Fabrication of aluminium matrix composites reinforced by submicrometre and nanosize Al2O3 via accumulative roll bonding

Abstract

Aluminium matrix composites reinforced with submicrometre and nanosize Al₂O₃ particles were successfully manufactured in the form of sheets through eight cycles of accumulative roll bonding process. The mechanical properties of the produced composite are compared with accumulative roll bonded commercially pure aluminium. It is shown that only 1 vol.-% of submicrometre or nanosize alumina particles as reinforcement in the structure can significantly improve the yield and ultimate tensile strengths. Scanning electron microscopy revealed that particles have a random and uniform distribution in the matrix especially in the less volume fraction of alumina particles, and strong mechanical bonding occurs at the interface of the particle matrix. According to the results of the tensile tests, it is observed that with less alumina content, the composite reinforced by nanosize particles has higher strength than that by submicrometre size particles. However, more reinforcement up to 3 vol.-% of submicrometre particles, as a result of including fewer microstructural defects, leads to better mechanical properties in comparison to the nanoparticle composite.     

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.     

Processing of Al/B4C composites by cross-roll accumulative roll bonding

In the present study, Al/B₄C composites were successfully produced in the form of sheets, through accumulative roll bonding (ARB) and cross-roll accumulative roll bonding (CRARB) processes. The CRARB process was performed in two steps. In the first step, the strips were roll-bonded with a draft percentage of 66% reduction, while in the second step the strips were roll-bonded with a draft percentage of 50%. The results indicated that the dispersion of the B₄C particles in the CRARB process is more homogeneous than the ARB process. In addition, the tensile strength of the CRARBed composite is higher than that of the ARBed composite.     

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.     

Assessment of surface bonding strength in Al clad steel strip using electrical resistivity and peeling tests

Abstract

Aluminium clad steel strip successfully combines the surface properties of an aluminium alloy coating with the satisfactory mechanical properties of the steel substrate. The production of Al clad steel strip by rolling, however, is a more efficient and economical approach compared with other processes. In this investigation, trilayer strips of aluminium/steel/aluminium were produced using the cold roll bonding technique. The bonding strength between the layers and the electrical resistivity of the samples were measured using a peeling test and four point probe test, respectively. The effects of reduction of thickness, the friction condition between the outer layer and rolls, and the rolling velocity on the bonding strength and electrical resistivity of the samples were assessed. Finally, it is shown that the resistivity test can be used as a non-destructive test for the evaluation of the quality of bonding between the layers of aluminium clad steel strip.     

Cold roll bonding of bimetallic sheets and strips

Abstract

The successful production of wide bimetallic sheets and strips by cold roll cladding depends on the technical solution of reduction of rolling load while still guaranteeing good bond quality. In the present paper, systematic experimental data on the cold roll cladding of aluminium–stainless steel, copper–stainless steel, and mild steel–stainless steel are correlated and the basic mechanism is discussed, aided by a scanning electron microscopy study of the separated interface. The effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared. It is found that use of the cross-shear cold rolling technique results in a significant reduction in rolling load for equal primary bonding strength and that the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.

MST/971     

Nanostructured AA5005/Al2O3 composite manufactured by anodising and accumulative roll bonding

In this study, nanostructured AA5005/6 vol.-% Al₂O₃ composite manufactured by anodising and accumulative roll bonding (ARB) processes was investigated. The microstructure of the AA5005/Al₂O₃ composite after ninth ARB cycle exhibited a good distribution of alumina reinforcement particles in the AA5005 matrix. It was found that with increasing the number of cycles, the tensile strength of the monolithic and composite samples increased, but their ductility decreased at the first ARB cycle and then increased. The mean grain size of the composite sample after the ninth cycle was 88?nm. The tensile strength of the composite was 3.3 times higher than the initial AA5005 sheet. Observations revealed that the failure mode in the AA5005/Al₂O₃ composite was the shear ductile fracture.     

Interfacial reactions in K2Ti6O13(w)/Al2O3/Al composite

Abstract

A pure Al matrix composite, reinforced by potassium titanate whiskers coated with sol–gel alumina, was fabricated by squeeze casting. Good interface bonding was achieved in the coated composite. Interfacial reactions in the composite were found to be less severe than those in an uncoated composite, owing to the barrier effect of sol–gel -Al₂O₃ coating. After the composite was thermally exposed at 530°C for 30 h, the alumina coating still restrained the decomposition of the whisker structure, and thus prevented a decrease in the strength of the composite. However, after a thermal exposure at 700°C for 10 h, the coating was no longer held on whisker surfaces. Mechanical testing showed that tensile fracturing of the coated composite tended to occur at the coating/matrix interface where the interfacial bonding is weaker than at the coating/whisker interface.     

Fabrication of 6061 aluminium alloy/Al18B4O33(w) composite by using sol–gel alumina binder

Abstract

For fabrication of aluminium borate whisker (Al₁₈B₄O_33(w)) reinforced 6061 aluminium alloy composites, a sol–gel alumina binder instead of conventional silica binder was used for preparing the whisker preforms of the squeeze cast composites. The results show that a sound whisker preform and a uniform composite can be made by this method. Unlike the reactive silica binder, the sol–gel alumina binder is rather stable throughout the entire high temperature fabrication process. Under appropriate conditions, the sol–gel alumina binder can also serve as a thermal barrier for minimising interfacial reactions between aluminium borate whiskers and the matrix alloy. With a binder concentration of 0.6 mol L^-1, the ultimate tensile strength of the composite is as high as 277.6 MPa at room temperature and moderate at elevated temperatures. The tensile fracture of the alumina bound composite shows a mixed mode of dimple fracture and interface debonding.     

Cold roll bonding bond strengths: review

Abstract

Cold roll bonding (CRB), a well established and widely used manufacturing process, is a solid state bonding process to join similar and dissimilar metals. The present work offers a review of the CRB process and effective parameters on bond strength of cold roll bonded materials. The effects of different amounts of reduction in thickness, annealing treatment, initial thickness, rolling speed, rolling direction, friction coefficient and presence of particles between strips on bond strength were evaluated. It was found that higher reduction in thickness and friction coefficient, lower initial thickness, rolling speed and amount of particles were the important factors involved in improving bond strength. In addition, annealing treatment before and/or after the CRB process increased bond strength, while the effect of prerolling annealing was more pronounced. Finally, it has been indicated that bond strength of cold roll bonded fcc materials is stronger than that of the bcc and hcp materials.     

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.     

Aluminium based composites reinforced with alumina coated carbon fibres

Abstract

A fine Al₂0₃ coating could be obtained from alumina sols modified by chelator acetylacetone, with exact control of parameters. Coating with alumina by the sol–gel method on a carbon fibre surface was investigated in detail to improve the oxidation resistance of carbon fibre. Further study focused on making the alumina coated fibre reinforced aluminium composite prefabrication. X-ray diffraction and SEM methods were used to analyse the alumina gels and the carbon fibre/aluminium (CF/Al) preformed wire. After the coating treatment, oxidation resistance of carbon fibres is enhanced, the wettability between the fibres and melting aluminium is greatly improved, and the tensile strength of CF/Al preformed wire is increased.     

Effect of friction,annealing conditions and hardness on the bond strength of Al/Al strips produced by cold roll bonding process

Layered materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB) process, as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing process. In this paper, characteristics such as bond strength and threshold deformation of as-received commercial pure aluminum (AA1100) strips prepared by the cold roll bonding process are investigated. Bond strength is evaluated by the peeling test. The main factors evaluated included effects of different annealing time, annealing temperature, hardness, and the effect of friction coefficient on bond strength. It is found that bond strength is enhanced by increasing annealing time, friction coefficient, and annealing temperature but that it is inversely proportional to hardness.     

Technical note Fabrication of alumina dispersion strengthened copper strips by internal oxidation and hot roll bonding

Abstract

Alumina dispersion strengthened copper strips were fabricated by internal oxidation and hot roll bonding of Cu–Al alloy strips. Cu–Al alloy strips were internally oxidised without using any oxidant powders by a surface oxidation method. Several of the internally oxidised alloy strips were stacked and bonded by rolling at high temperatures. The bonded strip was cold rolled to achieve tensile strengths of 484–539 MPa and yield strengths of 472–522 MPa with thermally stable mechanical properties.     

Forging of the AA2618/20 vol.% Al2O3p composite: Effects on microstructure and tensile properties

The use of aluminium-based particulate reinforced MMCs for automotive components and aircraft structures have been shown to be highly advantageous over their unreinforced alloys, due to their high specific strength and stiffness and superior wear resistance in a wide temperature range. The aim of this paper was to evaluate the effect of the hot forging process on the microstructure and tensile properties (at room and high temperature) of a MMC based on the aluminium alloys AA2618 reinforced with 20 vol.% of alumina particles (Al₂O_3p). Microstructural analyses of the as-cast and heat-treated composite showed large grain size of the aluminium alloy matrix and a quite non-homogeneous distribution of the reinforcing particles. The forging process led to an evident grain refinement, while it did not lead to significant variations in the size and distribution of the reinforcement particles. Regarding the effect of the forging process on the mechanical properties, it induced a slight increase in hardness, tensile strength, elastic modulus and an evident increase in tensile elongation. SEM analyses of the fracture surfaces of the tensile specimens showed substantially similar morphologies for the as-cast and forged composites, both at room and high temperature. The mechanism of damage was mainly decohesion at the matrix–particle interface.     

Chemical reaction assisted transient liquid phase bonding of alumina in combination with cold isostatic pressing

Abstract

A new method of transient liquid phase (TLP) bonding of alumina specimens has been developed using a mixture of aluminium powder and silica powder as insert materials. A chemical reaction of aluminium with silica occurs in the inter layer to produce alumina and silicon. Some of the specimens were subjected to cold isostatic pressing (cipping) before bonding to improve the bonding strength. Specimens with an interlayer of powder mixture were joined for Al/SiO₂ ratios of 1 : 0.84 and 1 : 0.42, but did not join for an interlayer with a theoretical ratio of 1 : 1.67. When specimens were subjected to cipping before bonding, bonds were far stronger than bonds without cipping in a temperature range from room temperature to elevated temperatures above the melting point of aluminium. In the mechanical test (bending test), fracture occurs at the boundary between the alumina matrix and the interlayer at room temperature, and in the interlayer at temperatures above the melting point of aluminium.     

The mechanical properties of rolled wire-reinforced aluminum composites at different strain values

Abstract

The analysis of strain parameters at rolling of aluminum composite with wire-reinforcement was carried out in the present experimental work. The roll bonding of two strips of EN AW-5083 alloy with and without diagonal stainless-steel net-reinforcement between them was experimentally proceeded with different reductions. It is analyzed the influence of the rolling reduction in the range from 25% to 55% on the straining of the wires and composite bonding mechanisms. The present experimental work is established and used the set of describing parameters of the net behavior in the composite such as net cell elongation, wire elongation and wire ovalisation. The means of longitudinal and transversal tensile testing, impact testing and microscopic analysis determine the properties of the rolled composite. The analysis of the rolling reduction influence on the mechanisms of bonding formation in the composite its properties and fracture behavior are carried out. Based on the conducted tests, it was established the optimum range of rolling reductions.     

Property optimization of nanostructured ARB-processed Al by post-process deformation

The effect of post-process deformation on the mechanical properties of nanostructured aluminum (99.2% purity) has been investigated by cold rolling of samples which have been processed by accumulative roll bonding (ARB) to a strain of ε_vM = 4.8. Samples have been cold rolled to 10, 15, and 50% reductions and ultimate tensile strength (UTS), yield stress and elongation have been determined by tensile testing at room temperature. The mechanical testing shows that cold rolling to low strains (10% and 15%) leads to softening and increase in elongation compared to the as-processed ARB material. In contrary, cold rolling to large strain (50%) results in significant strengthening. This leads to the suggestion of a transition strain within the range of 25–35% reduction by rolling. The microstructural evolution during post-process deformation has been followed by transmission electron microscopy showing a significant change in the dislocation structure when the strain is increased. Based on the experimental observations the mechanical behavior is related to the structural changes focusing on the characteristics of the dislocation structure present between the narrowly spaced lamellar boundaries in the deformed structure.     

Effects of temperature and B4C content on the bonding properties of roll-bonded aluminum strips

The presence of ceramic particles between metal strips in metal matrix composite processing by roll bonding affects their bonding properties. In this study, roll bonding of commercial pure aluminum (AA1100) strips in the presence of various B₄C contents at different thickness reductions was focused. Furthermore, the effect of rolling temperature (at ambient temperature and 473 K) on the bonding properties of the strips was investigated via peeling tests. The results showed that the presence of the B₄C particles between the aluminum strips reduces the bond strength and weld efficiency; in contrast, they are increased by increasing temperature. Therefore, by increasing temperature it is possible to use the higher amounts of the B₄C particles between the aluminum strips.     

Nano‐porous Alumina Coatings for Improved Bone Implant Interfaces

A new method is proposed for coating implants that produces a metal implant covered in a layer of nano‐porous alumina ceramic. These layers are produced by first depositing a layer of aluminium on the implant surface and then anodising it in phosphoric acid to produce the nano‐porous structure. This process results in the conversion of the aluminium to alumina containing 6‐8wt% phosphate ions. The surface alumina layer is bonded to the substrate via an interfacial layer of fully dense anodised titanium oxide. Mechanical measurements have shown that the shear and tensile strength of this coating are in excess of 20MPa and 10MPa, respectively. The biological performance of nano‐porous alumina material has been assessed and shown to be highly favourable, supporting normal osteoblastic activity and maintaining the osteoblastic phenotype. The filling of the nano‐porous coating with bioactive material to achieve enhanced biological performance has been investigated using colloidal silica as an analogue for a Bioglass sol. The coating has been loaded with silica by dipping in colloidal silica with a pH of 5.6. Pore filling equivalent to 1.3 wt% SiO₂ in the coating as a whole has been achieved in this way.