strip while it undergoes a rolling process is studied. This research adopts large deformation-large strain theory to develop rolling process analysis of an aluminum strip by a coupled thentto-elastic-plastic model using the updated Lagrangian formulation (ULF) and incremental method. The flow stress of the materials is considered as a function of strain, strain rate and temperature, and the finite difference method is used simultaneously to solve equations of transient heat transfer. Finally, the numerical analysis method developed from this study is used to determine the temperature change and deformation of an aluminum strip when it undergoes hot rolling. At the same time, the simulation results on normal stress and contact angle are compared with the results of experiments and other published references; the comparison results verify that the present model is reasonable.In addition, the average rolling force during hot rolling is simulated and comparison is also made with the results of experiments provided by the China Steel Corporation. The simulated results in this article are generally considered to be reasonable.     

Cold gas dynamic spraying of aluminum: The role of substrate characteristics in deposit formation

Aluminum powder of 99.7 wt.% purity and in the nominal particle size range of −75+15 μm has been sprayed onto a range of substrates by cold gas dynamic spraying (cold spraying) with helium, at room temperature, as the accelerating gas. The substrates examined include metals with a range of hardness, polymers, and ceramics. The substrate surfaces had low roughness (R _a < 0.1 μm) before deposition of aluminum in an attempt to separate effects of mechanical bonding from other forms of bonding, such as chemical or metallurgical bonding. The cross-sectional area of a single track of aluminum sprayed onto the substrate was taken as a measure of the ease of initiation of deposition, assuming that once a coating had begun to deposit onto a substrate, its growth would occur at a constant rate regardless of substrate type. It has been shown that initiation of deposition depends critically upon substrate type. For metals where initiation was not easy, small aluminum particles were deposited preferentially to large ones (due to their higher impact velocities); these may have acted as an interlayer to promote further building of the coating. A number of phenomena have been observed following spraying onto various substrates, such as substrate melting, substrate and particle deformation, and evidence for the formation of a metal-jet (akin to that seen in explosive welding). Such phenomena have been related to the processes occurring during impact of the particles on the substrate. Generally, initiation of aluminum deposition was poor for nonmetallic materials (where no metallic bonding between the particle and substrate was possible) and for very soft metals (in the case of tin, melting of the substrate was observed). Metallic substrates harder than the aluminum particles generally promoted deposition, although deposition onto aluminum alloy was difficult due to the presence of a tenacious oxide layer. Initiation was seen to be rapid on hard metallic substrates, even when deformation of the substrate was not visible. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Sciences and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

Energy parameters in a mathematical model of a dynamic welding arc

Summary

This paper describes a method for experimental determination of the dynamic characteristics of an arc sensor in GMA (MIG/MAG) welding in droplet transfer mode. The method basically involves a vibration device being used to excite sinusoidal waveforms of the torch height as well as data processing by means of an FIR digital low-pass filter and dispersive Fourier transformation (DFT). The experimental results show that the sensitivities of the arc sensor are much greater than in DC open arc welding. The response of the welding current to torch height variation is maximised at around 3 Hz. Although the response continues up to a higher level when the frequency exceeds around 5–6 Hz, the SN ratio is poorer than that at 3 Hz. The response of the welding current shows a phase lag relative to the torch height variation. The response of the welding voltage, however, shows a phase advance relative to the torch height variation, and the response increases with an increasing variation frequency of the torch height, but its SM ratio is much poorer than that of the welding current.

To clarify the effects of shielding gases on the arc sensor, experiments using four types of shielding gas - pure Ar, Ar + 10% CO₂, Ar + 20% CO₂, and CO₂ — were conducted. The results show that, contrary to those obtained in open arc welding, the responses in short-circuiting arc welding using pure Ar are higher than those using Ar and CO₂ mixed gases.

Simulations using an arc sensor model proposed by the authors are also run for short-circuiting arc welding and the results analysed. The analytical results based on this model show the theoretical and experimental results to be similar qualitatively but to disagree quantitatively. The theoretical results further show that not only the average short-circuit frequency, but also the rate of change of the short-circuit frequency induced by variation of the arc length strongly affect the sensitivities of the arc sensor.     

Self-adjusting dynamic characteristics of pulsed MIG welding for aluminum alloys

Pulsed MIG welding is suitable for aluminum alloys welding, because spray transfer and excellent profile can be arrived during whole welding current range, and the energy of droplet can be controlled to overcome losing of alloy elements with lower melting and steam point by controlling pulse current and pulse time. Because of the special physic properties of aluminum alloys, there are different requirements for pulsed MIG welding between starting arc short circuit and drop transfer short circuit, pulse period and base period. In order to satisfy the need of aluminum alloys MIG welding, self-adjusting dynamic characteristics are designed to output different dynamic characteristics in different welding startes. The self-adjusting dynamic characteristics of pulsed MIG welding are achieved through a short circuit controller and a dynamic electronic inductor. The welding machine(AL-MIG 350) with self-adjusting dynamic characteristics has a high rate of successfully starting arc up to 96%, and the short circuit time during transfer is less than 1ms, in the mean time, the arc is stiffness, spatter is low and weld appearance is good.     

Model of the kinetics of dynamic recrystallization of aluminum alloy 1235

Metal Science and Heat Treatment - The process of dynamic recrystallization of aluminum alloy 1235 upon hot compression is studied. Methods of nonlinear regression analysis are used to obtain an...     

The anisotropy of aluminum and aluminum alloys

The anisotropy of textured aluminum is approximated by a yield criterion with an exponent of eight. The use of this criterion in metal-forming analyses has improved the understanding of the formability of aluminum and other metals. The effect of anisotropy on the limiting drawing ratio in cupping is less than that expected from the quadratic Hill yield criterion and the effect of texture on forming limit diagrams is negligible. A method of predicting the effect of strain-path changes on forming limit curves of aluminum alloy sheets has proven to agree with experiments.     

大型电解槽温度管理

以贵阳铝镁设计研究院92台280kA电解槽和沈阳铝镁设计研究院182台280kA电解槽为基础，研究了大型槽温度变化规律以及与诸多因素的关系，公布了最佳电解质温度研究结果，并且在生产实践中得到了验证。同时对其它槽型提出了建议．具有一定的参考价值。     

Continuous dynamic recrystallization and discontinuous dynamic recrystallization in 99.99% polycrystalline aluminum during hot compression

The dynamic restoration behavior of 99.99% polycrystalline aluminum was investigated. The deformation was carried out by compression test at 533 - 773 K and initial strain rate of 0. 002 - 2 s^-1 to a true strain of 1.0 followed by water quench. Polarized optical microscopy and transmission electron microscopy were applied to observe the deformation microstructure. It‘s found that discontinuous dynamic recrystallization, which is commonly observed in lower stacking fault energy metals or ultra-high purity aluminum(≥99.999%), occurs when Zenner-Hollomon parameter(Z parameter) is low, but the true stress strain curve doesn‘t accompany stress oscillation.Continuous dynamic recrystallization occurs when Z parameter is intermediate, and only dynamic recovery takes place if Z parameter is high.