Title of Invention

A PROCESS OF MAKING Al-Al₂O₃COMPOSITES USEFUL IN ENGINEERING APPLICATIONS

Abstract

This invention provides a process of making AI-AI2O3 composites useful in engineering applications, wherein partially oxidized object(s) are subjected to microwaving in the presence of air, resulting in the generation of AI2O3 phases in the aluminium matrix due to microwave heating. Percentage of alumina phase loading in the aluminium matrix can be tailored as a function of microwave exposure time. Thus, there is provided a process of making AI-AI2O3 composites useful in engineering applications, which is simpler and cost-effective than the hitherto known prior art.

Full Text

The present invention relates to a process of making AI-AI2O3 composites useful in engineering applications. The present invention has a great utility in terms of numerous applications of Al- AbOs composites. AI-AfeOs composites have immense potential for aerospace, automotive, electronic packaging, and recreational applications because of their high specific strength, high specific stiffness, high toughness, good wear and abrasion resistance and high temperature mechanical properties. AI-AfeOa composites are particularly useful to make a wide variety of automotive and aerospace components including drive shafts, cylinder liners, rocker arms, connecting rods and suspension components. In the future, AI-AI2O3 composites are expected to become an important class of materials in other commercial applications. There are several processes for producing metal matrix composites including thermal spraying, casting, sintering and plating etc. The casting process has already been widely practiced due to its high productivity. Reference may be made to United States Patent No. 6,253,831, Genma; Yoshikazu; Tsunekawa; Yoshiki; Okumiya; Masahiro; Mohri; Naotake, in Casting process for producing metal matrix composite, wherein metal matrix composites are produced by a casting process. The process involves the application of ultrasonic vibration to the melt containing metal and reinforcing particles in association with electromagnetic stirring during the solidification of the melt. Ultrasonic vibration facilitates wetting of the second phase particles with the metal melt and electromagnetic stirring prevents sedimentation of the second phase particles. AI-AfeOs composites can be formed by the above method wherein reinforced AI2O3 particles are uniformly distributed in the Al matrix. The drawback is the requirement of an ultrasonic vibration and electromagnetic stirring apparatus for dispersing second phase particles in a metal melt which has made the process costlier. One of the more successful techniques for producing metal matrix composites is by infiltrating liquid metal into a fabric or prearranged fibrous configuration called a preform. Reference may be made to U.S. Patent No. 5,702,542, Brown; Alexander M.; Klier; Eric M., in Machinable metal-matrix composite, wherein molten metal has been infiltrated into a ceramic preform and allowed to solidify. The preform contains particles of average particle size about 3 microns and porosity occupies about one half of the volume of the preform. Inert gas pressures of less than about 3000 psi can be used to facilitate infiltration of the performs. AI-AI2O3 composites can be produced by the referred method. Melt infiltration technique is generally adopted where complex shapes are to be formed or a high proportion of reinforcement is desired. The drawback of the above process is that processing steps are complicated. The DIMOX™ (Directed Metal OXidation) process can be used for the production of alumina particulate reinforced AI-A^Oa composite. Reference may be made to a paper published in the British Ceramic Transactions, 1994, Vol. 93, No. 4, p 129, F.J.A.H. Guillard, R.J. Hand, and W.E. Lee, wherein a preform is infiltrated by the outward oxidation of suitably doped molten aluminium (purity-99.9999%). The preform was made of calcined reagent grade AfeOa powder (Fisons) having a mean particle size of 0.3±0.05 urn. Reagent grade Mg and MgO (Fisons) and ultra pure Si (Wm Rowland) were used as dopants with mean particle sizes 77±10, 36±6 and 0.2±0.05 urn respectively. The drawback is that it involves cumbersome processing steps. Recently, thermal spraying method has attracted attention for the fabrication of high tech composite materials as coatings and as freestanding near net structures. Reference may be made to U.S. Patent no. 5,206,059, Marantz; Daniel R., in Method of forming metal-matrix composites and composite materials, wherein a composite coating has been formed by using thermal spraying technique. In this method, a particulate material is heated and accelerated with a thermal spray gun and a molten metal is atomized to produce a combined, high velocity stream of the heated particulate material and the atomized molten metal. This high velocity stream is then directed to a substrate to form a composite coating. Al- A^Oa composites can be formed by the above method. The drawbacks are requirement of large-scale equipment and complicated processing steps. In the hitherto known prior art, as referred above, there are many existing techniques such as casting, melt infiltration, powder metallurgy which are well practiced for producing AI-AbOs composites. But these techniques are not economically favored in respect of high costs of reinforcements and processing. Hence, there is a definite need and scope for improvement and providing a process of making AI-AfeCb composites which overcomes the drawbacks. The main object of the present invention is to provide a process of making Al- AI203 composites useful in engineering applications, which obviates the drawbacks of the hitherto known earlier methods as detailed above. Another object of the present invention is to provide a simple method for the production of AI-AfeOs composites. Still another object of the present invention is to produce AI-A^Oa composites using a cost-effective method. Yet another object of the present invention is to produce AI-AlaOa composites with different amount of alumina phase loading. The present invention provides a process of making AI-AI2O3 composites useful in engineering applications. In general, composites are formed by introducing second phase particles, whiskers, and short fibres as reinforcements in a material keeping an eye to enhance specific properties. But, this is expensive due to high costs of reinforcements and processing costs. The present invention provides a simple and cost-effective method to develop AI-AI2O3 composites, wherein partially oxidized object(s) are subjected to microwaving in the presence of air, resulting in the generation of AI2O3 phases in the aluminium matrix due to microwave heating. In addition to this, percentage of alumina phase in the aluminium matrix can be tailored by varying microwave exposure time. Above all, the present invention provides a means to form AI-AI2O3 composites having great demand in aerospace and automotive industries. Accordingly the present invention provides a process of making Al-Al2O3 composites useful in engineering applications, which comprises pre-cleaning and drying aluminium object(s); partially oxidizing the said pre-cleaned and dried aluminium object(s) in air at a temperature in the range of 590°C to 615°C for a period in the range of 5 to 200 hours to obtain partially oxidized object(s); subjecting the said partially oxidized object(s) to microwaving in the presence of air wherein the microwave exposure time is directly proportional to the requirement of percentage alumina phase loading in the aluminium matrix to obtain the said composite. In an embodiment of the present invention, aluminium object(s) used is of any geometrical shape. In another embodiment of the present invention, the pre-cleaning and drying of the aluminium object(s) is done by polishing the aluminium object(s) followed by rinsing with acetone for a period in the range of 5-20 minutes and drying in air at a temperature in the range of 120°C to 150°C for a period in the range of 15 to 30 minutes. In yet another embodiment of the present invention, the microwave exposure time is directly proportional to the requirement of percentage alumina phase loading in the aluminium matrix. In still another embodiment of the present invention, the microwaving is effected using commercially available microwave oven. In another embodiment of the present invention, the microwave power used is of minimum 500 watts. Metal matrix composites (MMCs) are metals or alloys reinforced with tiny inclusions of another material. Metal matrix composites have drawn attention as newer materials having higher temperature capabilities and higher specific strength properties compared to the conventional metals and alloys. Till recent years, applications of MMCs were restricted to aerospace and other strategic areas due to high costs of both reinforcements and processing. Now, cheaper reinforcements and better processing methods have extended its applications in automotive and general engineering fields. There is a growing need for producing MMCs-economically without expensive machinery and complicated processing techniques. AI-AfeOa composites are well recognized due to its enormous potential applications. Materials without bipolar electric charge such as metals do not react to microwaves. To overcome this, aluminium metal is initially oxidized. Thermal oxidation develops an oxide coating that is essential for further processing in microwave radiation. The oxide coating is heated by microwave energy by the conversion of the energy absorbed from oscillating field into thermal energy of lattice. Energy loss mechanisms may be linked to ionic migration, ionic vibration and electronic polarization. When oxidized aluminium metal is given a microwave exposure, the oxide coating absorbs ^crowave energy and becomes i volumetrically heated. Consequently, the meiaiiic layer in the vicinity region of the coating gets heated by the conduction method. In the present case, aluminium oxide coating can absorb and couple with microwave energy in an enhanced rate at higher temperatures because of large values of the loss tangent and the relative dielectric constant as evidenced by the following formula: P = 2TTf£0£r'tan6| E |2 Where, P is power absorbed per unit volume, f is frequency of incident radiation, £0 is the permittivity of the free space, £r' is relative dielectric constant of material, tanS is loss tangent of material and E is magnitude of the internal field. For this reason, metal is heated to a high temperature during long microwave exposure. This leads to activated diffusion resulting in high rate of oxidation. Oxygen atoms diffuse through the pores of the oxide coating to the aluminium metal. Depending upon provision for the diffusion of oxygen atoms towards the inner side, aluminium metal gets oxidized. This has resulted in the formation of AI-AI2O3 composites, which has been confirmed by thorough EDAX analysis across the cross-sectional surface. The novelty of the present invention is that there is no reinforcement cost. Additionally, processing cost is not high. The non-obvious inventive step which enables achievement of the novel features resides in subjecting partially oxidized object(s) to microwaving in the presence of air, resulting in the generation of AI203 phases in the aluminium matrix due to microwave heating. Percentage of alumina phase loading in the aluminium matrix can be tailored as a function of microwave exposure time. Thus, there is provided a process of making AI-AI2O3 composites useful in engineering applications, which is simpler and cost-effective than the hitherto known prior art. The details of the process steps of the present invention are: 1. Aluminium objects of various geometrical shapes are polished and rinsed with acetone for 5 to 20 minutes. 2. Rinsed samples are dried at a temperature in the range of 120°C to150°C for 15 to 30 minutes. 3. Dried samples are partially oxidized in air at a temperature in the range of 590°C to 615°C for a period of 5 to 200 hours. 4. Partially oxidized samples, obtained in step 4 are microwaved in air inside microwave oven for different microwave exposure times depending upon the requirement of percentage alumina phase loading in the aluminium matrix. The following examples are given by way of illustration of the process in actual practice and therefore should not be construed to limit the scope of the present invention. EXAMPLE -1 A solid cylindrical sample (diameter: 5 mm; length: 1.5 mm) of commercial aluminium was polished and rinsed with acetone for 5 minutes. The rinsed sample was dried in air at 150°C for 15 minutes. Thereafter it was partially oxidized at 615°C for 100 hours in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 40 minutes. The average EDAX data showed the typical composition to be alumina~13.46 wt% and aluminium~86.54 wt%. EXAMPLE - 2 A solid cylindrical sample (diameter: 5 mm; length: 1.5 mm) of commercial aluminium was polished and rinsed with acetone for 10 minutes. The rinsed sample was dried in air at 140°C for 20 minutes. Thereafter it was partially oxidized at 615°C for 100 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 80 minutes. The average EDAX data showed the typical composition to be alumina~77.08 wt% and aluminium~22.92 wt%. EXAMPLE - 3 A solid cylindrical sample (diameter: 5 mm; length: 1.5 mm) of commercial aluminium was polished and rinsed with acetone for 15 minutes. The rinsed sample was dried in air at 130°C for 25 minutes. Thereafter it was partially oxidized at 615°C for 100 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 90 minutes. The average EDAX data showed the typical composition to be alumina~91.45 wt% and aluminium~8.55 wt%. EXAMPLE-4 A solid cube sample (side length: 2 mm) of commercial aluminium was polished and rinsed with acetone for 20 minutes. The rinsed sample was dried in air at 140°C for 20 minutes. Thereafter it was partially oxidized at 600°C for 100 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 35 minutes. The average EDAX data showed the typical composition to be alumina~5.25 wt% and aluminium~94.75 wt%. EXAMPLE - 5 A solid cube sample (side length: 2 mm) of commercial aluminium was polished and rinsed with acetone for 10 minutes. The rinsed sample was dried in air at 150°C for 15 minutes. Thereafter it was partially oxidized at 600°C for 100 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 40 minutes. The average EDAX data showed the typical composition to be alumina~12.76 wt% and aluminium~87.24 wt%. EXAMPLE-6 A solid cube sample (side length: 2 mm) of commercial aluminium was polished and rinsed with acetone for 5 minutes. The rinsed sample was dried in air at 120°C for 30 minutes. Thereafter it was partially oxidized at 600°C for 100 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 55 minutes. The average EDAX data showed the typical composition to be alumina~25.19 wt% and aluminium~74.81 wt%. EXAMPLE -7 A thin block sample (length: 10 mm; breadth: 8 mm and width:1 mm) of commercial aluminium was polished and rinsed with acetone for 10 minutes. The rinsed sample was dried in air at 150°C for 15 minutes. Thereafter it was partially oxidized at 600°C for 50 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 40 minutes. The average EDAX data showed the typical composition to be alumina~12.49 wt% and aluminium~87.51 wt% EXAMPLE - 8 A thin block sample (length: 10 mm; breadth: 8 mm and width: 1 mm) of commercial aluminium was polished and rinsed with acetone for 15 minutes. Commercial aluminium was used. The rinsed sample was dried in air at 140°C for 20 minutes. Thereafter it was partially oxidized at 600°C for 50 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 50 minutes. The average EDAX data showed the typical composition to be alumina~21.81 wt% and aluminium~78.19 wt%. EXAMPLE -9 A thin block sample (length: 10 mm; breadth: 8 mm and width: 1 mm) of commercial aluminium was polished and rinsed with acetone for 5 minutes. Commercial aluminium was used. The rinsed sample was dried in air at 130°C for 25 minutes. Thereafter it was partially oxidized at 600°C for 50 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 65 minutes. The average EDAX data showed the typical composition to be alumina~58.84 wt% and aluminium~41.16 wt%. EXAMPLE-10 Thin block sample (Length-10 mm, breadth-8 mm and width-1 mm) was polished and rinsed with acetone for 20 minutes. The rinsed sample was dried in air at 120°C for 30 minutes. Thereafter it was partially oxidized at 600°C for 50 hrs in air using a muffle furnace. The partially oxidized sample was microwaved in air inside a domestic microwave oven (800 W) for 75 minutes. The average EDAX data showed the typical composition to be alumina~68.31 wt% and aluminium~31.69 wt%. Based on the above examples, we can conclude that AI-AI2O3 composites with different amount of AI2C>3 phase loading can be produced as a function of microwave exposure time resulting in AI-AfeOs composites which are useful for engineering applications. The main advantages of the present invention are: 1. It provides a means to develop AI-AI2O3 composites. 2. It provides a simple process for the development of AI-AI2O3 composites in comparison to the earlier processes. 3. It has made the process for the development of AI-AI2O3 composites costeffective than the earlier processes. 4. It provides a means to tailor alumina phase loading in the aluminium matrix in terms of varied microwave exposure time. We claim: 1. A process of making AI-AI2O3 composites useful in engineering applications, which comprises pre-cleaning and drying aluminium object(s); partially oxidizing the said pre-cleaned and dried aluminium object(s) in air at a temperature in the range of 590°C to 615°C for a period in the range of 5 to 200 hours to obtain partially oxidized object(s),characterized in that subjecting the said partially oxidized object(s) to microwaving in the presence of air wherein the microwave exposure time is directly proportional to the requirement of percentage alumina phase loading in the aluminium matrix to obtain the said composite. 2. A process as claimed in claim 1, wherein the aluminium object(s) used is of any geometrical shape. 3. A process as claimed in claims 1 -2, wherein the microwave power used is of minimum 500 watts. 4. A process of making AI-AI2O3 composites useful in engineering applications, substantially as herein described with reference to the examples.

Documents:

245-DEL-2003-Abstract-(19-02-2009).pdf

245-del-2003-abstract.pdf

245-DEL-2003-Claims-(09-03-2009).pdf

245-DEL-2003-Claims-(19-02-2009).pdf

245-del-2003-claims.pdf

245-DEL-2003-Correspondence-Others-(09-03-2009).pdf

245-DEL-2003-Correspondence-Others-(19-02-2009).pdf

245-del-2003-correspondence-others.pdf

245-del-2003-correspondence-po.pdf

245-DEL-2003-Description (Complete)-(19-02-2009).pdf

245-del-2003-description (complete).pdf

245-del-2003-form-1.pdf

245-del-2003-form-18.pdf

245-del-2003-form-2.pdf

245-DEL-2003-Form-3-(19-02-2009).pdf

245-del-2003-form-3.pdf