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.

Porosity of aluminum alloy in lost foam casting process

The effects of modification, grain refinement, polystyrene pattern, pouring temperature and reduced pressure degree on aluminum alloy porosity in lost foam casting (LFC) process were studied. The results show that the solidification rate of LFC process is slower than that of resin sand process or clay sand process. The effect of modification and grain refinement on the aluminum alloy casting density in LFC is greater than that on resin sand process. Through α Al phase refinement process with 0.2%Ti for aluminum melt, the subversive effect of Sr modification in LFC process is decreased greatly, and the aluminum casting density in LFC process is nearly equal to that in resin sand process. To decrease the porosity of aluminum castings in LFC process, lower density of polystyrene pattern, higher pouring temperature (760～780 ℃) and lower reduced pressure degree (≤20 kPa) should be applied.[

Rotary bending fatigue behavior of A356 –T6 aluminum alloys by vacuum pressurizing casting

Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.

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.

Effect of pattern coating thickness on characteristics of lost foam Al-Si-Cu alloy casting

An experimental study on lost foam casting of an Al-Si-Cu alloy was conducted. The main objective was to study the effect of pattern coating thickness on casting imperfection and porosity percentage as well as eutectic silicon spacing of the alloy. The results showed that increasing slurry viscosity and flask dipping time influenced the casting integrity and microstructural characteristics. It was found that thinner pattern coating produced improved mould filling, refined microstructure and higher quality castings containing less porosity.

牵引电机铸铝结构件失效分析及结构优化

某牵引电机铸铝结构件在长寿命振动试验过程中开裂失效。通过对铸铝结构件的断口形貌分析、化学成分检测、显微组织观察、硬度检测、强度仿真分析等方法,对铸铝结构件的失效模式进行分析。结果表明:铸铝结构件的失效模式为疲劳断裂,裂纹起源于端盖油嘴的凹槽底部。断裂原因为结构件该处较薄,仅为4 mm,加之此处存在铸造缺陷,材料的连续性被打断,有效承载强度减弱;且该处为直角过渡,在使用应力作用下形成应力集中。通过增加凹槽处厚度,把凹槽直角过渡改为圆角过渡,减小了应力集中,提高了铸铝结构件的安全系数。

2A12铝合金圆铸锭疏松产生原因及防止措施

2A12铝合金以优良的性能广泛应用于航空航天等工业领域。大规格圆铸锭易出现疏松缺陷,影响最终产品的综合性能。对2A12铝合金圆铸锭生产工艺和铸锭组织分析表明,疏松为补缩型疏松。系统分析了2A12铝合金半连续铸造过程中熔体的氢含量、化学成分、铸造工艺参数以及环境湿度对疏松的影响。提出了减少2A12铝合金铸锭疏松缺陷的措施。

孔洞对铸造铝合金疲劳性能的影响

研究了铸造铝合金中孔洞在裂纹萌生、扩展过程中发挥的作用,孔洞的尺寸、体积分数、分布位置、形貌率等因素对材料的疲劳性能有重要影响。从试验现象和疲劳寿命模型两个方面综述了国内外学者研究的最新进展,指出了应力-寿命模型与线弹性断裂模型之间的内在联系,并讨论了存在的问题及研究方向。

稀土对B319铝合金组织性能的影响

利用等离子发射光谱仪、能谱仪、图像分析仪、差分扫描量热仪（DSC）以及金相分析等手段,研究了稀土（RE）对消失模铸造B319铝合金孔隙率、组织和性能的影响.研究结果表明,在铸件冷却速度为0.2℃/s的消失模铸造条件下,B319铝熔体中加入0.15％RE（质量分数）,可以使Si相得到一定程度的变质.并可使消失模铸造铝件的孔隙率明显降低.这是消失模铸造慢冷条件下RE提高合金力学性能的重要原因.随着RE加入量的增加,合金的抗拉强度和延伸率得以提高,当RE含量为0.15％时,相对于未加RE时的情况,σb和δ分别增加了14％和23.5％.当RE含量>0.15％时,出现富稀土的块状金属间化合物Ti2LaAl20,使合金的机械性能,尤其是塑性降低.

铸造铝合金中氧化夹杂物的研究进展

就铸造铝合金中氧化夹杂物的来源和形成过程、对铝液吸氢、铝铸件中孔洞形成和铸件力学性能的影响进行了分析,并对国内外铝合金铸件中氧化夹杂的研究进展进行了综述。在熔铸过程中形成的氧化夹杂物,是铝液中夹杂物的主体,对铝液吸氢和铝合金铸件中孔洞的形成有着不可忽视的影响。铝合金铸件的力学性能与铝液中的氧化夹杂密切相关,夹杂物可作为显微裂纹的发源地,严重削弱铝合金铸件的力学性能。

铝合金下壳体压力铸造充型与凝固过程的数值模拟

利用ProCAST软件对铝合金压铸件下壳体充型、凝固过程进行了数值模拟,得到了速度场、温度场的分布和变化规律。据此提出了减少缩孔、缩松数量的优化方案。结果表明,降低浇注温度、增大压射比压,降低模具预热温度都能够有效控制缩孔、缩松的数量。按照优化后的压铸工艺参数生产出了合格的铸件。

涂料吸着性对消失模铸造铝铸件孔隙率影响的研究

研究了涂料组成、密度、涂层厚度、温度等对涂料吸着性的影响。研究发现 ,涂料组成中以凹凸棒土对涂料吸着性的影响最大 ,涂料中加入 2 %凹凸棒土可以使涂料的吸着性提高 81%。探讨了涂层的吸着性与铝铸件孔隙率之间的关系 ,认为对于铝合金消失模铸造 ,涂料吸着液态聚苯乙烯的能力越强 ,越有利于减少铝铸件的孔隙率。试验结果表明 ,自制的HW 1涂料可与美国Ashland涂料相媲美 。

铝合金铸件缩松缺陷的热等静压处理

为了消除某铝合金铸件通过铸造工艺无法消除的缩松缺陷,试验了热等静压技术对此缩松缺陷消除的效果。结果表明,铸件经热等静压处理后,X射线检测缩松缺陷得到了显著改善,内部质量能达到验收标准要求。这说明热等静压技术消除该铝合金铸件缩松缺陷是可行的,也能为铝合金铸件消除缺陷提供一些参考。

局部加压铝合金的凝固变化及其数值模拟

局部加压方法是压铸中用于消除铸件厚壁处缩孔缺陷的一种新工艺。该研究通过试验模型测量局部加压过程中金属型、铸件和加压杆的温度变化曲线,分析了传热与凝固现象。结果表明,局部加压使铸件的凝固时间大为缩短,加压杆前端的温度大幅上升,而金属型的温度则无明显变化。利用变网格技术,根据加压深度通过适时修改网格文件、初始条件和边界条件的方法,模拟了铝合金在局部加压过程中的凝固变化,并与试验结果进行了对比和讨论。

铸造铝合金精炼技术现状及发展

阐述了铸造铝合金的气孔形成机制、精炼理论及各种精炼技术的特点、研究现状和发展前景。旋转喷头吹气技术、FILD法、MINT法、FIP法和Heproject法等新型复合精炼技术的出现,极大地提高了铝合金熔体精炼水平。

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。

微观孔洞对铝合金压铸件疲劳性能的影响

基于高分辨率三维X射线断层扫描技术,对实际ADC12铝合金压铸件疲劳试样内部微观孔洞进行了检测和重构,对7组不同孔隙率的试样进行了5级应力水平的高周疲劳实验。三参数Weibull分析表明:随着应力水平升高,疲劳寿命分散性逐渐降低。采用SEM观察疲劳断口,确定诱发疲劳裂纹起源的孔洞,并对其进行了分析;基于断口表面的孔洞特征以及X射线断层扫描重构数据,建立了孔洞-疲劳寿命预测方程,并与实验结果进行了对比分析。将三维X射线断层扫描重构数据与有限元分析相结合,计算和分析了实际微观孔洞引起的应力情况,为研究材料内部实际微观孔洞特征对性能的影响提供新的途径。

低压铸造铝合金薄壁件成型压力因素模拟

采用有限元模拟仿真软件对铝合金汽车座椅骨架低压铸造工艺进行数值模拟,研究了低压铸造加压工艺中的充型压力、充型加压速率及增压压力对铸件缩松缩孔的影响。模拟结果表明:充型压力和充型加压速率的提高,有助于提高薄壁件的充型能力;对于特定的薄壁件,存在一个临界增压速率,使得缩松缩孔率最小。另外,随着增压压力的提高,缩松缩孔率减小。

￠605mm 2A12铝合金圆铸锭的热顶铸造工艺及避免疏松缺陷的措施

研究了￠605mm 2A12铝合金圆铸锭的热顶铸造工艺,分析了大规格2A12铝合金圆铸锭产生疏松缺陷的原因,提出了避免疏松缺陷的技术措施,通过技术措施的实施,获得了疏松程度符合后续压力加工要求的高品质的大规格2A12铝合金圆铸锭。

压铸工艺参数对铝合金汽缸体孔隙率的影响

通过测量铸件热处理前后密度变化率,系统研究了压铸过程中浇注温度、铸造压力、快压射速度、快压射切换位置等工艺参数对铝合金汽车空调压缩机汽缸体孔隙率的影响规律。结果表明,铸件内的孔隙率随着浇注温度的升高和快压射速度的增加而增大,随着快压射切换位置的增加而减小,随着铸造压力的增加先增大后变小。综合考虑,浇注温度为700～720℃,铸造压力为104MPa,压射速度为1.5m/s,快压射位置为320mm时,铸件孔隙率最小,性能最好。