Refinement of microstructure and improvement of mechanical properties of Al/Al2O3 cast composite by accumulative roll bonding process

Some important problems associated with cast metal matrix composites (MMCs) include non-uniformity of the reinforcement particles, high porosity content, and weak bonding between reinforcement and matrix, which collectively result in low mechanical properties. Accumulative roll bonding (ARB) process was used in this study as a very effective method for refinement of microstructure and improvement of mechanical properties of the cast Al/10 vol.% Al₂O₃ composite. The average particle size of the Al₂O₃ was 3 μm. The results revealed that the microstructure of the composite after eleven cycles of the ARB had an excellent distribution of alumina particles in the aluminum matrix without any noticeable porosity. The results also indicated that the tensile strength and elongation of the composites increased as the number of ARB cycles increased. After eleven ARB cycles tensile strength and elongation values reached 158.1 MPa and 7.8%, which were 2.54 and 2.36 times greater than those of the as-cast MMC, respectively.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Evaluation of aluminium/alumina/titanium composites produced by continual annealing and roll-bonding process

Anodising, continual annealing and roll-bonding (CAR) processes were employed to fabricate aluminium/alumina/titanium composites with different amounts of alumina. After each rolling cycle, annealing treatment was performed at 300°C for 1?h. After six cycles of CAR process, the Al/0.22 vol.-% Al₂O₃/13vol.-%Ti composite showed uniform alumina and titanium particles distribution. The tensile strength of the composites first decreased after the first cycle, then increased up to 200?MPa after the sixth cycle. Conversely, by increasing the alumina content (Al/0.43vol.-%Al₂O₃/13vol.-%Ti composite), microhardness and tensile strength immediately increased. SEM micrographs demonstrated that by increasing the number of cycles, the dimples density increased from 0.007 to 0.028?µm^?2 for the first and the last cycles, respectively.     

High-strength and highly-uniform composite produced by anodizing and accumulative roll bonding processes

The anodizing and accumulative roll bonding (ARB) processes are used in this paper as a new, effective alternative for manufacturing high-strength and highly-uniform aluminum/alumina composites. Four different thicknesses of alumina layers are grown on the substrate using an anodizing process and the microstructural evolution and mechanical properties of the resulting aluminum/alumina composite are investigated. Microscopic investigations of the composite show a uniform distribution of alumina particles in the matrix. It is found that alumina layers produced by the anodizing process neck, fracture, and depart as the number of accumulative roll bonding passes increases. During ARB, it is observed that as strain increases with the number of passes, the strength and elongation of the produced composites correspondingly increase. Also, by increasing alumina quantity, tensile strength improves so that the tensile strength of the Al/3.55 vol.% Al₂O₃ composite becomes ∼3.5 times greater than that of the annealed aluminum used as raw material.     

Simultaneously enhanced tensile and compressive response of AZ31–NanoAl<Subscript>2</Subscript>O<Subscript>3</Subscript>–AA5052 macrocomposite

New bimetal AZ31–Al₂O₃/AA5052 macrocomposite comprising (a) Al₂O₃ nanoparticle-reinforced magnesium alloy AZ31 shell and (b) aluminum alloy AA5052 millimeter-scale core reinforcement was fabricated using solidification processing followed by hot coextrusion. Microstructural characterization revealed more rounded intermetallic particle of decreased size, reasonable Al₂O₃ nanoparticle distribution, and non-dominant (0 0 0 2) texture in the longitudinal and transverse directions in the AZ31–Al₂O₃ nanocomposite shell. Interdiffusion of Mg and Al across the core–shell macrointerface into each other was also significant. Compared to monolithic AZ31, the AZ31–Al₂O₃ shell exhibited significantly higher hardness (+33%). In tension, the presence of Al₂O₃ nanoparticles (in the AZ31 shell) and AA5052 core significantly increased stiffness (+39%), yield strength (0.2% TYS) (+9%), ultimate strength (UTS) (+19%), average failure strain (+7%), and work of fracture (WOF) (+27%) of AZ31. In compression, the presence of Al₂O₃ nanoparticles (in the AZ31 shell) and AA5052 core significantly increased yield strength (0.2% CYS) (+58%), ultimate strength (UCS) (+4%), average failure strain (+11%), and WOF (+49%) of AZ31. The effect of joint presence of (a) Al₂O₃ nanoparticles (in the AZ31 shell) and (b) AA5052 millimeter-scale core on tensile and compressive properties of AZ31 is investigated in this article.     

Effect of deformation temperature and degree on tensile properties of the extruded 2024Al/Al18B4O33w composite with extrusion – forging multistage hot deformation

The effect of extrusion – forging multistage hot deformation on tensile properties of the 2024Al/Al₁₈B₄O₃₃w composites is investigated. The extruded 2024Al/Al₁₈B₄O₃₃w composites are used as blanks. The tensile properties of the extruded 2024Al/Al₁₈B₄O₃₃w composite followed by secondary deformation are studied. The effects of holding temperature and deformation degree on tensile properties of the extruded composite are discussed. The results show that due to the reduction in stress concentration and dislocations, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h is lower than that of the extruded composite without holding. Increasing holding temperature from 300 °C to 450 °C, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite increases firstly and then decreases. The extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h followed by secondary forging with the larger length to width ratio of 4 : 1 has the ultimate tensile strength of 456.1 MPa, higher than that of the extruded 2024Al/Al₁₈B₄O₃₃w composite without secondary forging.     

Dynamic mechanical response of a 1060 Al/Al2O3 composite

The flow stress of a 1060 Al/Al₂O₃ composite increases rapidly with strain rate due to the higher dislocation accumulation rate and the increasing strength of dislocation barriers. The Al/Al₂O₃ interfaces were found to be well bonded even after high-rate deformation of the composite. MgAl₂O₄ particles observed at Al/Al₂O₃ interfaces in the composite of the present study are thought to improve the interface strength. Unlike in pure aluminium, a well-developed cell structure was not observed in the deformed 1060 Al/Al₂O₃ composite. The absence of a well-developed cell structure is thought to result from a more homogeneous slip distribution in the composite.     

Fabrication of AA6061/Al2O3p composites from elemental and alloy powders

The tensile properties and microstructures of AA6061/Al₂O_3p composites fabricated by the pressureless infiltration method under a nitrogen atmosphere were examined. Since the spontaneous infiltration of molten metal into elemental powders bed as well as alloy powders bed occurred at 700°C for 1 hour under a nitrogen atmosphere, it was possible to fabricate 6061 Al matrix composite reinforced with Al₂O_3p irrespective of the type of metal powders. Both MgAl₂O₄ and MgO were formed at interfaces between Al₂O₃ and the matrix. In addition, MgAl₂O₄ was formed at within the matrix by in situ reaction during composite fabrication. Fine AlN was formed by in situ reaction in both composites. A significant strengthening in the composites occurred due to the formation ofin situ AlN particle and addition of Al₂O₃ particles, as compared to the commercial alloy, while tensile properties in the both elemental and alloy powders composites showed similar trend.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> coating on interfacial wettability and tensile properties of Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript>w/Al composite

A pure aluminum matrix composite reinforced by Bi₂O₃-coated Al₁₈B₄O₃₃ whisker was fabricated by squeeze casting method. The effects of Bi₂O₃ coating on the whisker/matrix wettability and the ultimate tensile strength and elongation to fracture of the composite are investigated. The results show that Bi₂O₃ coating can react with aluminum matrix during casting process, which improves the whisker/matrix wettability. Moreover, the ultimate tensile strength and elongation to fracture of the composite attain the maximum values at the mass ratio of 40:1 between whisker and Bi₂O₃ coating.     

The crack propagating behavior of composite coatings prepared by PEO on aluminized steel during in situ tensile processing

This paper investigates the in situ tensile cracks propagating behavior of composite coatings on the aluminized steel generated using the plasma electrolytic oxidation (PEO) technique. Cross-sectional micrographs and elemental compositions were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The composite coatings were shown to consist of Fe-Al, Al and Al₂O₃ layers. The cracks propagating behavior was observed in real-time in situ SEM tensile test. In tensile process, the cracks were temporarily stopped when cracks propagated from Fe-Al layer to Al layer. The critical crack opening displacement δ_c was introduced to quantitatively describe the resistance of the Al layer. There was a functional relation among the thickness ratio tAl/tAl₂O₃, the δ_c of composite coatings and tensile cracks’ spacing. The δ_c increased with the increasing of the thickness ratio (tAl/tAl₂O₃). The high δ_c value means high fracture resistance. Therefore, a control of the thickness ratio tAl/tAl₂O₃ was concerned as a key to improve the toughness and strength of the aluminized steel.     

Microstructure,tensile properties and fracture behaviour of Al2O3 particulate-reinforced aluminium alloy metal matrix composites

The tensile deformation and fracture behaviour of aluminium alloy 2014 discontinuously-reinforced with particulates of Al₂O₃ was studied with the primary objective of understanding the influence of reinforcement content on composite microstructure, tensile properties and quasi-static fracture behaviour. Results reveal that elastic modulus and strength of the metal-matrix composite increased with reinforcement content in the metal matrix. With increase in test temperature the elastic modulus showed a marginal decrease while the ductility exhibited significant improvement. The improved strength of the Al-Al₂O₃ composite is ascribed to the concurrent and mutually interactive influences of residual stresses generated due to intrinsic differences in thermal expansion coefficients between constituents of the composite, constrained plastic flow and triaxiality in the soft and ductile aluminium alloy matrix due to the presence of hard and brittle particulate reinforcements. Fracture on a microscopic scale initiated by cracking of the individual or agglomerates of Al₂O₃ particulates in the metal matrix and decohesion at the matrix-particle interfaces. Failure through cracking and decohesion at the interfaces increased with reinforcement content in the matrix. The kinetics of the fracture process is discussed in terms of applied far-field stress and intrinsic composite microstructural effects.     

Improvement of yield strength of LM24 alloy

In this study, Al₂O₃ particles were employed to improve the microstructure of LM24 and therefore, to increase the yield strength and tensile strength of this kind of alloy. In situ Al₂O₃ particles were obtained by direct reaction between oxygen and Al melt at 750–800 °C. Microstructure examination shows that the size of in situ formed Al₂O₃ particles was about 1–2 μm, and interestingly, with addition of in situ Al₂O₃ particles, the coarse primary Si phase was disappeared completely. More important, the yield strength and the tensile strength of Al₂O₃/LM24 are increased by 52 MPa, 16 MPa than that of LM24 alloy with 0.1% Sb addition. The value of 181 MPa and 315 MPa is for yield strength and tensile strength of Al₂O₃/LM24 respectively. Besides, the yield strength and tensile strength are 180 MPa and 314 MPa respectively for Al₂O₃/LM24 alloy after remelting and casting. This verifies that the improvement of mechanical properties of such kind of material possesses stability and reliability.     

纳米Al2O3改性玻璃纤维增强复合材料低温力学性能研究

简述了纳米Al2O3改性玻璃纤维增强环氧树脂基复合材料的制备,并对其常温、低温力学性能进行实验。结果表明,常温、低温下,复合材料的力学性能随着纳米Al2O3含量的增加都呈现先增强后减弱的趋势。低温处理使复合材料的力学性能得到提升,并且低温下Al2O3的引入对复合材料强度的改善效果比常温下明显,Al2O3含量为1%(质量分数)时,拉伸强度提高比例高达16.61%。其原因是低温下基体强度增大,另外基体热膨胀系数大,收缩明显,界面粘接强度增大,纳米Al2O3颗粒在界面处与树脂基体结合更深入,从而使纳米粒子阻碍微裂纹扩展的能力更强。     

Enhancement of tensile and thermal properties of epoxy nanocomposites through chemical hybridization of carbon nanotubes and alumina

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid carbon nanotube–alumina (CNT–Al₂O₃) filler, via chemical vapour deposition and a physically mixed CNT–Al₂O₃ filler, at various filler loadings (i.e., 1–5%). The tensile and thermal properties of both nanocomposites were investigated at different weight percentages of filler loading. The CNT–Al₂O₃ hybrid epoxy composites showed higher tensile and thermal properties than the CNT–Al₂O₃ physically mixed epoxy composites. This increase was associated with the homogenous dispersion of CNT–Al₂O₃ particle filler; as observed under a field emission scanning electron microscope. It was demonstrated that the CNT–Al₂O₃ hybrid epoxy composites are capable of increasing tensile strength by up to 30%, giving a tensile modulus of 39%, thermal conductivity of 20%, and a glass transition temperature value of 25%, when compared to a neat epoxy composite.     

Fabrication and mechanical properties of woven Al2O3 fibre – ZrO2 matrix minicomposite reinforced Al2O3 matrix composites by slurry infiltration – sintering process

Abstract

A plain woven Al₂O₃ fibre - ZrO₂ minicomposite reinforced Al₂O₃ matrix composite ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃) has been fabricated by a simple, pressureless, multiple slurry infiltration - sintering process. The fabrication process consisted of two major steps: fabrication of the woven Al₂O₃ fibre - ZrO₂ minicomposite ((Al₂O₃)_f/ZrO₂)_mc) and fabrication of the composite ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃. The woven fibre form of ((Al₂O₃)_f/ZrO₂) _mc was made by dipping a plain woven Al₂O₃ fabric into colloidal ZrO₂ solution. Then Al₂O₃ powder dispersed slurry was infiltrated into the open spaces of the woven fabric ((Al₂O₃) /ZrO₂)_mc. The infiltrated minicomposites were stacked, pressed, and sintered in ambient air to form a plate of ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃. The optimum sintering temperature of ((Al₂O₃)_f/ZrO₂)_mc/Al₂O₃ was investigated via tensile strength and matrix density. Tensile behaviour and fracture resistance of the composite fabricated under the optimum processing condition were evaluated. The tensile stress - strain behaviour of the optimised composite showed non-catastrophic fracture behaviour with bundle bridging and extensive fibre bundle pullouts. The maximum tensile stress revealed that almost full strength expected from the bare bundle strength was exploited by the proposed process.     

Tensile deformation and fracture behavior of a ductile phase reinforced dispersion strengthened copper composite

Niobium particle reinforced aluminum oxide (Al₂O₃) dispersion strengthened copper composite is an attractive and emerging engineered material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. In this paper, the microstructure, tensile deformation and fracture behavior of the composite is examined. The strength of the material decreases with an increase in temperature with a concomitant improvement in ductility. The composite microstructure maintains a high value of yield strength/ultimate tensile strength ratio. The factors contributing to increased strength and the intrinsic mechanisms governing fracture characteristics of the composite are examined in light of intrinsic microstructural effects, nature of loading and deformation characteristics of the matrix.     

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al₂O₃ matrix composites with unidirectionally oriented high-purity Al₂O₃ fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al₂O₃ fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al₂O₃ (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m^1/2) compared to the composite with an uncoated fibre (4.5 MPa m^1/2) and monolithic Al₂O₃ (5.5 MPa m^1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip. This revised version was published online in November 2006 with corrections to the Cover Date.     

Optimization of cold-sprayed AA2024/Al2O3 metal matrix composites via friction stir processing: Effect of rotation speeds

In this study, friction stir processing (FSP) was employed to modify cold-sprayed (CSed) AA2024/Al₂O₃ metal matrix composites (MMCs). Three different rotation speeds with a constant traverse speed were used for FSP. Microstructural analysis of the FSPed specimens reveals significant Al₂O₃ particle refinement and improved particle distribution over the as-sprayed deposits. After FSP, a microstructural and mechanical gradient MMC through the thickness direction was obtained. Therefore, a hybrid technique combining these two solid-state processes, i.e. CS and FSP, was proposed to produce functionally gradient deposits. The Guinier-Preston-Bagaryatskii zone was dissolved during FSP, while the amounts at different rotation speeds were approximately the same, which is possibly due to the excellent thermal conductivity of the used Cu substrate. Mechanical property tests confirm that FSP can effectively improve the tensile performance and Vickers hardness of CSed AA2024/Al₂O₃ MMCs. The properties can be further enhanced with a larger rotation speed with a maximum increase of 25.9% in ultimate tensile strength and 27.4% in elongation at 1500 rpm. Friction tests show that FSP decreases the wear resistance of CSed MMCs deposits due to the breakup of Al₂O₃ particles. The average values and fluctuations of friction coefficients at different rotation speeds vary significantly.     

Effect of the microstructure on the mechanical properties of a directionally solidified Y3Al5O12/Al2O3 eutectic fiber

The strength and fracture behaviors of a directionally solidified Y₃Al₅O₁₂/Al₂O₃ eutectic fiber were investigated. The fiber was grown continuously by an edge-defined film-fed growth (EFG) technique. The microstructure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The room temperature tensile strength and Weibull's modulus of the eutectic fiber before and after heat treatment at 1460°C were measured. The fracture toughness and crack propagation behaviors were investigated using an indentation technique. Significant coarsening of the lamellar microstructure was observed after heat treatment at 1460°C in air. The degradation of the room temperature tensile strength in the Y₃Al₅O₁₂/Al₂O₃ eutectic fiber after heat treatment was attributed to the development of surface grooves at the surface of the fiber. Also, the Y₃Al₅O₁₂/Al₂O₃ eutectic fiber showed a radial (Palmqvist) crack type and exhibited an anisotropic crack propagation behavior during the indentation tests.     

Tailoring the tensile/compressive response of magnesium alloy ZK60A using Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

ZK60A nanocomposites containing Al₂O₃ nanoparticle reinforcement were fabricated using solidification processing followed by hot extrusion and T5 heat treatment. Agglomeration of Al₂O₃ nanoparticles was observed in the nanocomposites. However, in the case of ZK60A/1.0 vol%Al₂O₃ nanocomposite (compared to monolithic ZK60A), increase in tensile strength (up to 14%) without significant decrease in ductility and simultaneous increase in compressive strength (up to 12%) and ductility (+23%) were observed. Here, the strength of ZK60A was increased without significant decrease in ductility. On the other hand, in the case of ZK60A/1.5 vol%Al₂O₃ nanocomposite (compared to monolithic ZK60A), simultaneous increase in tensile strength (up to 6%) and ductility (+26%), but decrease in compressive strength (up to 40%) with increase in ductility (+43%) were observed. Here, the ductility of ZK60A was significantly increased without significant increase in strength. This tailoring of tensile and compressive properties of ZK60A via integration with Al₂O₃ nanoparticles are investigated in this article.