This invention relates to a process for the manufacture of functionally graded aluminium alloy based in-situ metal matrix composites (FG-AMC). These types of functionally graded (FG) composites have potential application in various automobile and aerospace components, where the outer surface is harder than the inner surface or lice versa.
This intention will now be described with reference to the following lixamples, which illustrate, but do not limit, the scope of this invention.
EXAMPLES
Preparation of Al based Tirn in-situ Composite melt
A melt of Al based alloy were prepared in a pit type resistance furnace. The salts. K3T1F4 and IvBF^ powder., were dried separately in an oven maintained at 150°C for I hour to remove the moisture completely and minimize hydrogen pick up in the meh. The salts were blended thoroughly to get a homogeneous mixture. The stoichiometric ratio of Ti to B was maintained at 2.2:Vin the Wend. The salt mixture was wrapped in Al foils {m small packets) to facilitate easier addition to the Aluminium based melt. The graphite crucible and graphite stirrer used were coated with zirconia paste and dried we// to prevent the contamination of melt with carbon from stirrer as well as crucible during melting. Zirconia coating also ensures higher crucible life.
When the temperature of the Alunuraum based melt reached the predetermined set temperature it was degassed using, C2C6 (hexach/oroethane), which is accompanied by a slight drop in temperature. When the melt reached - 8&0aC temperature, the salt mixture was added to the roeJt gradually (in small packets) with continuous stirring- Intermittent stirring was carried out manually at every It) min. interval to ensure uniform mixing and reaction throughout the melt. The reaction is complete in an hour.
The dross floating on top of the melt was decanted and the clean melt (in-situ composite) is now ready for centrifugal casting.
Preparation oV Al based TiC m-siin Composite melt'.
K/n>6 and graphite powder were dried separately as explained before. The salt and graphite were mixed and the mixed powders were wrapped in Al foils. The stoichiometric ratio of Ti to O was maintained at 4.1 in the blend. When the Aluminium based melt temperature reached - ^OfVC^ the

wrapped ions where added to the liquid metal with continuous stirring. Intermediate stirring was carried out manually at 10 min. intervals and the melt was kept for an hour so that the reaction is complete. After that the dross was removed from Che melt and the clean melt is ready for centrifugal casting.
Preparation of functional graded in-siUi composites;
The in-situ composites prepared in these experiments are Al-Si and Al-Cu based alloys with 5 wt% TiB3 and Tit'. The reinforcement of 5 wt.% (2.5 volume percent was. chosen, to have a lower viscosity of the melt, so that it can easily flow into the centrifugal mould. Once the exothermic reaction for funning in-situ TiB+ is completed, die nieff temperature was raised from 800 to 900 T to have a better fluidity and for TiC the melt temperature was reduced from 12(10 to 900"C. Once the liquid slurry reached the desired temperature, it is poured into the centrifugal mould with the help of a funnel. Before nourinp,, the sAuvvy was stivvevl in cevtaincases to change the location of functionally graded layer. The mould was preheated before pouring (he slurry in a tubuiar furnace to different temperatures (500, 600 am) iMM)cO. The funnel was also preheated to remove the moisturehy varying the rotational speed of the mould from 1000 to 2000 rnm.The centrifugal force was controlled by varying the rotational speed oi" the mould from I WW to 20M vpm, The liquid sluvv> ftf apfwrnumrate weight of S00-850g was used to get a tube with outer diameter as 70 uirn^ length as 100 mm and thickness as 12 mm. figure i(a) shows the centrffugaffy cast composites. The centrifugal casting process parameters used in this work are given in the Ta hit* 1.


Micros true hire analysis was carried out on the cross sections of the tubes that were sectioned perpendicular to the centrifugal axis. Volume fraction of the particles in the gradient micros tructures was measured by image analyzer from the micrographs taken ftxtnt the periphery to the interior surface of the cross-sectioned tube as per ASTM E1245~i)3. The Vicker's hardness was measured with 5kg load on the cross section of the graded microstrueture at every 1mm distance.
Figure 1(a) shows the macroscopic view of the section of the Al-Cu-IiBj runctirmany gradient tube by centrifugal casting. There are three regions across the thickness of the tube and these ve*ijons are uniform in thickness throughout the length of the casting. Outer region consists of dense IiBi particles in die matrix, mi'oYffr region has clear interface oefweeii die composite and matrix and the inner region consists of the matrix. The hardness also increases from the inside to the outside of the mould (Fig. 1 b).
The location of the functionary graded layer can be varied (i.e., at the outer surface or at the interior) with suitable process parameters as described before. Figure 2 shows a macroscopic view of the Al-Si-TiB^ composite with reinforcement being at the interior surface (V\%. 2 a) or at the outer surface (Fig, 2b). Similarly Vl-('u-TiC and \1-Si-TK composites have also been processed. Also using this technique it is possible to get more than 15 volume fraction of iti-sita particles when compared to the nominal volume fraction of 2.5% in the composite. The above process can he extended to all Aluminium based commercial casting alloys to obtain functionally graded composites with in-situ TiBi and TiC reinforcements.
It will be appreciated from the foregoing description that various other embodiments and modes of carrying out the process proposed herein are possible without departing, from the scope and ambit of this invention.

We Claim:
1. A process for the manufacture of functionally graded, aluminium
based in-silu metal matrix composites (VG-AMC) comprising the steps
of drying a mixture selected from (KjTiFf, - KBF4) and (K^TiFb +
graphite) in an oven maintained at I50°C for T hour to remove the
moisture completely and minimize hydrogen pick up in the melt-, the
salts he'mg blended thoroughly to get a homogeneous mixture; wrapping
the selected mixture in Al foils in small packets: degassing the melt
when it reaches the predetermined temperature: adding the sah mixture
to the melt gradually (in small packets) with continuous stirring to
ensure uniform mixing and reaction throughout the melt: decanting the
dross floating on top of the meft and pouring the cfestn mett (composite)
into a centrifugal casting mold.
2. A process as claimed in Claim 1 wherein the selected mixture is dried in an wen maintained at 150°C n\r \ HOUR.
3. A process as claimed in Claim 1 or Claim 2 wherein the VI hased alloy is heated in a pit type resistance furnace.
4. A process as claimed in am one of the preceding Claims wherein a graphite evueihte and graphite stirrer are used while preparing the composite t said crucihle and stirrer being coated with zirconia paste.
5. A process as claimed in any one of the preceding Claims wherein the stoichiometric ratio oiTi to H and of Ti to C is maintained at 2.2:1 and 4:I ,iespectivef6. A process as claimed in any one of the preceding Claims wherein the selected mixture is added to the meft graduate* (in small AT hased foil packets) at - 8M)°C and - 1200C respectively.
7. A process as claimed in any one of the preceding Claims wherein the clean melt (composite) is poured into a horizontal mould, preheated to different temperatures and nith varied centrifugal mould rotational sppeds to produce Aluminium based in-situ composites.

8. A process to control the location of functionally graded layer at any
location (for example outer surface or inner surface) through
mechanical stirring the melt before casting.
9. A process for the manufacture of functionally graded, aluminium
atfov based in-situ metaf matrix composites (FG-AMC) substantially
as herein described and illustrated by the Examples and drawings.