Microstructure evolution,mechanical properties and fracture behavior of Al-xSi/AZ91D bimetallic composites prepared by a compound casting

In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically.The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer(MRL),whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites,while the hypereutectic Al-Si/AZ91D composites were opposite.The MRL included eutectic layer(E layer),intermetallic compound layer(IMC layer)and transition region layer(T layer).In the IMC layer,the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg_(2)Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites.Besides,increasing Si content,the thickness proportion of the T layer increased,forming an inconsistent preferred orientation of the MRL.The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content,and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa,which was 73.4% higher than the Al-6Si/AZ91D composite.The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content.The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg_(2)Si particle reinforcement,the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.

Oxidation mechanism of high-volume fraction SiCp/Al composite under laser irradiation and subsequent machining

Conventional mechanical machining of a composite material comprising an aluminum matrix reinforced with a high volume fraction of SiC particles(hereinafter referred to as an SiCp/Al composite)faces problems such as rapid tool wear,high specific cutting force,and poor surface integrity.Instead,a promising method for solving these problems is laser-induced oxidation-assisted milling(LOAM):under laser irradiation,the local workpiece material reacts with oxygen,thus forming loose and porous oxides that are easily removed.In the present work,the oxidation mechanism of SiCp/Al irradiated by a nanosecond pulsed laser is studied to better understand the laser-induced oxidation behavior and control the characteristics of the oxides,with laser irradiation experiments performed on a 65%SiCp/Al composite with various laser parameters and auxiliary gases(oxygen,nitrogen,and argon).With increasing laser pulse energy density,both the ablated groove depth and the width of the heat-affected zone increase.When oxygen is used as the auxiliary gas,an oxide layer composed of SiO_(2)and Al2O3 forms,and CO_(2)is produced and escapes from the material,thereby forming pores in the oxides.However,when nitrogen or argon is used as the auxiliary gas,a recast layer is produced that is relatively difficult to remove.Under laser irradiation,the sputtered material reacts with oxygen to form oxides on both sides of the ablated groove,and as the laser scanning path advances,the produced oxides accumulate to form an oxide layer.LOAM and conventional milling are compared using the same milling parameters,and LOAM is found to be better for reduced milling force and tool wear and improved machined surface quality.

Effect of mixed rare earth oxides and CaCO_3 modification on the microstructure of an in-situ Mg_2Si/Al-Si composite

The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...

Formation and capacitance properties of Ti-Al composite oxide film on aluminum

Al specimens were covered with TiO2 film by sol-gel dip-coating and then anodized in ammonium adipate solution.The structure,composition and capacitance properties of the anodic oxide film were investigated by transmission electron microscopy (TEM),Auger electron spectroscopy (AES),X-ray diffractometry (XRD) and electrochemical impedance spectroscopy (EIS).It was found that an anodic oxide film with a dual-layer structure formed between TiO2 coating and Al substrate.The film consisted of an inner Al2O3 layer and an outer Ti-Al composite oxide layer.The thickness of layers varied with the number of times of sol-gel dip-coating.The capacitance of anodic oxide films formed on coated specimens was at most 80% higher than that without TiO2.In film formation mechanism,it was claimed that the formation of composite oxide film was mainly affected by the structure of micro-pores network in TiO2 coating which had an influence on Al3+ and O2? ions transport during the anodizing.

Morphology and Frictional Characteristics Under Electrical Currents of Al_2O_3/Cu Composites Prepared by Internal Oxidation

Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.

Microstructures,mechanical and oxidation behaviors of C/C composites modified by NiAl alloy

Carbon/carbon composites modified by NiAl alloy were prepared using vacuum reactive melt infiltration methods with NiAl and titanium mixed powders as raw materials. The microstructures were investigated by scanning electron microscopy. The fracture behavior, infiltration and oxidation mechanism were further discussed. The results indicated that NiAl alloy exhibited good wettability on the C/C preform because a TiC reaction layer formed at the interface. Multi-layer（PyC/TiC/NiAl＋TiC） coating evenly and compactly distributed on the surface of the carbon fiber in tubular form. The penetration depth of molten NiAl alloys depended on the reaction between the PyC and titanium. The impact fracture was inclined to along the interface between the NiAl permeability layer and C/C matrix. Al_2TiO_5 and TiO_2 formed on the surface, while the interior multi-layer tubular structure partially remained after oxidation at 1773 K for 30 min.

Synthesis, Characterization of Mesoporous Al-Mg Composite Oxide and Catalytic Performance for Oxyethylation of Fatty Alcohol

A mesoporous Al-Mg composite oxide with a hexagonal structure was synthesized with aluminium nitrate and magnesium nitrate as the reagents and sodium dodecyl sulfate（SDS） as the template in the presence of ethylenediamine. The XRD, nitrogen adsorption-desorption and TEM studies indicate that the composite has a hexagonal framework structure and an average pore diameter of 2. 6 nm. The TG/DTA spectra indicate that the decomposition and the removal of the occluded surfactant of the sample take place in a range of 230-550 ℃. The mesoporous Al-Mg composite oxide exhibites a highly catalytic activity for the oxyethylation of fatty alcohols. Narrow-range distributed ethoxylates are formed in the presence of the mesoporous Al-Mg composite oxide catalyst. The distribution selectivity coefficient（Cx） is 24 when the mesoporous Al-Mg composite oxide was used as a catalyst for the oxyethylation of octanol and the average adduct degree of ethoxylates is 6. 4.

Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

Synthesis and Faraday Effect of Fe-Al Oxide Composite Ferrofluid

A kind of ferrofluid containing Fe-Al oxide composite nanometer particles was synthesized. The ferrofluid made of Fe-Al oxide composite nanometer particles which ratio was Fe:Al2O3 = 3:1 and thermally treated at 300°C showed Faraday effect approximate linearity versus the magnetic field B, and a relatively excellent Faraday effect without saturation in varying 0 - 1.5T magnetic field, which provided a method for synthesizing the ferrofluid of Faraday rotation still continuing in a relatively high magnetic field.

Y/Al-5Ti-1B复合变质对Al-7Si合金微观组织和力学性能的影响

在传统铸造Al-Si合金中存在的粗大树枝晶α-Al相以及针状共晶Si严重割裂基体,显著降低合金的力学性能。为细化Al-Si合金的组织,提升其力学性能,本文使用扫描电镜(SEM)、电子探针(EPMA)、X射线衍射仪(XRD)以及万能材料试验机,研究了不同添加量Y/Al-5Ti-1B变质剂(Al-5Ti-1B均为2%,稀土Y分别为0.05%、0.1%、0.2%、0.3%、0.4%、0.5%,质量分数)对Al-7Si合金微观组织和力学性能的影响,并探究了其对Al-7Si合金的变质机理。实验结果表明,当Al-5Ti-1B含量为2%、稀土Y含量为0.4%时,变质效果最佳,共晶Si由粗大针状变为细小颗粒状,长和宽分别减小至2.7和0.8μm,相较于未经变质处理的Al-7Si合金,减小了90.6%和4.7%。合金抗拉强度由原来的168.1 MPa提升至209.1 MPa,增加了24.4%。同时伸长率从6.23%提升至9.62%,增长了54.4%。此外,合金的断裂方式也从脆性断裂转变为韧-脆混合断裂。

Preparation and corrosion resistance of the micro-arc oxidation coating on Al_2O_3f/ZL109 composites

A ceramic layer was prepared on the surface of Al2O3f/ZL109 composites by means of micro-arc oxidation （MAO） technique. The surface morphology and phase constituent of the ceramic layer were analyzed using scanning electron microscope and X-ray diffraction. The polarization curves of the composites before and after MAO treatment were measured and analyzed. The results showed that after Al2O3f/ZL109 composites were treated using MAO technique in silicate solution, the ceramic layer formed, and it was composed of Al, Si, and mullite phase. Al and Si came from Al alloy matrix of the composites, and the mullite phase formed in process of MAO. Al2O3 fiber in the composites affects the electric conductivity of the composites, the MAO reaction is promoted, and the cera- mic layer forming on the composite material side is slightly thicker than that on the Al alloy side. After Al2O3f/ZL109 composites were treated using MAO technique, the corro- sion resistance of the composites is significantly improved.

Kinetics of Oxidation for β-Sialon in Diphase β-Sialon/Al_2O_3 Composite

Non-isothermal kinetic research has been carried out on oxidation behavior of β-Sialon in diphaseβ-Sialon/Al_2O_3 composite at high temperatures. A kinetic formula is established for non-isothermal oxidation process of β-Sialon. The rate of oxidation process is controlled by chemicalreaction at the initial stage and then by diffusion. The apparent activation energies and appar-ent rate constants at different temperatures are determined by treating TG data of the overallprocess.

Fabrication of Ceramic Composites by Directed Metal Oxidation

To explain the growth mechanism of Al 2O 3/Al Lanxide composites,the dynamics of the directed oxidation of Al-Mg-Si alloys are analyzed.The experimental methods to produce Lanxide composites by directed oxidation of metal melts at high temperatures are presented.The effect of the processing factors on the microstructures and properties of Al 2O 3/Al composites and enforced Al 2O 3/Al composites is also analyzed.Compared with sintering ceramic composites,the advantages of Lanxide process and Lanxide materials are as following:it is a near net shaped process;the process is very simple;the microstructures and properties of Lanxide materials can be adjusted;and this process can be used to infiltrate ceramic fiber or particle preforms.

Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

Oxidation Performance of Fe-Al/WC Composite Coatings Produced by High Velocity Arc Sprayed at 650 ℃

The Fe-Al/WC intermetallic composite coatings have been prepared by high velocity arc spraying(HVAS) technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings has been studied by means of thermogrativmetic analyzer. The results demonstrate that the kinetics curve of oxidation approximately follows the logarithmic law. The composition of the oxidized coating surface mainly is composed of A12O3, Fe2O3, Fe3O4 and FeO which distribute unevenly. The protective A12O3 film firstly forms and preserves the coatings from further oxidation.

选区激光熔化成形TiB_(2)/Al-Si-Mg大尺寸复杂构件

选区激光熔化(SLM)成形大尺寸复杂构件厚度多样、成形高度较高、方向复杂,需要研究构件微观组织均匀性和力学性能稳定性。本文以SLM成形TiB_(2)/Al-Si-Mg复合材料为研究对象,分析复合材料多级微观组织,对比不同成形厚度、高度、方向下复合材料的力学性能。结果表明:复合材料表现出熔池特征结构,细小等轴晶粒组织均匀分布且随机取向,纳米TiB_(2)颗粒在材料内部弥散分布。随成形厚度增加,复合材料伸长率保持稳定,抗拉强度受本征热处理影响略微增大;在不同成形高度下,复合材料抗拉强度和伸长率保持稳定;在不同成形方向下,复合材料抗拉强度保持稳定,伸长率受熔池结构影响在水平方向略高。基于以上结果,成功制备大飞机舱门铰链臂(588 mm×318 mm×470 mm)复杂结构件。

Microstructure and properties of Al/Si/SiC composites for electronic packaging

The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.

EVOLUTION OF MICROSTRUCTURE IN OXIDATIVE GROWTH OF Al_2O_3／Al ALLOY COMPOSITES

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Preparation of SiC_p/Al_2O_3-Al Composites by Directed Metal Oxidation

SiCp/Al2O3-Al composites were synthesized by means of direct metal oxidation method. The composition and microstructures of the composites were investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） and metallurgical microscope. The effects of technical parameters on the properties of the product were analyzed. The results indicate that the composite possesses a dense microstructure, composed of three interpenetrated phases. Of them, SiO2 layer prohibits the powdering of the composites; Mg promotes the wetting and infiltration of the system and Si restricts the interfacial reaction while improving the wetting ability between reinforcement and matrix.

SiCp/Al-Si基复合材料界面结构调控及强化机制的研究进展

SiCp/Al-Si基复合材料具有高的比强度、比刚度、比模量,良好的导热、导电、耐磨性及尺寸稳定性等优点,作为结构功能性材料应用于空间工程、电子封装、交通运输和精密仪器等领域。其研究热点主要集中在界面结构调控、强化机制及性能调控等方面。在SiCp/Al-Si复合材料中存在着增强体与基体界面、析出相与基体界面、析出相与增强体界面,这些界面受各种因素影响,会出现多种界面反应和界面产物,界面结构和结合状态复杂而多样。基于此,本文综述了制备工艺、基体合金成分和SiCp表面改性等方面对SiCp/Al-Si基复合材料界面结构的影响及调控,并总结了影响其力学性能的因素及强化机制的研究现状,最后对复合材料未来的发展及研究方向进行了展望。