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.     

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.     

Cold spray of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with soft metal incorporation: A technical contribution

Al + SiC, Al + Al₂O₃ composites as well as pure Al, SiC, and Al₂O₃ coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition of metal (Al) and ceramic (SiC, Al₂O₃) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was fixed at 0.7 MPa. SiC and Al₂O₃ have been successfully sprayed producing coatings with more than 50 μm in thickness with the incorporation of Al as a binder. Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was no crater formation on hard Si substrates. However, when Al mixed with SiC and Al₂O₃, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.     

Fabrication of A356 composite reinforced with micro and nano Al2O3 particles by a developed compocasting method and study of its properties

Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al₂O₃ nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al₂O₃ or 3 and 5 wt.% micro Al₂O₃ was added, while, further increase in Al₂O₃ (4 wt.% nano Al₂O₃ and 7.5 wt.% micro Al₂O₃) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles.     

Experimental and Morphological Investigations Into Electrical Discharge Surface Grinding (EDSG) of 6061Al/Al2O3p 10% Composite by Composite Tool Electrode

In this study, a special experimental setup of EDSG using EDM and surface grinding machine has been developed in the laboratory to investigate the effect of seven input parameters namely tool polarity, peak current, pulse on-time, pulse off-time, rotational speed, abrasive particle size, and abrasive particle concentration on material removal rate (MRR) as performance measure of the process. The novelty of the present research work is that successful efforts have been made to machine the 6061Al/Al₂O_3p 10% metal matrix composites (MMC) by composite tool itself. The copper-based composite tool electrodes were fabricated by powder metallurgy route with different sizes of abrasives of silicon carbide, while 6061Al/Al₂O_3p 10% MMC were fabricated through stir-casting process. The research outcome will identify the important parameters and their effect on MRR of 6061Al/Al₂O_3p 10% composite in EDSG. The experimental results reveal that tool polarity, peak current, and rotational speed are the most influential parameters that affect MRR in EDSG process. The micro-structural and morphological analysis of machined surfaces has also been carried out to analyze the surface topography. It has been concluded that the abrasive particles substantially improves the MRR after removing the resolidified layer from the machined surface.     

Taguchi approach to influence of processing parameters onerosive wear behaviour of Al7034-T6 composites

Taguchi technique was used to predict the influence of processing parameters on the erosive wear behavior Al7034-T6 composite reinforced with SiC and Al₂O₃ particles in different mass fractions. These hybrid metal matrix composites (HMMCs) were fabricated by using a simple technique called stir casting technique. Scanning electron microscope (SEM) was used to study the surface morphology of the composite and its evolution according to processing time. The design of experiment (DOE) based on Taguchi's L₁₆ orthogonal array was used to identify various erosion trials. The most influencing parameter affecting the wear rate was identified. The results indicate that erosion wear rate of this hybrid composite is greatly influenced more by filler content and impact velocity respectively compared to other factors. This also shows the significant wear resistance with the increase in the filler contents of SiC and Al₂O₃ particles, respectively.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles on the microstructure and sliding wear of 7075 Al alloy manufactured by squeeze casting method

Aluminum (Al) alloy 7075 reinforced with Al₂O₃ particles was prepared using the stir casting method. The microstructure of the cast composites showed some degree of porosity and sites of Al₂O₃ particle clustering, especially at high-volume fractions of Al₂O₃ particles. Different squeeze pressures (25 and 50 MPa) were applied to the cast composite during solidification to reduce porosity and particle clusters. Microstructure examinations of the squeeze cast composites showed remarkable grain refining compared with that of the matrix alloy. As the volume fraction of particles and applied squeeze pressure increased, the hardness linearly increased. This increase was related to the modified structure and the decrease in the porosity. The effect of particle volume fraction and squeeze pressure on the dry-sliding wear of the composites was studied. Experiments were performed at 10, 30, and 50 N with a sliding speed of 1 m/s using a pin-on-ring apparatus. Increasing the particle volume fraction and squeeze pressure improved the wear resistance of the composite compared with that of the monolithic alloy, because the Al₂O₃ particles acted as load-bearing constituents. Also, these results can be attributed to the fact that the application of squeeze pressure during solidification led to a reduction in the porosity, and an increase in the solidification rate, leading to a finer structure. Moreover, the application of squeeze pressure improved the interface strength between the matrix and Al₂O₃ particles by elimination of the porosity at the interface, thereby providing better mechanical locking.     

Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology.Microstructures and effect of thermal-cooling cycle treatment(TCCT) on the thermal expansion behaviors of three composites were investigated.The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly.Inflections at about 300 °C are observed in coefficient of thermal expansion(CTE) versus temperature curves of two SiCp/Al composites,and this characteristic is not affected by TCCT.The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles.However,no inflection is observed in Al2O3p/Al composite,while TCCT has effect on CTE of Al2O3p/Al composite.These results should be due to different relaxation behavior of internal stress in three composites.     

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.     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

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.     

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.     

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.     

The effect of temperature of magnetic pulsed compaction on the characteristics of nanostructured aluminum compacts

Magnetic pulse compaction (MPC) allows one to maintain a nanostructured state in nano powder metallic compacts and to achieve near theoretical density. In this study, nano Al powders of about 80 nm in diameter were prepared with the Pulse Wire Evaporation (PWE) method and passivated with a thin Al₂O₃ layer on a surface about 2 nm thick to prevent further agglomeration and oxidation. The powders were compacted with the dynamic compaction of magnetic pulsed force. The effects of the compaction temperature and passivated oxide layer of Al powders on mechanical properties were investigated. The prepared compacts were considered as the composite materials of the metal-matrix containing oxides of their own metal. A fine and uniform bulk structure was kept up to 400°C, which showed neither further agglomeration nor grain growth during compaction and heat treatment due to the formation of Al/Al₂O₃ composites. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials”, organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

Characterizations of cold-sprayed Nickel-Alumina composite coating with relatively large Nickel-coated Alumina powder

Previous studies have shown that the fabrication of metal matrix composites (MMCs) by cold spraying is effective and promising. When light materials, such as SiC and Al₂O₃, were used as reinforcements, it was diffcuclt to obtain a high volume fraction of hard phase in the composite just through the simple powder mixture. Therefore, in this study, a Ni-coated Al₂O₃ powder, which was produced through hydrothermal hydrogen reduction method, was employed aiming at increasing the volume fraction of ceramic particles in the deposited composite coating. It was found that a dense Ni-Al₂O₃ composite coating could be deposited with the Ni-coated Al₂O₃ powder under the present spray conditions. X-ray diffraction analysis indicated that the composite coating had the same phase structures as the feedstock. The volume fraction of Al₂O₃ in the composite was about 29 ± 6 vol.%, which is less than that in the feedstock (nominal: 40-45 vol.%) due to the rebound of some Al₂O₃ particulates upon kinetic impacting. The microhardness of the composite coating was about 173 ± 33Hv_0.2.     

Thermal residual stresses and their toughening effect in Al2O3 platelet reinforced glass

Fluorescence spectroscopy has been used to measure the thermal residual stresses in Al₂O₃-platelet/borosilicate glass composites. Tensile residual stresses were found in the platelets, implying the presence of compressive residual stresses in the glass matrix. Measurements of stresses in the bulk of the composite could be obtained using fluorescence from platelets below the specimen surface. The measured stresses lay between the predictions of models for spherical particles and thin platelets, but were closer to the former for the range of platelet contents investigated (5–30 vol.%). Estimates of the increase in toughness associated with the compressive residual stresses in the matrix suggest that this mechanism makes a significant contribution to the toughening effect of the Al₂O₃ platelets.     

搅拌摩擦加工制备纳米RE/Al2O3增强铝基复合材料

铝基复合材料因其优异的物理性能及机械性能已得到广泛应用.文中通过在2219-O铝合金内部添加不同比例的RE/Al₂O₃纳米粉末,利用搅拌摩擦加工技术,制备铝基复合材料.并对搅拌区进行金相、拉伸、硬度、SEM,EDS和XRD等试验.结果表明,搅拌区金属在搅拌头强烈的搅拌摩擦作用下发生显著的塑性变形和连续动态再结晶,形成细小的等轴晶粒,并具有明显的洋葱环组织.复合材料的抗拉强度为母材的163%、屈服强度为母材的195%,同时硬度也明显增加.但是不同稀土比例对金属基复合材料的组织形貌和力学性能影响不大.大块复合材料制备过程粉末添加及隧道型缺陷的控制是关键.     

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.     

Al2O3/Mo composite and its tribological behavior against AISI201 stainless steel at elevated temperatures

Al₂O₃-reinforced molybdenum (Mo) composites were successfully prepared by powder metallurgy to improve the wear resistance of Mo components at high temperature. The reinforced Al₂O₃ particles are uniformly distributed in the Mo matrix; thus, the Al₂O₃/Mo composite is harder than monolithic Mo. The friction coefficients of both monolithic Mo and the Al₂O₃/Mo composite decrease by 37% and 42%, respectively, at 700 °C compared with those at room temperature (self-lubricating phenomenon). This phenomenon is attributed to the formation of very soft MoO₃ and FeMoO₄ metal oxides on the friction surface at high temperature. The Al₂O₃/Mo composite has better wear resistance than monolithic Mo at both room temperature and at 700 °C. The notable resistance of the composite particularly at 700 °C can be attributed to its increased hardness and the soft tribofilm forming on the worn surface.