Preparation of open-celled aluminum foams by counter-gravity infiltration casting

A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.

Thermal properties of open-celled aluminum foams prepared by two infiltration casting methods

Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.

Effect of centrifugal counter-gravity casting on solidification microstructure and mechanical properties of A357 aluminum alloy

To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.

Surface composites fabricated by vacuum infiltration casting technique

Alumina （Al2O3） particles reinforced copper matrix surface composites were fabricated on the bronze substrate using the vacuum infiltration casting technique. Three cases were obtained in the vacuum infiltration casting technique： no infiltration, partial infiltration and full infiltration （the thickness of preforms do not exceed 3.5mm）. The reason of no infiltration is that the vacuum degree is not enough so that the force acting on the liquid metal is lower than the resistance due to the surface tension. Partial infiltration is because of somewhat lower vacuum degree and pouring temperature. Full desired infiltration is on account of suitable infiltration casting conditions, such as vacuum degree, pouring temperature, grain size and preheating temperature of the preform. The most important factor of affecting formation of surface composites is the vacuum degree, then pouring temperature and particle size. The infiltration mechanism was discussed on the bases of different processing conditions. The surface composite up to 3.5 mm in thickness with uniformly distributed Al2O3 particles could be fabricated via the vacuum infiltration casting technique.

Preparation of big size open-cell aluminum foam board using infiltration casting

This paper presents an infiltration casting technique for manufacturing big size open-cell aluminum foam boards. The principle and key technologies of infiltration casting are also analyzed. Based on the previous practice of the small size aluminum foam production, the die for preparing big size aluminum foam boards is designed and manufactured. The experiments on aluminum boards of 300 mm × 300 mm × （20-75） mm, with the pore size ranging from 1.0 to 3.2 mm and average porosity of 60%, have been performed. The experimental results show that a reliable infiltration process depends critically on the pouring temperature of the molten AI-alloy, the preheated temperature of the mould and salt particles and vacuum. Current research explores the possibility of large-scale manufacturing and application of the aluminum foams.

Effect of mold temperature and casting dimension on microstructure and tensile properties of counter-gravity casting Ti-6Al-4V alloys

The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.

Fabrication and compressive behavior of open-cell aluminum foams via infiltration casting using spherical CaCl_(2) space-holders

The infiltration casting fabrication process based on spherical CaCl_(2) space-holders and the compressive behavior including the mechanical performance and energy absorption capacity of open-cell aluminum foams were investigated.Open-cell aluminum foams with different porosities in the range of 63.1%to 87.3%can be fabricated by adjusting compression ratios of CaCl_(2) preforms prepared by precision hot-pressing.The compression tests show that a strain-hardening phenomenon always occurs especially for open-cell aluminum foam with low porosity,resulting in the inclining stress-strain curve in the plateau region.The energy absorption capacity of open-cell aluminum foam decreases with increasing porosity when compared at the same strain.However,when compared at a given stress,each foam can absorb the maximal energy among the five foams in a special stress range.Additionally,open-cell aluminum foam possesses the maximum energy absorption efficiency at its optimum operating stress.At this stress condition,the foam can absorb the highest energy compared with other foams at the same stress point.The optimum operating stress and the corresponding maximal energy absorption decrease with increasing the porosity.The optimum operating stress for energy absorption can also be determined similarly when taking into consideration of the lightweight extent of foams.

Effect of some parameters of formation on surface graphite-bronze composite layer prepared by vacuum infiltration casting technique

Surface composite up to 3.0 mm in thickness with compact microstructure was fabricated successfully via vacuum infiltration casting technique on the bronze substrate under the optimum experimental conditions: the vacuum degree of -0.08 MPa, pouring temperature of 1220℃, grain size of 0.20-0.24 mm, preheating temperature of 180℃. The preform was mainly composed of graphite particles and binder NJB (self-fabricated binder). The vacuum degree, pouring temperature, preheating temperature and grain size during infiltration casting play an important role on the process of forming the surface composite. The results show that three cases are obtained in the vacuum infiltration casting technique: no infiltration, partial infiltration and full infiltration. The main reason of no infiltration is that the vacuum degree is not enough so that the force acting on the liquid metal is lower than the resistance due to the surface tension and the pouring temperature is somewhat low. Partial infiltration is because of somewhat lower vacuum degree and pouring temperature. Full desired infiltration is on account of suitable infiltration casting conditions, such as vacuum degree, pouring temperature, grain size and preheating temperature. The influencing effect of vacuum degree is most obvious for the formation of surface composite, then pouring temperature and particle size. The infiltration mechanism is discussed on the bases of the different processing conditions.

THE PRODUCTION OF FOAM ALUMINIUM ALLOY BY LOW-PRESSURE INFILTRATION METHOD

The influence of technical parameters on the infiltrating height of the moltenmetal in the process of Producing aluminium alloy foam by low-pressure infiltration method were investigated.Experiments indicated that the height increases with the preheating temperature of granules,theexternal pressureand the pouring temperature of molten alloy,among which the action of pre heating temperature of granules is more effective.There exists a critical pre heating temperature for different size of granules.

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.

Effect of microalloying on wettability and interface characteristics of Zr-based bulk metallic glasses with W substrate

The infiltration casting method is widely employed for the preparation of ex-situ composite materials.However,the production of composite materials using this method must necessitates a comprehensive understanding of the wettability and interface characteristics between the reinforcing phase and the bulk metallic glasses(BMGs).This work optimized the composition of Zr-based BMGs through microalloying methods,resulting in a new set of Zr-based BMGs with excellent glass-forming ability.Wetting experiments between the Zr-based BMGs melts and W substrates were conducted using the traditional sessile drop method,and the interfaces were characterized utilizing a scanning electron microscope(SEM)equipped with energy dispersive X-ray spectroscopy(EDS).The work demonstrates that the microalloying method substantially enhances the wettability of the Zr-based BMGs melt.Additionally,the incorporation of Nb element impedes the formation of W-Zr phases,but the introduction of Nb element does not alter the extent of interdiffusion between the constituent elements of the amorphous matrix and W element,indicating that the influence of Nb element on the diffusion of individual elements is minute.

直写3D打印TiC网络陶瓷/高铬铸铁复合材料的制备及性能研究

采用浆料直写3D打印技术制备了TiC网络陶瓷,并结合无压浸渗制备了TiC网络陶瓷/高铬铸铁复合材料。采用扫描电子显微镜对TiC网络陶瓷预制体与浸渗后的组织进行了观察,采用EDS对界面元素分布进行了分析,并对复合材料的硬度、抗压强度和耐磨性进行了测定。结果表明:复合材料中TiC线条与高铬铸铁线条在空间上形成了三维互穿网络结构,实现了空间韧化的效果,提高了复合材料的整体力学性能;随着复合材料中TiC线条体积分数的增加,硬度随之增加,抗压强度与耐磨性都表现为先增后减,在Ti C体积分数50%时达到最佳值。

Surface Infiltrating Composite of Fe-base Metal and Ceramics

1.IntroductionMetal matrix composites consist of afamily of advanced materials which mayhave attractive properties including highstrength,high specific modulus,lowcoefficient of thermal expansion,good wearresistance,and attractive high temperature

原料配方对微孔陶瓷渗灌管道性能的影响

为解决现有多孔陶瓷渗灌管道制备工艺不规范、产品性能低下的问题,采用注浆成型法,以黏土为骨架材料,炉渣为造孔剂,硅酸钠为解凝剂,制备一种低成本、性能优良的微孔陶瓷渗灌管道。分析了黏土颗粒粒径和炉渣掺量2个因素对微孔陶瓷渗灌管道孔隙率、线收缩率、弯曲度、抗弯强度、渗透系数和流量的影响规律,以较大的抗弯强度、较小的线收缩率和弯曲度、合适的孔隙率为优选标准,得到微孔陶瓷渗灌管道的最优原料配方。结果表明:随着黏土颗粒粒径增大,微孔陶瓷渗灌管道的线收缩率、弯曲度、抗弯强度降低,孔隙率和渗透系数增大,进而使流量增大;随着炉渣含量的增加,微孔陶瓷渗灌管道的抗弯强度降低,孔隙率、线收缩率、弯曲度、渗透系数增加,流量增大。微孔陶瓷渗灌管道渗透系数与孔隙率成幂函数关系。综合比较,黏土颗粒粒径0.180~0.355 mm、炉渣掺量15%为最优原料配方,微孔陶瓷渗灌管道的孔隙率为33.9%、线收缩率为3.98%、弯曲度为0.95°、抗弯强度为8.6 MPa、渗透系数为0.36 cm/h,在10 kPa工作压力下的流量为6.12 L/(h·m),兼具良好的材料性能和水力性能,能较好满足田间使用要求。

铍/铝复合材料制备技术与性能设计研究进展

铍/铝复合材料因其高比强度、高比刚度等优异性能,在航空航天等领域备受关注。本文综述了近30年来国际上在铍/铝复合材料制备技术方面的研究进展,总结了改善铍/铝复合材料微观组织、提高材料性能的方法,并对未来铍/铝复合材料研究方向提供了思路,对铍/铝复合材料的制备技术发展以及性能的突破进行了展望。

铝熔体在多孔介质中的渗流过程

在流体流动相似原理的基础上，提出了铝熔体在多孔介质间隙（简称多孔介质）中渗流模拟的原理和方法．设计建造了用于铝液和模拟液在外加压力下进行单向渗流的两套试验装置模拟试验揭示渗流时铝液在多孔介质中渗流的若干规律实践表明理论模型与试验吻合良好．

碳化钨颗粒在WC/Fe基复合材料基体中的断裂和熔解

利用V-EPC铸渗法制备了碳化钨颗粒增强铁基表面复合材料,结合差热分析测试,研究了碳化钨颗粒在基体中的断裂和熔解。结果得出,在铸渗过程中,温度的急剧变化所产生的热应力导致碳化钨颗粒在基体中发生断裂,而原始碳化钨颗粒的表面尖角促使其与基体间界面的平衡熔点降低,从而导致碳化钨颗粒发生熔解。结果还得出,可以通过改善碳化钨颗粒的导热性能和减少其显微缺陷来阻止碳化钨颗粒在基体中的断裂,同时可以通过控制原始碳化钨颗粒的表面质量和浇注温度来控制碳化钨颗粒在基体中的熔解。

高硅铝合金电子封装材料研究进展

阐述电子封装材料的基本要求,论述高硅铝合金材料的研究概况及其性能特点,分析熔炼铸造、浸渗法、快速凝固/粉末冶金和喷射沉积制备方法的优缺点,并指出高硅铝合金电子封装材料的发展方向。

用铸渗工艺对消失模铸铁件进行表面合金化的研究

利用干砂消失模铸造工艺 ,对铸铁件表面合金化铸渗机理进行了研究 ,通过建立数学模型 ,对铸渗过程中铁水传输进行了理论分析 ,给出了铸渗量与浇口的大气压力、铁水静压力、渣液阻力及附加压力的关系式 ,提出了铸渗量大小主要取决于铸渗孔道半径的新观点 .用正交试验对合金涂层中合金粉粒度、合金粉加入量、溶剂加入量及涂层中聚苯乙烯泡沫加入量等进行了考证 ,得出最佳工艺配方为 :合金粉粒度 75 10 0目 ;泡沫加入量 30 % 5 0 % (φ(B) ) ;溶剂加入量 4% .在配制合金涂料时 ,适当加入一定量泡沫珠粒 ,有利于母液渗透 ,这与理论推导结果相符 ,易获得 3mm以上合金层厚度 .合金层具有珠光体基体及大量M7C3 碳化物 。

铸渗机理与改善铬铸渗层质量的研究

提出了铬铸渗层是田合金烧结层、纤焊层和熔合层三个区域构成的。指出机器高压制造合金膏块是改善铬铸渗层质量的有效工艺措施。