磁化学熔体反应法合成TiB2/7055复合材料的组织和性能

通过磁化学熔体反应法在7055(Al?3%B)?Ti反应体系中成功制备TiB2/7055复合材料。利用XRD、OM和SEM等分析检测技术研究复合材料的相组成和微观组织。结果表明,脉冲磁场作用下生成的TiB2颗粒呈多边状或近球形,尺寸小于1μm,均匀分布于基体中。与未施加脉冲磁场的复合材料相比,施加磁场后α(Al)晶粒平均尺寸从20μm减小到约10μm,第二相从连续的网格状分布变为非连续性分布。在磁场作用下,复合材料的抗拉强度从310 MPa提高到333 MPa,伸长率从7.5%提高到8.0%。此外,与基体相比,在载荷为100 N,磨损时间为120 min时,复合材料的磨损量从111 mg降低到78 mg。     

Microstructure and mechanical properties of extruded Al/Al2O3 composites fabricated by stir-casting process

A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites (AMCs) reinforced with Al₂O₃ particles. Different mass fractions of micro alumina particles were injected into the melt under stirring speed of 300 r/min. Then the samples were extruded with ratios of 1.77 or 1.56. The microstructure observation showed that application of the injection and extrusion processes led to a uniform distribution of particles in the matrix. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al₂O₃ and stirring speed and decreased by extrusion process. Hardness, yield and ultimate tensile strengths of the extruded composites increased with increasing the particle mass fraction to 7%, while for the composites without extrusion they increased with particle mass fraction to 5%.     

Feasible process for producing in situ Al/TiC composites by combustion reaction in an Al melt

In situ Al/TiC composites with a homogeneous distribution of TiC reinforcements were prepared by adding a reactant mixture of Al-Ti-C to an Al melt. A certain amount of CuO addition facilitates a combustion reaction of the Al-Ti-C system and thereby enables the formation of in situ TiC at a reasonably low temperature range of 750–920 °C. Synthesised TiC particles with sizes of 1–2 μm are present in the Al matrix along with Al₃Ti. Besides the CuO addition, the melt temperature plays a significant role in the final microstructure of the composites. Increase in the melt temperature up to 920 °C with CuO provides more external heat input and initiates the combustion reaction within a few seconds. Pellet microstructure evidently shows that the polygonal Al₃Ti originates from the unreacted layer of which the distance is significantly shortens by increasing the melt temperature. The suppression of the Al₃Ti formation is the most likely to occur at 920 °C, with producing a large volume fraction of TiC in situ synthesised.     

In situ (Mg2Si+MgO)/Mg composites fabricated from AZ91-Al2(SiO3)3 with assistance of high-energy ultrasonic field

In situ(Mg2Si+MgO)/Mg composites fabricated from AZ91-Al2(SiO3)3 under high-energy ultrasonic field were investigated by XRD,DSC and SEM.The results indicate that the size,morphology and distribution of the in situ Mg2Si particles are greatly optimized with the assistance of the high-energy ultrasonic field.The amounts of the in situ Mg2Si particles are increased,the sizes are refined,the distributions become uniform,and the morphologies are changed to smooth olive-shape or spherical shape.The amounts of brittle β-Mg17Al12 phases are decreased and the morphologies are granulated.The values of the tensile strength σb and HB hardness are increased.These are due to the cavitation effects and acoustic streaming effects induced by the high-energy ultrasonic field.     

Microstructure, billet surface quality and tensile property of (Al2O3 + Al3Zr)p/Al composites in situ synthesized with electromagnetic field

The aluminum matrix composites reinforced by Al₂O₃ and Al₃Zr particulates were fabricated via in situ chemical reaction between Al-15 wt.% Zr(CO₃)₂ systems. In the process of in situ reaction, a low frequency electromagnetic field (EMF) is employed to improve the conditions of reaction between reactants powder and melt. The optimized electromagnetic density of low frequency EMF is 0.025 T. During the direct chill casting process of composites melt, the custom-designed electromagnetic fields are introduced to control the microstructures and improve the billet surface quality. XRD analysis shows that Al₂O₃ and Al₃Zr reinforcement phases have been obtained. The Lorenz force improves the kinetic condition and accelerates the nucleation of endogenetic particulates. Microstructure analysis by SEM indicates that the average size of particulates and grain size of matrix are refined to 0.5-1 μm and 20-40 μm, respectively. The surface quality of round billet is greatly improved by the high frequency EMF. The results of tensile properties test show that the tensile strength of composites in situ fabricated with EMF is 254.6 MPa, which is increased by about 104 MPa and 69.4% compared with those of composites in situ fabricated without EMF.     

Preparation and characterization of Mo/Al2O3 composites

In order to improve the performance of molybdenum, the Mo/Al₂O₃ composites were prepared by using a hydrothermal method for the synthesis of the precursor powders and subsequent powder metallurgical processing. The morphologies of the composite powders and the microstructures and properties of the composites were investigated. Compared with the pure Mo powder, the grains of composite powders are smaller because of the existence of the fine Al₂O₃ particles. The results from the sintered composites show that the fine Al₂O₃ particles are evenly distributed in the Mo matrix and well bonded with the Mo matrix. With increasing Al₂O₃ content, all the values of the micro-hardness, compressive strength and flow stress at 0.08 strain are increased. The strengthening effect is more remarkable at elevated temperatures. At room temperature, the compressive strength and the flow stress at 0.08 strain of the composite with 40 vol.% Al₂O₃ are 1.67 and 2.01 times greater than those of pure molybdenum, respectively, while the values are up to 2.02 and 2.52 at 1100 °C.     

Production of High-Strength Al/Al2O3/WC Composite by Accumulative Roll Bonding

In this study, Al/Al₂O₃/WC composites were fabricated via the accumulative roll bonding (ARB) process. Furthermore, the microstructure evolution, mechanical properties, and deformation texture of the composite samples were reported. The results illustrated that when the number of cycles was increased, the distribution of particles in the aluminum matrix improved, and the particles became finer. The microstructure of the fabricated composites after eight cycles of the ARB process showed an excellent distribution of reinforcement particles in the aluminum matrix. Elongated ultrafine grains were formed in the ARB-processed specimens of the Al/Al₂O₃/WC composite. It was observed that as the strain increased with the number of cycles, the tensile strength, microhardness, and elongation of produced composites increased as well. The results indicated that after ARB process, the overall texture intensity increases and a different-strong texture develops. The main textural component is the Rotated Cube component.     

Characteristic evaluation of Al2O3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide (Al₂O₃)/carbon nanotubes (CNTs) hybrid composites for micro-electrical discharge machining (EDM) was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. Al₂O₃ composites with different CNT concentrations were synthesized. The electrical characteristic of Al₂O₃/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope (FESEM). The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% Al₂O₃ (volume fraction). In the machining accuracy, many tangles of CNT in Al₂O₃/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of Al₂O₃/CNTs hybrid composites.     

搅拌摩擦加工原位反应制备Al_3Ti-Al表面复合层

通过在铝合金1100-H14表面加工矩形凹槽并添加微米级钛粉再进行搅拌摩擦加工(friction stir processing,FSP)的方法,在铝合金表面获得Al3Ti-Al复合层.采用扫描电镜(SEM),能谱分析(EDS)以及X射线衍射(XRD)对表面复合层微观结构及相组成进行了分析,并对复合层的显微硬度进行了检测.结果表明,在FSP强烈的热、力耦合作用下,钛粉产生了碎化,破碎后的钛颗粒与铝产生快速原位反应,生成微米和亚微米级Al3Ti颗粒,残留的钛颗粒和细小的Al3Ti颗粒一同均匀地分布于铝合金基体中,从而使得铝合金表面的硬度得到提高,其平均值达到了71.39HV,为基体硬度的2.1倍.     

Formation and microstructure of an in situ aluminum composite by oxygen spray technique

In situ particulate-reinforced Al and Al-Mg matrix composites were successfully fabricated by an oxygen spray technique. The results indicate that Al₂O₃ and MgAl₂O₄ particles directly nucleate and grow via gas-liquid oxidation reaction. The Al₂O₃ particles with the size of 0.1 to 0.5 μm are formed into the Al melt, according to an appropriate system and processing parameters. The reinforcements show a good wettability with the matrix. The hot-rolling process results in an improvement of the uniformity of the particle distribution in the matrix and an increase in the hardness of the composites.     

In situ formation of various intermetallic particles in Al–Ti–X(Cu,Mg) systems during friction stir processing

In situ Al composites reinforced by various intermetallic particles were fabricated from Al–Ti–X(Cu, Mg) systems by hot pressing, forging and subsequent 4-pass friction stir processing (FSP). The formation of various intermetallic particles during FSP and the tensile properties of in situ composites were investigated. For Al–Ti–Cu system, Cu enhanced the Al–Ti reaction and resulted in the formation of more Al₃Ti particles due to the presence of a small amount of liquid phase during FSP. After FSP, part of Cu was kept in the Al matrix as solute, whereas the other formed Al₂Cu particles. For Al–Ti–Mg system, except for Al₃Ti, some Ti₂Mg₃Al₁₈ particles with fine twin lamellas were formed during FSP, resulting in an increase in the total volume fraction of reinforcing particles. Cu and Mg addition increased the strength of the in situ composites substantially due to introduction of more strengthening modes and more reinforcing particles, however the elongation decreased dramatically.     

Microstructure and properties of Al<Subscript>3</Subscript>Zr/2024Al in situ composites after forging

To research the influencing rule of severe plastic deformation on Al matrix in situ composites, 10 wt% Al₃Zr/2024Al in situ particle-reinforced composite was prepared by direct melt reaction (DMR), and then, the composite was hot-forged by one direction with 90 % plastic deformation. Then, the microstructure of the forging state composite was observed, and the change law of mechanical properties and friction performances after and before plastic deforming was compared. The results indicate that the Al₃Zr-reinforced particle rotates and breaks into smaller size of 10–20 µm with the matrix flow; in addition, these smaller particles distribute more orderly in orientation and dispersedly. The 2024 matrix grain changes from as-cast tissue to fibrous tissue with length of 100 µm along the forging direction. Some mechanical properties of composites hot-forged by one direction with 90 % plastic deformation are improved much obviously. For example, the tensile strength is improved by 39.75 %, reaching 225 MPa, and the hardness is improved by 35.84 %, reaching HBW 76.83. Besides, the wear rate reduces, wear depth and area decline, and the wear-resisting property is improved after hot forging.     

Influence of addition of Grp/Al2O3p with SiCp on wear properties of aluminum alloy 6061-T6 hybrid composites via friction stir processing

Aluminum alloy base surface hybrid composites were fabricated by incorporating with mixture of (SiC+Gr) and (SiC+Al₂O₃) particles of 20 μm in average size on an aluminum alloy 6061-T6 plate using friction stir processing (FSP). Microstructures of both the surface hybrid composites revealed that SiC, Gr and Al₂O₃are uniformly dispersed in the nugget zone (NZ). It was observed that the addition of Gr particles rather than Al₂O₃ particles with SiC particles, decreases the microhardness but immensely increases the dry sliding wear resistance of aluminum alloy 6061-T6 surface hybrid composite. The observed microhardness and wear properties are correlated with microstructures and worn micrographs.     

Wear properties of rheo-squeeze cast aluminum matrix reinforced with nano particulates

There are many approaches to fabricate nanoparticles reinforced aluminum matrix composites. However, uniform distribution of nanoparticle within aluminum matrix remains a difficult challenge. In this study, a novel method is used by taking the advantages from squeeze casting of semi-solid aluminum slurry combined with electromagnetic field to refine the microstructure of the primary Al and eutectic Si phase, plus to obtain uniform distribution nano alumina particles in the aluminum matrix. It is noted that electromagnetic field plays an important role in the formation of non-dendritic primary α-Al particles and a great microstructure refinement occurs as a consequence of the pressure application. It can be seen that the increase in electromagnetic field causes smaller and rounder primary α-Al particles. A comparative study on abrasive wear behavior of nano Al₂O₃ reinforced aluminum metal matrix composite has been carried out in the present investigation. The mass loss of the pin was used to study the effect of Al₂O₃ addition on the wear resistance of the composite materials.     

Examination of wire electrical discharge machining of Al2O3p/6061Al composites

Alumina particle reinforced 6061 aluminum matrix composites (Al₂O₃p/6061Al) have excellent physical and chemical properties than those of a traditional metal; however, their poor machinability lead to worse surface quality and serious cutting tool wear. In this study, wire electrical discharge machining (WEDM) is adopted in machining Al₂O₃p/6061Al composite. In the experiments, machining parameters of pulse-on time were changed to explore their effects on machining performance, including the cutting speed, the width of slit and surface roughness. Moreover, the wire electrode is easily broken during the machining Al₂O₃p/6061Al composite, so this work comprehensively investigates into the locations of the broken wire and the reason of wire breaking.The experimental results indicate that the cutting speed (material removal rate), the surface roughness and the width of the slit of cutting test material significantly depend on volume fraction of reinforcement (Al₂O₃ particles). Furthermore, bands on the machined surface for cutting 20 vol.% Al₂O₃p/6061Al composite are easily formed, basically due to some embedded reinforcing Al₂O₃ particles on the surface of 6061 aluminum matrix, interrupt the machining process. Test results reveal that in machining Al₂O₃p/6061Al composites a very low wire tension, a high flushing rate and a high wire speed are required to prevent wire breakage; an appropriate servo voltage, a short pulse-on time, and a short pulse-off time, which are normally associated with a high cutting speed, have little effect on the surface roughness.     

Strengthening mechanisms in aluminum containing coherent Al3Sc precipitates and incoherent Al2O3 dispersoids

Dispersion-strengthened-cast aluminum (DSC-Al), consisting of a coarse-grained aluminum matrix containing two populations of particles (30 vol.% of 300 nm Al₂O₃ incoherent dispersoids and 0.2–0.3 vol.% of 6–60 nm coherent Al₃Sc precipitates), was studied. At ambient and elevated temperatures, both populations of particles contribute to strengthening. At 300 °C, creep threshold stresses are considerably higher than for control materials with a single population of either Al₂O₃ dispersoids or Al₃Sc precipitates. This synergistic effect is modeled by considering dislocations pinned at the departure side of incoherent Al₂O₃ dispersoids (detachment model) and simultaneously subjected to elastic interactions from neighboring coherent Al₃Sc precipitates.     

Preparation and formation mechanism of Al2O3 nanoparticles by reverse microemulsion

Al2O3 nanoparticles were prepared by polyethylene glycol octylphenyl ether（Triton X-100）/n-butyl alcohol/cyclohexane/ water W/O reverse microemulsion. The proper calcination temperature was determined at 1 150 ℃ by thermal analysis of the precursor products. The structures and morphologies of Al2O3 nanoparticles were characterized by X-ray diffraction, transmission electron microscopy and UV-Vis spectra. The influences of mole ratio of water to surfactant on the morphologies and the sizes of the Al2O3 nanoparticles were studied. With the increase of surfactant content, the particles size becomes larger. The agglomeration of nanoparticles was solved successfully. And the formation mechanisms of Al2O3 nanoparticles in the reverse microemulsion were also discussed.     

Microstructure and mechanical properties of 7075 Al alloy based composites with Al2O3 nanoparticles

A new method was used to fabricate 7075 Al alloy based composites with Al₂O₃ nanoparticles to improve the distribution of particles. In this study, nano-sized particles were fed into the molten alloy through the flow of argon gas, then the Al₂O₃/7075 composites were prepared by solid-liquid mixed casting. The results indicated that the composite samples showed fine microstructure and achieved a homogeneous distribution of particles. Also, it was found that relative to the as-cast 7075 alloy, the Al₂O₃/7075 composites exhibited higher mechanical properties, which is due to the effect of uniform distributed Al₂O₃ nanoparticles reinforcement.     

Microstructures and mechanical properties of BP/7A04 Al matrix composites

The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compared with those of BP/7A04 Al matrix composites. The results show that the basalt particles are dispersed in the Al matrix and form a strong bonding interface with the Al matrix. SiO₂ at the edge of the basalt particles is continuously replaced by Al₂O₃ formed in the reaction, forming a high-temperature reaction layer with a thickness of several tens of nanometers, and Al₂O₃ strengthens the bonding interface between basalt particles and Al matrix. The dispersed basalt particles promote the dislocation multiplication, vacancy formation and precipitation of the matrix, and the precipitated phases mainly consist of plate-like η (MgZn₂) phase and bright white band-shaped or ellipsoidal T (Al₂Mg₃Zn₃) phase. The bonding interface, high dislocation density and dispersion strengthening phase significantly improve the mechanical properties of the composites. The yield strength and ultimate tensile strength of BP/7A04 Al matrix composites are up to 665 and 699 MPa, which increase by 11.4% and 10.9% respectively compared with 7A04 Al alloy without basalt particles.     

Reciprocating wear behavior of 7075Al/SiC in comparison with 6061Al/Al2O3 composites

In the present study, the reciprocating wear behavior of 7075Al/SiC composites and 6061Al/Al₂O₃ composites that are prepared through liquid metallurgy route is analyzed to find out the effects of weight percentage of reinforcement and load at the fixed number of strokes on a reciprocating wear testing machine. The Metal Matrix Composite (MMC) pins are prepared with different weight percentages (10, 15 and 20%) of SiC and Al₂O₃ particles with size of 36 μm. Hardness of these composites increases with increase in wt.% of reinforcement. However, the impact strength decreases with increase in reinforcement content. The experimental result shows that the volume loss of MMC specimens is less than that of the matrix alloy. However, the volume loss is greater in 6061Al/Al₂O₃ composites when compared to 7075Al/SiC composites. The temperature rise near the contact surface of the MMC specimens increases with increase in wt.% of reinforcement and applied load. The coefficient of friction decreases with increase in load in both cases.