FEM Analysis of Spring-backs in Age Forming of Aluminum Alloy Plates

The age forming technology, characterized by huge spring-backs, has been developed to manufacture large integral wing-skin panel parts, which necessitates devising a method of predicting spring-backs. A 7B04-T7451 aluminum alloy creep test in tension is accomplished at 155 ℃, and the creep curves are obtained. The material constants of the mechanism-based creep constitutive equations are determined through experiments. The age forming process and the spring-backs of 7B04 aluminum alloy plates are analyzed using the commercial finite element software ABAQUS. The effects of plate thickness and forming time on spring-backs are researched. The spring-backs decrease with the increase of plate thickness and forming time. The test results verify the reliability of the finite element method （FEM） analysis.

Flow characteristics of aluminum coated boron steel in hot press forming

The flow characteristics of aluminum coated boron steel in hot press forming were investigated.Furthermore,the effects of aluminum coated layer on press forming were analyzed during deep drawing.The results show that aluminum coated boron steel exhibits a high sensitivity on temperature and strain rate.Aluminum coating layer appears in surface flaking in a temperature range of 700-800 ℃,but smooth surface is formed above 900 ℃.

Numerical Simulation of Warm Forming Behavior of High Strength Aluminum Alloy 7075

Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.

Influence of Axial Feeding on Hydroforming of Aluminum Alloy Tubular Part with Rectangular Section

The hydroforming experiment of aluminum tubular part with rectangular section was carried out to investigate influence of axial feeding on thickness distribution and calibration pressure of the corner.Thickness distribution and relation between corner radius and internal pressure were analyzed.The influence of lubricant was discussed.Microstructure and hardness of different region were observed.It is shown that thickness reduction in the transition region between the corner and center region is the biggest.Friction condition has influence both on the thickness distribution and calibration pressure of the corner.As the increase of the axial feeding,the calibration pressure is decreased.There is only little change for the microstructure,but the hardness is increased by 23.3% for the transition region.

The Heat Treatment Behavior of Super-High Strength Aluminum Alloys by Spray Forming

In order to understand the stress corrosion behavior of super-high strength aluminum alloys by spray forming, different aluminum alloys by different heat treatment was made. The results showed that the alloy with peak aging has the most sensitive stress corrosion cracking, the crack can even be seen using eyes;the alloys with two step aging were better than one step aging alloys, the alloys has not been found stress corrosion cracking.

Determination and application of stress-based forming limit diagram in aluminum tube hydroforming

The stress-based forming limit diagram(FLSD) established with limit stress is independent of the strain paths. Compared with traditional strain-based forming limit diagram(FLD),it is more convenient and practical to use as the criterion of forming limit under complex strain paths. The forming limit of 3A21 aluminum alloy sheet was tested and its forming limit diagram(FLD) was determined. Then the FLSD of 3A21 was constituted by transformation formulas between limit strain and limit stress. This FLSD was used in conjunction with LS-DYNA finite element simulations to predict the onset of fracture and limit forming pressure in tube hydroforming. The results indicate that the fracture often occurs in the transition region between corner and straight side of the tube,and the limit forming pressure is 46.4 MPa. The simulation result agrees with the experimental result,and the FLSD is able to predict the forming limit of tube hydroforming with remarkable accuracy.

Numerical simulation of aluminum alloy ladder parts with viscous pressure forming

Viscous pressure forming (VPF), a recently developed flexible die forming process that is suitable for difficult to form material, can obtain the better stress states of sheet blank during forming process in manufacturing complex shape parts. The process of manufacturing aluminum alloy ladder parts with VPF and solid metal punch was simulated by the FE software DEFORM. Under different blank holder pressure (BHP), the stress state, the strain state, the forming of small radius curved face and the distribution of thickness were analyzed. The simulation results show that, compared with solid metal punch forming, the sheet blank can flow into die cavity more easily with VPF due to the improvement of the stress states; the severe thickness reduction can be avoided, the sheet blank can contact the die perfectly and the parts have high dimensional accuracy.

Evaluation of forming limit in viscous pressure forming of automotive aluminum alloy 6k21-T4 sheet

A ductile fracture criterion is introduced into numerical simulation to predict viscous pressure forming limit of the automotive body aluminum alloy 6k21-T4. The material constant in the ductile fracture criterion is determined by the combination of the viscous pressure bulging (VPB) test with numerical simulation. VPB tests of the aluminum alloy sheet are carried out by using various elliptical dies with different ratios of major axis to minor axis(β), and the bugling processes are simulated by the aid of the finite element method software LS-DYNA3D. On the basis of the stress and strain calculated from numerical simulations, the forming limits of bulging specimens obtained are predicted by the ductile fracture criterion, and compared with experimental results. The fracture initiation site and the minimal thickness predicted by the ductile fracture criterion are in good agreement with the experimental results.

Formability and cavitation behavior of superplastic AA5083 aluminum alloy under biaxial tension

The superplastic forming potential of two fine-grained S083 aluminum alloys were studied under biaxial tension using a pneumatic bulge test. Experiments were performed at temperatures ranging from 475 to 525℃with three different strain paths ranging from equi-biaxial to approaching plane strain. The shape of the forming limited diagram(FLD) is found to be significantly different from FLDs commonly used in room temperature stamping. The effects of temperature on final thickness distribution, dome height and cavitation were investigated for the case of equi-biaxial stretching. Increasing temperature in free bulge forming can improve the thickness distribution of final parts but have no significant effect on dome height. The results indicate that determination of forming limits in SPF cannot be represented with a simple FLD and additional metrics such as external thinning and internal cavitation needed to determine the SPF potential of a material.

PREDICTION OF PATH-DEPENDENT FAILURE IN ALUMINUM SHEET METALS UNDER FORMING OPERATIONS

An approximate macroscopic yield criterion for anisotropic porous sheet metals is adopted in a failure prediction methodology that can be used to investigate the failure of sheet metals under forming operations. This failure prediction methodology is developed based on the Marciniak-Kuczynski approach by assuming a slightly higher void volume fraction inside randomly oriented imperfecte analysis. Here, a nonproportional deformation history including relative rotation of principal stretch directions is identified in a selected critical element of an aluminum sheet from a FEM fender forming simulation. Based on the failure prediction methodology, the failure of the critical sheet element is investigated under the non-proportional deformation history. The results show that thiven non-proportional deformation history.

Deformation Behavior and Microstructure Evolution of AA2024-H18 Aluminum Alloy by Hot Forming with Synchronous Cooling Operations

Hot forming with synchronous cooling(HFSC)is a novel technique for heat-treatable,high-strength aluminum alloys,which allows the alloys to acquire good formability,negligible springback,rapid processing and better mechanical properties.However,the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects.Uniaxial tensile tests in a temperature range of 250—450℃and a strain rate range of 0.01—1 s-1 for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester.And based on metallography observation and analysis,AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃.Strain rate shows different effects on ductility at different temperatures.Compared with traditional warm/hot forming methods,AA2024-H18 aluminum alloy achieves a better work-hardening result through HFSC operations,which promises an improved formability at elevated temperature and thus good mechanical properties of final part.After HSFC operations,the microstructure of the specimens is composed of elongated static recrystallization grain.

Shape formation of closed-cell aluminum foam in solid–liquid–gas coexisting state

The mold pressing process was applied to investigate the formability of closed-cell aluminum foam in solid–liquid–gas coexisting state.Results show that the shape formation of closed-cell aluminum foam in the solid–liquid–gas coexisting state was realized through cell wall deformation and cell movement caused by primary α-Al grains that slid,rotated,deformed,and ripened within cell walls.During formation,characteristic parameters of closed-cell aluminum foam were almost unchanged.Under proper forming conditions,shaped products of closed-cell aluminum foam could be fabricated through mold pressing.

Porosity and surface roughness simulation of nickel-aluminum coating in plasma spray forming

As the important evaluation parameters concerning the spray qualities, the porosity and surface roughness of the coatings obtained by thermal spray forming have great influence on their forming accuracy, mechanical properties and service lifetime. But it is difficult to predict or control the two parameters for such a highly nonlinear process. A two-dimensional simulation of coating porosity and surface roughness of nickel-aluminum alloy (Ni-5%Al) in plasma spray forming was presented, which was based on the multi-dimensional statistical behaviors of the droplets as well as the simplification and digitization of the typical splat cross sections. Further analysis involving the influence of the droplet diameters and the scanning velocities of the spray gun on the two parameters was conducted. The simulation and analysis results indicate that the porosity and surface roughness are more influenced by the droplet diameters, but less influenced by the spray gun velocities. The results will provide basis for the prediction or control of coating mechanical properties by depositing parameters.

Effect of blank holder pressure on viscous pressure forming aluminum alloy ladder parts

Viscous pressure forming (VPF), is suitable for forming difficult to form sheet metal parts. An investigation in the effect of blank holder pressure (BHP) on VPF aluminum alloy ladder parts was conducted. Based on experimental and numerical simulation results of the effect of BHP on dimensional accuracy, wall thickness reduction, forming pressure, material flow and defects (such as wrinkling and fracture) of specimens, the effect patterns of BHP load path on VPF ladder parts were explained. The limits of BHP corresponding to specimens with no defect and with wrinkling or fracture defect were determined. In the limits of formable BHP, the variable load path of BHP was beneficial to drawing blank into the die and decreasing wall thickness reduction of specimens. The experimental results show that the ladder parts of good surface fineness and high dimensional accuracy can be obtained by variable load paths of BHP.

Effects of Aging Temperature on Microstructure and High Cycle Fatigue Performance of 7075 Aluminum Alloy

The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.

含铝强化奥氏体钢在550℃液态铅铋中的腐蚀行为

先进铅冷快堆和加速器驱动次临界系统商业化的关键材料问题是结构材料与铅基冷却剂之间的相容性问题,结构钢材料需要在高温液态铅铋共晶中具有优异的抗腐蚀能力.含铝强化奥氏体钢(alumina-forming austenite steel,AFA钢)因其表面可以形成Al_(2)O_(3)膜而在极端环境中具有良好的耐蚀性能.本文研究了降低Ni元素成分和高温预氧化对AFA钢耐铅铋腐蚀性能的影响,利用扫描电子显微镜、能量色散X射线光谱仪、X射线衍射技术,对AFA钢在550℃液态铅铋饱和溶氧条件下腐蚀600 h的氧化层形貌及结构进行表征.结果表明:降低合金中Ni含量和高温预氧化处理都会促进样品表面形成保护性Al_(2)O_(3)氧化膜,进而降低腐蚀层厚度,提升材料耐铅铋腐蚀性能.

固溶处理对喷射成形7055铝合金组织及性能的影响

采用差示扫描量热仪(DSC)、扫描电镜(SEM)、电子背散射衍射(EBSD)技术、常温拉伸、剥落腐蚀试验等研究了固溶处理对喷射成形7055铝合金组织和性能的影响。结果表明:随着固溶温度的升高,合金中粗大第二相面积分数逐渐减小,AlZnMgCu相和Al_(2)CuMg(S)相基本回溶,只残留少量的Al_(7)Cu_(2)Fe相,亚晶尺寸和再结晶面积分数随着固溶温度的升高和固溶时间的延长而增大,导致抗拉强度先增大后减小。合金经470℃固溶处理2 h+时效处理后,抗拉强度、伸长率和剥落腐蚀性能分别为613.4 MPa、8.9%和EB+级。喷射成形7055铝合金的静态再结晶机制包括“原有晶界弓出机制”和“亚晶合并机制”。

电解铝材料生产中氟化物污染特征及形态

云南省电解铝材料产业近年发展迅猛,其氟化物排放引起的环境污染问题一直备受关注。就某电解铝材料厂为研究对象,对电解铝材料生产各环节固废中氟化物的含量和存在形态进行检测,并对生产过程中原料、产品、固废等进行了统计,结合实际开展了氟化物平衡计算。电解铝材料生产过程中,99.6%的氟化物由固废带出,0.4%的氟化物以有组织烟气、无组织天窗废气逸散的形式进入外环境,可通过增设高效脱硫协同脱氟设施和提高电解槽集气效率等措施,减缓氟化物对环境的污染。经检测分析,固废中氟化物以Na 5 Al 3 F 14、NaAlF 4、Na 3 AlF 6、K 2 SiF 6、CaF 2和AlF 3等难溶或微溶于水的化合物形态存在,土壤中水溶性氟化物含量占总氟化物的比例不足1%,表明氟化物排放和土壤环境污染之间存在一定的关联性。氟化物在土壤中累积效应较为明显,在第一类用地和第二类用地条件下,电解铝厂周围区域表层土壤中氟化物的总危害指数分别为0.794和0.09,周围土壤健康风险评估结果为可接受。

跑道型线圈板料电磁成形磁场分布的调控

为有效调控跑道型线圈电磁成形过程中合金板料的变形行为,采用实验-模拟与理论计算的方法揭示了板料与线圈装配的相对位置对电磁力、电流密度、变形速度和成形高度的影响规律,推导出线圈中心面空间磁感强度的工程计算模型。随着板料装配时偏置量的增大,电磁成形试样变形区的最大高度差逐渐减小,试样由“内低外高”转变为“外高内低”;电磁力密度峰值从板料内侧向中心移动。偏置量为2.5~3.0 mm时,两侧高度差存在最小值;偏置量为3.0 mm时,板料的横向变形速度趋近于0,电磁力沿板料中心轴对称分布。基于跑道型线圈磁感强度工程模型推导了磁感强度对称中心区位置与线圈直段半长、匝间距、中心距及板料装配间隙的关系,确定最佳偏置量为2.2~3.9 mm。该结果与模拟实验结果相符合,证实了模型的可靠性。

成膜温度对无铬达克罗涂层结构组成和耐蚀性的影响

[目的]温度对水性无铬达克罗涂层成膜机制的影响尚不明确。[方法]采用KH560硅烷偶联剂作为成膜物,钼酸盐作为钝化剂,片状锌、铝粉作为牺牲阳极组分,制备出一种水性无铬达克罗涂料。采用扫描电镜(SEM)、能谱(EDS)、X射线衍射(XRD)、中性盐雾试验、电化学测量等手段对不同温度(240~600℃)下成膜后涂层的表面形貌、相组成及耐蚀性进行表征与分析。[结果]成膜温度为330℃和390℃时,涂层微观结构最佳,片状锌、铝粉层层叠加,且表面光滑平整,无明显缺陷,经720 h中性盐雾试验后无红锈。成膜温度为330℃时,涂层的腐蚀电流密度最小,极化电阻最大,表现出优异的防护性能。[结论]成膜温度太高或太低都不利于获得耐蚀性良好的无铬达克罗涂层。