基于响应面法的铝合金间接挤压铸造工艺研究

为研究间接挤压铸造工艺,选取ZL101铝合金,以孔隙率为指标,首先通过单因素实验,分析了挤压压力、模具温度与比例系数3个因素对孔隙率的影响。然后采用Box-Behnken实验设计方法来设计响应面实验,建立了间接挤压铸造工艺参数与孔隙率相互关系的预测模型,方差分析结果表明,实验结果和数学模型拟合良好。通过对各个因素交互作用的响应面进行分析,得知模具温度和挤压压力对孔隙率的影响存在显著的交互作用,模具温度和比例系数、比例系数和挤压压力对孔隙率的影响不存在显著的交互作用。通过对环形件浇注系统的直浇道边缘部位进行金相检测分析,得知由于压力的施加,会使已经凝固的金属壳层发生不均匀的塑性流动。     

Influence of random shrinkage porosity on equivalent elastic modulus of casting: A statistical and numerical approach

Shrinkage porosity is a type of random distribution defects and exists in most large castings.Different from the periodic symmetry defects or certain distribution defects,shrinkage porosity presents a random "cloud-like" configuration,which brings difficulties in quantifying the effective performance of defected casting.In this paper,the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach.An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity.Then,a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm.The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated.Based on a statistical approach,the effects of shrinkage porosity's distribution characteristics,such as area fraction,shape,and relative location on the casting's equivalent mechanical properties were discussed respectively.It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods.The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5％;(2) the average Stress Concentration Factor (SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5％ more than a defect of other position.     

Research progress on squeeze casting in China

Squeeze casting is a technology with short route,high efficiency and precise forming,possessing features of casting and plastic processing.It is widely used to produce high performance metallic structural parts.As energy conservation and environmental protection concerns have risen,lightweight and high performance metal parts are urgently needed,which accelerated the development of squeeze casting technology over the past two decades in China.In this paper,research progress on squeeze casting alloys,typical parts manufacturing and development of squeeze casting equipment in China are introduced.The future trend and development priorities of squeeze casting are discussed.     

脉冲电流对铸造ZA27合金中缩孔和疏松的影响

在砂型铸造ZA27合金的凝固过程中用脉冲电流进行处理。结果表明这种处理方法可以提高铸件的致密性,大大减少铸件中的缩孔和疏松。脉冲电流处理后铸件密度增加2．5％,电流对铸件中缩孔的分布也有影响。     

Semi-solid squeeze casting process of a ZL109 alloy

The structure evolution of the ZL109 alloy in the process of semi-solid squeeze casting and the mechanical properties of the components were investigated. The results show that (1) the eutectic silicon phase in original billets is refined in the low super-heat casting process; (2) the eutectic structure in billets starts to fuse and the crystals of the eutectic silicon phase are refined further and sphericized in the remelting process of billets; (3) in the semi-solid ,squeeze casting process, the sphericity of the α phase and the refining of the silicon phase occur, owing to the friction between solid and liquid; (4) in the process of heat treatment, the eutectic α phase aggregates with the primary α phase and the eutectic silicon pieces aggregate together. The elongation of the semi-solid component after heat treatment rises to 1.42%.     

Prediction and improvement of shrinkage porosity in TiAl based alloy

The present research has developed a novel investment casting process for ingot production of TiAl alloys through forming a small vertical temperature gradient on the mold.The advantage of this process is to guarantee that the castings solidify sequentially from bottom to top.The analysis of numerical simulation and experimental results showed that the shrinkage porosity of Ti-47Al-2Cr-2Nb alloy was significantly improved by forming a vertical temperature gradient of 3 oC/mm on the mold,while the increase o...     

照相机铝合金外壳压铸CAE分析

通过建立温度场计算数学模型,利用有限元软件ProCAST模拟了照相机铝合金外壳的充型过程。通过模拟结果分析,预测了铸件在充型过程中可能出现的相关缺陷以及缩孔疏松形成的位置,并提出了一些修改方案和改进措施。     

Optimization of investment casting process for K477 superalloy aero-engine turbine nozzle by simulation and experiment

In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process, the effects of different gating systems on mold filling, solidification process, and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods. Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process, and the outer runner is not necessary. With the decrease in number of runners, the hot spot moves down towards the casting, and the shrinkage and porosity defects are formed in the casting below the riser. In the original designs, a certain tendency of shrinkage and porosity defect is found in the vanes, inner rings, and outer rings of the castings by both simulation prediction and experiment. Finally, based on the processing optimization, the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.

     

Semisolid casting using a vertical-injection squeeze casting machine: material flow and tensile properties of Al-7Si-0.3Mg alloy

Semisolid die casting of thixotropic Al-7Si-0.3Mg alloy has been carried out using a vertical-injection squeeze casting machine. The flow of the billet surface layer during casting was determined by X-ray examination of embedded markers. Tensile properties of the castings were then evaluated and metallographic observations were made. The original billet surface layer was found to be largely confined to the surface layer in the biscuit, except for the top of the billet surface, which flowed to the upper surface of the casting. As a consequence, the incidence of oxide inclusions within the casting was very low, leading to high elongation values with low scatter. Significantly lower strength and higher elongation values were observed in the biscuit. This effect was attributed to there being a significantly lower concentration of the solute elements in the biscuit compared to the casting.     

连铸大方坯自然热收缩行为的有限元模拟分析

结合国内某钢厂360 mm×450 mm大方坯连铸的实际生产工艺,利用商用有限元软件MSC.MARC对连铸大方坯自然热收缩行为进行三维热力耦合模拟。本次有限元模拟采用热弹塑性模型,研究不同拉速下铸坯温度场与凝固收缩规律。研究结果表明：拉速越高,温度变化越慢,铸坯总收缩量越小;拉速越小,温度变化越快,铸坯总收缩量越大;铸坯在宽度方向和厚度方向表现出不同规律的自然热收缩行为。     

Influence of shrinkage porosity on fatigue performance of iron castings and life estimation method

Shrinkage porosity exists more or less in heavy castings, and it plays an important role in the fatigue behavior of cast materials. In this study, fatigue tests were carried out on the QT400-18 cast iron specimens containing random degrees of shrinkage porosity defect. Experimental results showed that the order of magnitude of life scattered from 103 to 106 cycles when the shrinkage percentage ranged from 0.67% to 5.91%. SEM analyses were carried out on the shrinkage porosity region. The inter-granular discontinuous, micro cracks and inclusions interfered with the fatigue sliding or hindering process. The slip in shrinkage porosity region was not as orderly as the ordinary continuous medium. The shrinkage porosity area on fracture surface(SPAFS) and alternating stress intensity factor(ASIF) were applied to evaluate the tendency of residual life distribution; their relationship was fitted by negative exponent functions. Based on the intermediate variable of ASIF, a fatigue life prediction model of nodular cast iron containing shrinkage porosity defects was established. The modeling prediction was in agreement with the experimental results.     

Measurement of temperature inside die and estimation of interfacial heat transfer coefficient in squeeze casting

As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient (IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a"plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units (TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance (1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient (IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform (FFT). The feature of the IHTC at the metal-die interface was discussed.     

Influence of technical parameters on strength and ductility of AlSi9Cu3 alloys in squeeze casting

An orthogonal test was conducted to investigate the influence of technical parameters of squeeze casting on the strength and ductility of AlSi9Cu3 alloys. The experimental results showed that when the forming pressure was higher than 65 MPa, the strength (σ_b) of AlSi9Cu3 alloys decreased with the forming pressure and pouring temperature increasing, whereas σ_b increased with the increase of filling velocity and mould preheating temperature. The ductility (δ) by alloy was improved by increasing the forming pressure and filling velocity, but decreased with pouring temperature increasing. When the mould preheating temperature increased, the ductility increased first, and then decreased. Under the optimized parameters of pouring temperature 730 °C, forming pressure 75 MPa, filling velocity 0.50 m/s, and mould preheating temperature 220 °C, the tensile strength, elongation, and hardness of AlSi9Cu3 alloys obtained in squeeze casting were improved by 16.7%, 9.1%, and 10.1%, respectively, as compared with those of sand castings.     

Effect of ladle outlet geometry on internal porosity in gravity casting automotive brackets: An experimental investigation

This study investigated whether the pouring ladle's outlet shape could reduce the porosity of aluminum alloy casting products and whether it could be applied to mass production of automotive brackets based on computer simulations and experiment.The filling behaviors of the melt were simulated to compare the flow characteristics of the molten metal poured from the conventional ladle and the proposed ladle.Results show that for the conventional ladle,the pouring metal is V-shaped,while it is relatively circular and poured at a more constant rate in the proposed ladle.CT scans reveal that the proposed ladle reduces the porosity of the cast product.The proposed ladle resulted in an average of 30 fewer pores,a 299.56 mm3 smaller average total pore volume,and a 0.041% lower difference in average porosity.It is concludes that the proposed ladle can be used in the gravity casting process.By changing the ladle outlet shape can reduce the casting failure rate of massproduced automobile bracket.     

Segregation in squeeze casting 6061 aluminum alloy wheel spokes and its formation mechanism

Segregation can seriously damage the mechanical properties of the aluminum alloys.6061 aluminum alloy wheel spokes were prepared by squeeze casting.To investigate the formation mechanism of segregation,the microstructure of the alloy was observed using scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction and electron microprobe analysis methods.The Gibbs energy of each phase during solidification was calculated by JMat Pro.Results show that the segregation phases in the R-joint of the wheel spokes are mainly composed of Mg₂Si,β-Al Fe Si and Al₅Cu₂Mg₈Si₆intermetallics.During the solidification of the 6061 aluminum alloy wheels,Mg₂Si andα-Al Fe Si phases precipitate in the mushy zone at first.With the decrease of temperature,α-Al Fe Si transforms intoβ-Al Fe Si,while Al₅Cu₂Mg₈Si₆precipitates from the solid-state aluminum alloy after solidification.Segregation at the R-joint of wheel spokes is mainly caused by insufficient cooling,so the cooling during alloy solidification should be enhanced to avoid segregation.     

镁合金AZ91D压铸的数值模拟

运用有限元模拟软件对镁合金AZ91D零件在普通压铸与真空压铸下进行计算机数值模拟,有效的预测液态金属在充型过程、凝固过程中的流场、温度场及宏观缺陷,以此对宏观缺陷的出现进行控制,优化铸造过程。此外比较真空压铸与普通压铸对铸件气孔率的影响。结果表明,当铸造工艺参数分别为冲头压射速度2.4 m/s、浇注温度655℃、模具初始温度180℃时,与压铸相比,真空压铸能有效减少铸件的气孔率,改善铸件质量。     

A study on the effect of coating''s sorption capacity on the porosity in lost foam aluminum alloy casting

Effects of coating constituent, coating density, coating layer thickness and temperature on coating sorption capacity for polystyrene decomposition products have been studied systematically. It has been found that the effect of attapulgite clay on sorption capacity is the largest among coating constituents. The sorption capacity of the coating with 2 %attapulgite clay is elevated by 81%. The relationship between casting porosity and coating sorption capacity has been studied. It has been pointed out that higher coating sorption capacity for polystyrene decomposition products is helpful to decrease the casting porosity. Results also show that the sorption capacity of self- developed HW- 1 coating for polystyrene decomposition products is as good as that of Ashland coating from America.     

数值模拟技术在汽车螺塞压铸工艺设计中的应用

采用ProCAST模拟软件对汽车螺塞压铸过程进行数值模拟,得出了铸件的温度场变化,并预测了铸件中缩孔、缩松出现的部位。依照模拟结果,提出了改进方案,并对改进方案进行模拟比较,发现改进方案缺陷明显减少。     

Ti-Al合金精密铸件的疏松预测

应用铸造软件ViewCast模拟精密铸造Ti-46%Al合金叶片的充型与凝固过程,预测了疏松的形成,模拟结果与实验结果相吻合.通过分析凝固温度场、凝固收缩百分数并结合实验结果,对原浇注系统进行改进:摒除了原先的顶注及顶、底联合浇注的方式,只采用底注方式,有效克服了充型不平稳、易卷气的缺点;提高壳型预热温度、增大冒口尺寸,使铸件实现顺序凝固.改进后的模拟结果显示,铸件凝固顺序合理,疏松完全转移至凝固后的冒口中,保证了叶片的致密性.