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热裂是铸造镁合金成形过程中常见的缺陷,该缺陷的产生极大限制了高性能镁合金的工业应用。了解热裂形成机理、掌握热裂评估方法和影响因素对科学选材和批量应用具有重要的理论和实践价值。总结了现有的热裂理论、试验评估方法、热裂影响因素以及大部分镁合金热裂行为的评估结果,期望能为研究同行提供参考。强度理论、液膜理论、晶间搭桥理论、凝固收缩-补偿理论、裂纹形成功理论和冲击应力理论指导了热裂评估设备的设计,并为研究合金成分、凝固条件和微观组织等因素对热裂行为的影响提供了理论基础。现有的热裂数据并非采用同一评估方法获得,很难进行横向比较。未来热裂研究应尽量统一评估所采用的设备方法,以便建立镁合金相关的数据库,进而为大数据科学选材提供可能。 相似文献
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镁合金热裂行为研究进展 总被引:2,自引:2,他引:0
热裂是合金铸造过程中最常见的严重铸造缺陷之一。随着镁合金材料应用范围的不断扩大和复杂薄壁铸件的增加,热裂成为镁合金商业化应用的瓶颈。全面阐述了国内外对镁合金热裂行为的测试方法,归纳出了镁合金热裂形成机制,以及镁合金中热裂倾向定量评价方法等。根据多年的深入研究结果详细总结了镁合金热裂的影响因素。同时,还介绍了镁合金热裂的理论预测方法和最新数值模拟模型。为建立稳定、统一的热裂评价标准提供了有实际价值的参考。 相似文献
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在半连续真空定向凝固设备上进行了Al-0.6wt%Cu和Al-2.0wt%Cu两种铝合金的热裂试验,结果表明,两种成分铝合金试样的热裂程度随抽拉速率的提高而增大,理论分析认为,抽拉速率的提高,增加了合金凝固后期的收缩速率,因而造成热裂程度的增加。 相似文献
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孔洞与热裂是铸件在凝固过程中最常遇到的典型缺陷。两者均形成于合金凝固末期,与液相补缩不足相关,但又有各自的形成机理。铝合金熔体对氢气有很大的溶解度,凝固过程中又因为溶解度的剧降而析出。孔洞是液相中过饱和的气体压力与凝固收缩引起的压力降共同作用的结果。热裂则是在凝固末期由于铸件收缩受阻而产生的应力以及液相补缩不足而导致的,其不仅与合金性质、铸造条件有关,并且受铸件形状的影响。文章基于近年来该方面的理论研究成果,总结了关于孔洞与热裂的形成机理以及几种目前所应用的经典预测模型,并对这几种模型的理论基础以及所考虑的关键参数进行了分析与讨论,在此基础上提出了未来新模型的研究方向和亟需解决的关键问题。 相似文献
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目的 针对铝铜合金热裂敏感性高、难以进行金属型铸造的难题,研究其合金成分、铸造工艺、组织与性能的关系。方法 首先充分分析铸造铝铜合金的凝固机制与特点,在ZL205A合金基础上,设计了新型合金成分以及两种铸造试样模,经过熔炼、铸造与热处理,获得砂型铸造与金属型铸造试样,进行力学性能测试、组织分析,并观察试样的抗热裂性。结果 两种铸造试样都获得了较高的力学性能,铸态及T6态全部为等轴晶组织,成功避免了热裂问题,并提高了合金的力学性能;金属型铸造试制了油马达铸件。结论 证明了通过铝铜合金的成分优化设计,以及含钪复合细化剂的合理匹配,采用金属型铸造获得等轴晶组织,进而避免粗大枝晶组织,是克服热裂问题的关键,从而实现金属型铸造高强度铝铜合金。 相似文献
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为研究定向凝固柱晶高温合金薄壁铸件凝固过程的热裂纹形成倾向,采用定向凝固空心薄壁管状试样,考察了Ti,Zr,Hf,Al和B等元素对定向凝固柱晶高温合金热裂倾向性的影响;采用SEM、断口分析及DSC方法,分析了热裂的晶界宏观形态.结果表明:随着Ti含量的增加,γ/γ′共晶增多,尺寸增大,合金凝固温度范围变大,定向合金的热裂倾向性严重;Zr元素含量增加,促成共晶形成,合金出现热裂纹;Hf含量的变化对合金的热裂没有影响;Al,B含量增加,微观组织无明显变化,但合金凝固温度范围变大,导致定向凝固合金出现热裂. 相似文献
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定向凝固叶片类铸件热裂倾向评定方法 总被引:2,自引:0,他引:2
针对空心叶片类铸件薄壁特点和定向凝固热裂纹形成时横向收缩受阻的特点,设计了薄板工字型向向凝固合金热倾向性试样,并提出了相应的合金热裂倾向半定量等级评定方法。 相似文献
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K403合金铸造涡轮叶片热裂的研究 总被引:1,自引:0,他引:1
研究表明,热裂是合金枝晶间液体处于不连通状态的温度与合金完全凝固温度范围内产生,铸造涡轮叶片热裂最常出现的部位是叶冠与叶身或者榫根与叶身的连接段,热裂在外貌上呈弯曲不规则形状,通常是不连续的,常有几条裂纹沿枝晶间或晶界向相同的方向扩展,热裂严重区断口呈光滑的“土豆”状,在热裂扩展出现光滑区与撕裂并存。降低合金初熔温度的微量合金化元素(如B,Zr)明显增加了热裂的敏感性。 相似文献
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目的通过对压力机底座的充型凝固过程进行数值模拟,预测其浇铸质量同时基于模拟结果提出相应的工艺改进措施。方法使用UG与CAE软件对压力机底座铸造工艺进行三维建模和数值模拟分析。通过研究零件的结构特点,确定选取砂型手工铸造方法,并使用三箱造型,选取合适的分型面与浇铸位置。采用UG软件做出锻压机底座的三维模型和浇注系统设计,然后利用Anycasting软件进行充型模拟。对充型与凝固过程进行了整体的缺陷分析。结果利用Anycasting模拟浇铸过程发现,在整个充型过程中,充型平稳,无卷气、夹渣、缩孔、缩松等缺陷的出现。结论通过模拟结果确定了浇注系统和补缩系统设计合理,相应工艺设计合理,可以铸造出符合要求的压力机底座。 相似文献
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A. M. Nabawy A. M. Samuel F. H. Samuel H. W. Doty 《Journal of Materials Science》2012,47(9):4146-4158
This study was undertaken to investigate the effects of chemical composition and mold temperature (MT) on the hot-tearing
susceptibility (HTS) of an experimental Al–2% Cu–1% Si alloy using a constrained rod casting mold. The HTS results were then
compared with 206 (Al–5 wt% Cu) alloys containing the same additions. In general, the Al–2% Cu–1% Si based alloys exhibited
higher resistance to hot-tearing than did the 206-based alloys. It was found that an elevated MT is beneficial in reducing
the HTS of the Al–2% Cu–1% Si and 206 alloys in that the HTS value decreased from over 21 to less than 5, as the MT was increased
from 250 to 450 °C. Increasing the Si content reduced the HTS of the Al–2% Cu–1% Si alloy considerably; this reduction may
be attributed to an increase in the volume fraction of eutectic in the structure. The addition of Sr caused deterioration
in the hot-tearing resistance of the base alloy due to the formation of Sr-oxides and an extension of the freezing range of
the alloy. The refinement of the grain structure obtained with the Zr–Ti–B addition decreased the severity of hot-tearing
as a result of an increase in the number of intergranular liquid films per unit volume and a delay in reaching the coherency
point. It was also observed that α-Fe intermetallic particles may impede the propagation of hot-tearing cracks. The Al–2% Cu–1% Si alloy with 1 wt% Si addition
was judged to be the best composition in view of its low HTS. 相似文献
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钛铝合金是性能优异的高温合金,在航空航天领域有广泛的应用前景,但由于其熔体具有较高的活性,制备时熔体与所有已知的铸型材料会发生不同程度的反应,限制了钛铝合金铸件的发展.定向凝固技术作为制备高精度钛铝合金的新工艺,使铸件组织定向排列,可以进一步提高钛铝合金的使用性能,因此如何调控凝固过程中钛铝合金熔体与铸型材料间的界面反应成为目前有关定向凝固钛铝合金研究的一个热点.从目前国内外关于钛铝合金熔体与铸型材料间界面反应的研究出发,综述了定向凝固过程中铸型材料、涂层成分、工艺参数及合金元素等对界面反应的影响,介绍了界面反应的理论水平,系统收集了界面反应的各项研究结果. 相似文献
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Jean Robert Pereira Rodrigues Mirian de Lourdes Noronha Motta Melo Rezende Gomes dos Santos 《Journal of Materials Science》2010,45(9):2285-2295
In this study, the influence of magnesium content on thermal and structural parameters during the unsteady-state unidirectional
solidification of Al–Mg alloys is analyzed. Using a special device, Al–Mg alloys containing 5, 10, and 15 wt% Mg were submitted
to unidirectional solidification. Using a data acquisition system, the temperature variations along the casting during solidification
were measured. From these results, the variations of solidification parameters as growth rate of dendrite tips, thermal gradient,
cooling rate, and local solidification time were determined. The variation of global heat transfer coefficient at metal/mould
interface was estimated through the adjustment of experimental temperature variation close to the interface and numerical
predictions. Primary and secondary dendrite arms spacing variations during solidification were measured by optical microscopy.
From these results, comparative analysis were developed to determine the influence of magnesium content. 相似文献
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Numerical study of porosity in titanium dental castings 总被引:4,自引:0,他引:4
Wu M Sahm PR Augthun M Spiekermann H Schädlich-Stubenrauch J 《Journal of materials science. Materials in medicine》1999,10(9):519-525
A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal–mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings. © 1999 Kluwer Academic Publishers 相似文献
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随着镁合金产业的快速发展,如何通过塑性成形方法提高镁合金的耐蚀性成为了重要课题。镁及其合金因具有低密度、高比强度和较好的回收性等优点而受到广泛关注,然而室温变形能力和耐腐蚀性能差等缺点是其广泛应用的瓶颈。在总结镁合金腐蚀特点及面临问题的基础上,综合分析了国内外塑性成形方法对镁合金腐蚀领域的相关研究,综述了不同加工成形方法在提高镁合金耐蚀性应用方面的进展,从腐蚀机理和工艺参数2个方面进行了讨论。介绍了不同塑性成形方法对镁合金耐蚀性的影响机制,其中包括挤压–ECAP、超声滚压处理、等通道转角挤压、热轧处理、触变成形、板材挤压、板材轧制、交叉轧制、异步轧制和异步交叉轧制、压铸、快速凝固、搅拌摩擦焊、增材制造、喷丸等。从成分分布、析出相等微观角度阐述了影响镁合金腐蚀行为的机制,指出了塑性成形方法在提高镁合金耐蚀行为方面存在的问题,为提高镁合金的耐蚀性提出建议。 相似文献
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The effect of die geometry on the microstructure of indirect squeeze cast and gravity die cast 7050 (Al-6.2Zn-2.3Cu-2.3Mg) wrought Al alloy 总被引:1,自引:0,他引:1
The indirect squeeze casting process has been used to cast a 7050 (Al-6.2Zn-2.3Cu-2.3Mg) wrought Al alloy to near-net shape
with excellent die replication. Defects which occur with gravity casting, in particular (1) shrinkage pipe, (2) macro-porosity
and (3) hot-tearing, are largely removed by squeeze casting, although regions of macro-porosity can re-appear when thick sections
are fed through substantially thinner sections. Squeeze casting results in a considerable refinement of microstructure compared
to gravity casting due to a marked decrease in solidification time. The decrease in solidification time is caused by intimate
contact between the pressurised melt and the die, which leads to an increase in the heat transfer coefficient. Decreasing
the section thickness also results in a refinement of the microstructure due to a reduction in solidification time.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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蝶阀阀体是蝶阀上的核心零部件,服役时承受高温高压,因而要求其组织致密,不允许有缩孔、缩松和气孔等缺陷.本文先用SolidWorks软件对蝶阀体进行实体造型,然后利用JSCAST软件对铸件进行充型和凝固过程模拟,预测铸件充型过程中可能产生的充填不良、裹气现象及凝固过程中可能发生缩孔、缩松缺陷的位置,然后对模拟结果进行工艺优化.模拟结果表明,改进后的铸造工艺能够实现平稳的充型,充型结束后铸件各部位温差较小;铸件能够顺序凝固,有害热节全部消失,缩孔或缩松缺陷也相应的消除.实际生产对模拟结果进行了有效的验证. 相似文献