Title of Invention

A PROCESS FOR THE MANUFACTURE OF ALUMINUM ALLOY COMPOSITES REINFORCED WITH FINER SIZE HARD PARTICLES

Abstract

The present invention describes a process based on liquid metallurgy technique for dispersion of fine ceramic particles (as low as 5 µm) up 20 wt.% in an aluminium mett through specially designed mechanical stirrer which provides both mixing and shearing action in the melt during particle addition. The particles are chemically treated firstly with HCI solutions and then with borax solution followed by drying and firing at 900 to 1000°C prior to introduction in the melt to attain thin coating of sodium borosilicate which improves the wetability of the particles with melt. Uniform distribution of particle with good bonding is achieved in the composite processed through this invention. The processed composite could be cast using any of the conventional and non-conventional casting techniques.

Full Text

The present invention relates to a process for the manufacture of aluminium alloy composites reinforced with finer size hard ceramic particles. The present invention particularly relates to the development of a liquid metallurgy process for manufacturing tailor made aluminium alloy composites reinforced with fine and hard ceramic particles, having particle size of the order of 5-1 Oum and concentration of the order of 5 to 20 wt.%, to achieve improved physical and mechanical properties. The present invention describes a process based on liquid metallurgy technique for dispersion of fine ceramic particles (as low as 5 urn) up 20 wt.% in an aluminium melt through specially designed mechanical stirrer which provides both mixing and shearing action in the melt during particle addition. The particles are chemically treated firstly with HCI solutions and then with borax solution followed by drying and firing at 900 to 1000°C prior to introduction in the melt to attain thin coating of sodium borosilicate which improves the wetability of the particles with melt. Uniform distribution of particle with good bonding is achieved in the composite processed through this invention. The processed composite could be cast using any of the conventional and non-conventional casting techniques. The end product obtained is bulk fine particle reinforced aluminium metal matrix composites where the particles are uniformly distributed and the bonding between particle and matrix is reasonably good. The main field and uses of the present invention is to reinforce finer size hard particles in aluminium alloys which are emerging as potential materials to develop light weight improved performance components in automobile, aerospace and general engineering applications. The property of aluminium composites could be improved significantly when the size of the reinforcing phase could be finer enough and the reinforcing phase is dispersed uniformly in the matrix maintaining a good bonding between the matrix and the reinforcing phase. Several attempts have been made to short out the problem of the dispersoid matrix wetting and segregation of the dispersoid phase in the melt. Reference may be made to (Lloyd et al: US patent 5028392, 1990) wherein the process involved dispersion of ceramic particles, preferably aluminium oxide, in the aluminium melt in a closed reactor which is evacuated initially prior to particle addition and thereafter is statically pressurized (more than one atmosphere) with nitrogen gas during particle addition for better wetting. The magnesium content in the melt is maintained between 0.15 to 3 wt.% and the particles are coated with thin layer of nickel for further improvement in wettability between the particle and the matrix. After complete dispersion, the reactor again evacuated slowly and the melt mixture is cast through conventional casting technique. The drawbacks of the process are that it involves lots of mechanization like attachment for applying vacuum, pressurization of melt with nitrogen and a closed chamber furnace, and coating of particles with nickel. The process is also limited for dispersion of particles upto 35% maximum. As a result, the process becomes very costly. Further, reference may be made to (Skibo and his groups: US patents 5402843, 4786467, 5531425) wherein the particles are mixed into a molten alloy when gas within the melt and over the melt, in a closed reactor, is minimized through application of vacuum. The particles are added in the melt through a hollow rotating cylinder attached with impellers at the bottom end in such a way that the melt is agitated vigorously and the particles, preferably silicon carbide, and the metal are sheared past each other to promote wetting. The process also reports usage of roasted silicon carbide particles prior to mixing and rotating speed of the impeller is to be in the range of 500 to 3000 rpm. These investigations further use another sweeping impeller in addition to the dispersing impellor which facilitates more uniform mixing with minimum vortex formation and gas incorporation. The composite mixture is cast through bottom pouring technology. Further, in other investigations by Skibo et.al (US patent 4759995, 4865806) ceramic particles in Aluminium melt was added following the above techniques with addition of Magnesium in the melt. According to these investigations, magnesium segregates on the particles and thus the matrix alloy become deficit in magnesium. For maintaining desired strengthening effect, magnesium deficit is compensated by adjustable amount of magnesium addition after dispersion. The same investigators also reported removal of carbon from the surface of silicon carbide particles and forming a thin oxide layer through preheating the particles prior to addition in the Aluminium melt to prevent the formation of Aluminium carbide which is detrimental for mechanical properties of composites. The drawbacks of the process are the maintenance of high vacuum (10-30 torr) over the melt, use of complicated stirring system, and closed chamber reactor/furnace. Additionally, through this process reinforcement addition more than 40 volume fraction is not achievable. Because of the above complexities and automation, the process requires high skill and it become costly and complicated. Reference may be made to (Rohatgi et. al.:US patent 4946647) wherein the surface activated graphite particles are dispersed in an Aluminium melt pretreated with reactive metal preferably magnesium to the extent of 1 wt%, where in reactive metal in the melt improves the wettability of graphite particle with Aluminium melt, mechanical stirring technique wherein the stirrer rotates at a speed of 500 to 600 rpm at a temperature between 700 to 720°C. The stirrer contains a set of blades welded at the bottom end at an angle 45° with respect to the axis of the shaft and baffle was placed at one side of the vortex made due to stirring so that it breaks the smooth flow of the vortex and the melt creates more shearing action over the particle and thus improves the wettability. The draw back of the process is that the process is suitable for maximum 5.5 wt% of graphite particle addition. The graphite particles would reduce the mechanical property of the composite even though it improves the antifrictional properties. Reference may also be made to Hammond et.al. (US patent 5186234, 5394928) wherein reports the mixing of free flowing ceramic particle into Aluminium-silicon alloy melt is carried out in a closed reactor through mechanical stirring while the introduction of gas in the chamber is minimized by application of vacuum. The melt mixture is cast and remelted, and stirred again for more uniform distribution and alloyed again during remelting for preparation of composite with desired amount of ceramic particle and alloy composition. The process involves uses of closed reactor for maintenance of vacuum and supply of non reactive inert gas over the melt during stirring and involves two stages for better distribution. Thus the process becomes cost and energy inefficient. The process is also limited for only Aluminium-silicon alloys and particles up to 35% could be dispersed. Accordance with another investigation, reference may be made to Hayashi et.al. (US patent 5,372,775) wherein composite melt is atomized into fine composite droplets which were then mechanically ground/reflocculated preferably using ball milling to prepare ground powder containing particles of the size range 3 to 20 urn which are then warm-formed to give Aluminium hard particle composite without segregation of fine particles of size as low as 3 urn. The drawbacks of the process are that it involves several steps and final material is produced through powder compaction. Thus, the process is not cost and energy efficient and not capable of producing large size components. Further, reference could be made to Kenney et. Al. (US patent: 4473103) wherein a two stage process was adopted for continuous casting of composite melt which involved firstly preparation of a highly concentrated dispersion in a metallic precursor either through powder metallurgy or other techniques. These precursor and Aluminium melt in proportion are continuously fed into the chamber where the composite melt is prepared through stirring technique. Finally the well dispersed slurry is fed into a holding crucible for prior to solidification processing, which is stirred simultaneously and finally fed into die for making billet. The drawbacks of this process are that it is two stage process, the precursor production through powder metallurgy route is a energy and cost inefficient process. Another reference may be made to Kenney et al. (US patent 4,473,103) and Klier et. Al. (4961461) wherein the mixing of ceramic particulates and Aluminium melt was carried out by adding ceramic particles and Aluminium melt in proportion into an chamber which is vigorously and continuously agitating to produce well dispersed Aluminium composite melt. Prior to mixing, the melt is treated with at least 0.1% magnesium. The composite melt from the chamber is transferred to a forming and/or shaping station. The drawbacks of this method are occurrence of large cluster and absorption of air due to severe turbulence while mixing the melt stream, which primarily leads to inferior interface and large porosity in the product. Reference may also be made to Eckert (US Patent 5462581) wherein the particles are added into the melt through mechanical stirring using a special type of stirring arrangement in which the stirrer moves in one direction and thereafter in reverse direction while adding the disperse particles. The direction of the stirrer is reverse periodically to reduce substantially the formation of vortex around the shaft and to provide increased shear action between the particles and the melt to achieve more uniform dispersion. But the process is expected to have some draw backs which are (i) possibility of entrapment of gas vis-a-vis occurrence of more porosity because of high turbulence in the melt, poor interface bonding because of the presence of gaseous layer between the particle and the matrix. Reference may be made to (US patent 3970136, 4450207, 7097807, 4499048, 4539175) wherein any kinds of Aluminium alloys could be infiltrated in a precursor of particulates (called perform) and solidified simultaneously for making composite materials. The draw back of the process are significantly thicker preforms could not be possible to make and thereafter not possible to infiltrate, the performs would be of the shape of the components or the selected portion of the component where the composite would be inserted, and requirement of suitable infiltration facility. In addition the process is a two stage process where the quality and cost of each of the process to be monitored. The above investigations, in general, emphasized on well dispersion of the dispersoid through mechanical agitation of the melt so that maximum shear rate between the particulates and the alloy melt could be achieved and the surface of the particulates is modified to facilitate better wetting with the melt or the melt is treated with some reactive metal which improves the wetability of the melt with the reinforcing particles. The attention was paid to perform the mixing in a chamber either in vacuum or in a controlled inert gas atmosphere. The maintenance of vacuum needs additional capital investment and is a crucial step. The dual impellor design for mixing of particulates in a reactor with minimized gaseous environment is more complex. It may help in thorough mixing of particles of finer size but may lead to more gas absorption and poor interface bonding. Two stage processes are not cost and energy efficient. The introduction of impellor which is subjected to move periodically in reverse direction cause more turbulences which results in more gas absorption, more porosity and poor bonding. In addition the process is associated with occurrence of clustering of fine particle if the schedule of periodic change of direction is not carefully selected. The main object of the present invention is to provide a process for the manufacture of aluminium alloy composites reinforced with finer size hard ceramic particles, which obviates the drawbacks of the hitherto known prior art as detailed herein above. Another objective of the present invention is to provide a process wherein the stirring speed, melt temperature, pouring temperature, rate of particle addition enables achieve uniform distribution of particle and good bonding. Still another objective of the present invention is to provide an efficient technique for particle treatment so as to modify the surface characteristics suitable for uniform distribution and good bonding. Yet another objective of the present invention is to provide a means for effective stirring and shearing of particles over the liquid metal so as to achieve introduction of finer size particle. The present invention discloses a method for dispersing of ceramic particulates in any kind of aluminium alloys using more simplified and cost effective technique wherein a mechanical stirrer with multi-layer blades is designed which leads to less vortex, less turbulence but efficient shearing of particles with the liquid metal. This will solve the problem of absorption of gas, avoidance of porosity, achieving good interface bonding and minimization of clustering of particles. The particles used are silicon carbide, alumina, zircon, silicon sand etc wherein the size of the particles are in the range of 5 to 10 urn; and the fraction of the particles are varied upto as high as 20 wt.%. Each of the steps in the process is energy efficient and cost effective and easily adoptable to the industry. The blades are welded with the rotating shaft at angles of inclination with respect to its vertical axis. In the lower most layer, the angle is 45° whereas in top layer the angle is 135°. This is done in order to get maximum sharing action and the sweeping action for more homogeneous mixing of the melt. The particulates are pretreated with hydrochloric acid to remove any foreign particles, flammable mass and to reduce the surface energy so that it could be easily introduced into the melt. The leached out particles are coated with a thin layer of borax through a simple and inexpensive technique to improve their wetability with the aluminium melt, wherein the particles are wetted with aqueous solution of borax solution followed by drying and preheating at 900 to 1000 °C. The coated and preheated particles were mixed into the aluminium melt treated with magnesium addition through simple mechanical stirring using the specially designed stirrer as mentioned above. Using this method any kinds of aluminium alloys could be dispersed with any kinds of ceramic particles. The molten composite slurry could be cast using casting technique such as gravity die casting, pressure die casting, sand casting, and squeeze casting. Accordingly the present invention provides, a process for the manufacture of aluminium alloy composites reinforced with finer size hard ceramic particles, which comprises dispersing pretreated hard ceramic particles of sizes in the range of 5 to 10 urn in varying quantity upto 20 wt.% in molten fluxed and degassed aluminium alloy in the absence of oxygen by means of a stirrer having plurality of multi-layer angular blades at regular intervals, wherein the upper set of blades makes an angle of 135° and bottom most set of blades makes an angle of 45°, rotating at a speed of 400 to 1000 rpm; followed by casting in mould. In an embodiment of the present invention, the particles prior to addition to melt are sieved to required sizes in the range of 5 to 10 urn and treated with dilute HCI solutions, such as 3%HCI, and aqueous borax solution, such as 3 to 5 wt% borax solution, followed by drying at a temperature in the range of 120 to 150 °C and firing subsequently at a temperature in the range of 900 to 1000°C for a period of 1 to 2 hours. In another embodiment of the present invention, the hard ceramic particles are such as silicon carbide, alumina, zircon, silica, natural minerals, TiC, TiB, BC, in the size range of 5 to 10 um. In yet another embodiment of the present invention, the amount of hard ceramic particles varies in the range of 5 to 20wt%. In still another embodiment of the present invention, the wetability of the alloy melt with the ceramic particles is improved by addition of surface reactive metal such as magnesium in the range of 0.2 to 1 .0 wt%. In still yet another embodiment of the present invention, the alloy is treated with grain refiner like AI-Ti, Al-Zr and Al-SiC alloys for improving distribution of particles. In a further embodiment of the present invention, the particles are fed in the melt at a rate of 10 to 500 gm per minute. In a still further embodiment of the present invention, the surface reactive metal such as magnesium pieces fed into the melt by keeping the pieces of magnesium below the surface of the moving melt in the crucible. In a yet further embodiment of the present invention, after completion of particle additions; the stirrer is continued to rotate for about 5 to 10 minutes and taken out; thereafter the melt is allowed to be heated at higher temperature in the range of 800 to 850 °C and finally the melt is cast by method such as gravity casting, pressure die casting, squeeze casting, investment casting, in preheated die maintained at a temperature in the range of 200 to 450 °C . In the present invention, composites with hard particles (size: 5-10 urn and fraction: 5 to 20 wt.%) have been synthesized. The process has been developed to attain uniform distribution of particles and strong bonding between particles and the matrix to exhibit superior wear and seizure resistance, high specific strength and stiffness suitable for wear resistance applications as well as for structural applications after secondary processing. For the purpose of better distribution and improved properties finer grain size of matrix is attempted through addition of grain refiner such as 0.1%Ti/Zr/Sr in the form of master alloy. This patent describes a process for the synthesis of Aluminium alloy-hard particle (silicon carbide, alumina, zircon, silica, natural minerals etc) composites used for automobiles and other general engineering applications. The process involves the synthesis of Aluminium hard particle composites through a modified liquid metallurgy route using vortex technique wherein the size of reinforcing particles ranges from 5 to 10 urn and the reinforcement distributed uniformly. The process also provides improved bonding with controlled interface. The processing steps includes pretreatment of hard ceramic particles with aquous dilute HCI solution followed by aquous borax solution and then drying and preheating at 900-1000°C, melting of alloys to a predetermined temperature (700 to 850°C), cleaning of alloy melt, melt treatment with wetting agent like magnesium and master alloys (AI-Ti, Al-Zr and Al-Sr) and subsequently addition of dispersoids using a specially designed mechanical stirrer followed by solidification of composite melt is a preheated die (sand mould, permanent mould) through gravity casting or pressure die casting. The process is developed to ensure uniform distribution and strong bonding. The novelty of the present invention lies in the following: 1. A cost effective method as compared to use of metal coated particles and require no energy and skill. 2. Particles in the size range 5 to 10 urn have been incorporated in any types of Aluminium alloys such as 2XXX, 3xxx, 5xxx, 6xxx and 7xxx and Aluminum-silicon alloys, wherein the particles are of the range of ceramic particles such as silicon carbide, alumina, silica etc. Thus the present process is suitable for preparing a wide range of Aluminium alloy composites. 3. The concentration of the particles in the matrix has been varied in the range of 5 to 20wt% without affecting the uniformity in distribution, bonding and flowability (castability) of the composite melt. 4. The above has been made possible both in bottom pouring and conventional pouring system. 5. The composite so prepared have more uniform distribution of particles, stronger bonding between the particle and the matrix. 6. The process is simple, cost effective and energy efficient. It does not use any sophisticated equipment and the existing soft floor could be used for its implementation. The novel features of the present invention have been realized by the non obvious inventive steps, such as: (i) Pre treatment of hard particles wherein the particles are leached with HCI to remove impurities and reduce the dipolar moment, dipped with borax solution and then dried to have thin coating of borax on the particle which improves the wetability of particle and thus distribution. The distribution is improved further by grain refining the alloy with master alloy addition like AI-Ti, Al-Zr, Al-St. (ii) Dispersing pretreated hard ceramic particles of sizes in the range of 5 to 10 urn in varying quantity upto 20 wt.% in molten fluxed and degassed aluminium alloy in the absence of oxygen by means of a stirrer having plurality of multi-layer angular blades at regular intervals, wherein the upper set of blades makes an angle of 135° and bottom most set of blades makes an angle of 45°, rotating at a speed of 400 to 1000 rpm. In the process of the present invention the non-consumables required are: (1) Oil fired furnace or electrically resistance furnace for preparation of melt. (2) Electrically resistance holding furnace with a arrangement for tapping the hot metal from bottom (3) Muffle furnace for preheating reinforcing agent (4) Electrical oven for drying of chemically treated reinforcing particles (5) Sieve shaker for sieving of particle of required dimension (6) Stirrer assembly for mechanical stirring liquid melts in order to disperse the reinforcing agent uniformly in the melt. The stirrer assembly consists of 1HP 240V, 50Hz motor with speed controller (max speed: 1200rpm). The stirrer is attached with the flexible shaft to the motor. Any type of arrangement could be designed with an aim to rotate the stirrer assembly at variable speeds (1200 rpm max). The stirrer consists of a rod having stirrer blades welded at 45° with it. Four blades are welded at two locations: at the bottom and 50 mm above the first series. The stirrer blades would varies in size depending on the size of crucibles. (7) Baffle of 30 to 50 mm wide and 100 to 150 cm long and 3 to 5 mm thick made of steel to disturb the regular movement of reinforcement in the melt during stirring in order to break down the agglomeration of the reinforcements. This helps in more uniform distribution and more effective incorporation of reinforcements. (8) Spoons, tongs, C-clamps, gloves, moulds or die etc. for casting the composite melt (9) Thermocouple to measure the temperature or temperature controller for controlling and measurement of temperature. In the process of the present invention the consumables required are: (1) Aluminium metal or alloys both cast and wrought alloys. (2) Hard particles of natural mineral like granite, siliminite, iron oxide etc., Silicon carbide, alumina, zircon, silica, etc. (3) Magnesium metal of 99.9% purity (4) Coveral 11 or any other flux (cover flux) used for Aluminium alloy preparation (5) Nitrogen gas or degasser tablets for degassing of Aluminium alloy melt (6) Graphite crucibles for melting of alloys (7) Borax and HCI for pretreatment of reinforcing agents The process details of the present invention are given below: Preparation of dispersoids: Particles of required dimensions (5-10 urn) were sieved and their particle size distributions were examined. The particles after sieving and confirming their size distribution, were soaked in HCI solution. After cleaning in HCI Soln (3 to 5 ml in 1000ml), the particles were soaked in borax solution (10 to 20 gm in one litre of water) and then dried in an oven. After drying the particles were heat treated at a temperature between 900 to 1200 °C for one to two hours. The particles are preheated at this temperature just before pouring them in the alloy melt. Alloy preparation: Aluminium alloy of required composition is melted in the furnace. The melting temperature was optimized to be 700 to 750 °C for melt treatment. The melt was treated with cover flux, Coveral-11, to cover the melt so that it does not come in direct contact with alloy. After fluxing, degassing of melt is done either by nitrogen gas purging. The dross over the alloy is cleaned and the temperature of the alloy is maintained between 700 to 750°C prior to reinforcement addition. Composite preparation: Aluminium alloy melt is prepared in the furnace and the temperature of the melt is maintained between 700 to 750 °C. The stirrer is positioned at the center of the crucible and then inserted in the alloy melt. Precaution was taken so that the bottom end of the stirrer does not touch the base of the crucible in which the melt is kept. After positioning of the stirrer, it is allowed to rotate at a speed of 500 to 1200 rpm so that effective vortex is created. The speed of stirrer varies with the amount of reinforcing agent to be added in the melt. Magnesium of amount 0.2 to 1 wt% was added simultaneously in the melt during stirring to improve the wetability of ceramic reinforcement with alloy melt. In the same time hard ceramic reinforcement in controlled quantity (50 to 100gm/min) is added at the inner-surface in the vortex created so that the reinforcing particles get effectively sucked by the vortex and mixed with the melt. The particles are added through conical sieve so that any unwanted large size foreign particles does not come into the melt. Baffling is done by placing the baffle at the 90° to 180° away from the location of particle addition. The baffle is also moved in this portion for breaking up the vortex to some extent so that the stream line motion of the reinforcing agent as agglomerate in the vortex is disturbed and the particles get distributed more uniformly. After completion of addition of desired quantity of the reinforcing agent, the stirrer is allowed to rotate further for 5 to 10 mins at a speed of 200-400 rpm for further improvement in particle distribution. The stirrer is then taken out from the melt and the melt is then allowed to mixed with spoon for 2 to 5 mins for better mixing. The viscosity of the alloy melt is so controlled that the particles could not float or sink during transferring the composite melt to the mould. The composite melt temperature is maintained between 700 to 750 °C so that the flowability of the melt is maintained for successful casting and reaction of Aluminium with reinforcing phase like SiC is prevented. Finally the composite melt is either transferred to the preheated holding furnace for bottom pouring to the mould or directly to the mould through spoon or other means. During bottom pouring, the composite melt is stirred in the holding furnace with the help of another stirrer at slower speed 200 to SOOrpm to ensure better distribution and to prevent settling tendency. Using the same procedure other metals and alloys such as zinc, copper, magnesium alloys etc. could also be processed for composite preparation by maintaining temperature of the melt in such a way that the composite melt is suitable for casting. The preferred particles are SiC, Zircon, alumina, silica, silicon nitride, boron carbide, titanium boride and titanium carbide etc, although other particles such as natural minerals, sailon, alumino-silicates etc can be used. The temperature of the melt must be maintained below 750 °C before incorporating the particles into the melt. A high temperature of the melt would rejects the particles. The composite melt could be cast in any of the die: sand mould, permanent mould, by gravity die casting, or by pressure die casting, squeeze casting, centrifugal casting and investment casting. The distribution of particles and bonding between particle and matrix were examined using scanning electron microscope and the materials were characterized in detailed in terms of strength, modulus, hardness, wear resistance, corrosion resistance. The composite materials made by the method of the invention shows a cast microstructure of the metallic matrix with the distribution of particles generally uniform throughout the cast volume. The particles are well bonded to the metallic matrix. No significant reaction layer is interposed between the particle and the metallic matrix. The cast composite can be heat treated using normal heat treatment cycle, as used in the case of matrix alloy. The cast composite is also suitable for mechanical processing such as rolling, forging and extrusion to a useful shape. Composite materials have been prepared with a wide range of particle concentration i.e. from 5-20 wt% and size range 5-10 urn, so that a range of properties such as strength, stiffness and physical properties can be available. Summary of observations: It can be observed that (i) the process is suitable for any kind of Aluminium alloys and ceramic dispersoids wherein the size of the dispersoids is in the range of 5 to 10 urn and volume fraction of the dispersoid could be as high as 20%, (ii) the simple stirrer design and control of process parameter along with particle treatment with HCI and Borax solution provides uniform distribution of dispersoid and its good bonding with the matrix, (iii) further improvement in the distribution could be achieved through grain refinement of Aluminium alloys with master alloys like AI-Ti, Al-Zr and Al-St, (iv) the prepared composite melt could be cast using any of the conventional casting technique and could be cast to any intricate shape. The overall observation states that the process so developed over come the drawbacks of the earlier methods as mentioned detailed in prior art section. The novelty of the process is to adopt simple inexpensive and energy efficient methods to achieve uniform dispersion upto 20 vol% of particle as fine as 5-10 urn with good bonding between the particle and the matrix and the soft floor could be used to adopt the process. The main Advantages of the present invention are: 1. Any kind of Aluminium alloys and ceramic particles could be used for preparing Aluminium composites. 2. The size of the dispersoids could be reduced as fine as 5 urn. The process is also suitable for coarser particle dispersion. 3. Upto 20% dispersion could be added for 5-10 pm particles. 4. The good bonding between the particle and the matrix. 5. The process is simple, cost and energy effective; no special skill, sophisticated automation and control system are required, 6. It could be adopted in the existing soft floor without any major change and investment. We Claim, 1. A process for the manufacture of aluminum alloy composites reinforced with finer size hard ceramic particles, which comprises dispersing pretreated hard ceramic particles of sizes in the range of 5 to 10 [im in varying quantity upto 20 wt.% in molten fluxed and degassed aluminum alloy in the absence of oxygen by means of a stirrer having plurality of multi-layer angular blades at regular intervals, wherein the upper set of blades makes an angle of 135° and bottom most set of blades makes an angle of 45°, rotating at a speed of 400 to 1000 rpm; followed by casting in mould. 2. A process as claimed in claim 1, wherein the particles prior to addition to melt are sieved to required sizes in the range of 5 to 10 nm and treated with dilute HCI solutions, such as 3%HCI, and aqueous borax solution, such as 3 to 5 wt% borax solution, followed by drying at a temperature in the range of 120 to 150 °C and firing subsequently at a temperature in the range of 900 to 1000°C for a period of 1 to 2 hours. 3. A process as claimed in claim 1-2, wherein the hard ceramic particles are selected from silicon carbide, alumina, zircon, silica, natural minerals, TiC, TiB, BC, SISNA in the size range of 5 to 10 nm. 4. A process as claimed in claim 1-5, wherein the alloy is treated with grain refiner selected from Al- Ti, Al-Zr and Al-SiC alloys for improving distribution of particles. 5.A process as claimed in claim 1-6, wherein the particles are fed in the melt at a rate of 10 to 500 gm per minute. I i 6. A process as claimed in claim 1-7, wherein the surface reactive metal selected from magnesium pieces fed into the melt by keeping the pieces of magnesium below the surface of the moving melt in the crucible. 7. A process as claimed in claim 1-8, wherein after completion of particle additions; the stirrer is continued to rotate for 5 to 10 minutes and taken out; thereafter the melt is allowed to be heated at higher temperature in the range of 800 to 850 °C and finally the melt is cast by method such as gravity casting, pressure die casting, squeeze casting, investment casting, in preheated die maintained at a temperature in the range of 200 to 450 °C . Dated this 22"' day of March 2006 I j i / Scientist j Intellectual Property Unit Council of Scientific & Industrial Research

Documents:

793-del-2006-1-Claims-(12-08-2013).pdf

793-del-2006-1-Correspondence-Others-(12-08-2013).pdf

793-del-2006-abstract.pdf

793-del-2006-Claims-(05-02-2014).pdf

793-del-2006-Claims-(18-02-2014).pdf

793-del-2006-claims.pdf

793-del-2006-Correspondence Others-(05-02-2014).pdf

793-del-2006-Correspondence Others-(18-02-2014).pdf

793-del-2006-Correspondence-Others-(12-08-2013).pdf

793-del-2006-correspondence-others.pdf

793-del-2006-description (complete).pdf

793-del-2006-description (provisional).pdf

793-del-2006-form-1.pdf

793-del-2006-form-2.pdf

793-del-2006-form-3.pdf

793-del-2006-form-5.pdf