离心铸造法制备陶瓷颗粒增强Al合金基功能梯度复合管

利用熔融Al合金基体与颗粒增强相（SiC及Al2O3颗粒）在离心铸造条件下所受的离心力的不同，再通过调整其它的工艺参数，利用水平式离心铸造机制备了3种具有不同强化部位（外层强化、内层强化以及内外层同时强化）的功能梯度复合管，颗粒的3种分布方式使复合管的微观组织及显微硬度呈现了相应的梯度变化，强化部件的多样化可为功能梯度复合管的应用开辟新的领域。     

Enhancing wettability of SiC in semisolid A356 aluminium matrix composites

Abstract

Stir casting plus cooling plate technique has been used for the fabrication of Al matrix composites based on alloy 356. Improvement of the wettability of SiC particles was carried out, employing the oxidisation of SiC particles, the use of wetting agents by adding magnesium into the matrix and the coating of SiC particles using a sol–gel technique. The introduction of SiC particles into partially solidified alloy with high viscosity prevents the particles from floating and agglomerating. Unoxidised SiC particles are mostly detached from the Al matrix during the grinding suggesting poor adhesion and poor wettability between the matrix and the particles. Oxidised SiC particles and sol–gel silica coated SiC particles indicate good binding between composite and matrix. The use of magnesium promoted wettability of SiC with A356 alloy. The eutectic silicon phase formed on the surface of SiC particles during solidification may be due to nucleation effects provided by the particles.     

离心铸造原位初生Si/Al3Ni颗粒增强铝基复合材料

采用离心铸造制备原位初生Si和Al3Ni颗粒混合增强铝基复合材料的筒状铸件。通过光学显微镜(OM)、XRD、SEM、EDS以及洛氏硬度计等研究了复合材料的组织和性能。结果表明,所制备的复合材料铸件外层偏聚少量初生Si和大量Al3Ni颗粒,内层偏聚大量初生Si和少量Al3Ni颗粒,中间层没有增强颗粒。从铸件的外层到内层,增强颗粒的含量先降低后升高,复合材料的硬度也呈现出相应的变化规律。分析了离心场中多相流体的运动规律,发现复合材料中增强颗粒的分布与高重力系数G参数条件下初生Si和Al3Ni颗粒的密度以及它们的相互碰撞、粘结等作用有关。     

Processing and compressive strength of Al–Li–SiCp composites fabricated by a compound billet technique

Al–Li–SiC_p composites were fabricated by a simple and cost effective stir casting technique. A compound billet technique has been developed to overcome the problems encountered during hot extrusion of these composites. After successful fabrication hardness measurement and room temperature compressive test were carried out on 8090 Al and its composites reinforced with 8, 12 and 18 vol.% SiC particles in as extruded and peak aged conditions. The addition of SiC increases the hardness. 0.2% proof stress and compressive strength of Al–Li–8%SiC and Al–Li–12%SiC composites are higher than the unreinforced alloy. In case of the Al–Li–18%SiC composite, the 0.2% proof stress and compressive strength were higher than the unreinforced alloy but lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. This is attributed to clustering of particles and poor interfacial bonding.     

Microstrucmral characteristics and properties in centrifugal casting of SiCp/Zl104 composite

The microstructural characteristics and Brinell hardness of a cylinder produced by centrifugal casting were investigated using 20% (volume fraction) SiC_p/Zl104 composites. Macrostructure and XRD analysis show that most of SiC particles segregate to the external circumference of the cylinder, the other SiC particles maintain in the inner circumference of the cylinder, and a free particle zone is left in the middle circumference of the cylinder. Microstructural characteristics and quantitative assessment of SiC particles show that most of congregated SiC particles in 20%SiC_p/Zl104 composites are dispersed by centrifugal force, and the other congregated SiC particles and most of alumina oxide are segregated to the inner circumference of the cylinder. The SiC particles in aluminum melt can promote the refinement of primary α(Al) during solidification, and fine primary α(Al) grains can also promote the uniform distribution of SiC particles. Brinell hardness of SiC_p/Zl104 composites is connected with not only the volume fraction of SiC particles, but also the distribution of SiC particles in matrix alloy.     

T6热处理对Al+SiC预制颗粒增强ZL101/ZL101-Mg基复合材料组织和力学性能影响的研究

通过半固态搅拌铸造的方法制备了Al+SiC预制颗粒增强ZL101基及ZL101-Mg基复合材料,研究了T6热处理对该复合材料微观组织及力学性能的影响。结果表明,T6热处理对Al+SiC预制颗粒增强ZL101基复合材料和Al+SiC预制颗粒增强ZL101+Mg基复合材料中SiC颗粒的分布没有明显影响。但T6热处理使Al+SiC预制颗粒增强ZL101复合材料中共晶硅细化,Al+SiC预制颗粒增强ZL101+Mg复合材料中共晶硅长大变粗。T6热处理对Al+SiC预制颗粒增强ZL101复合材料抗拉强度的平均提升率达到了54.44%,对其伸长率的平均提升率为5.47%。对Al+SiC预制颗粒增强ZL101+Mg复合材料抗拉强度的平均提升率为13.52%,对其伸长率的平均提升率为31.5%。     

Centrifugal casting processes of manufacturing <Emphasis Type="Italic">in situ</Emphasis> functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg₂Si particles and a portion of primary silicon particles in the inner layer, a little Mg₂Si and primary silicon particles in the outer layer, and without any Mg₂Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg₂Si and primary silicon particles is.     

电冶熔铸SiC增强钢基复合材料的组织与性能

用电冶熔铸的方法制备4%SiC颗粒增强轴承钢复合材料,对其组织性能进行探索.实验结果发现:SiC颗粒在电冶熔铸工艺中发生分解,原始颗粒没有保留下来,溶入钢基体的Si和C原子在快速冷却下会发生原位反应重新生成细小的原位SiC;磨损试验发现,原位SiC的存在使基体硬度上升,复合材料的整体耐磨性比基体材料相比有明显改善,磨损机理以粘着磨损和磨粒磨损为主.     

离心铸造法制备Al3Ti/Al原位自生功能梯度复合材料

采用离心铸造法，用TiO2粉末与纯铝熔液原位反应生成Al3Ti颗粒增强相，获得了组织和性能在径向上呈梯度分布的Al3Ti/Al功能梯度复合材料。考察了材料的显微组织和硬度，Al3Ti颗粒和材料硬度在径向上由外向内呈梯度分布。研究分析了离心和转速、TiO2加入量和激冷强度对复合材料组织和硬度的分布梯度的影响。结果表明，这些因素对复合材料组织和性能分布梯度的影响较大。     

Fabrication of SiC particle dispersed spheroidal graphite cast iron composite by vacuum assisted casting and its microstructure

Abstract

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2˙5 mass%, the phase consisting of mainly Fe₃Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.     

Effect of Heat Treatment on the Properties of AlCu26Si8

ABSTRACT

In this paper, in situ centrifugal casting was proposed to fabricate Al-26 wt.% Cu-7.8 wt.% Si FG pipe with the density of 3.5 g/cm³ and also the wear resistance of 0.0241g/mm². The casting mould is preheated to approximately 200°C to avoid chilling effects, segregation, porosity and compensation of the shrinkage of the alloy during the casting. The microstructure results show that the Al₂Cu content smoothly decreases from the outer layer to inner layer. Vickers hardness, coefficient of thermal expansion (CTE) and mechanical properties of the present FG pipe are measured to show the significant dependence of the microstructure. Furthermore, the heat treatment of the samples are conducted in boiling water (100°C) for 4.5 h to promote the formations of new Al₂Cu particles into the α–Al phase and consequently improve the hardness and CTE of the FG pipe.     

Centrifugal casting of in-situ Al-Mg2Si(1-x)Snx composites: a study of radial segregation

During centrifugal casting of Al-Mg₂Si hypereutectic cylinders, the light Mg₂Si particles are commonly segregated in centripetal direction towards the inner periphery. In order to change this inevitable centripetal segregation of Mg₂Si particles, some amounts of tin up to 8 wt pct were added to Al-15wt.% Mg₂Si alloy to enhance the formation of Mg₂Si_(1?x)Sn_x particles with variant stoichiometry thus variant density. XRD, EDS, optical metallography and hardness measurements were used to evaluate the stoichiometry and segregation patterns of in situ formed Mg₂Si_(1?x)Sn_x particles. According to the results, the cylinder containing 6 wt pct Sn illustrates a rather uniform distribution of particles thus hardness in all radial sections. However, the cylinders with higher amounts of Sn exhibit a radial segregation of Mg₂Si_(1?x)Sn_x particles in centrifugal direction towards the outer periphery. The results are interpreted in view of the Stokes’ law and the difference in density of the particles and the melt.     

Studies on eutectic Al–Si alloy–flyash composites

Abstract

In this investigation, an attempt was made to study the influence of melt treatments like grain refinement and modification on the mechanical properties of cenospheres of flyash–LM6 composites. Stir casting route was employed to disperse the flyash (1–15?wt‐%) in the LM6 alloy matrix. For each percentage of flyash, melts were subjected to grain refinement, modification or combined grain refinement and modification. The results reveal that castings subjected to melt treatments showed increased hardness, ultimate tensile strength and elongation compared with untreated Al–Si base alloy up to 10% flyash. Addition of flyash beyond 10% resulted in decreases in hardness and ultimate tensile strength. Percentage elongation showed a decreasing trend for all the cases studied. Nevertheless, in all the cases studied, mechanical properties were higher than that of the Al–Si base alloy. Among all the composites, the best results were obtained with 10% flyash subjected to modification alone.     

Fatigue properties of Al–Si casting alloy with cold sprayed Al/SiC coating

Abstract

The fatigue properties of Al–Si alloy cold sprayed Al and Al–SiC composite coatings have been studied. The specimens coated with composites reinforced with a large volume (25%) of fine SiC particles exhibited improved adhesion strength at the interface due to crater formation, and cyclic fatigue lives at room temperature more than three times those of uncoated specimens. In high temperature low cycle fatigue tests at 250°C, the pure Al coatings showed longer fatigue lives than the Al–SiC composite coatings, which is attributed to an increment in ductility at the surface retarding fatigue crack initiation.     

Investigation of the microstructure and properties of Al–Si–Mg/SiC composite materials produced by solidification under pressure

Composite materials based on alloys of the Al–Si–Mg system have been obtained via the introduction of 5, 10, and 15 wt % of SiC particles into the alloy melt and the solidification under a pressure. As a result of solidification under pressure, the porosity of the composite materials decreased substantially. An increase in the content of SiC particles in the composites enabled a smaller size of dendritic cells to be obtained. It has been shown by the X-ray diffraction method that, in the process of solidification under pressure, an interaction occurred between the matrix and reinforcing SiC particles. The presence of SiC particles in the structure of composites led to the acceleration of the aging process and to an increase in the peak hardness in comparison with the matrix alloy.     

Effect of fabrication method on the aging behavior of 6061 Al matrix composites reinforced with SiC whiskers

Age hardening behaviors of SiC whisker reinforced composites with 6061 Al matrix fabricated by P.M. (powder metallurgy) and squeeze casting were investigated to examine the effect of the fabrication method on the aging kinetics. In the squeeze cast composite, numorous triangular particles which is believed to be MgAlp₂O₄ were observed at Al/SiC interfaces whereas no visible interface particles were observed in the P. M. composite. P.M. composite showed faster age hardening and reached the maximum hardness earler than the squeeze cast composites. The decrease of the aging kinetics in squeeze cast 6061 Al matrix composites compared to that in P.M. composites is thought to result from more severe depletion of Mg atoms due to interfacial reactions in squeeze cast composites. The uniformity of whisker distribution is suggested to influence the general aging behavior through its effect on the local dislocation density. Data on the aging kinetics and the interfacial reactions in other Al alloys were also examined to study various factors which can influence the aging kinetics.     

Fabrication and Characterization of Functionally Graded Al/SiCp Composites Produced by Remelting and Sedimentation Process

A new process termed here as remelting and sedimentation (RAS) was developed to produce functionally graded Al/SiC composites with a smooth concentration gradient of SiC particles along the height of samples, as opposed to a step change. For this purpose, first settling velocities of different-sized SiC particles in aluminum A356 melt were measured, and the results exhibited a reasonably good agreement with those predicted via the modified Stokes law. Then slices of particulate Al/SiC composites with different SiC contents of 5, 10, 15, and 20 vol.% were stacked in a cast iron mold and heated at 650 °C resulting in remelting and unification of the different composite parts. Considering the preliminary settling experiments, the composite slurry was held at this temperature for three different times to investigate the optimum holding time for obtaining a smooth gradient of SiC concentration along the height of the sample. After quenching, the samples were sectioned and subjected to metallographic studies and hardness measurements. The results confirmed that holding the melt for 60 s provides sufficient settling and redistribution of SiC particles and results in successful production of a functionally graded material.     

搅拌铸造SiC_p/A356复合材料的显微组织及力学性能

采用搅拌铸造技术制备质量分数为15%的SiCp增强A356铝基复合材料,并对所制备的复合材料进行后续热挤压变形。通过金相观察(OM),扫描电镜(SEM)及力学性能测试等手段,对该复合材料显微组织与力学性能进行了研究。结果表明,所制备的复合材料铸态组织中,SiCp较均匀地分布于基体中,SiCp与Al界面处存在Si原子的富集;热挤压变形后,显微气孔等铸造缺陷明显减少,材料致密度显著提高,SiCp沿热挤压方向呈流线分布特征,颗粒均匀分散性明显提高;采用535℃×5h固溶+180℃×5h时效处理后,热挤压棒材的力学性能为:σs=370MPa,σb=225MPa,δ=5.3%,时效后析出强化相大小约为200nm,且弥散分布于基体中;断口分析表明,SiCp/A356铝基复合材料的断裂主要是由基体的塑性断裂及SiCp的断裂导致的。     

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al(Si)/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al(Si)/diamond composites.     

Dispersion of ultrafine SiC particles in molten Al-12Si alloy

The bulk Al-12 Si eutectic composites were fabricated through a conventional liquid metal casting route, especially with the help of ultrafine ceramic powders made by self-propagating high-temperature synthesis (SHS) process. The SHS powders were fabricated by the chemical reaction between micro-sized SiC and Al particles at very high combustion temperatures, producing the coarse Al particles (several tens of microns) containing ultrafine SiC ceramic particles. Microstructural observation revealed that the addition of ultrafine SiC particles has a crumbling tendency of Si eutectic phase. It is suggested that the casting method combined with SHS process is promising for fabricating the Al-based MMC with ultrafine ceramic particles.