Claims:What is claimed is

1) An alloy composite with LM6 aluminium alloy – copper coated steel fiber (2.5 – 10wt%) as its basic constituents with additives of reinforced composites capable of offering desirable mechanical properties and wear resistance compared to other aluminium alloys, essentially comprising of properties of
increase in hardness of composites with increasing fiber wt% in matrix. Maximum hardness of 72BHN was observed for 10 wt% of composites ;
increase in ultimate tensile strength for up to 5 wt% of composites and decreased with further addition of steel fibers due to crack nucleating points such as fiber–matrix interface, micro pores, etc., that in turn resulted in premature failure however, Maximum tensile strength of 173 MPa was observed for 5 wt% of composites;
decrease in weight loss of squeeze cast of 10 wt% by 46% when compared to matrix, for a sliding distance of 2000 m, 10 N load and a velocity of 1.7 m/s ;
decrease in coefficient of friction and decrease in wear rate with the addition of fiber content (2.5 – 10wt%) and increase in sliding distance with the average coefficient of friction for matrix was 0.27 and that for 10 wt% of composite was 0.20 ;
cumulative weight loss of composites decreased with increasing fiber content and decreased up to 57% for 10 wt% of composites when compared to LM6 aluminium alloy;
copper coated steel fiber reinforced composites usage as automotive pistons because of its better wear resistance and mechanical properties.
2) A method for manufacture of copper coated steel fibre and reinforced with composites, for making of automotive pistons, the said method imparting more of desired properties viz., increase in hardness, increase in ultimate tensile strength, decrease in co efficient of friction
, Description:Methodology
Copper coated steel fibers (2.5 – 10wt%) are reinforced in LM6 aluminium alloy by squeeze casting process. Steel fibers are copper coated using electrode less method to achieve better interface bonding between steel fibers and LM6 aluminium alloy. Microstructure of castings is examined using image analyzer to study the distribution of fibers in matrix. Samples are machined to check the hardness and tensile strength of composites. Hardness is measured using Brinell hardness testing machine with a load of 500 kg (Model KB—3000H and Krystal equipments make, India). Two tensile specimens of 6 mm width, 25 mm gauge length and 6 mm thickness are machined using wire-cut electrical discharge machine as per ASTM E8 standard. Extensometer (Model TECSOL and TMC Engineering make, India) is used for performing tensile test on the specimens.

LM6 matrix and composites are tested using wear testing pin-on-disc apparatus (Model TR-20LE-M108 and Ducom make, India) to study the wear behavior of composites at dry sliding condition as per ASTM G99 standard. Specimens of 10 mm diameter and 40 mm height are prepared and rotated against a steel disc of 64HRc for a sliding distance of 2000 m at a velocity of 1.7 m/s and 10 N load. An electronic weigh balance with an accuracy of 0.001 mg is used to measure the weight of the pin. At every 500 m sliding distance interval, the samples are cleaned with acetone and weight was measured. The samples are rotated for a continuous run of 2000 m, load of 10 N and the frictional force is measured using electronic sensor. The coefficient of friction is calculated using tangential and normal force. Wear rate of matrix and composites are calculated using weight loss and sliding distance. Also the samples are tested for a constant run of 2000 m by varying the load as 10, 20, 30 and 40 N to understand the wear behavior of composites against load. Fractures surface of tensile specimens and worn out surfaces are preserved and examined using field emission scanning electron microscope (Model Sigma and Carl ZEISS make, Germany).

Design
LM6 aluminium alloy with 2.5 to 10 wt% of copper coated short steel fiber reinforced composites have been prepared using squeeze casting process. Steel fibers available in the market with chemical composition as given in Table 1 are used as reinforcement. A less expensive electrode less method is used to obtain the copper coating on steel fibers. Copper coated steel fibers are deoxidized in a hydrogen atmosphere for 2h at a temperature of 800ºC. The steel fibers of 194 µm diameter and 500 - 3500 µm length are obtained as shown in Figure 1 with copper coating thickness of 24µm. Wt% of reinforcement is varied as 0, 2.5, 5 and 10.
Table 1 Chemical composition of steel fiber
Sample
(wt%) C Si Mn Ni Cr S Fe
Fe 0.10 0.41 2.17 6.89 7.68 0.24 Bal

A 40 tonne capacity squeeze casting machine as shown in Figure 2 with bottom pouring arrangement is used for conducting the experiments. 1.2 kg of LM6 aluminium alloy with chemical composition, as given in Table 2 is melted in an electric resistance furnace using a stainless steel crucible. The melt is degassed with hexachloroethane tablets and the temperature is raised to 730ºC. The melt is stirred using stainless steel stirrer at 600 – 750 rpm to form a vortex. Steel fibers are preheated to 200ºC and added to the melt in a continuous stream while stirring is continued. The die is made up of H11 die steel, preheated to 225ºC using ceramic electric heater and the composite melt is poured using bottom pouring arrangement. A squeeze pressure of 125 MPa is applied on the melt through EN8 alloy steel punch until the solidification is complete. For testing and analysis purpose, cylindrical castings of 50 mm diameter and 170 mm height are produced and shown in Figure 3.
Table 2 Chemical composition of LM6 aluminium alloy
Sample (wt%) Si Fe Cu Mn Mg Ni Sn Pb Zn Ti Al
LM6 11.7 0.40 0.02 0.02 0.03 0.006 0.05 0.06 0.12 0.1 Bal

Microscopic observation of LM6 matrix and composites are shown in Figure 4a-d. It is observed that the fibers are uniformly distributed in matrix with random orientation. Copper coating on reinforcements offers better interface bonding between matrix and steel fibers. The composite melt is stirred in the range of 600 - 750 rpm which results uniform distribution of fibers in LM6 alloy. Application of pressure during the solidification makes the LM6 matrix and composites more dense resulting in fine grain structure. Copper coating on steel fibers prevents the interfacial reaction between matrix and reinforcement which results in better interface bonding between steel fibers and LM6 aluminium alloy

Hardness of LM6 matrix and composites is shown in Table 3. Samples have been prepared and the hardness values are observed at four locations in a sample. The average of four hardness value is presented. The hardness of composites against fiber wt% is plotted in Figure 5. It is observed that there is significant improvement in hardness with addition of steel fiber in matrix. Addition of steel fiber increased the hardness of composites and maximum hardness of 72 BHN is observed in 10 wt% of fiber composites. This is due to diffusion of copper into the matrix, solid solution or due to generation of high dislocation density. Application of squeeze pressure during the solidification of casting also contributed for minimizing the porosity, fine grain structure of samples offering resistance to plastic deformation which increased the hardness of composites.
Table 3 Mechanical properties of LM6 alloy with varying wt% of copper coated steel fiber composites
Wt% of copper coated steel fiber Hardness (BHN) Micro hardness (VHN) Ultimate tensile strength (MPa) Elongation (%)
0 48 81 145 10.2
2.5 54 91 158 7.6
5 63 308 173 5.3
10 72 823 164 2.1

Two tensile specimens have been prepared for testing purpose and the average of two tensile test values are reported in Table 4. It can be seen that reinforcement of steel fibers increases the tensile strength of composites compared to matrix. Fractured tensile specimens are shown in Figure 6 reveals ductile fracture of composites.
Wt% of copper coated steel fiber reinforced into LM6 aluminium alloy is varied from 2.5 to 10. The tensile strength of composites against fiber wt% is plotted in Figure 7. It is found that increasing fiber content from 2.5 to5 wt% increases the tensile strength of composites. Further, the addition of steel fiber reduces the tensile strength of composites. This is due to the crack nucleating points such as fiber – matrix interface and micro pores that in turn results to premature failure.
Composite strengthening can be improved by incorporating fibers having higher tensile strength than the matrix. Interface between matrix and fiber is improved by proper coating of fiber such as copper. This forms a good interface bonding between aluminium and steel, solid solution strengthening by dissolution of copper in LM6 matrix. Application of squeeze pressure during the solidification of casting minimizes the porosity and increases the tensile strength of composites.
Ductility of the composites is measured by percentage of elongation as shown in Table 4. It is observed that ductility of composites decreases by the addition of copper coated steel fibers in matrix. Interfacial bonding between fiber and matrix forms micro pores or brittle phases, initiates flaw which propagates that cause fracture of composites. This reduces the plasticity behaviour of composites.
Fracture surface of LM6 aluminium alloy and composites are examined using field emission scanning electron microscope and the photographs are shown in Figure 8a – d. It is observed that fracture mechanism is dominated by dimple formation and fiber pull out from matrix. Fracture surface of LM6 matrix shows more dimple formation. In case of 2.5 wt% fiber composites, the fracture mechanism is dominated by dimple formation rather than fiber pull out. However with 10 wt% of fiber composites, fiber pull out is dominated rather than dimple formation. Crack initiated at the fiber / matrix interface, propagated and linked with other cracks that caused ductile fracture. In case of 5 wt% of fiber reinforced composites, fracture mechanism is occurred by fiber pull out but comparatively lower than 10 wt% of fiber composites.
Weight loss against sliding distance of 2000 m at 10 N load for LM6 matrix and composites is plotted in Figure 9. It is observed that weight loss of composites decreases with the addition of fiber from 2.5 to 10 wt%. Weight loss of matrix is more and in general, weight loss increases with the increase of sliding distance. Weight loss decreased up to 46% by addition of 10 wt% of fiber in matrix.
Coefficient of friction of composites and matrix for a continuous run of 2000 m at 10 N load is depicted in Figure 10. It is evident that coefficient of friction decreases with the increase of sliding distance and fiber content. It can be seen that coefficient of friction of composites is minimum as compared to matrix. This is due to the addition of steel fibers into matrix and higher hardness of composites. The average coefficient of friction of 10 wt% composites and matrix was 0.20 and 0.27 respectively.
Figure 11 shows the variation of wear rate of LM6 alloy and composites at 10 N load for a sliding distance of 2000 m. It can be seen that wear rate decreases with the increase of sliding distance. It is also observed that wear rate of composites decreases with the increasing fiber content.
Cumulative weight loss of composites and matrix for a constant run of 2000 m with the varying load of 10 N, 20 N, 30 N and 40 N is plotted in Figure 12. It is observed that the cumulative weight loss of composites decreases with increase of fiber wt%. Also the weight loss increases with increase of load from 10 to 40 N. The cumulative weight loss decreased upto 57% with the addition of 10 wt% of fiber in matrix.
Micrograph of LM6 matrix and composites for a sliding distance of 2000 m at 10 N load is shown in Figure 13. Long continuous grooves are observed on the surface parallel to its sliding distance. Figure 13a depicts continuous grooves due to local delamination on the surface. Figure 13b-d show relatively fine and smooth grooves due to ploughing rather than local delamination. This is due to the incorporation of copper coated steel fibers in matrix. The size of grooves decreases with the increase of wt% of fibers.
Figure 14 a-d shows the micrograph of 5 wt% composites for a sliding distance of 2000 m under different load ranging from 10 to 40 N. The size of grooves increases with the increase of load and local delamination is observed at higher load. Figure 14c shows the worn out surface of 5 wt% reinforcement at 30 N load. Matrix alloy smeared over the ends of projecting fiber and long continuous grooves are observed against sliding distance. The wear mechanism changes from mild to severe with increasing load. At 40 N load, extensive surface ploughing and local delamination are observed.